User:NorwegianBlue/refdesk/biology

Chromatophores

Hello Scientists. I know this isn't really the place, however, i wonder if i could get a few opinions on the chromatophore article? I requested a peer review, but have had no takers. I'm trying to get it to good or featured article status and would like the opinion of intelligent non-experts, on whether it is too technical, not technical enough or whether anything is missing. Would appreciate it any comments. Thanks. Rockpocket 06:25, 30 May 2006 (UTC)

Looks very nice! Don't see anything wrong with it. Good references, and external links. — The Mac Davis] ?? ญƛ. 07:51, 30 May 2006 (UTC)

I agree that the article is well-written, interesting, and visually pleasing. The article contains many technical terms, and it could be made more accessible to non-expert readers by making sure that the meanings of these are explained when introduced, or that there are links to pages defining them. An example: the sentence beginning with "Biochromes, such as pteridines and carotinoids...". In context, I suppose it is clear that biochromes are a subset of chromatophores, but I had to stop and think, and read the sentence a couple of times. There is a page (stub) called pteridines, a link would have been helpful if the link points to the correct molecule. Even a term such as de novo could have confused a non-expert reader, especially because the disambiguation page for de novo had a definition of de novo in the biological sense that was, in my opinion wrong ("newly synthesised", instead of "synthesised from simple building blocks". I have fixed that now.) But all in all, a very interesting and thorough article. --NorwegianBlue 19:04, 30 May 2006 (UTC)

Thanks for your comments. Actually, a 'biochrome' is defined as a 'pigment produced by an organism' (as opposed to a schemochrome, which is a colorless organic substance that reflects or refracts light). These aren't types of chromatophore per se, just different ways of generating colour. Its clear that that particular sentence can be improved, i'll work on that. Thanks again. Rockpocket 03:35, 31 May 2006 (UTC)

My pleasure. I have added some additional comments on the Chromatophore talk page. --NorwegianBlue 18:31, 31 May 2006 (UTC)

Gray Matter

Other than medicine, what kind of food can increase the amount of gray matter in our brains? Is there any exercise can increase the amount of gray matter?

Its matters more not how many neurons, it is how well they are connected. And how well you can use them. — The Mac Davis] ?? ญƛ. 00:11, 28 May 2006 (UTC)

Gray matter contains mostly cell bodies of neurons and glia; of the two, only glia are generally capable of dividing in the adult nervous system. I suspect you're more interested in the growth of new neurons, but currently this isn't possible outside of certain regions of the brain (ie, the olfactory bulb and hippocampus)—and even then the physiological significance of such growth is poorly understood. Why do you ask? --David Iberri (talk) 00:19, 28 May 2006 (UTC)

My question is what food, like lithium, can possibly increase the amount of grey matter, if we eat them? What I am looking for is somethings specific, like what kind of fruits or what king of exercises?

The brain is composed mostly of fat not gray matter. Let the first reply be your guide. Laziness can not be compensated for by increasing physical gray matter. What you need to do is to increase logical gray matter. There is a picture of a kid somewhere who got shot in the head and lost over half of his brain and yet he only had minor physical and mental incapability as a result! One of the TV documentary programs showed him being fitted with a prosthesis that was bigger than a grapefruit! The brain is like a wild cat - it may be born with physical agility and prowess and a bunch of other amazing attributes but if nothing is going on and it is sleeping all the time then those attributes only represent potential that is subject to atrophy. Put that same cat on a hot tin roof and all of those attributes will come alive and be put to good use dealing with a problem. Each time the cat is stimulated in such a way it is challenged to learn a better and faster way to deal better with a similar problem. What you need to do is look for challenges that will force upon you to the need to increase your logical gray matter. ...IMHO (Talk) 04:58, 28 May 2006 (UTC)

I very much doubt that any serious research has been done relating the amount of gray matter to nutrition. The only way to get this information would be do mri scans of a large number of people, calculate the gray matter volume (which I suspect in itself would be a difficult task), and do in-depth interviews of each person about their lifetime dietary habits. What has been done, however, is to study the correlation between nutrition and cognitive functions. There is no doubt that childhood malnutrition is related to lower scores in measurements of cognitive function. Omega-3 Essential fatty acids such as EPA and DHA are probably important. I suggest you follow this link to do a medline search. A search for "(epa or dha) and (cognitive functions)" gets some interesting hits. You might also want to try simply "nutrition and (cognitive functions)". As for exercising the gray matter, isn't that the same thing as using it? --NorwegianBlue 10:47, 28 May 2006 (UTC)

cancer treatment and research 1450-1750 (Medicine)

I am looking for information related to the prevalence, attitude, understanding, and treatment of cancer during the time period 1450-1750. I think this is known as the early modern period. Any assistance would be appreciated.

Is this homework? I sense a lack of focus. You are asking several quite disparate questions about a broad range of diseases. An in-depth treatment sounds like a major piece of work. If that is what you are doing, and the problem is that you lack experience in browsing the internet, I suggest you start right here.

Google is an excellent tool for finding starting information. Hint: use Cancer as a search word, together with a term that you would be likely to find in the article you are looking for, and unlikely to find elsewhere, such as "century". If you add "-20th -20st", you will narrow it further down. The minus signs excude articles that contain 20th and 21st. Adding "History of medicine" (including the quotes) will narrow it further down.

A quick search yielded the following:

• medicineworld.org
• training.seer.cancer.gov
• www.chemheritage.org

I cannot vouch for the quality of the sources.

If this is homework, feel free to cut-and-paste, but remember:

• your teacher may be better at googling than you are.
• your teacher has the advantage of being able to search for uncommon words or phrases that you have used.

Cheers, --NorwegianBlue 23:37, 1 June 2006 (UTC)

Thanks for the tips on browsing the internet. You are very perceptive. This was/is part of a homework assignment. I was doing some leg work for my 14 year old son. As a nurse I found the topic of some interest also. The hospital librarian put me onto the first site you mention. Apparently thru the 1500's the most common theory as to the cause of cancer was an excess of black bile. ( the bile I have encountered is yellow ) With the discovery of the lymphatic system this belief ended. Time, ability to do autopsis and the inquiring minds of many physicians " laid the foundation for scientific oncology during the 1700's. I have added this Reference desk to my favorites. I've found it fascinating reading, and the responses of the researches often amusing.Thanks again.

Amino acids

hello,

why are L-AMINO acids and not D-amino acids used in proteins?

I have searched through google and got only this fact but not the reason......can any one help me out...plz?

This is a fact of evolution. It is an interesting exercise to try and imagine alternative biologies, which with information-carrying molecules different from DNA and RNA, and structural molecules composed of something else than the amino acids we know. And even within the constraints of DNA and RNA, with 64 codons, there could have been 63 different structural building blocks (leaving one for a stop codon). Yet there are only 20.

Amino acids turned out to be good building blocks because of the peptide bond, which links the amino acids together in proteins. Polypeptide chains fold into complex structures. In parts of the chain typical folding patterns like alpha helices and beta-pleated sheets form stable substructures ("secondary structure") within the three dimensional structure of a protein. For such substructures to be stable, all the amino acids have to be of the same type, i.e. either L or D. Therfore, in the primordial soup, nature had to make a choice. And the choice fell upon L-amino acids, possibly for no particular reason. But it had to be one or the other. --NorwegianBlue 16:38, 31 May 2006 (UTC)

Are there cases where D-Amino acids are used rarely like reverse transcriptase in certian viruses? Or am I on the wrong track?

I'm not sure about reverse transcriptase, but a medline search for "(D-amino acid)" reveals that D-amino acids are indeed used to some extent for specialized purposes. "(D-amino acid) AND (reverse transcriptase)" gave no relevant hits as far as I could see. This article suggests that D-serine may be a regulator of glia cells, and thus indirectly control the exitability of neurons --NorwegianBlue 18:56, 31 May 2006 (UTC)

My read on this enzyme in Wiki suggests it is made from normal L-AMINO acids, but has a reverse function of making DNA out of RNA instead of the normal way of making RNA out of DNA. This is necessary for viruses to hijack the cells functionality.

Since viral proteins are made by the protein synthesising machinery of the host, they would be expected to consist entirely of L-amino acids, and your interpretation of the reverse part of the enzyme's name is correct. What I thought the questioner had in mind was whether there was something funny going on with this particular enzyme, such as a posttranslational modification, but as stated, no hits in medline. --NorwegianBlue 21:42, 31 May 2006 (UTC)

Chirality is often overlooked; see thalidomide. Isopropyl 20:32, 31 May 2006 (UTC)

The link should be Chirality (chemistry). --NorwegianBlue 21:48, 31 May 2006 (UTC)

I asked this on the Chirality page, but I am sure a lot more people read this one so I will ask it here. Is it possible to have an optical isomer using isotopes? Suppose the Alanine molecule has the Methyl group replaced with Deuterium instead of Hydrogen? Would that create an optical isomer?

Yup (also answered on the Talk:Chirality (chemistry) page wher eyou asked it). The carbon atom would be tetrahedral as usual and would have four different substituents on it, thus it is an asymmetric center. One might expect the optical rotation to be small--I can't find the exact number at the moment. DMacks 21:18, 1 June 2006 (UTC)

The optical rotation is expected to be small because the chemical difference between the two is small, right?

Yeah...from a non-scientific viewpoint, one might say "well, they're both hydrogen, so why is it considered a stereocenter at all (see the initial question), and even if it is in a technical or pedantic sense, would there be any rotation at all?" Until I found the actual ref (see my response below), I only remembered that indeed it was "a small number". DMacks 16:01, 2 June 2006 (UTC)

Tetrahedron 1959 6 338-344 reports measurements of optical rotation of several isotopically-chiral molecules such as RCHDOH, finding [a]_D up to ~1°. DMacks 23:08, 1 June 2006 (UTC)

No. of chromosomes in Neanderthals?

I know that it is not a well researched topic. But it'd be great if anyone could give me an idea about the number of chromosomes in the genome of Neanderthals? Thanks.nids(♂) 22:19, 28 January 2007 (UTC)

Neanderthals are now widely believed to have bred with homo sapiens, therefore they must have had a corresponding number of chromosomes, 46. Vespine 00:42, 29 January 2007 (UTC)

Widely believed? I thought this was merely a theory. Do you have some references? Clarityfiend 03:03, 29 January 2007 (UTC)

Isn't it truer to say that, if Neanderthals bred with homo sapiens then they must have had 46 chromosomes and therefore must have been human beings and therefore the distinction between Neanderthals and homo sapiens breaks down; or, if they didn't have 46 chromosomes then they were not humans and could never have bred with homo sapiens? JackofOz 03:09, 29 January 2007 (UTC)

Recent genetic work (e.g. the work of Krings [1], Bryan Sykes, and others) strongly argues that the humans and Neanderthals did not interbreed. Samples of mitochondrial DNA from well preserved Neanderthal fossils are too distinct from modern humans for the gene pools to have been mixing. Given that the two populations almost certainly had opportunities to interact, a lack of interbreeding would likely indicate that they were genetically incompatible, and one plausible (but by no means certain) explanation for that would be that Neanderthals had a different number of chromosomes from modern homo sapiens. Notably, homo sapiens have 46 chromosomes, while living great apes have 48, and that transition could have occurred after the Neanderthal population split from the pre-homo sapien line. Dragons flight 05:42, 29 January 2007 (UTC)

No it isn't, number of chromosomes isn't a unique species identifier, a domestic cat and a domestic pig has 38, doesn't mean they are the same species, nor that they can interbreed. But animals that DO interbreed do need to have the same number of chromosomes. Neanderthals had 46 chromosomes but that doesn't mean they were the same as humans, but they were probably close, it doesn't 'prove' that they bred. And I think recently it went beyond being just a theory, there was evidence found that Neanderthals could have actually just been bred into the population, not died out due to homo sapiens as previously thought. I'll try to find the sources. Vespine 05:15, 29 January 2007 (UTC)

We can have both the scenarios. i.e. Neanderthals had 48 chromosomes and they interbred with humans to produce Hybrids (they would be mostly sterile though). Also, Neanderthals may be having 46 chromosomes but still unable to interbreed with Humans. So, even if they interbred with humans, this does not prove that they had 46 chromosomes. But have you read somewhere that Neanderthals had 46 chromosomes. I am not asking for a source, just confirming if you had read that in a reliable source.nids(♂) 10:30, 29 January 2007 (UTC)

Skull suggests human-Neanderthal link. Anchoress 05:55, 29 January 2007 (UTC)

This skull, by itself, suggests nothing. For all we know, he could have been just a sterile hybrid.nids(♂) 10:11, 29 January 2007 (UTC)

Just another note. It is not required that species that breed have the same number of chromosomes (see Donkey, Horse, Mule). If the homo sapien population exploded and interacted with Neanderthals, cross breeding (and the subsequent sterile offpsring) would have wiped Neanderthals off the planet quickly and with no genetic trace. Imagine 10,000 horses and 100 donkeys. Females are almost constantly pregnant and the large majority of female donkeys would be carrying sterile offspring. Homo Sapien/Neanderthal offspring wouldn't be sterile for the same reason as mules but they may be for other reasons. (This is my own pet theory, no pun intended :) ). --Tbeatty 06:25, 29 January 2007 (UTC)

The Cell paper from Svante Pääbo's group that was linked to, studied mitochondrial DNA. Humans are but a medium in which mitochondria propagate themselves. The fact that Neanderthal mtDNA is not found in contemporary populations, only shows that there is no unbroken maternal line between contemporary humans and neanderthals. If the carriers of particular mitochondrion variants had even the slightest disadvantage compared to others, they would be less likely to have children, and those mitochondria would die out. This does not mean that the people that carried these mitochondria have no ancestors today, only that there is no unbroken chain of maternal ancestors. Consider also, that the fitness of mitochondria reasonably might depend on climate, since they are the cells' "power plants". And the neanderthals lived in a climate that was very different from today's. Therefore, to me it proves absolutely nothing that neanderthal mitochondria are extinct. I also disagree with the statement made in the Cell paper, that the observation that the time of divergence between neanderthal mitochondria and modern human mitochondria, being much longer ago than than the estimated divergence time of modern human mitochondria, argues against interbreeding. The fact that all contemporary human mitochondria stem from the mitochondria that lived in a woman some 200,000 years ago only proves that mitochondria are subjected to evolutionary pressure. Studies of the Major histocompatibility complex of primates, show that humans, chimps, orangutans and gorillas share many polymorphisms, particularly in the class II region. This argues strongly against very narrow bottlenecks in the size of the human (and ape) populations, and also shows that speciation is not an event that happens in a single individual, but in large groups which, while diverging, gradually lose the ability to interbreed. Jan Klein wrote a very interesting review on this way back in 1987 (Origin of major histocompatibility complex polymorphism: the trans-species hypothesis. Hum Immunol. 1987 Jul;19(3):155-62.). Note, incidentally, that this also shows that a difference in the number of chromosomes cannot be an absolute obstacle to interbreeding. --NorwegianBlue ^talk 20:22, 29 January 2007 (UTC)

Magnetic Resonance Imaging

In trying to understand how MRI's work, I discovered that the wikipedia article on the subject is a bit dense. I would like to try and rewrite the physics aspects of the article so that it might be a bit more accessible to non-physicists. But, I still don't understand the physics myself. I posted the following message to the MRI talk page, but it doesn't seem to get much traffic. The following is a disection of Wikipedia's mri article section called 'Principal'. Any and all feedback greatly appreciated:

Medical MRI most frequently relies on the relaxation properties of excited hydrogen nuclei in water and lipids.

Does the MRI work only with hydrogen atoms? Does it work only with hydrogen atoms in water and lipids? Are there any hydrogen atoms in a human (or other things commonly scanned) which are not contained in water or lipids? (i.e., could this be changed to state simply it relies on relaxation properties of hydrogen nuclei (or perhaps any nuclei with net non-zero spin)?

When the object to be imaged is placed in a powerful, uniform magnetic field, the spins of atomic nuclei with a resulting non-zero spin have to arrange in a particular manner with the applied magnetic field according to quantum mechanics. Hydrogen atoms (= protons) have a simple spin 1/2 and therefore align either parallel or antiparallel to the magnetic field.

My understanding of spin is a little rusty; "with resulting non-zero spin" - what does the word 'resulting' mean here? The spin is created as a result of applying the magentic field? Any given proton may obtain either spin 0, 1/2 or -1/2? Is the direction of alignment (parallel/antiparallel) arbitrary or a result of some other property of the proton which will precisely determine the direction (+ or - spin)?

Common magnetic field strengths range from 0.3 to 3 T, although field strengths as high as 9.4 T are used in research scanners [2] and research instruments for animals or only small test tubes range as high as 20 T. Commercial suppliers are investing in 7 T platforms. For comparison, the Earth's magnetic field averages around 50 μT, less than 1/100,000 times the field strength of a typical MRI.

Is this paragraph appropriate/needed in the principal section?

The spin polarization determines the basic MRI signal strength. For protons, it refers to the population difference of the two energy states that are associated with the parallel and antiparallel alignment of the proton spins in the magnetic field and governed Boltzmann's statistics.

Is this saying that spin polarization is the integral difference in protons in one state versus the other? So, if I have 500,001 protons that are parallel and 500,000 protons that are antiparallel then my spin polarization is 1? What is Boltzmann's statistics and what does that have to do with the calculation of spin polarization? What is the cause for the descrepancy; is it arbitrary or is it a result of some fundemental property of protons?

In a 1.5 T magnetic field (at room temperature) this difference refers to only about one in a million nuclei since the thermal energy far exceeds the energy difference between the parallel and antiparallel states. Yet the vast quantity of nuclei in a small volume sum to produce a detectable change in field.

The thermal energy causes protons to switch between parallel and antiparallel? (which seems to argue that the state is arbitrary) If the selection of parallel and antiparallel is arbitrary than each "small volume" would statistically cancel out each other "small volume" (since that would not be helpful; seems to argue that the selection isnt arbitrary and must favor either parallel or antiparallel statistically. If so, why?) '...detectable change in magnetic field...'?

Most basic explanations of MRI will say that the nuclei align parallel or anti-parallel with the static magnetic field though, because of quantum mechanical reasons, the individual nuclei are actually set off at an angle from the direction of the static magnetic field. The bulk collection of nuclei can be partitioned into a set whose sum spin are aligned parallel and a set whose sum spin are anti-parallel.

This is describing the heisenberg effect? Each proton could never be precisely in a specific alignment, but simply has a probablity cloud of alignments which is centered along the magnetic field? If thats the case then there is a certain probablity that a given proton is precisely aligned with the magnetic field and the probablity cloud is statistically parallel with the magnetic field? Can be partitioned theoretically or is partitioned in practice during the scan?

The magnetic dipole moment of the nuclei then precesses around the axial field. While the proportion is nearly equal, slightly more are oriented at the low energy angle. The frequency with which the dipole moments precess is called the Larmor frequency.

Ok, starting to get really lost... Is this saying that similar to -- electron orbitals around a nuclei--, the proton's axis has multiple quantized "orbitals" which effect the probablity cloud of its angle of incidence with the magnetic field? Ok, all my previous theories start to breakdown when adding that the proton precesses at a specific rate. And the angle of incidence with the magnetic field is a function of energy level. Perhaps the higher level orbitals are donuts centered around the magnetic field which allows for a specific frequency, but then it seems that the 0 level orbital should still have no frequency (and should still include the magnetic axis itself). ...the proportion is nearly equal... Proportion of 0 level to 1 level? Why would it be nearly equal? Why are the protons in the level 1 state at all? Aren't there states above level 1? Larmor frequency is specific to the level 1 state or all states precess at the same frequency?

The tissue is then briefly exposed to pulses of electromagnetic energy (RF pulses) in a plane perpendicular to the magnetic field, causing some of the magnetically aligned hydrogen nuclei to assume a temporary non-aligned high-energy state. Or in other words, the steady-state equilibrium established in the static magnetic field becomes perturbed and the population difference of the two energy levels is altered. The frequency of the pulses is governed by the Larmor equation to match the required energy difference between the two spin states.

Is the EM applied from a single direction or radially? The EM waves hit the protons and move them from level 0 to level 1? How are the states measured; photons created when the proton relaxes and released in a random direction as opposed to the original direction of the source beam? What does that information tell one about the material being scanned? What is really being measured; proportion of hyrdrogen atoms at every given location? Different regions are detected by measuring intensity of photons detected bouncing randomly? I have no idea how far off from reality I am at this point, but if that's the case how does measurement work in 3D?

Anyway, I'm sure I'll have more questions and if this goes well I'd like to try and tackle the k-space section also. Aepryus 18:02, 25 January 2007 (UTC)

Hmm - that's a lot of questions. MRI is a pretty involved topic, and I don't think you'll get far without reading a lot of more basic material that makes up the technique. I'll try to answer some of the questions and reference you to pages that you could read to understand nuclear magnetic resonance better. First of all, as you can see from the MRI article, there are many different variations on MRI technology which are used to image different aspects of a sample, but I'll go over the basics. The first article you should read is quantum spin, which should clear up many of your question. You could also take a look at a somewhat poor article on spin 1/2, and at another poor article on the Bloch sphere, which is an essential theoretical tool for understanding NMR. Speaking of which, Nuclear Magnetic Resonance is the basic theory, and the article is decent - you should read the "Theory of nuclear magnetic resonance" section.

Ok. Here's the basic idea. Protons are spin 1/2 particles, meaning they are a two state quantum system. That is, you can find only two orthogonal eigenstates, and the proton will be in some superposition of the two eigenstates. For instance, $/sqrt{2}(|z+>+|z->)$ is an equal superposition of the eigenstate in the positive z direction and the negative z direction in the basis of the z-direction eigenstates, and $|x+>$ represents a proton only in the x+ direction eigenstate. The idea behind the Bloch sphere representation is that any superposition of eigenstates can be represented by a vector in space which represents the direction of the magnetic moment of the spin (each spin produces a magnetic field like a little bar magnet). In the absence of an external magnetic field, your choice of basis is arbitrary - there is no eigenstate with more energy than any other eigenstate. However, when you apply a magnetic field (say, in the z direction), the z+ eigenstate gains a higher energy than the z- eigenstate. It is the peculiar property of a 2-state quantum system that when it is put in a superposition of the energy eigenstates, it precesses. I am amazed that we don't have an article on spin precession - perhaps I'll write one. In the Bloch sphere geometrical representation, that means if you point the spin off axis, it will spin about the magnetic field axis at the larmor frequency. Now: the idea behind NMR. If you have a bunch of these proton spins in a magnetic field, then you zap them with a circularly polarized RF pulse at the larmor frequency, then an interesting thing happens. Imagine a small magnetic field component (the RF pulse) rotating with the precessing spins at the larmor frequency. The spin sees a small constant magnetic field perpendicular to it (the RF field in it's rotating frame), and precesses about it. The result is a spiral down the Bloch sphere which, depending on the duration of the RF pulse, can put the spin at any latitude on the sphere. Once the spin is precessing at a nonzero angle to the z-axis, it acts like a little antenna, and can be detected by placing an induction coil around the sample. Thus, you can zap the sample, then detect a response.

How do you use this for imaging? That is another very long story, and you'll have to do some reading before you'll understand the fourier space idea. -bmk

Do animals have nationality?

For example Knut (polar bear). Is it German? or Ah Meng, Sumatran Orangutan, Is it Indonesian?. Should we categorize them together with nationality? Frankedjsjs (talk) 18:30, 8 February 2008 (UTC)

Governments may opt to enforce a national ownership over animals, but the animals themselves rarely regard this enforced ownership as part of their identity. -- kainaw™ 18:34, 8 February 2008 (UTC)

Saying that Knut is German does not imply that he is a German nacional. So as you can say that Berlin is a German city, Knut is a German bear. Mr.K. (talk) 19:38, 8 February 2008 (UTC)

A pleasant instance of polysemy. German may mean, among other things, (1) "having the German nationality" and (2) "of, pertaining to, originating from Germany". These shades of meaning obviously differ from one another (or else they would not be shades). It is unlikely that a piece of Swiss cheese would be issued with a Swiss passport on application. Bessel Dekker (talk) 00:46, 9 February 2008 (UTC)

Our article states: "Nationality is a relationship between a person and their state of origin, culture, association, affiliation and/or loyalty. Nationality affords the state jurisdiction over the person, and affords the person the protection of the state. Traditionally under international law and conflict of laws principles, it is the right of each state to determine who its nationals are."

If we accept this, the question boils down to whether a non-human animal is a person or not. A closely related question has been tested in court in Austria, see here and here. The chimpanzee Hiasl was denied the right of having a legal guardian. I have not read the ruling documents, but one reason it was denied, was that acceptance of a chimp having a legal guardian could ‘create the public perception that humans with court-appointed legal guardians are at the same level as animals’. Wild animals cross borders without passports. How would you define the nationality of a migratory bird? So, IMO the answer is no, non-human animals do not have a nationality in any legal sense. --NorwegianBlue ^talk 12:51, 9 February 2008 (UTC)

What is the resistance of the human body?

Italic text —Preceding unsigned comment added by 59.93.198.63 (talk) 06:08, 3 February 2008 (UTC)

It's quite variable, depending on where you measure, skin condition, fat/lean content, the connections used, and other factors I can't think of offhand. This article should be illustrative. — Lomn 06:39, 3 February 2008 (UTC)

It also depends on what you're trying to resist.--Shantavira|^{feed me} 09:43, 3 February 2008 (UTC)

Presumably electricity (electrical resistance). —Pengo 14:22, 3 February 2008 (UTC)

Maybe Shantavira meant what type of signal? I doubt skin is an ohmic conductor. Trimethylxanthine (talk) 04:28, 4 February 2008 (UTC)

1200 Ohm was published on some obscure website.--Stone (talk) 13:02, 4 February 2008 (UTC)

That is clearly wrong. Although we're not supposed to, here's some original research. I found my ohmmeter and a box of resistors. Measuring from arm to arm, after having licked my fingers to reduce resistance at the surface, gave a reading of slightly over 100 kOhm. To verify this, I checked against various resistors, the closest being 130 kOhm. With dry skin, the resistance is considerably higher, and I was unable to get a consistent reading, but it is certainly higher than 500 kOhm. --NorwegianBlue ^talk 14:03, 4 February 2008 (UTC)

I had the same experience when measuring with an ohmmeter, but I think that it's lower at higher voltages (if it weren't then it would be safe to touch household power supply - you need about 50 mA to die or so I learnt). BTW, I've heard rumors that someone killed himself with a 9 V battery by inserting the contacts into the veins in his right and left hand .... Icek (talk) 02:03, 6 February 2008 (UTC)

Wow! Do you have a source? Googled it with no luck. Should qualify for a Darwin Award! --NorwegianBlue ^talk 09:10, 6 February 2008 (UTC)

Unfortunately not - I read it somewhere on the internet a few years ago. What is the electrical conductivity of blood and lymph? With a salinity of 0.7% it's maybe about 1 S/m (seawater's is 5 S/m according to our article, but other ions like phosphate will probably make blood's conductivity larger). If the current is 50 mA, then the conductance should be 1/180 S. If the distance between the contacts is 1.5 m, and we assume equal thickness along the conductor, its cross section should measure 83 cm², e. g. a cylinder about 5 cm in radius. At least it looks as if it could be true. Icek (talk) 14:41, 6 February 2008 (UTC)

The biggest family-tree you've ever seen...

I was kind-of a fan of the Fox series New Amsterdam (apparently I was the only one, it got canceled after 8 episodes), which was centered around a character named John Amsterdam. In 1642, this fella was a Dutch soldier who saved the life of a young native American girl (in a battle in the place that would become New York) who blessed/cursed him with immortality (he will become mortal again when he meets his true love). Unlike many other immortal people in fiction, he was able to father children. In one episode he states that he has fathered a total of 63 children. When he said that it struck me that he probably was the ancestor of a large chunk of the population in New York.

His last kid (well, latest) is called Omar and was born in 1943. If we assume that he had kids with some regularity between 1642 and 1943, that would mean he fathered a kid every four years ((1943-1642)/63=4). My question is this: approximately how many living descendants would he have? Making some reasonable assumptions, we could say that everyone of his kids had two kids at the age of 25, who themselves had two kids, and so on. I tried calculating this, but I couldn't quite nail down the sum properly (haven't done real maths in a looooong time), could you guys help me? I realize this is a fairly trivial question, but I thought it would be fun to find out. I also realize that the answer will be highly approximate, but I'm really just looking for an order of magnitude here (1,000? 10,000? 100,000? 1,000,000?). Cheers! --Oskar 19:46, 15 May 2008 (UTC)

I get $\sum _{k=1}^{63}2^{{\frac {61+4k}{25}}-1}\approx 27950$. So that's about 30000 or so, using your formula and ignoring possible intermarriages between his descendants. —Ilmari Karonen (talk) 20:03, 15 May 2008 (UTC)

Which is, of course, just the size of the last generation, and doesn't include surviving members of the previous generations. Assuming the three latest generations are still alive on average means multiplying the figure by 1 + 1/2 + 1/4 = 1.75, giving a total of about 48912. Four surviving generations would make that 52406. That rounds to about 50000 either way, given the crudeness of the approximation we're dealing with, and I wouldn't be too confident about that 5. Or about the number of zeros either. But for a quick back-of-the-envelope calculation, which is what you were asking for, it should be within a few orders of magnitude. —Ilmari Karonen (talk) 20:08, 15 May 2008 (UTC)

One of the biggest problems with this kind of calculation is that you're assuming his descendants all marry people that aren't descendants. If two descendants get married, their two kids end up being counted twice, and if a large chunk of the population are descended from him then the chances of that happening become quite large, so you get an overestimate. Although 2 children per family is probably an underestimate, since that would involve 0 population growth. Perhaps we're lucky and it cancels out! These problems become more apparent if you go back further - consider the people that claim to be descended from Jesus. If Jesus had two children and they each had two children when they're about 25, 2000 years later you end up with about 10²⁴ descendants alive today - 15 orders of magnitude larger than the total world population! Over a 300 year period, the effects are significantly less, but it still shows how enormously wrong such a simple model can end up being. --Tango (talk) 20:59, 15 May 2008 (UTC)

As a computational problem: One child every 4 years from 1642 to 1943 and each descendent having exactly 2 children with an unrelated spouse at their 25th birthday, I get 336,261 descendents through 2008. All the above caveats of course apply. Dragons flight (talk) 04:51, 16 May 2008 (UTC)

On the other hand, even though Tango is right in that calculating the number of descendants that way is an overestimate, it is true that many people who lived ages ago have lots of descendants because everyone has two parents. You don't have to be immortal for this. I think, if you take a human from a few thousand years ago, then most probably he or she either has no descendants or a significant proportion of the contemporary population is his or her descendant. On the other hand, if you count only male-line descendants, this is far from true, because everyone has only about two male-line ancestor in any generation. – b_jonas 07:46, 16 May 2008 (UTC)

Surely everyone has precisely one male-line ancestor in each generation? --Tango (talk) 13:18, 16 May 2008 (UTC)

I believe b_jonas means something like 'people of whom you are a male-line descendant', in which case you get two per generation, barring incest. Algebraist 13:45, 16 May 2008 (UTC)

You'd only be a male-line descendant of two people per generation if you're male: otherwise zero (well, I suppose it depends on your definition). Anyhow, b_jonas is touching on the identical ancestors point, a point in history where every person then alive is either the ancestor of everyone now alive, or of noone now alive; our article says this likely happened 5000 to 15000 years ago. (Related are most recent common ancestor, mitochondrial Eve, and Y-chromosomal Adam.) Eric. 86.153.201.165 (talk) 00:10, 17 May 2008 (UTC)

The difference in mine and Dragons flight's results appears to stem from the original poster's assertion that (1943-1642)/63 = 4, which of course isn't true (it's actually 43/9 = 4.777…). Besides, the correct divisor isn't 63 (the number of children) but 62 (the number of gaps between children), giving an average interval of about 4.8548 years. Combining this figure with the other assumptions given, I get a total number of 202,689 descendants, of which the latest generation of course makes up exactly half, or 101,344. With three surviving generations, the number of surviving descendants would then be about 177,353. —Ilmari Karonen (talk) 01:11, 19 May 2008 (UTC)

Dunbar's number and the autism spectrum

Do people on the autism spectrum have a lower Dunbar's number than average? NeonMerlin 03:22, 15 August 2008 (UTC)

Drawing on the articles' section Alternative numbers, the Dunbar number is actually a measure of sizes of community networks, more than a measure related to individuals. Since dunbar developed his theory, there's been notable advances in Network theory which casts doubt on his extrapolation from community to individual. For instance, a group of 150 people can be quite close-knit even if each person knows only 50 others. A few highly connected individuals may be all that it takes.

When it comes to autists, it's my impression that their sensory and cognitive difficulties present difficulties in making and maintaining social interaction with individuals, for instance in picking up non-verbal cues, but they do not generally have some memory deficiency that makes them loose track of what they've learned about individuals. So I'd say that if the Dunbar number had made sense ascribed to an individual, the answear to your question would be no. EverGreg (talk) 08:47, 15 August 2008 (UTC)

I haven't heard of extreme Autism sufferers having bad memory - exactly the opposite in fact. They don't "loose track" of what they've learned about individuals, they simply don't recognise that there is consciousness in people other than themselves so the very idea of "individuals" beyond themselves is impossible for them. Autism is a fault in the part of the brain that lets you gain some insight into what other people are thinking. In order to (for example) follow a conversation, you have to be aware of what the other person is thinking. If you can't do that then you can't interact with people naturally. In the extreme, you perhaps can't even recognise that other people are conscious beings - so they don't interest you any more than some inanimate object. At that extreme, there is no interaction - you don't "forget" about other people - you simply don't care about them any more than you care about a wall or a door.

In the middle of the spectrum (where I happen to be), the ability to recognise that there are other people is clearly there (I have no problem with that!) - and I recognise that you guys are conscious, thinking beings - but I do find it very hard to know what you are thinking about - or what you might be feeling. Hence my conversational style is terrible - I'm always failing to notice when someone says something ironically - or sarcastically. I also tend to be thoughtless when it comes to other peoples feelings...I'll tell the truth as I see it and quite utterly fail to take into account the consequences for other people's feelings when I do that. (SORRY!) This is because I don't instinctively keep a 'mirror' of the other person's thoughts in my head. It gets worse than that...when someone is making fun of me - I have no clue that this is happening until some VERY BIG cue comes along - like someone tells me. (I wish they'd do that more often!) It also means that I tend to over-explain things (sometimes a benefit - but often something that makes people roll their eyes and lose interest) - that's because I tend to forget that their minds work like mine does and that they already know all of this. Add to that the almost total inability to recognise body language and the importance of eye contact at a subconscious level (A few years ago, when I was diagnosed, I took lessons on how to fake it - you normal guys are a VERY weird bunch!).

SteveBaker (talk) 15:28, 15 August 2008 (UTC)

I remember the fun year I 'discovered' eye contact. Exciting to learn such a simple thing could have such a dramatic effect. I quickly learnt to control and limit it when I realised the assumed implications when a girl makes a lot of eye contact with a guy. 217.42.157.143 (talk) 15:28, 18 August 2008 (UTC)

Let's be a little careful. The "autism spectrum" ranges from "normality" (whatever that is!), through Asperger's syndrome all the way through to profound Autism.

• At the most extreme, most profound end of the spectrum, Dunbar's number is likely to be near zero - these poor people can't interact with others to any measurable extent - not even family members. They may not even be aware that there ARE other people...not as thinking beings like themselves. Other people must seem just like any other more or less inanimate object in the world. The parents of such a person might have a higher than expected Dunbar number because they seek help with support groups and such like - but the actual sufferer is getting a big far zero.
• In the middle of the spectrum there are those with Asperger's syndrome (I'm one of them - we call ourselves 'Aspies'). We mostly don't like to interact with strangers face-to-face much - it's quite stressful. Making close friends is extremely difficult - but not impossible. But aspies take to computers and computer networks like ducks to water. It's a great way to get human interaction (which we actually need as much as anyone else) but without the painful business of remembering to fake "realistic" eye contact and consciously use body language in a way that "normal" people do instinctively (How the heck do you guys do that?...and WHY?!). Interacting via a thin text-only interface eliminates all the things we 'aspies' are bad at and that levels the playing field. Aspies are also obsessive about things like computers and we like to delve very deeply into narrow areas of study. That makes us more able to get into things like mailing lists and forums where a bunch of people with very narrow interests gather. So since the advent of the Internet, I strongly suspect that people in the middle of the "autism spectrum" actually have a much higher Dunbar number than "normal" people who don't seem to find it so easy to get on in a world of email, text messaging, blogs, forums and IM as aspies do.
• Normal people...at the other extreme of the spectrum obviously have "normal" Dunbar numbers...around 150 people who they know well enough to comfortably interact with.

The idea that aspies have a higher Dunbar number than "normal" in the age of the Internet is pure supposition. I'm not aware of any solid evidence of this. Certainly before the advent of the Internet, (which, being 54 years old, I remember rather well) we were much more cut off from society - my Dunbar number as a teenager was probably around 20 - if I'm completely honest, maybe a lot less. Since the early days of BBS and UseNet newslists, the number of people I interact with regularly and "know" well has consistently been WAY more than 150.

Also, thinking of the "autism spectrum" as a straight line with everyone in the world sitting at a particular position along that line is a drastic over-simplification. Even amongst people with Asperger's, there is wide variation in how these symptoms exhibit themselves. You get the 'savants' who seem to have an almost magical unconscious way to do math or play music or whatever (I'm DEFINITELY not one of those!) - but you also have the ones who have to work to nestle into some comforting narrow field of study (that's me) - but who don't mind doing that. The range of social skills is pretty broad too (mine are terrible).

SteveBaker (talk) 15:06, 15 August 2008 (UTC)

Body Language

I am not sure if your question about why "normals" use body language was a real one. If it was real, I have some thoughts to offer. I did teach it to negotiators, both the reading of it and the ways in which to emphasize it. I am not an academic with any credentials, however. If you are interested, I will comment further. I will not be in any way upset if you say that you meant the question to be rhetorical. (Oh yes, and I, too, am very pleased to see your name back at the Ref Desk.) ៛ Bielle (talk) 01:01, 22 August 2008 (UTC)

Well - it's a bit of both really. I learned how to interpret some basic body language when I attended therapy for my Aspergers Syndrome. They also teach how to fake it - also the whole eye-contact thing (which is the toughest one for me to do because maintaining eye contact is uncomfortable for me). This is all very interesting stuff - but to someone who was born without the 'innate' ability to do those things, the whole business seems incredibly messy. It's pretty obvious how it comes about - most animals use body language because they don't have a spoken one - and it's clear that humans have not lost that trait. Dogs that are brought up with humans - never interacting with other dogs - all know how to use and decode tail wagging and the "play bow". They can't have learned it from us - so it must be a genetic trait. It follows that it's very likely that humans have body language hard-coded in their DNA also...although I evidently didn't!

What kinda bothers me is that body language in humans isn't happening at the conscious level. Hardly anyone realises that in a meeting of a handful of people sitting around a conference table, you can tell who is agreeing with the person who is talking by seeing who has their arms folded the same way as him/her - that leaning back means "I dislike what you're saying" and folding your arms it a defensive thing. If most people don't know that - but they do it anyway - then it's not a conscious act. This was not initially obvious to me - because for me, it is a conscious act - and if I have too many other things occupying my thoughts, I don't always remember to do it.

So if we don't know that we're doing it - and we don't consciously realise that we're decoding it - how do the people who study these phenomena know that they are catching everything? Perhaps there are all sorts of significant signals being passed around from subconscious-mind-to-subconscious-mind communication in this sneaky way! Perhaps the reason I still can't reliably tell when someone is kidding me along is because I'm missing some really subtle signal.

My son is also an aspie - and he and I have decided to make up our own body language. For example, placing one hand on the back of your neck like you're rubbing it and subtly moving your now protruding elbow up or down is a message between us that means "I think someone is making fun of you/me/us". The choice of which elbow to use indicates the direction in which the offender is sitting relative to the signaller.

It's always interesting to hear other people's take on the "library" of gestures that are out there "in the wild". I was watching a documentary some years ago that said that the seemingly-universal nod-of-head-means-"Yes"/shake-of-head-means-"No" gestures are not in fact universal. Oddly - that's not a gesture I've ever had trouble with - even before I learned I was an Aspie and did the course, I knew what that meant. But now I find that in some cultures the two signals have opposite meanings and that a third motion (the rolling of the head from side-to-side) is a third gesture that can mean something in some societies. That's odd because that means it can't be genetic like the arm-folding thing...which means it's taught - and that explains how come I know about it and presumably how come we do it and decode it consciously.

It's an endlessly fascinating topic - and I often wonder just how weird it would be if my body went off sending out these signals - moving my arms around and who-knows-what-else without "me" (my conscious mind) screening them for appropriateness first! It seems incredible to me that you normal people don't realize that all this weird stuff is going on without you deciding to do it! But it's evidently true because now I can see it happening just like in the book. Why isn't there some weird conflict between unconsciously wanting to look all defensive with folded arms at the subconscious level - while your conscious mind is saying "I need to write something down now - can I please have the use of my right arm?". How can these "resource usage" conflicts be going on without you guys noticing it?

I suppose it's like my breathing happens subconsciously - but my conscious mind can overrule that when I decide to hold my breath. But I'm really aware that my subconscious is insisting on taking over again before I pass out - is there a similar mechanism that forces you to drop your pen and fold your arms after a while? I guess that if there is, nobody noticed it yet.

This is all SO bizarre (more so because I only found out about the extent of it when I was closing in on 50 years old). It's like being told that you're really living in a world where everyone else but you is a telepathic alien. It's downright creepy! Just how much do you guys tell each other that I'm missing?

It's no wonder you "normal" guys can't sit still long enough to read thick computer manuals or learn to name all the parts of a 1963 Mini Cooper! You're too busy flapping your arms around sending sneaky telepathic messages to each other! (I'm kidding - of course)

SteveBaker (talk) 02:07, 22 August 2008 (UTC)

I am fascinated by what you write. I wonder if you “send” body language signals of which you are not aware, like the twitches of the small muscles under the eye that give away tension or lies, or the sudden constriction of the pupil of the eye that denotes surprise. There are very few people who can control such reactions, though there are many who can control the grosser gestures and reactions. My wondering arises from the idea that, in order to mimic body language, you first have to have noticed it at some level. In general, we do this mimicking from babyhood. (And that is the “why” of body language, of course: we do it because everyone -or almost everyone- else does it.) Does Asperger’s prevent such noticing?

Body language is like oral language in many ways. For the most part, adults don’t think about every word or every sentence or even, and this is all too obvious in listening to almost anything “live” on TV, every paragraph. We just start talking. Something has obviously happened at an unconscious level, and happened very, very fast, but, unless we come to an idea that needs thinking about, we just keep talking. Somehow, for the most part, the ideas come together into words, sentences and paragraphs. Body language is similar except that only a small percentage of the population (actors, politicians, public speakers, con men, gamblers, etc.) ever stop to consider what it is that their body is saying.

We tend to trust people whose body language is consistent with their words, and mistrust those whose body language is not. The real problem arises because we may be able to read the body language with extreme accuracy, but we cannot be certain of the cause. If I see you in a defensive posture (which, to be read correctly, would involve much more than just the folding of the arms across the chest) I cannot know whether the defensiveness is in reaction to the intent of something I have just said or done, or whether it is a reaction to something else you are thinking about. I may have used a specific word that sent your mind off on a different track, one more important to you, and it is to that track that you are reacting. Untold confusion results if I then react to your defensive body language with aggression or placation, depending upon what I want to achieve.

I sometimes wonder how any two people manage to find enough understanding of each other to get through a conversation without mayhem or madness, and that’s even when they speak the same oral language! The research suggests that we put more reliance on the body language than the words. I met someone in grad school who had almost no body language of the gross sort; even quadriplegics don’t sit as still as she did. I often wondered if she was joking about some things she said, though longer exposure convinced me she also had no sense of humour. She made no friends that year, and every study group complained about her lack of co-operation, even though she did all the work she was supposed to do. That was the beginning of my interest in the language we speak even when we are uttering no words.

Thank you for your response. You have given me much think about. I love the anecdote about the private body language you invented with your son. Most spouses have similar signals for public occasion, and some families develop them. My grandmother used to look at us over her glasses after we had said something unacceptable to her in a public space and say “Thank you, dear”. That meant, in words she may not have known, and certainly would never have used. “Shut the fuck up! It’s all downhill for you from here to home.” ៛ Bielle (talk) 03:10, 22 August 2008 (UTC)

I'm unaware of sending any body language that I'm unaware of...hmmm - I guess that doesn't help.

Asperger's is a small step on the way to Autism. As far as we know, Asperger's is a (partial?) failure of the part of the brain that enables you to keep a mental image of the other person's mind. I have no magical clues about whatever it is you might be thinking. I might see your body language - but the part of my brain that would record that information and insert it into my image of your mental state - simply isn't there. Autism takes that further by perhaps not even realising that other people HAVE minds - another person is just like a wall or a car - some kind of inanimate 'thing'.

Having to learn body language and apply it consciously means that there is no reasonable possibility of reproducing it exactly. So you've gotta go with some kind of "shorthand" version of it. Sure there are lots of things you need to do to look "realistically" defensive - but folding your arms and leaning away from the speaker is about the limit of what I'm able to do while still listening to what's being said. Doing those kinds of thing does seem to help other people to deal with me. The trick where you mimic the pose of people you agree with and sit differently to them when you don't like what they are saying is a really neat thing. It's almost cool that I'm doing it deliberately and everyone else is doing it without knowing. At a glance I can tell who is with me and who isn't - I really wish I'd known that 40 years earlier than I did!

The person you met in grad school sounds like a classic Aspie. When I finally realised I had a problem - very late in life - and was properly diagnosed - it was like a bright light was suddenly turned on in my life. I was able to look back on past disasters (somehow most of them involved failures with girls) - and I just cringe when I realize just how badly I screwed up - and how trivially easy it would have been to fix it if only I'd known. Just imagine having sex with someone who hasn't a clue about your mental state...yeah...exactly. Early diagnosis is a really important thing.

One last story...recent...horrifying...heartbreaking: My son (it turns out) is colorblind. Very mildly - the most mild kind possible. We found out because I was forever telling him to switch his Wii game from 'standby' (where the disk keeps spinning and wearing out the motor) to 'off'. There is a single tri-color LED on the front - green for "running", orange for "standby" and red for "off". He complained that he couldn't possibly know what state it was in - so I pointed the LED out to him: "Look - red for off, orange for standby"..."But Daddy - those are almost the exact same color! How could anyone be expected to know?"...at that moment, I made the mental connection that he could just possibly be color-blind. I was suddenly fascinated by the possibility of tracking this down...it was like answering a question on the RefDesk. I looked online for a color blindness test - Oliver tried it and failed in the classical manner - I showed him that I could pass the test - I surfed Wikipedia to get a more accurate answer for what exactly the result meant in terms of human physiology and explained it to Oliver. Then I tried to find the limits of the range of his problem by making some color swatches on the computer and asked him to tell me whether they looked the same or not. I figured out that a piece of red gel taped over the Wii's LED would enhance the difference between orange and red for him...that actually worked...I was elated!

This went on for AGES.

What I'd UTTERLY neglected to do was to reflect his mental state - he was DEVASTATED - he had suddenly been declared handicapped - his entire future life as a budding graphics artist might change - and I (his father for chrissakes) wasn't comforting him or telling him it wasn't that bad or simply hugging him - I was joyously exploring the problem - solving the intellectual puzzle, piling on more proof.

I feel absolutely AWFUL about that...do you have any idea how bad I felt when I stopped and did the little "What might the other person be feeling?" exercise? I'd let him down in the worst possible way. But that's what Asperger's syndrome is all about - a deep fascination with exploring a new topic - a total inability to notice how other people might be feeling.

(Worse still - it turns out - Oliver is also an Aspie, so he couldn't reflect my mental state and realize why I seemed so happy that he was color blind.)

SteveBaker (talk) 04:39, 22 August 2008 (UTC)

I continue to be amazed at your ability to solve problems that would overwhelm most people. I think your story about discovering your son’s colour blindness, and the different ways in which you each reacted, ought to be in every handbook for parents.

Does it help to know that large percentage of the people I have met, worked with and/or taught, also give no thought to what others might be thinking or feeling, as they crash through life? As far as I know, Asperger’s is relatively rare, and thus these people have the ability, they have just never considered it important to use. (As an aside, how would your son feel about being identified on Wikipedia and discussed by strangers?) And then, even among those of us who try, we frequently forget, in the midst of an adventure, a search, a project, that not everyone will be delighted with our success or even with our enthusiasm.

If you think of body language the way you might think about blushing, for example (and do you blush?) as something that just happens in certain situations, that often, if not always, is under no conscious control, that advertises an inward state but not the reason for it, you would be closer to understanding how body language works for most of us. If you are successful in your mirroring techniques, then you might be very good at much of what Neuro-Linguistic Programming teaches. I understand that if you practice it often enough, it becomes automatic and does not require much conscious control or “front of mind” room, in just the same way that "normals" use body language. I don't have to analyze the body postures at a table at a conscious level. I have been a negotiator for almost all my life; I just turn towards those who are not in agreement and "entreat" them to join the rest of us, and all without a specific word being uttered. I have watched this on tape so that I know it is true and that it just happens because I know I never gave the actions one single conscious thought. You asked earlier about a mechanism that forces us to "drop our pens and fold our arms". Yes, it does exist. It is not, for most of us, just high drama, or a calculated act, when we throw down our pens, cross our arms hard, and glare across the table. It just happens, though it can be controlled. And why do we do it? Because it works! The body conveys in a very compact form exactly how we feel. It is not subject to advanced vocabulary skills, or any specific experience, and it is difficult, though not impossible, to fake over any length of time. We smile for the same reason, and that is also hard to fake. ៛ Bielle (talk) 06:21, 22 August 2008 (UTC)

I certainly do blush - I don't notice other people blushing though...unless I'm specifically looking for it. I smile naturally too (that's just as well because I know it's almost impossible to fake) - but not always at appropriate times. As you say, normal people broadcast and understand internal state - but not the reason for being in that state. I'm missing the understanding of state because I lack Mirror neurons (or at least there aren't enough of them - or they don't work - or maybe they just found something more interesting to do!) - I don't naturally broadcast my internal state (although some things like blushing and smiling seem to work OK).

When someone throws down their pen, crosses their arms and glares across the table - that's not a subconscious thing. That's a very conscious act - and completely obvious (even to me) at a conscious level. That's not the problem. It's the subtle undercurrents that express an internal state that has not yet reached the level of conscious action that is the problem. When my conversation has turned into a speech and the people around me have heard enough - I simply can't tell. This is really annoying - for them, no doubt - but also for me. I'm trying to have a polite conversation at a party - and I'm boring people to death by explaining the intricate details of TCP/IP switching protocols when they just wanted to know what I do for a living. Trust me - I'd rather not be doing that! Before I learned strategies to cope (like don't put across more than three or four sentences without stopping until the other person says something to encourage me to say more)...I was in a terrible social state. But even knowing this information, it's really tough to be self-monitoring for duration, remembering to keep appropriate amounts of eye contact, mirroring body posture, watching for signs of the other person getting annoyed with me - and at the same time actually saying something interesting! That's hard work!

It's interesting that you mentioned Neuro-Linguistic Programming (NLP). My sister (who lives in the UK - where this stuff seems to be widely accepted) has just signed up to train for that. Since I'd never heard of the subject before (it's evidently not 'big' in Texas yet!) I've been reading about it. It bothers me that it seems awfully pseudo-scientific new-age stuff without any scientific grounding whatever. It claims to have roots in (of all things) computer programming and cybernetics! Well - as it happens, I am one of the VERY few people in the world who has a degree in Cybernetics (from the University of Kent) - and from everything I see in NLP, (I've read "Frogs into Princes" and some of the papers in the Journal of Counseling Psychology that relate to NLP) it has nothing whatever to do with Cybernetics or any relationship to the disciplines of computer programming (which is what I do for a living). From what I read, its claims to have a basis in neurology are vehemently denied by experts in that field - which leaves only psychology as a basis for it's claims (I have no way to know because I know nothing of that field). If at least three of the four planks it's based on are in fact not contributing anything to it's methodology - then it seems to me that it might very well be about as scientific as mood rings and crystal healing! I'm nervous about saying this to my sister because she's getting very excited about getting into the field - but I have a bad feeling about it! I'm going to study it some more...but it's not looking good so far.

SteveBaker (talk) 15:37, 22 August 2008 (UTC)

Psychology is likely a good place for assigning NLP until we -the world community at large- understand more about it. I have the Bandler and Grinder books. (No scientist is likely to be attracted to books entitled The Structure of Magic.) I did try to register for a course, but there was too much "push" at the local office when I went in to make my payment. I withdrew because I was uncomfortable. I have never gone back. I have two friends, one a psychiatrist and the other a psychologist, both with undergraduate degrees in biology, who have proven to their own satisfaction that a number of the actual techniques work, though they also both found that some were too manipulative to be used except with the greatest of care and in a therapeutic session. Neither of them trusted the "science" of NLP, which is quite different from finding the practices, or some of them, useful.

As for your remark that the throwing down of the pen etc, is conscious, I ask you to consider that it is not, or it is no more conscious than the eruption of an angry series of words. If one stops to think, which is what those with "anger management issues" are asked to do, then any gesture or word becomes conscious, but I tell you that many of the gestures you may be thinking of as conscious are not really so. When I roll my eyes heavenward in exasperation, the gesture is started and finished before I have even thought about it unless, and this is important, I have a reason (conscious) not to be so demonstrative. So, as you force yourself to keep track of your own body language and that of others until it is too tiring to do so, most of the so-called "normals" only keep track of what needs to be suppressed, until it is too tiring to do so. If you have ever been in a discussion that, seemingly quite suddenly, and over a small point, exploded into angry words and gestures, you are likely to have been talking to someone who just got tired of holding down his natural response and they burst forth.

These are all gestures over which one, in the usual course, has control: motions of head, hands, eyes, etc. The other group, what the gambling world calls "tells", the tiny, almost impossible to change or control like twitches, colour changes, temperature changes, moisture changes are all entirely unconscious from the initial noticing through to the response. We know about them from detailed observation, and it is possible we are missing some. Smell, for example, is seldom discussed and I think it may be yet another set of coded signals. I also suspect that some of the brain's redundancy is actually busy at this level. ៛ Bielle (talk) 19:51, 22 August 2008 (UTC)

Apologies to out-dent, but that was getting tough to read. I'm a long time ref-desk lurker, and I wanted to chime in my cheer at your return (my condolences on the circumstances) but then I saw this exchange, which is absolutely fascinating. I've been chewing on analogizing our common situation as something like listening to a pop song, as a person of pop sensibilities, and having the backbeat completely muted. Some people depend so thoroughly on the "backbeat" that nothing else about the "performance" matters, it's cacophonous and displeasing, period - most are just off-put and try and fill it in "automatically" - and a precious few just dig the different composition. I imagine that the spectrum is a question of more instruments getting muted... but hey, what's red to the blind, anyway? As regards NLP, I suspect that there's a bit of magic (in the sense of the word Penn&Teller, or Derren Brown, might use) with bloat as icing on top to push the concept. There's a lot that's fairly repeatably demonstrable about convincing other people of other things - some study about velveteen ears in Disneyland escapes my recall - but beyond that? Maybe it's like dieting - eat fewer calories, exercise more, and then dress those ideas up with some random claptrap. Be well. 98.169.163.20 (talk) 04:15, 24 August 2008 (UTC)

Frequency of Meiotic Crossover

OK, if human gametes always acquired their chromosomes intact, then I'd have, on average, 11.5 from each of my grandparents, 5.75 from each great-grandparent, etc. Thus if I went back in my pedigree 7 generations—and with the further simplifying assumption that all of my ancestors were unique—then since there are 128 people back there and only 46 opportunities, the expected contribution from any one of them to my genome would be zilch. And seen the other way round, any one of my descendants 7 generations hence could expect to inherit nothing from me.

But, of course, meiosis doesn't work so tidily. So my question is, in practice how far off is the above reasoning? To state it more rigorously, how likely is it that any particular human gamete is free of crossovers, that each of its 23 chromosomes is simply a complete copy of one from the homologous pair?—PaulTanenbaum (talk) 03:41, 25 August 2008 (UTC)

The crossover rate varies by chromosome, but one would expect in general one crossover per chromosome. So one would have to go back more than seven generations to be reasonably certain that at least one ancestor in that generation had no genetic contribution to your makeup. - Nunh-huh 03:52, 25 August 2008 (UTC)

So, for instance my son's X chromosome likely contains some scraps from both of my in-laws?—PaulTanenbaum (talk) 04:04, 25 August 2008 (UTC)

Yes. And, in general, though not invariably, your son's autosomal chromosomes will likely contain some scraps from all four grandparents. The bigger the chromosome, the more likely there was a crossover event. - Nunh-huh 04:22, 25 August 2008 (UTC)

The number of crossover events per chromosome is higher than Nunh-huh suggests. According to this book, "On average, between two and three crossover events occur on each pair of human chromosomes during meiotic division I." I was surprised by the confirmatory answer to the question about the likelihood of crossovers between the X and Y chromosomes, but Nunh-huh is right on this one - there are indeed tiny regions in the Y chromosome which do cross over with their X chromosome counterparts, see this figure from this article. --NorwegianBlue ^talk 18:17, 25 August 2008 (UTC)

While it's true that there is a small area of the Y & X chromosomes that are homologous, and so permit crossover, it's not pertinent to the question asked about Paul's son's X chromosome, which came from Paul's wife (the crossover here occurred between the two X chromosomes of the mother, each of which contain portions of an X chromosome from her mother, and an X chromosome from her father, again due to crossover). - Nunh-huh 03:13, 26 August 2008 (UTC)

Nun-huh is right about the point of my question. But I do appreciate NorwegianBlue's info about crossovers between X and Y, and the pointer to the NIH article is extremely helpful. Muchos gracias to both of you!—PaulTanenbaum (talk) 03:25, 26 August 2008 (UTC)

Anatomy

Can someone link me to some information on the evolution of the ear, or make a wikipedia page on it? Evolution of the nose wanted, too :) I'm curious... Also, any information on the evolution of blood (not individual blood types like A and B but the substance of blood) would be cool. Could someone compare and make a cross-section on the differences between different species' blood? Or at least groups of species (insects, mammals, fish etc.), please. Also, how do the immune systems of smaller organisms like insects work? Can someone further explain the system through which lymph is conveyed through the body, and also compare that to other organisms' lymph transportation? Some more questions about blood - I know that Red blood cells live about 120 days, and they go to the Liver to be "cleaned" (this is correct, right?), but how often do they go? How are they cleaned? Also, how does Hemoglobin work? I know that arteries move RBCs through peristalsis - does this mean that arteries are smooth muscle? How do veins keep that momentum of the blood up, especially far away from the heart? veins use valves, don't they? Are the valves cells of their own, or inanimate proteins or what? Oh, and evolution proponents say that one human chromosome is the fusion of 2 chimp ones or something like that. Without getting into a pro/anti-evolution debate, how could these have fused gradually/quickly?

Thanks for all your time. Answer as much as you can :) I really like learning and am curious about this stuff... —Preceding unsigned comment added by 216.102.78.170 (talk) 16:45, 18 November 2008 (UTC)

That's too many questions for a humble refdesker like me to answer, but I'll point out that arteries do not move red blood cells through peristalsis! See heart. --Sean 18:51, 18 November 2008 (UTC)

True, of course. However, the questioner is correct in asserting that the arteries have smooth muscle. Its function is vasoconstriction, which is used for the regulation of blood pressure, conservation of heat (directing blood away from the skin when it's cold) etc. --NorwegianBlue ^talk 21:17, 18 November 2008 (UTC)

Just a comment on the valve question. Those aren't valves that the body controls, they are simple valves, just a flap over an opening, such that the flap is closed when movement occurs in the opposite from normal direction, and open when flow is in the correct direction:

_____________________
           /|
 Flow  -> /   Flow
 Dir     /    Dir
 Closes /     Opens
 Valve /  <-  Valve
      /
            |        

StuRat (talk) 19:09, 18 November 2008 (UTC)

And the valves are MUCH larger than individual cells, they are macroscopic, and composed of both cells and extracellular proteins. The proteins are mostly collagen, many of the cells are fibroblasts, and the valve is covered by endothelial cells. --NorwegianBlue ^talk 20:31, 18 November 2008 (UTC)

• The lymph question is answered in the articles Lymph and Lymphatic system. Basically, what is to become lymph is part of the plasma of the blood as it leaves the heart. In the capillary network, some of the plasma leaves the blood and becomes interstitial fluid. Most of it goes back into the venous blood in the venules. The surplus enters lymphatic capillaries. Note that the lymph vessels start as "blind alleys" into which this liquid enters, before moving towards the great veins in the neck, where it enters the bloodstream. Lymph vessels have valves, and the transport of the lymph against gravity is in part caused by pressure from nearby pulsating arteries, in part by contraction of striated muscles (e.g. in your legs -- same thing as for the veins). According to our article, lymph vessels also have peristalsis. (I didn't know that, and am a bit sceptical -- could someone confirm? (User:Nunh-huh, are you reading this?))

• Well, I hadn't been, but now you've gone and invoked the name of the devil, and so I am. Small lymph vessels are thin-walled channels, typically just tubes consisting of endothelium, so they can have no peristalsis. Only the larger vessels have any muscular layer, and there is some sequential contraction in these that aid lymph flow. However, like you, I recognize that pretty much the only thing ever actually referred to as having peristalsis is the GI tract. I think the jury is out on which method of lymph propulsion is predominant: skeletal muscle compressing the lymphatics (with the one-way valves assuring that propulsion occurs in the proper direction), vs. propulsion intrinsic to the lymphatic vessel, and my money's on the importance of the former. But both have been observed, and described, and so both occur, regardless of which is more important. - Nunh-huh 03:13, 21 November 2008 (UTC)

• The liver/"blood cleaning" question: I have no idea what "cleaning" of red blood cells would mean. It is correct that the Kupffer cells of the liver may phagocytose aging red blood cells, but that is far from the most important function of the liver, and a task which is believed to be primarily performed by the spleen. See Liver. The key point in understanding its function, is realizing that it receives all the blood from the gut, with all the nutrients, and also all the nasty stuff, toxins etc. (For the exception, see Chyle - the lymph from the gut, which contains fat, and which bypasses the liver). So two of its most important tasks are buffering glucose as glycogen, to keep the blood glucose level stable between meals, and detoxifying otherwise toxic substances that are absorbed from the gut. In doing so, it also often modifies drugs that are taken orally. In addition to this, the liver has many other functions which are described in the article.
• The chimp question: see Chimpanzee genome project for a comparison of the genomes (human chromosome 2 is a fusion of two chimp chromosomes), and here for an explanation of the mechanics of how such a chromosomal rearrangement could happen. A single chromosomal rearrangement does not necessarily prevent meiosis from occurring, but heterozygotes tend to be less fertile and may have an evolutionary disadvantage. --NorwegianBlue ^talk 21:06, 18 November 2008 (UTC)

Why blood groups and Rh?

I couldn't find in our article or figure out in google why blood groups are needed. What is their actual purpose, why don't we have some universal blood group? And what is the purpose of Rh? 85.132.54.6 (talk) 20:32, 5 March 2009 (UTC)

Why should they be "needed"? As with most evolutionary matters, they simply are. Also, for quick reference: blood type/ABO blood group system and Rhesus blood group system. — Lomn 21:04, 5 March 2009 (UTC)

Blood groups exist because they turned up one day and they don't do any harm, so they stuck around. Blood groups only became significant in any way when we started doing blood transfusions, which was extremely recently in evolutionary terms. (I guess there is a slight disadvantage to them since there are sometimes problems with Rh- mothers having Rh+ babies [I think it's that way around], but it's very rarely a problem because, if memory serves, it's only the second such baby that dies, and even then only if there were complications with the first one.) --Tango (talk) 21:11, 5 March 2009 (UTC)

There was (until recently) no evolutionary pressure in favour of compatibility or homogeneity (and so things just drifted apart, as they are wont to do). Right now there is a modest pressure - if someone has a group that requires transfusion with a rarer type, they run the disk of the hospital not having the right kind, and thus their dying without issue. If medicine were to remain exactly as it is for a few thousand years then you would expect to see a modest increase in the proportion of individuals who have transfusion-friendly blood when compared with those who don't. 87.115.143.223 (talk) 21:13, 5 March 2009 (UTC)

There is one modest piece of evolutionary pressure, Hemolytic disease of the newborn (HDN), which is part of why the Rh system was discovered in the first place. ABO rarely has a role in HDN. The ABO and Rh red cell antigen groups are not known to be functional, but there are some red cell antigens, such as the Duffy antigen system (usually "Fy" in shorthand) which are known to be meaningful outside of blood typing for medical or investigative purposes. In most of these cases, it's likely that no one has found out exactly what these bits of stuff on the extracellular matrix of the cell are for. SDY (talk) 21:15, 5 March 2009 (UTC)

Hmm, that's interesting. So that would imply either that human blood groups are slowly converging (from a more disparate ancestry - RH+ == grandma was a Neanderthal) or there is weak opposing pressure from some unknown utility in heterogeneity (e.g. resistance to some blood-borne disease). 87.115.143.223 (talk) 21:25, 5 March 2009 (UTC)

I'm not sure when the mutation happened which causes some people not to have the RhD antigen (I think everyone had it originally, but I may be wrong), but it wasn't necessarily that long ago. It only takes one mutation followed by the person with that mutation having lots of children for it to spread fairly widely within just a few thousand years. There may be some evolutionary pressure towards heterogeneity, but don't forget the importance of random chance. If the evolutionary pressure, in whatever direction, is very weak then random chance can end up being far more significant, even over the long term. --Tango (talk) 21:34, 5 March 2009 (UTC)

(outdent)

In general, when a genetic polymorphism is maintained in a population, some kind of balancing selection is at work. Polymorphisms that are neutral tend to disappear rather quickly. In this paper, the authors develop a model which attempts to explain the ABO gene frequencies by frequency-dependent selection (a type of balancing selection). They hypothesize that the reason is that bacteria may adapt differentially to the different carbohydrate structures of ABO antigens, and that, in addition, the natural antibodies that we have against the A and B antigens we lack, may offer protection from viruses that carry A and B antigens in their envelope derived from their previous host.

Rh proteins are believed to be ion transporters, involved in ammonia transport. I have not come accross any articles that attempt to explain the maintenance of Rh polymorphisms, although Hemolytic disease of the newborn may play a part, as suggested by SDY. --NorwegianBlue ^talk 21:40, 5 March 2009 (UTC)

[3] discusses the matter, I'm still reading it so I'm not sure what it concludes (it seems to be suggesting there must be a balancing selection of some kind). --Tango (talk) 21:50, 5 March 2009 (UTC)

Not necessarily relevant, but my favorite bit about blood is that the gene for type "O" is the gene for type "A" with single base pair different, a nonsense mutation. Tiny change in genetics, potentially lethal difference in transfusions. SDY (talk) 22:11, 5 March 2009 (UTC)

One of the mysteries in transfusion medicine is why people who have never been exposed to other ABO types have antibodies to those types. For example, a person who is type B (not to be confused with the immune system's B cells) has antibodies to type A immediately after the immune system develops (by about 3-6 months of age). Speculating: this would give a strong evolutionary advantage if both A and B "look like" viral antigens, since even if only half of the population is immune, the disease may have trouble persisting. Type "O" in this case would be the best of both worlds, since it would grant immunity to both "A-like" and "B-like" viral antigens. SDY (talk) 22:55, 5 March 2009 (UTC)

Re the paper that Tango linked to: Note that it was written at a time when the D, c/C and e/E antigens were thought to be encoded by three separate, linked genes. It has since been discovered that the c/C and e/E antigens are two epitopes on the same molecule. --NorwegianBlue ^talk 22:23, 5 March 2009 (UTC)

Didn't I read something somewhere about some mild correlation where people with blood group X were a bit more likely to get disease Y but a bit less likely to get disease Z, for suitable values of X, Y, and Z; and that the geographical distribution of the genes for different groups (if you corrected for recent migrations) could be related to the geographical distribution of the relevant diseases? This would make sense as a factor to preserve a diversity of blood types (in the ABO system) in the global population. (The practice of transfusing blood is too recent to have had any effect on this, of course.) Anyone remember reading something like this? --Anonymous, 05:48 UTC, March 6, 2009.

I don't remember a specific news item like that. In the disease associations that come to mind, negativity for an antigen is associated with resistance to a disease. This is the case for Duffy antigens (malaria), and A and B antigens (malaria and thrombosis). However, fetal A and B antigens may be protective hemolytic disease of the newborn, because anti-A or anti-B antibodies in an Rh(D) negative mother, who carries a child that is Rh(D) positive and positive for the A or B antigen that the mother lacks, protect against maternal Rh-immunisation. --NorwegianBlue ^talk 12:34, 6 March 2009 (UTC)

Moved comment by SDY that was posted in the middle of my reply. --NorwegianBlue ^talk 09:44, 6 March 2009 (UTC)

Can't give a definitive reason but the presence of Blood type (non-human) amongst numerous animals and its persistence from the apes to us indicates having blood groups must have a strong evolutionary advantage. Dmcq (talk)

Is This a Valid Concept in Evolution?

When speaking of evolutionary change, often only a single characteristic of a creature is considered. Similarly, only a single external influence affecting a creature is considered. But, of course, there are many characteristics in each member of a species that relate to evolution (fitness to survive), and many external influences have an effect on evolutionary change.

Furthermore, each member of a species is unique. It differs from other members of the same species in many small ways. The totality of the characteristics held in common, the unique characteristics, and external influences, determine a member's survivability and longevity, and hence its direction of evolution. (Long life normally results in more offspring being produced. Members with the most offspring will come to prevail in numbers over other members of the species, and will establish the evolutionary trend. This assumes that at least some unique characteristics are inheritable.)

Each unique characteristic will vary in its potency in relation to longevity. Also, the degree of potency may vary from one generation to the next, or even disappear from a new generation. External influences which affect longevity may also vary in potency from generation to generation. To clarify the principle being described, it will be assumed in this discussion that the potency of a unique characteristic, and the potency of environmental factors, remain unchanged over generations.

For any particular member of a species, the various unique characteristics that aid longevity can be expressed, respectively, by the capital letters A, B, C, …. The unique characteristics that hamper longevity can be expressed by the letters a, b, c, …. The total effect of all unique characteristics (U) on longevity can be expressed as U = A+B+C…. – (a+b+c ….).

Characteristics held in common that affect longevity can be expressed as C.

The external influences that aid longevity can be expressed by the Italic capital letters A, B, C, …. The external influences that hamper longevity can be expressed as a, b, c, …. The total effect of all external influences (I) on longevity can be expressed as I = A+B+C…. – (a+b+c ….).

The combined effect of unique characteristics, common characteristics, and external influences on longevity (L) can be expressed as L = U + C + I.

The above considers only an individual member of a species, and its descendents that breed true. Other members have their own unique characteristics and will have their own survivability and longevity. There will be unwitting competition between members with regard to which member will have the most true-breed descendents. The true-breed descendants of a member that has the highest L will eventually prevail over all other descendants. The descendants of other members will eventually become extinct because they will be in competion for food with increasing numbers of high-L (long-lived, more offspring) members.

Complicating the matter is the fact that unique characteristics, common characteristics, and external influences are not quantifiable in their effect on longevity. Indeed, some of the characteristics and influences would probably be unknown to science. Therefore, while the above formulas express general principles, they cannot give specific results.

A further complication is that nearly all species of living things reproduce sexually. Therefore, species members may interchange any unique characteristics that can be passed on by sexual reproduction. None of the resulting half breeds will have maximum longevity.

Maximum L may be only very slightly longer than other values of L. But over thousands of generations it will make a big difference in the numbers of members that will survive.

A single species member that by chance had an extra long life, and its descendents which inherit that capability, will determine the direction of evolution of the species. Shorter lived members, with their uniqe characteristics, will die out.

With regard to a single member of a species determining the direction of species evolution, I remember reading something about that for humans. The effect is indicated in cells and in the female line of descent. – GlowWorm.

External influences are not inherited, so what you are saying makes no sense. How well a particular organism reproduces depends on how well its inherited characteristics suit the environment it is in and a generous dose of luck. Over a long enough time the influence of luck reduces and those organisms which best suit the environment will prevail over the others. That is evolution. The environment is continually changing (both due to changes over time and due to organisms moving from one place to another), so evolution is a continuous process. One key part of the environment is other living organisms (of the same and different species), which are also subject to evolution, which means you get all kinds of complex interactions making the whole thing rather chaotic and unpredictable. --Tango (talk) 23:42, 8 March 2009 (UTC)

I did not say external influence is inherited. I said it affects evolution. Also, earlier on this thread I mentioned that other living things may be considered part of the environment. – GlowWorm.

You said "A single species member that by chance had an extra long life, and its descendents which inherit that capability", that's just not the case. Its descendants only inherit the genetics, which is only one component in determining longevity. (And longevity isn't the only thing to consider - number of offspring that reach breeding age is related to longevity, but it isn't directly proportional.) --Tango (talk) 00:12, 9 March 2009 (UTC)

So many errors - so little time!

• When speaking of evolutionary change, often only a single characteristic of a creature is considered. - Well, in the simple examples quoted for simplicity in text books and such - but in reality, no.
• Similarly, only a single external influence affecting a creature is considered. - Again, not in practical applications of evolutionary theory.
• Furthermore, each member of a species is unique. - No, in many animals there are identical twins and in the case of creatures that reproduce asexually (an Amoeba, for example) - the offspring are essentially clones of the parent - except for DNA transcription errors and such.
• Long life normally results in more offspring being produced. - Not so - in fact most species are programmed to cease reproductive capability later in life. Female humans (for example) cease to be reproductively capable at about the same age all around the world - despite drastically different life expectancies.
• Members with the most offspring will come to prevail in numbers over other members of the species, - PROVIDING that the reason they were able to produce more offspring is (a) genetically heritable and (b) exposed to a similar set of environmental pressures. If (for example) a species is exposed to extreme drought - but ample food is available - then a drought-resistant strain that can more efficiently extract moisture from the food will survive into the next generation. However, if in ensuing years there is plenty of rain - but horrible food shortages - then the offspring of that successful earlier generation may suffer horribly.
• Each unique characteristic will vary in its potency in relation to longevity. - No. Longevity isn't everything - proclivity and reproductive success is very important. It's not as simple as you try to make it sound.
• To clarify the principle being described, it will be assumed in this discussion that the potency of a unique characteristic, and the potency of environmental factors, remain unchanged over generations. - That might clarify your explanation - but it's far from being true. When you look at very successful species, you come across animals like Wolves and Bears - which will eat almost anything - species which are HIGHLY adapted to (for example) eat just one food or hunt in just one way or which can only produce young if they swim up some highly specific river to spawn...those are very fragile...and a tiny change in the environment can wipe them out. Response to change is a vital part of why evolution works. Consider sexual versus asexual reproduction: Species that reproduce asexually can reproduce much more efficiently - but the problem is that there is very little genetic variation - so they are unable to change rapidly when the need arises. The evolution of sex itself is in response to the somewhat abstract evolutionary pressure - which is the ability to respond rapidly to changes in evolutionary pressure!
• For any particular member of a species, the various unique characteristics that aid longevity can be expressed, respectively, by the capital letters A, B, C, …. The unique characteristics that hamper longevity can be expressed by the letters a, b, c, …. The total effect of all unique characteristics (U) on longevity can be expressed as U = A+B+C…. – (a+b+c ….). - I disagree - it's more likely to be something like U = A x a + B x b + C x c. If you have the gene for 'B' (ability to survive a drought, say) and the environmental pressure 'b' is zero because it rains a lot - then B has no benefit so it's contribution is zero. But in reality it's going to be a VASTLY more complex equation U = ( A + B ) x ( a + b ) + A x C x c ...or something.
• The combined effect of unique characteristics, common characteristics, and external influences on longevity (L) can be expressed as L = U + C + I. - but Longevity isn't it - it's ability to reproduce...which is not at all the same thing.
• The descendants of other members will eventually become extinct because they will be in competition for food with increasing numbers of high-L (long-lived, more offspring) members. - Not always. The Origin Of Species (to coin a phrase) requires that sometimes the members with the new and novel genetic makeup may be geographically separate (eg stuck on an island) or may have evolved to exploit a different ecological niche. Hence there are now two species where there was once one - and hence there may be no extinction involved.
• A further complication is that nearly all species of living things reproduce sexually. - Is that true? I really doubt it. Bacteria, many plants, fungii, worms...lots of species do not.
• Therefore, species members may interchange any unique characteristics that can be passed on by sexual reproduction. None of the resulting half breeds will have maximum longevity. - That's nonsense. If some individuals of the (say) anteater species have a gene for longer noses - and other individuals have a gene for longer tongues - then neither of them may be able to reach into the deepest termite mounds. But a lucky breeding might produce an anteater with both the gene for long noses and the gene for long tongues - and therefore succeed where neither of it's parents could. The resulting "half breed" (poor choice of terminology...but whatever) has only characteristics that were present in the general population - yet is better than any of them.
• A single species member that by chance had an extra long life, and its descendents which inherit that capability... - No - if they lived longer by CHANCE then there is nothing to pass on genetically. Only those that reproduce more efficiently BECAUSE of their genes will pass that on to their offspring. The Zebra that happens not to meet any big lions (because it lives in a zoo) will have offspring that are no more 'lion-resistant' than their parent - and if returned to the wild will do no better than all of the other zebras.
• With regard to a single member of a species determining the direction of species evolution, I remember reading something about that for humans. The effect is indicated in cells and in the female line of descent. - all humans are descendants of a single person - all animals are descendants of a single animal. There are characteristics (in humans at least) that are carried on X chromosome. Women have two X chromosomes - men have an X and a Y instead. If a child is born that gets the X chromosome from the man (and, inevitably, an X from the mother) - then it must have two X's and therefore be female. If it gets the Y chromosome from the father, it will be a boy and his X chromosome will be from the mother. So X information carried on the X chromosome follows the female line because a father cannot pass his X chromosome onto his son(s). But that's a small minority of genes - and it's not true in all species.

PHEW! SteveBaker (talk) 00:30, 9 March 2009 (UTC)

Regarding your last point - the organelles all come from the ovum, so the mother, so things like mitochondrial DNA are inherited solely through the female line. Y-chromosomal DNA is inherited solely through male line. That doesn't mean we all get of mitochondria and Y chromosomes from the same individual, though. There isn't a single "first human" from whom everyone is solely descended. There are common ancestors of all the individuals in a species, but there are lots of them. See most recent common ancestor and identical ancestors point for more discussion of this. --Tango (talk) 00:46, 9 March 2009 (UTC)

• Actually, both chance and how well an individual is adapted to survive in its current environment play their part. Evolution is statistical mechanics in action.
  • Hypothetical: You have 100 zebras. 50 can run faster but need more food as a result (group A), and 50 zebras are "normal" (group B).
  • 7 A's and 4 B's die by random chance.
  • 8 A's and 4 B's starve to death.
  • 5 A's and 22 B's get eaten by lions.
  • All the rest reproduce, giving 2 offspring per individual.
• Next generation has 60 A descendants and 40 B descendants. If this pattern keeps up, soon B's will be a small minority. (But if food and/or lions become scarce, those proportions could easily change.) This also serves to illustrate why single genes are rarely the single determining factor in an individual's likelihood of reproducing. There's almost always a tradeoff for every "advantage," and the balance can easily shift depending on changes in the environment.
• I know the above is oversimplified, i.e. not taking into account that A's and B's can mate, dominant/recessive genes, multiple alleles, polygenic traits, etc. But I thought it might be illustrative.
• Finally, yeah - humans have 23 chromosome pairs. Only one is sex-linked. And don't even get me started about the plethora of ways gender is determined, and determines how genes get passed, in other species. XY isn't the only model, by far. arimareiji (talk) 01:08, 9 March 2009 (UTC)

If your model would hold water we'd have a hard time explaining why we still have genetic disorders that kill their carriers at a young age. Sickle cell anemia is one of the more commonly known, but not the only one. As it happens this trait offers its carriers some protection against Malaria. So, although longevity is very much curtailed, individuals have a higher chance of reaching reproductive age and reproducing. Fits evolution very nicely. One thing that often gets mixed up is that benefiting the individual and benefiting the survival of the species aren't the same. The world is full of examples of odd appendages, bright colors instinctive behaviors that serve no other function than to attract a mate. This can be and often is very detrimental to the individual. But as long as that individual manages to mate with more females than an individual without, the trait will get passed on. Looking around lots of short lived creatures from bacteria that live in your gut to cockroaches (Hopefully not under your floorboards:) to mice contradict your equation. A single mouse can spawn thousands of descendants in several generations in the time it takes a long lived human just to reach sexual maturity. Adding a couple of examples to Steve's list of asexual reproduction: many species of snails choose their sexual orientation when they meet. Female sharks can reproduce with or without males. 76.97.245.5 (talk) 02:25, 9 March 2009 (UTC)

"So many errors" that even the eagle-eyed SteveBaker missed an obvious one. The OP states, "Characteristics held in common that affect longevity can be expressed as C." However, he has previously defined C otherwise. He needs a different symbol. Here, try §.
— B00P (talk) 06:05, 9 March 2009 (UTC)

And one by SteveBaker, shock horror! Most animals are not programmed to cease reproductive activity later in life. That humans are is of great interest and there have been a number of putative explanations why. I'm not sure there's any other animals with such a definite menopause as opposed to just not being so fertile when very old, some apes and elephants probably are the closest with the way they lose fertility I'd guess. Dmcq (talk) 16:30, 9 March 2009 (UTC)

An easily misunderstood statement by SteveBaker as well: "all humans are descendants of a single person". Keep in mind that the transition from non-human to human was a smooth one, and that it is impossible to pinpoint a time when it occurred. If one were to make an arbitrary decision about when the transition occurred, there were thousands of persons living and interbreeding at that time, and more or less every one of them was an ancestor to every person alive today. When it comes to mitochondria, however, it is well established that all human mitochondria alive today descend from a most recent single common ancestor that lived in a woman in East Africa, about 140,000 years ago, the so-called Mitochondrial Eve. The most recent common ancestor of all humans alive today may have lived as recently as 3000 years ago, see Mitochondrial Eve#Misconception: The Mitochondrial Eve and Most Recent Common Ancestor (MRCA) are the same. --NorwegianBlue ^talk 19:48, 9 March 2009 (UTC)

"The most recent common ancestor of all humans alive today may have lived as recently as 3000 years ago,..." Ahem! A common ancestor of all Icelanders, Maoris, Khoi-San, and Japanese only 3,000 years ago? No. B00P (talk) 01:35, 10 March 2009 (UTC)

The statement from our article is, On the arbitrary assumption that people mate with a random individual drawn from the whole of the global population, the theoretical MRCA could have lived as recently as 3,000 years ago, citing a 2004 Nature paper as a source. Whether that arbitrary assumption is reasonable, may of course be questioned, but I assume it is discussed in the paper (which I haven't read, but I'll try and get a copy). --NorwegianBlue ^talk 08:03, 10 March 2009 (UTC)

Update: The abstract of the paper is here. The paper takes known migrations into account, trying to capture historical population dynamics realistically through Monte Carlo simulations. The authors conclude that "the genealogies of all living humans overlap in remarkable ways in the recent past. In particular, the MRCA of all present-day humans lived just a few thousand years ago in these models. Moreover, among all individuals living more than just a few thousand years earlier than the MRCA, each present-day human has exactly the same set of genealogical ancestors.". --NorwegianBlue ^talk 10:31, 10 March 2009 (UTC)

Why do humans need fat in their diet?

It is commonplace that humans get fat when they overeat. In other words, they can synthesise fat. Why then do humans need fat in their diet? 89.243.84.208 (talk) 10:28, 24 May 2009 (UTC)

Because lipogenesis costs more energy than in taking lipid from the diet? We can also synthesize sugars. --Mark PEA (talk) 10:33, 24 May 2009 (UTC)

Also, quite a few of the vitamins we need are 'fat soluable' - they are dissolved into fats that we eat - so if you have a totally fat-free diet, you can suffer rabbit starvation. 14:04, 24 May 2009 (UTC)

Also and, we can't synthesise all the fatty acids we need - check out Essential fatty acid. Aaadddaaammm (talk) 16:33, 24 May 2009 (UTC)

Fat is an important energy source. It has nine calories per gram, 2.25 times more than carbohydrates and proteins. Fat is necessary to displace carbohydrates as an energy source, and consuming less than twenty percent of calories from fat will almost invariably cause the carbohydrate intake to be too high. Very high carbohydrate diets (such as those obtaining more than two-thirds of calories from carbohydrates) can adversely impact lipid profiles, increasing triglycerides and suppresses HDL cholesterol.

The Institutes of Medicine said this in 2005:

The AMDR for fat and carbohydrate is estimated to be 20 to 35 and 45 to 65 percent of energy for adults, respectively. These AMDRs are estimated based on evidence indicating a risk for coronary heart disease (CHD) at low intakes of fat and high intakes of carbohydrate and on evidence for increased risk for obesity and its complications (including CHD) at high intakes of fat. Because the evidence is less clear on whether low or high fat intakes during childhood can lead to increased risk of chronic diseases later in life, the estimated AMDRs for fat for children are primarily based on a transition from the high fat intakes that occur during infancy to the lower adult AMDR. The AMDR for fat is 30 to 40 percent of energy for children 1 to 3 years of age and 25 to 35 percent of energy for children 4 to 18 years of age. The AMDR for carbohydrate for children is the same as that for adults—45 to 65 percent of energy. The AMDR for protein is 10 to 35 percent of energy for adults and 5 to 20 percent and 10 to 30 percent for children 1 to 3 years of age and 4 to 18 years of age, respectively.(http://books.nap.edu/openbook.php?record_id=10490&page=769) The Institutes of Medicine talk about the harmful effects of both fats and carbohydrates (see the lengthy chapters beginning here and here).

The USDA says:

A low intake of fats and oils(less than 20 percent of calories) increases the risk of inadequate intakes of vitamin E and of essential fatty acids and may contribute to unfavorable changes in high-density lipoprotein (HDL) blood cholesterol and triglycerides.

(http://www.health.gov/dietaryguidelines/dga2005/document/pdf/DGA2005.pdf, see Chapter Six)

"The AHA notes that in the absence of weight loss, diets high in total carbohydrate (e.g., >60% of energy) can lead to elevated triglycerides and reduced HDL cholesterol. These effects do not occur with substitution of monounsaturated or polyunsaturated fats for saturated fat. NCEP suggests that monounsaturated fat can be up to 20% of total energy and polyunsaturated fat up to 10% of total energy."(http://www.diabetes.org/uedocuments/ADACardioReview4.pdf)

Foods that are high in fat tend to be palatable (they taste good) and high in calories per ounce. There are very few foods (with the exception of whole milk) that obtain a huge percentage of their calories from fat and are also high in water. This is why high intakes of fat may be associated with obesity, but studies comparing high-carbohydrate diets have produced conflicting results. Some studies, of course, show that carbohydrates are more likely to cause obesity than fats.75.89.27.94 (talk) 23:13, 24 May 2009 (UTC) —Preceding unsigned comment added by 71.31.105.41 (talk)

Thank you very much for all that, I shall try to study and comprehend that very carefully. I'm still surprised that its beneficial to eat what seems to me quite a lot of fat - I thought it was sinful in dietry terms. 89.241.155.179 (talk) 18:16, 25 May 2009 (UTC)

Wood trimmer (person)

What exactly does a wood trimmer do, and what exactly is his workplace? Googling mostly results in pictures of various tools for trimming wood, but that's not what I'm after. I'm asking because I need synonyms to, and be sure I understand, what a "wood trimmer" is. The reason I ask is that there is a disease called "Wood-trimmer's disease", which is a variant of allergic alveolitis, caused by IgG antibodies to molds that presumably thrive in the wood-trimmer's workplace. Links to relevant workplaces (with pictures if possible) would be nice! Thanks! --NorwegianBlue ^talk 20:49, 27 September 2011 (UTC)

A sawmill worker? From here. Mikenorton (talk) 20:58, 27 September 2011 (UTC)

(ec) Formerly, a person would rough trim a log by splitting it, use an adze to make it flat, then a plane to make it smooth. I think that's a job now done almost exclusively by machines in a lumber mill, so now I'd look at people who work there. StuRat (talk) 21:00, 27 September 2011 (UTC)

Thanks both! That was my feeling too. And the reference was really excellent, Mikenorton! --NorwegianBlue ^talk 21:20, 27 September 2011 (UTC)

Laboratory tests

I'm making a list of legitimate reasons for requesting laboratory tests, and have come up with the following:

On a population level:

• Screening, to prevent the development of avoidable disease.

On the individual level:

• To look for a specific disease predisposition, in a person with a family history of the disease
• To help making or excluding a diagnosis
• To help choose the most appropriate treatment for a disease
• To help predicting the patient's prognosis
• To monitor the patient's disease activity

I'm aware that paternity testing isn't on the list. Other than that, have I left out something important?--NorwegianBlue ^talk 15:50, 28 October 2012 (UTC)

You left out monitoring for correct drug dosage. Examples of this is the usage of INR tests to check/adjust the dosage of warfarin, and the the testing of blood cell counts to check/adjust the dosage of chemotherapy for cancer.

Another reason: During surgery for cancer (lumpectomies), the surgeone makes a judgement call on how much to cut out. Typically, a 2 cm margin of safety is is aimed for. The surgeon sends the excised flesh (hopefully containing the malignant tissue surrounded by the 2 cm margin) to the lab for immediate analysis. While the patient is on the table anethetised and opened up, the lab reports back to the surgeon, essentially saying "you got it all", or "no you didn't - the tumour extends to the edge of the sample". This provides feedback to the surgeon as to his judgement quality, and lets him decide whether or not to cut a bit more out, cognizant of other factors. Wickwack 124.182.136.192 (talk) 15:58, 28 October 2012 (UTC)

Thanks, I'll add

• To evaluate treatment (or diet) efficacy,

diet effects (such as monitoring whether gluten is effectively eliminated from the diet) is certainly relevant to the list I'm preparing. Anything else?--NorwegianBlue ^talk 19:54, 28 October 2012 (UTC)

There are a number of other uses I would think of as illegitimate, but you might not, e.g. testing for recreational drugs, performance enhancing drugs, consumption of banned food/drink/tobacco, identifying the person tested or members of his family as criminal suspects by genetic matching, etc. Wnt(talk) 20:54, 28 October 2012 (UTC)

I'm not sure whether you'd consider "Monitoring for side effects of treatments" is already covered in your list (under choosing the most effective treatment) but it seems like it should be made explicit. I would also include testing of blood type and HLA types for potential organ donors (I suppose for recipients it would already be covered by "choosing effective treatment". There's also genetic testing for study of population migration/anthropology, and for genealogical curiosity (even when paternity is not in question). And in addition to Wnt's suggestion, CODIS testing of convicted criminals (rather than suspects) might be included, depending on your criteria for "legitimate". - Nunh-huh 01:48, 29 October 2012 (UTC)

yeah, one more vote for some version of "Monitoring for side effects of treatments", "monitoring for correct drug dosage", etc; want to check for liver enzymes in general, check for rhabdomyolysis due to statins, etc.Gzuckier (talk) 02:03, 29 October 2012 (UTC)

Without too much consideration as to whether they're already subsumed in one of the listed criteria, I'd think of autopsies (or any pathological testing on the dead, done for the purpose of establishing cause of death, for forensic purposes, the curiosity of the survivors, or assessment of familial risk factors); epidemiologic monitoring (in hospitals; to govern antibiotic usage; to provide monitoring for antibiotic coverage; in animals (to predict flu varieties in order to produce flu vaccine), or any such testing to establish the most common serotypes of viruses or bacteria for vaccine purposes; and testing to determine if preexisting conditions or disease exists for insurance purposes. There's testing for matters of public health ( epidemiology, STD contact tracing, TB drug monitoring (to establish if patients are actually taking their drugs, which is done as much for other's benefit (to avoid the selection for multi drug-resistant strains of TB) as for the "patient's"; and also scientific (rather than clinical) testing (tests which may have eventual clinical significance, but are at present of unproven value). - Nunh-huh 03:14, 29 October 2012 (UTC)

Some other possibilities:

• Because the patient requested the test. If a patient feels they might have a certain medical condition, and the test isn't risky, then it makes sense to perform the test, if only for their peace of mind.

• To establish a base line. This is important for some repeated tests, like mammograms, as you need something to compare later tests with, to check for any changes. StuRat (talk) 06:17, 29 October 2012 (UTC)

Is there a non-legitimate reason for requesting a lab test? --TammyMoet (talk) 09:34, 29 October 2012 (UTC)

"Because the patient requested it" is a reason, if tests are in fact done for that reason. Stu's USA may be different, but doctors are trained to not order a test unless it is their professional opinion that the result will decide which of 2 or more treatment options is to be used. Certainly in Australia they will refuse a patient's unnecessary test - this is because costs are mainly governemnt funded, and the bean counters may penalise a doctor is they think he has cost the govt unnecessary expense. I imagine other countries that have a similar "medicare" or National Health govt funded system (which is most countries apart from 3rd world) will be similar. Wickwack 120.145.177.211 (talk) 11:17, 29 October 2012 (UTC)

Thanks everyone! @TammyMoet: yes, definitely, there are many. For one thing, for each test that is taken, there is a certain probability that the test will be positive even if the patient is perfectly healthy. If many tests are taken in a non-targeted way, you can be pretty sure that you'll have a false positive among the results. See Ulysses syndrome.This 1954 paper is also a good read, and features a list of what could be considered non-legitimate reasons (see below), although I agree with StuRat that #5, i.e. giving the patient peace of mind, is not without merit. Unless you get a false positive...

Quoting from the paper: Perhaps it would be a good idea to have a space on every laboratory form in which the doctor had to state exactly why he had ordered a test. I believe if answers were honestly filled in we might get this sort of thing:

(1) I order this test because if it agrees with my opinion I will believe it, and if it does not I shall disbelieve it.

(2) I do not understand this test and am uncertain of the normal figure, but it is the fashion to order it.

(3) When my chief asks if you have done this or that test I like to say yes, so I order as many tests as I can to avoid being caught out.

(4) I have no clear idea what I am looking for, but in ordering this test I feel in a vague way (like Mr. Micawber) that something might turn up.

(5) I order this test because I want to convince the patient there is nothing wrong, and I don't think he will believe me without a test.

--NorwegianBlue ^talk 11:29, 29 October 2012 (UTC)

That is a fascinating comment, for the following reasons: Firstly, in my experience, doctors do usually write on the requisistion form in the text box provided something that at least gives a clue as to why they ordered the test. They write abreviated things like "Sus c. rht breast" ie "I suspect carcinoma in right breast", A lot of times they don't need to write anything - the only reason a doctor would order an epstein barr test for example is that he suspects the presence of the eptein barr virus (glandular fever). Secondly, when a quantitative test result comes back from the lab, they usually give three figures like this: Xyzetc 3.0 >3.2 <6.0 ug/ml, which means the Xyzetc concentration was measured at 3.0 micrograms per millilitre, and the normal range is 3.2 to 6.0. A text summary will be at the bottom, saying something like: The Xyzetc was found to be marginally below the normal range for a male of this age group. We suggest you request a so-and-so test to exclude such-and-such disease. This is Australian practice at any rate. A professional would never use reason (4) above. If he got found out he'd be in trouble. Reason (3) will not occur in most countries for the reason I already stated - tests cost money, and someone's counting somewhere. Wickwack 120.145.177.211 (talk) 12:25, 29 October 2012 (UTC)

Stating on the form what you are looking for could bias the test results, in cases where tests are subjective.

Also, in the US, another invalid reason for tests is to avoid lawsuits. You can have a group of rare conditions, where the risks of the tests outweigh the benefits, and the risks are not immediately apparent, such as radiation exposure. So, medically, the tests don't make sense, but, legally, the doctor could be sued if the person turns out to have this rare disease, which the test could have found, and he failed to order it. (The test not being medically indicated is not necessarily a sound legal defense, as the law really doesn't much care about science.) StuRat (talk) 18:36, 29 October 2012 (UTC)

Re avoiding lawsuits, yes, I've heard that tests are ordered in the USA for that reason. In other countries, if a patient wants to sue a doctor, the first thing that happens is that the doctor's practice insurance company reviews that case. If they think the patient just might succeed with a suit, a panel of medical peers is assembled to look at it. Mostly, the peers side with the doctor (surprise surprise), and courts are reluctant to go against the panel opinion. It does keep the number of court cases down.

Re bias, this is obviously a possibility. However, again in my observation (my wife has quite a history with cancer), if the test is subjective but the result is crucial, doctors tend to requisition from two different labs. If they get opposing or different views back, they either decide which is the right one based on other factors (yep - bias again, possibly NorwegianBlues's item (1)), or they go with the safest option, or they order another sort of test. So, another valid reason to order a test: to confirm or refute a subjective pathologist opinion.

Wickwack 124.182.21.153 (talk) 01:21, 30 October 2012 (UTC)

Thanks again, everyone! @Wickwack: This is indeed a valid point, not only when there is a subjective element in the interpretation of the sample. Sample mix-ups occur, and different test methodologies may give discrepant results. --NorwegianBlue ^talk 07:00, 31 October 2012 (UTC)

Arachis hypogaea

The binomial name of peanut is Arachis hypogaea. I understand "hypogaea", but does anyone know the origin of the genus name, "Arachis"?--NorwegianBlue ^talk 11:25, 28 October 2012 (UTC)

I googled [meaning of arachis] and a number of entries came up. It appears the original meaning of the word is uncertain, but that it was used by ancient Greeks in reference to some type of legume. One theory is that it means "without spine", indicating no central support "axis". ←Baseball Bugs^{What's up, Doc?} carrots→ 12:33, 28 October 2012 (UTC)

"Arachidna" is Greek for some sort of legume (which gives us, through Latin, the French "arachide"). I can imagine "arachidna" having an ultimate root "arachis" but nothing appears in the dictionaries. Maybe it was just invented by someone who imagined the same root. Adam Bishop (talk) 12:37, 28 October 2012 (UTC)

Thanks! --NorwegianBlue ^talk 13:38, 28 October 2012 (UTC)

PSA

What is the difference between immune responses to microbes versus tumors? Please explain it in technical terms for a biology major.--74.190.109.171 (talk) 14:33, 9 November 2013 (UTC)

Do you mean cancerous tumors ? StuRat (talk) 18:21, 9 November 2013 (UTC)

Yes, and the tumor antigens like PSA secreted by the cancerous tumor cells.--74.190.109.171 (talk) 18:27, 9 November 2013 (UTC)

While this looks like a homework question for a biology-related course to me, and I don't normally respond to enquiries posted without a name, it seems that you may have been mislead by the term PSA (Prostate Specific Antigen). An antigen is a substance that an immune system antibody can bind to, so that the immune system can recognise the substance or its carrier as something abnormal and so to be dealt with. But PSA is a substance normally occurring in both the male and female body, attracts no human antibodies and evokes no immune system response. It is produced in the prostate (males) and vagina (females) as part of a range of substances that protect the sperm from residual urine and assist the sperm to swim and reach an egg cell.

Measuring PSA blood level is of value because in the male ONLY the prostate and cancers derived from the prostate can make it. So PSA increasing may be an indication of prostate growth (especially if the man's sex life has wound down) , and if the prostate has been removed, then a measurable PSA level means that one or more secondary tumours must be in the body somewhere.

The reason PSA is termed an antigen is the way the PSA concentration in the blood is measured. Antibodies from a mouse sensitized to human PSA are added to the blood sample (after blood cells have been removed) and the amount bound is measured. It's done this way as otherwise an extraodinarily complex purification process would be required. PSA is thus not an antigen as far as the source human is concerned, it is an antigen as far as the mouse is concerned.

It is policy not to do homework for you, but we do like to assist where you are stuck. You will get a better response if you show that you have already made an attempt at answering a question of the form "Explain the difference between A and B....", say by describing where you are stuck. Your request for an answer in the correct technical language adds to my suspicion that you just want something you can copy-paste. As your question appears to be homework, I have not answered it directly.

124.178.135.228 (talk) 02:02, 10 November 2013 (UTC)

"But PSA is a substance normally occurring in both the male and female body, attracts no human antibodies" because PSA is a self-antigen. I would say that microbes stimulate CD8+ T cells whereas tumor cells stimulate both CD8+ T cells and CD4+ T cells.--98.88.144.218 (talk) 16:07, 10 November 2013 (UTC)

Hmm. I'm a bit unsure about whether PSA is generally expressed by women. Some women can have severe allergological reactions to the PSA in seminal fluid. See PMID 22653399. Seminal plasma allergy caused by IgE against PSA definately occurs. I would have assumed that these women had been tolerant to PSA if PSA were a protein they expressed. --NorwegianBlue ^talk 20:42, 10 November 2013 (UTC)

PMID 22653399 is not evidence that human females can be alergic to human PSA. See http://aje.oxfordjournals.org/content/162/7/704.long. I did simplify things a bit. There is a degree of confusion in medical circles about just where PSA is produced in the female, but there is no doubt that it is produced. As the citation I gave says, measurement shows that the concentration of PSA in the juices of excited females is not dissimilar to the PSA concentration in male ejaculate (see citation 3rd papa). And until recent years, the medical community had a very poor understanding of how sex works for the female. Indeed the name "PSA" arose because early researchers thought it was prostate-specific. Much like the folk that discovered the BRCA-1 gene thought it was specific to breast cancer (becasue they were looking for breast cancer causes, and didn't look at other cancers), whereas we now know that it is involved in all sorts of cancers. The PSA test was initially used in some jurisdictions with vaginal swabs from the alleged victim to "prove" rape! 124.178.135.228 (talk) 02:21, 11 November 2013 (UTC)

On the definition of repolarization

I've read in the book of ECG (Mariot): "Electrical systole continues until the positively charged ions are pumped out of the cell, causing its repolarization.". If I would say that the repolarization is defined as entering of negative ions into the cell, I was right? and in addition, is the word "polarization" literal means to positive charge only or to both- negative or positive charge? ThePupil17 (talk) 01:17, 26 February 2016 (UTC)

Polarization means "a separation of charge". See Dielectric polarization. --Jayron32 01:51, 26 February 2016 (UTC)

Yeah, but in neuroscience, "depolarization" means positive deviation of the membrane potential from the resting potential, with the ability to induce action potentials, and hyperpolarization means negative deviation. But you're right, the definition of polarization in the cell biology context is very sign convention-dependent. The membrane potential is defined as the intracellular potential minus the extracellular potential. Yanping Nora Soong (talk) 02:05, 26 February 2016 (UTC)

• Unfortunately even the authors of books often don't understand electrophysiology very well -- neither the statement in the book nor your statement is correct. Changes in membrane potential, including depolarization and repolarization, are primarily caused by changes in membrane conductivity, not by movement of ions. Pumps are essential over the long term but they play no important role on the short term. Our membrane potential article covers these things in some detail, but it isn't easy reading -- this is a topic that many people find difficult to grasp regardless of how clearly it is explained. To fully understand it, it is necessary to make a close study of the Nernst equation and Goldman equation. Looie496 (talk) 15:43, 26 February 2016 (UTC)