Wikipedia:Reference desk/Archives/Science/2012 October 15

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October 15

Malaria in Africa

The earlier thread Malaria in Europe mentioned that malaria had been essentially eliminated in Europe and North America during the twentieth century. I hadn't realized that there had been that much success in eliminating malaria in regions where it had gotten established. My question is, how different is malaria in Africa from malaria in other places? Do differences such as climate and different mosquito populations make it much harder to fight in Africa? Or is it more a matter that the economic resources aren't available to fight malaria in Africa? If I had a huge sum of money (say $100 billion) and complete freedom to go anywhere in Africa and employ the same aggressive techniques that worked previously in the US and Europe, would that be enough? Could you wipe out the malaria bacterium, or is there some reason why techniques that worked in the past couldn't work in Africa? Dragons flight (talk) 02:40, 15 October 2012 (UTC)

There is an on-going global effort to eradicate malaria. Have a look at this andthese papers. Zoonoses (talk) 04:53, 15 October 2012 (UTC)

You might run into people who think you are trying to poison them when you spray their land with DDT. StuRat (talk) 05:22, 15 October 2012 (UTC)

Malaria spreads when a mosquito bites an infected person, after which the plasmodium gametocytes differentiate, then reproduce. Then the mosquito has to bite someone else and rub off enough protists to get them sick. If malaria patients can afford to stay at a hospital until they're treated, where there are presumably fewer mosquitoes, that hampers the plasmodium lifecycle much more than if they had to continue working outdoors. --140.180.242.9 (talk) 05:59, 15 October 2012 (UTC)

The most effective methods used in the past were A) completely draining all standing water from a region and B) carpet bombing an area with DDT. Both methods are unpopular nowadays, in addition to the longstanding lack of any financial incentive to ridding Africa of malaria. I also suspect that the environment in sub-Saharan Africa is far less tenable to both methods, due to the sheer amount of warm, wet land. Someguy1221(talk) 09:04, 15 October 2012 (UTC)

$100 billion wouldn't begin to do it. Africa contains on the order of a million square miles of prime mosquito habitat. Note that malaria is also endemic throughout much of South America, which contains more millions of square miles of prime mosquito habitat. Looie496 (talk) 16:08, 15 October 2012 (UTC)

That works out to $100,000 per square mile. Is that really not enough to spray a square mile with DDT, especially if you employ natives at the local pay rate (and contribute to the local economy in the process) ? StuRat (talk) 06:47, 17 October 2012 (UTC)

WHO estimates US $6B annually would do the job (over a number of years). [1]. Zoonoses (talk) 05:36, 18 October 2012 (UTC)

Baumgartner vs Kittinger

Trying to put Felix Baumgartner's jump into perspective, without all the media hype. Some questions:

1. Why did it take more than 50 years from the previous height record of Joseph Kittinger? Is it so much more difficult to reach heigher altitudes or is it rather a lack of scientific value (of taking people up there) combined with the cost involved? Were there any attempts at breaking the record of Kittinger before?
2. What is the main achievement or difficulty to overcome in the Baumgartner dive?

bamse (talk) 08:09, 15 October 2012 (UTC)

1) It's basically just a stunt, as there's no real need for people to be able to bail out at such heights. StuRat (talk) 08:12, 15 October 2012 (UTC)

2) Take your pick: high speeds, cold temps at the start, high temps when first hitting thicker atmosphere, lack of air pressure, etc.StuRat (talk) 08:18, 15 October 2012 (UTC)

2) Yes, but Kittinger had the same, so my question is, whether there is any additional factor to take into account for Baumgartner which did not matter for Kittinger. Adding 3) Did Baumgartner and Kittinger use essentially the same tools and techniques, i.e. is the only difference that Baumgartner had more modern tools/better materials? bamse (talk) 08:27, 15 October 2012 (UTC)

Adding 4) It is often claimed that it is the first supersonic flight of a human without "vehicle". On the other hand, Baumgartner was naturally not on his own but in a "suit". How much does this suit differ from a supersonic "vehicle"? bamse (talk) 08:30, 15 October 2012 (UTC)

The most obvious difference is that the suit had no propulsion system - the speed attained was due to gravity's acceleration, making this qualitatively different from powered flight. As far as risks, I was under the impression that there were many - among the greatest being a flat spin resulting in circulatory derangement, loss of consciousness, death. Recovering from such a spin can be hard in a vehicle that has control surfaces and an engine, but Baumgartner just had his arms and legs. I'll try to provide a ref in a little while - I'm sure there are suitable ones. --Scray (talk) 08:46, 15 October 2012 (UTC)

Here's one: Reuters Factbox: Greatest risks of high-altitude skydiving, which says that the greatest risk was suit breach or accidental (early) parachute deployment. Another, fromNational Geographicdiscusses 5 principal risks as low pressure, cold, wind/weather, flat spin, and the hard-to-anticipate risks of breaking the sound barrier without a craft (as discussed above). -- Scray (talk) 09:07, 15 October 2012 (UTC)

Thank you. The National Geographic site you linked answered all my questions. bamse (talk) 18:29, 15 October 2012 (UTC)

In February 1966 Nick Piantanida did in fact go higher than Kittinger, and also higher than the officially planned height of Baumgartner but not the actual height. However, Piantanida didn't make the planned jump and didn't return with the balloon either but in the gondola with a large parachute. Our article has a poor description of the February flight. Click "Long Description" at [2] to see what happened. PrimeHunter (talk) 00:06, 16 October 2012 (UTC)

Perpetual motion

When did scientists first understand that perpetual motion machines are impossible? I can't find the answer in our articles. Duoduoduo (talk) 14:41, 15 October 2012 (UTC)

Like most scientific knowledge, this was a gradual development, as scientists began to formalize their understanding of experimental results. I'd start by reading our article on thermodynamics, especially the history section. For example, it's doubtless that Isaac Newton had a pretty good idea that friction slowed objects in real systems; and by the time Carnot wrote about formal engine thermodynamics, he stated the laws of thermodynamics outright. If you run farther back into history, Aristotleian physics was simply wrong, and Aristotle asserted the existence of perpetual motion machines without evidence. So, somewhere along the way, we figured out that perpetual motion didn't exist, and gradually made our explanations more clear and consistent with all other physical law. Nimur (talk) 15:04, 15 October 2012 (UTC)

• The impossibility of perpetual motion is a direct consequence of conservation of energy. That principle was first clearly formulated by Hermann von Helmholtz sometime around 1850. So there couldn't have been a really compelling rejection of perpetual motion before that time. However, as ourHistory of perpetual motion machines article says, "In 1775, the Royal Academy of Sciences in Paris made the statement that the Academy "will no longer accept or deal with proposals concerning perpetual motion." The reasoning was that perpetual motion is impossible to achieve and that the search for it is time consuming and very expensive." Looie496 (talk) 16:03, 15 October 2012 (UTC)

We do have the article History of perpetual motion machines. Leonardo da Vinci (15th century) designed some devices that he hoped would be perpetual motion machines, but upon studying them, decided that it probably wasn't possible. Buddy431 (talk) 17:05, 15 October 2012 (UTC)

I, personally, do not think that a perpetual motion machine of the second kind, which does not violate energy conservation, is impossible though, because I've figured out how to build one. With it, the empirical second thermodynamic law is no longer an obstacle (its scope being severely limited, of course, by virtue of the existence of my process, which I claim) and we can therefore get rid of fuels and put a stop to global warming. -Modocc (talk) 17:32, 15 October 2012 (UTC)

I saw your plans for it scribbled in the margin of some book you were reading:) DMacks (talk) 17:52, 15 October 2012 (UTC)

I fear that making my work public is thorny though, for a provisional patent and a subsequent public disclosure is not always adequate with regards to the all important step of reduction to practice. I have to be careful to include all the necessary details (unlike Fermat's scribbles).-Modocc (talk) 18:13, 15 October 2012 (UTC)

Unfortunately the US Patent Office has a policy of requiring a working model before granting a patent for a perpetual motion machine.Looie496 (talk) 18:32, 15 October 2012 (UTC)

Patent models have not been required in US patent applications since 1880. Someguy1221 (talk) 23:42, 15 October 2012 (UTC)

Ah, I found what you were referring to. The US patent and trademark office specifically requires perpetual motion machine applications to be accompanied by a working model, due to their tendency to be full of shit. Perpetual motion#Patents. Patents are still occasionally granted to such "inventions", however. Why, I don't know. Someguy1221 (talk) 23:47, 15 October 2012 (UTC)

Probably because patents are granted for all sorts of complete nonsense. A patent means nothing until it is tested in court. And if the patent holder can convince someone to buy the rights, well and good, regardless of whether the patent is truely valid or not. It is not the patent office's problem if you have wasted your money getting a patent that makes no sense or has no commercial value. The US Patent Office's decision on obvious perpetual motion devices probably arose from a desire to avoid dealing with complete wankers or perhaps a public service desire to prevent retards wasting their money. An example of a patent that is just as much nonsense thermodynamically as perpertual motion is US Patent 4945866, Altered Piston Timing, Bertin R Chabot, published 08/07/1990, describing an internal combustion engine in which the center line of each cylinder is offset from the rotational axis of the crankshaft in the direction of rotation. This patent is an amazing collection of nonsense claims showing a total lack of understanding of basic thermodynamics, but the idea gets represented under different titles and wording every 10 to 15 years or so. An example of a patent that does not violate basic thermodynamic principles but has no commercial merit whatsoever, a fact that is obvious at a glance to any engineer (it's full of flat surfaces and parts that can't be cooled, for a start), is the Sarich Engine. An example of a patent that is clearly invalid due to prior art is the Dolby noise reduction patent - it never the less was a huge commercial success due to excellent marketing. Ratbone121.215.28.169 (talk) 00:40, 16 October 2012 (UTC)

That is correct, obviously. -Modocc (talk) 01:20, 16 October 2012 (UTC)

A working model is needed for acceptance by the examiner. But, that only establishes its patent-ability to the patent office's satisfaction, subject to its appeals process, but the date of the examination (as with all appeals) will differ from the date of reduction to practice which will be earlier, and as you have pointed out, needs not be the date a working model is completed. -Modocc (talk) 00:21, 16 October 2012 (UTC)

That shouldn't be a problem, for I'm fairly certain that provisional patent application(s) can establish a reduction of practice, as long as it specifies how to build the working model that is submitted at a later date. My fear is that I may leave out some minor detail with my application(s) that prevents this. Similarly, should I consider simply putting it into the public domain anywhere with a full public disclosure, but this disclosure happens to be slightly incomplete or needs slight correction, it may not be considered a reduction to practice, and whoever recognizes such mistake(s) and fixes these with some mere paperwork may claim the invention! This is therefore a difficult dilemma for me to resolve. Also, further complicating matters, my skills (my eyesight is deteriorating and I'm getting too impatient to stay focused on my work) at actually building the machine are very limited too, but it is simple enough that I am in the process of building it (the parts and tools I've needed for it has cost me less than eighty bucks, but lately its been languishing on my desktop, as its only partially assembled). I've got to do more... -Modocc (talk) 18:47, 15 October 2012 (UTC)

If you have indeed figured out how to solve the world's energy problems, make it public domain and do it asap. Think of the good it can do. Unless you are evil, and just want money for yourself and don't care about the rest of the world, of course. — Preceding unsigned comment added by 217.158.236.14 (talk) 11:10, 24 October 2012 (UTC)

Putting what I have into the public domain does not guarantee that an eventual working invention which is developed will be entirely in the public domain. It would mean risking the possibility of someone who is more or less evil than I am obtaining a monopoly. -Modocc (talk) 10:34 pm, Yesterday (UTC−4)

Our speed in day vs night

Since we travel at 1674k/h around the earth and the earth travels at 108000k/h around the sun, during the day we travel 3300k/h slower than at night relative to the sun. Does this have any noticeable effect on anything?165.212.189.187 (talk) 14:58, 15 October 2012 (UTC)

Yes, that's what causes sun's contribution to the tides. Dauto (talk) 15:13, 15 October 2012 (UTC)

(ec) I first thought that ths might have an impact to aiming large telescopes; aligning the telescope and compensating for Earth's rotation would require some added complexity in addition to a standard equatorial mount. But I'd never heard of any telescope using such a compensation, so I went looking through the webpage of the largest telescope that came to mind: Control Systems for the 30-meter telescope. Everything is adaptive and closed-loop control now; atmospheric compensations, laser guide stars; and so on. These telescopes use feedback control to drive the scope the exact optical center of their imaging target. It's not clear from this high-level overview whether those mechanisms and algorithms explicitly include a correction factor for sidereal / solar rotation deviations; but it seems like that would be either unnecessary or superfluous given the already elaborate system. My suspicion is, if you work the math, the angular error to a distant object is negligible, whether you account for Earth's revolution around the sun or not; but you should be able to work out the math and see exactly how tiny that non-zero deviation actually is, and you can even calculate the error as it changes during a single day or night.

In other contexts, satellite communications require complicated doppler shift compensations, and the rotation of the planet should be included in this compensation. I once knew a guy who bounced a signal off of Mars, and the return echo sounded like a descending whistle. I can't recall which time-varying doppler shift was responsible for that; but I sort of seem to recall that it was the rotation of the transmitter on the surface Mars that caused it. I'll try to dig up the actual publication, which should explain the details with a bit more scientific rigor. Nimur (talk) 15:20, 15 October 2012 (UTC)

"My suspicion is, if you work the math, the angular error to a distant object is negligible"

Indeed. Let's work the math. Close stars like alpha Centauri show a parallax of about 0.7 arc seconds due to the earth orbiting the sun (which is ~1000 light-seconds or 300 million km measuring the orbit end to end). These 0.7 arc seconds are too small to be seen without a telescope but provide a good method of calculating distances between stars. The parallax Earth adds with its rotation is much smaller. You're looking at ~12700km back and forth, which would introduce a daily parallax of ~0.00003 arc seconds for alpha Centauri. This is a noticeable effect when looking at the Moon (it seems to wobble from side to side) but utterly insignificant when looking at the stars.

You could look at it this way: Average stars are about 100 times the size of planet Earth. Now you'd need a telescope capable of resolving a star into 100x100 pixel to see it wobble one pixel back and forth per day. Today's telescopes are not capable of resolving any star except exceptionally huge ones (huge telescopes looking at huge stars, that is). And... don't you think that could be easily remedied by, say, taking one photo per minute and then match and combine these photos to eliminate the motion blur? My digital camera has that kind of image stabilizer, so it's near-trivial to an observatory-grade telescope.

However, all Doppler experiments, including exoplanet detection, must compensate for the velocity itself. Earth goes around the Sun at about 29km/s, and Jupiter is about half that (~13km/s). Since Jupiter is 1/1000 the mass of the Sun, the Sun moves at 1/1000 the speed of Jupiter, i.e. ~13m/s. (If I got the math right, that is. I did it mentally) Compare that to the rotation of Earth, which is 40000km in slightly less than 86400 seconds, or ~480m/s at the equator. If orbit and/or rotation were not accounted, for even Jupiter-sized exoplanets in large orbits would be utterly undetectable. - ¡Ouch! (^{hurt me} / _{more pain}) 07:05, 18 October 2012 (UTC)

Oops. Don't take the "480" too seriously, it's about 460. I was doing the number-crunching mentally. Yeah, using my own blood for ink. ;) -¡Ouch! (^{hurt me} / _{more pain}) 13:01, 19 October 2012 (UTC)

Single original chloroplast?

(1) On p. 64 of the October 2012 National Geographic magazine it says:

Chloroplasts...evolved about 1.6 billion years ago when one cell, incapable of using the sun's energy, engulfed another cell -- a cyanobacterium --that could. That cyanobacterium became the ancestor of every living chloroplast.

And our article chloroplast says:

All chloroplasts are thought to derive directly or indirectly from a single endosymbiotic event (in the Archaeplastida), except forPaulinella chromatophora, which has recently acquired a photosynthetic cyanobacterial endosymbiont which is not closely related to chloroplasts of other eukaryotes.[4]

And the abstract of citation [4], which is all I can access, says:

There is accumulating evidence to support a single primary origin of plastids from a cyanobacterium (with one intriguing possible exception in the little-studied amoeba Paulinella)

(a) In layperson's terms, what is the nature of the evidence for a single originating event?

(b) Isn't this single-ancestor assertion highly implausible on the face of it? It seems that if conditions were amenable for this event and its propagation at that time, it would have occurred numerous times with the descendants surviving.

(2) Same questions for the original cell or the original self-replicating molecule. (I know I've seen it asserted quite a few times that all cells or self-replicating molecules have a common original ancestor, though I can't recall a particular source that says it.) Duoduoduo(talk) 16:36, 15 October 2012 (UTC)

For question (1), the crucial thing is that chloroplasts, like mitochondria, contain their own DNA, separate from the DNA in the cell's nucleus. It is possible to compare chloroplast DNA for various plants and other photosynthesizing organisms to get an estimate of how long ago their evolutionary ancestry diverged.

For question (2), the main reason is that there are a number of complex metabolic mechanisms that are shared by all existing organisms. Our article on the evolutionary history of life gives references for that statement, if you are interested in more information. Looie496(talk) 16:48, 15 October 2012 (UTC)

On point (1b), saying that all organisms of a given line (or all living organism) came from single events doesn't mean that the events were themselves the only instance of such an event before or since, just that the other lines from the other "events" have gone extinct. Just to use another example, Mitochondrial Eve wasn't the only Homo sapiens woman at the time she lived. She's just the one whose matrilineal line didn't eventually get subsumed by another (or die out) over the hundreds of thousands of years since then. --Mr.98(talk) 16:50, 15 October 2012 (UTC)

Good answers above. I'll just note that (at a glance), the article does seem to contain a good overview/review of the related work that has constitutes this "accumulating evidence" of single-origin chloroplasts. The content may or may not be easily accessible, depending on your background. Drop me a line if you'd like me to send you the article. SemanticMantis (talk) 16:55, 15 October 2012 (UTC)

"Careful" science too often involves deliberate semantic gaming to be vague. "A single event" or "a cyanobacterium" might not refer to a singlechloroplast. It is possible that a wide population of billions of symbiotic cyanobacteria was being taken up from the outside world by cells for a long time, then the cells gradually picked up genes from the cyanobacteria, which led to individual bacteria separately losing them under selective pressure, etc. The divergence of the individuals within a single population of a single species is far too small to show up against the larger mutational noise after all this time; so far as I can imagine (which is not proof...) there is no way to prove it was or was not a single individual chloroplast that produced the rest. Wnt (talk) 19:00, 15 October 2012 (UTC)

• This paper Origin and Phylogeny of Chloroplasts Revealed by a Simple Correlation Analysis of Complete Genomes suggests a separate origin for the chloroplasts of red algae from the remainder of the green plants. μηδείς (talk) 20:06, 15 October 2012 (UTC)

I don't think that's actually what they're saying. The two clades simply correspond to the most widely branched groups of plants. Wnt(talk) 23:56, 15 October 2012 (UTC)

This text

The paraphyly of Guillardia and Odontella, with respect to the two red algae, also suggests independent acquisition of secondary chloroplasts in the heterokont and cryptophyte, in contrast to the hypothesis of a single secondary endosymbiotic event among the chromophytes (Cavalier-Smith 2000). Although a single origin of the chloroplasts in this group is supported in some analyses (De Las Rivas, Lozano, and Ortiz 2002; Yoon et al. 2002), the topology of these four taxa in our tree is identical to that based on a recent, traditional analysis of protein-coding genes in the genomes (Martin et al. 2002). Analysis of small subunit ribosomal DNA in the chloroplasts from a wide variety of rhodophytes and chromophytes also indicates that chloroplasts of the latter group have independent origin

and thisdiagram indicating separate rhodophyte and chlorophyte lineages seem to indicate at least two separate events. μηδείς (talk) 00:45, 16 October 2012 (UTC)

Well, secondary chloroplasts are surrounded by three or four membranes and are the remnants of a larger endosymbiont. I think all the varieties mentioned are in reference to the secondary events. [3] emphasizes that all, in the beginning, came from one event. Wnt (talk) 01:26, 16 October 2012 (UTC)

Yes, I am familiar with that concept from reading I did in the 90's, although I don't fully know how to interpret what I am reading here. It seems strange that secondary endosymbiosis would have more origins than primary. I would think the bottom line would be, is there a phylogeny that shows one type of chloroplast is more closely related to one type of bacteria, while a second type of chloroplast is more closely related to a second type of bacteria than it is to the first type of chloroplast. μηδείς (talk) 01:41, 16 October 2012 (UTC)

Here is something interesting: a few months ago, in vivo research has indicated that an endosymbiotic event is close to completion, the event would result in a new generation of plants which capable of nitrogen fixation. The event is creating a new plastid termed a nitroplast.

One cell (a prymnesiophyte), incapable of nitrogen fixation, is engulfing another cell (Candidatus Atelocyanobacterium thalassa) -- a cyanobacterium that can. That cyanobacterium will become the ancestor of every future nitroplast. Plasmic Physics (talk) 07:17, 17 October 2012 (UTC)

They stress that the particular species of prymnesiophyte may not be the only host cell involved in this event, it is just the only one encountered thus far. Plasmic Physics (talk) 07:23, 17 October 2012 (UTC)

Cool! Let's decorate this with some sources:[4][5] [6] Wnt (talk) 06:33, 18 October 2012 (UTC)

Most Recent Common Ancestor - Pre-Columbus

I was perusing the article Most_recent_common_ancestor, and I was quite surprised to see it proposed that "With the advent of mathematical models and computer simulations, researchers now find that the MRCA of all humans lived remarkably recently, between 2,000 and 4,000 years ago." Of course, this is followed by a tag.

Assuming that this is the accepted time frame, the article states that this is attributable to the introduction of the genetic material of the European colonizers around the world. My question is, have pre-contact remains in the Americas or Australia been tested to determine how far back they would have shared a common ancestor with, say, the Spanish conquistadors?

I'm not expecting people to come to this conclusion, but I'm amusing myself about how it would certainly turn things upside down if it were discovered that Columbus and the poor Native American individuals he abducted and took to Spain as specimens were removed from the same ancestor by only 1500-3500 years. Falconus^{p t c} 21:58, 15 October 2012 (UTC)

I've been wondering about this recently too. Does the claim that the MRCA lived at most 4,000 years ago imply that every now-living person (including Australian aboriginals, and members of 'uncontacted' South American and Indian Ocean tribes) is descended from someone who lived before even the earliest 'modern' transatlantic contact, but long after the rise in sea levels and corresponding vanishment of ice bridges that placed Alaska out of reach of Asia, and Australia out of reach of Southeast Asia? AlexTiefling (talk) 22:10, 15 October 2012 (UTC)

I'm hunting for a paper that even makes that claim, but it's clear to me it's not a universal opinion.This paper from earlier this year, looking at particular populations amongst Asians and Native Americans is sticking to the more common claim of ~15,000 years. They do speculate that populations often described as "isolated" for however-many years may have had occasional interlopers entering their community from later migrations, reducing the age of the MRCA. Anyway, still looking for a source for the 2-4kya claim, which does seem kind of ridiculous. It's going to be heavily dependent on what model they used to produce that number. Someguy1221 (talk) 22:40, 15 October 2012 (UTC)

PMID 15457259 may be what you are looking for. The basic idea is that everybody throughout the whole world has at least some recent European ancestry. There is certainly no claim that the Indians who Columbus met had recent common ancestry with him -- the claim is all of their descendants have picked up some European blood in the meantime. I have edited the MRCA article a bit to make it clearer that the statement in question was referring to the material in the following two paragraphs. Looie496 (talk) 23:32, 15 October 2012 (UTC)

I have removed the claim, it's absolute nonsense. The source is one author, duplicated by citing the same work in a preliminary form that explicitly says not for citation. One computer modeling program cannot override the clear evidence that there are pure aboriginal populations in the Americas and Australia with pedigrees at least 15,000 years separated from the old world, let alone Europe. μηδείς (talk) 23:50, 15 October 2012 (UTC)

The proper reference would be the one I cited above (PMID 15457259), which covers the same material and was published in Nature.Looie496 (talk) 00:28, 16 October 2012 (UTC)

I don't have a huge problem with citing the study if it is attributed to the authors and if the implication, that there are no surviving pure Amazonian or Australian aborigines is made explicit. But the study is basically a report about a computer model, not about reality, (i.e., if you write a program with such premises you get such results,) and I don't see it meriting any weight. μηδείς (talk) 00:59, 16 October 2012 (UTC)

I haven't read the article, but from the abstract, I agree with Medeis. It is only a "what if" computer experiment, useful only if you are trying to establish the validity of other similar computer models. --Lgriot (talk) 07:39, 16 October 2012 (UTC)

Well, I think that the modelling study (which I also have not read) could be indicative of the facts - I'll see if I can get a friend with PubMed access to get me a copy. But yes - we should avoid repeating its conclusions as though they are the facts on the ground.AlexTiefling (talk) 09:31, 16 October 2012 (UTC)

SomeGuy - isn't that paper talking about MRCAs specifically for mitogenetic elements? If I've understood correctly, that means we'd be looking at specifically matrilineal common ancestors, and those could easily be an order of magnitude more ancient than the general MRCA. But maybe I've misunderstood (again). AlexTiefling (talk) 09:41, 16 October 2012 (UTC)

You're absolutely correct, and it's something I should have mentioned, and yeah, it doesn't really touch on the general MRCA (it just provides an upper bound). It's worth noting that MRC-patrilineal-A and MRC-matrilineal-A are much more active research subjects than the basic MRCA as they are easier to handle (virtually no recombination for Y-chromosomes or mito-DNA). Someguy1221 (talk) 03:45, 17 October 2012 (UTC)

Alright, thanks all! I thought it was really interesting, but then if it really came out that the genetics were that mixed up, it would have made for more than a brief note on a Wiki Article. Falconus^{p t c} 03:29, 17 October 2012 (UTC)

Well, let's suppose we start by imagining a possible MRCA living in the southern Urals around the time of the Trojan War (1100BCE). Let's suppose a moderate reproductive rate of 3 children per parent per generation surviving to reproduce. The 100-year rule implies that by the time of Julius Caesar, this person would have 30 generations' worth of descendants. If all of them were completely exogamous, that would be 3^30 = 200 trillion descendants. This is obviously absurd - but it's certainly credible for everyone in Eurasia, Africa and the surrounding islands at that date to be descended from our putative MRCA - mostly many times over. The same logic applies to the succeeding 1000 years - any one person alive at the time of Caesar could be an ancestor to the whole Old World by the time of Erik the Red. If just one of Erik's son Leif the Lucky's crew successfully reproduced with a 'skraeling' inhabitant of the New World just once, and that child survived to reproduce at the previously assumed rate, that child might have around 5 million descendants in the New World at the time of Columbus's arrival.

Meanwhile, on the other side of the world, the Macassans have been visiting northwestern Australia in their canoes for centuries. As they're based on the Asian mainland and adjacent islands, they're almost certainly all descended from our Uralic MRCA by now. Again, it only takes one of them to reproduce with one Australian Aboriginal person for a similar logic to apply to that entire population at the time of Europeans' first direct contact with them. So it's not unbelievable for the MRCA of all humanity to have been within 3000 years of Columbus at the time he set sail. I wouldn't want to guess, though, at the date of the universal MRCA at the time of Erik the Red. That might have been as long as 10,000 years previously.AlexTiefling (talk) 11:11, 17 October 2012 (UTC)