Talk:Stabilizing selection

Stable

Apparently, there is some confusion about this -- there are a lot of inaccurate things on these pages about stabilizing selection. Go read this article if you want to know about selection: Natisto (talk) 18:05, 5 February 2010 (UTC)

isn´t arrectifying selection a form of directional selection, and thus cannot be the same as stabilizing selection?

Not as far as I can see in my text books on this topic. -- Kim van der Linde ^{at venus} 20:27, 26 May 2006 (UTC)

Purifying selection = negative selection. You are right, it's not the same as stabilizing selection. See http://www.nature.com/scitable/topicpage/Negative-Selection-1136 Natisto (talk) 18:05, 5 February 2010 (UTC)

References

Birth weight

Asserting that the increase in C-sections has increased optimum birth weight is misleading, as increases in the incidence of high birth weight (due to increased incidence of maternal obesity and gestational diabetes) is a significant factor in the increase in C-sections.

The birth weight example is a good one, but the discussion on C-sections is completely irrelevant to the basic illustration of this genetic phenomenon. It is true, C-sections have possibly affected stabilizing selection in SOME, but hardly ALL, human populations. The way it is illustrated here makes no sense whatsoever. If you want to relate C-sections to this example, make it logical. "C-sections are relevant because..." —Preceding unsigned comment added by 173.26.197.21 (talk) 05:47, 20 November 2009 (UTC)

Negative selection vs. Stabilizing selection merger proposal

My interpretation of these different terms is this: while many instances of negative selection are also instances of stabilizing selection (aka. purifying selection), as there is selection against a change in the organism because the change is deleterious, it's also possible that a change in the environment can cause negative selection in a way that causes directional selection, rather than stabilizing selection.

I should not that I'm not an expert on population genetics and evolution, and neither of these articles have references, so I'm just going with my gut feeling on this with my general biology understanding. And some cursory google searching.

So, I'm going to remove the merger tag and edit the Negative selection page to no longer claim all instances are purifying selection. I'm sorry if it looks like I'm jumping the gun on this, but there aren't any references, these articles look poorly maintained, so I don't expect anyone would respond to a solicitation for opinions. If you do think I've made the wrong move and you can give a reference, please go ahead and revert my change and also add the reference to these articles. -- Madeleine 18:24, 6 April 2007 (UTC)

Merged them regardless (I just had a popgen advanced course if that matters). The simple reason that each is basically a 1-sentence dictionary entry with bells & whistles should be reason enough. Dysmorodrepanis (talk) 06:29, 16 February 2008 (UTC)

This merger is incorrect. Negative selection doesn't only get to "claim instances of" purifying selection -- the terms are synonyms ! The "Negative Selection" article has it right, saying "negative selection (AKA purifying selection) can cause stabilizing selection". Anyway, I made the change; now purifying selection redirects to negative selection, and I changed the stabilizing selection page so that it does not claim to be synonymous with purifying selection any longer. Natisto (talk) 18:05, 5 February 2010 (UTC)

References

Confusing

The article says that stabilizing selection is not the same thing as purifying selection, but then purifying selection redirects to stabilizing selection, and the article does not clarify the difference.

/130.237.120.251 (talk) 13:29, 11 July 2010 (UTC)

Purifying selection does not redirect to stabilizing selection, it redirects to negative selection, which is exactly what it is. Natisto (talk) 14:39, 21 July 2010 (UTC)

Wallace

I believe this was first proposed by Alfred Russel Wallace, in his original essay "On the Tendency of Varieties to Depart Indefinitely From the Original Type" --

"It has been shown that all varieties in which an unbalanced deficiency occurred could not long continue their existence. The action of this principle is exactly like that of the centrifugal governor of the steam engine, which checks and corrects any irregularities almost before they become evident; and in like manner no unbalanced deficiency in the animal kingdom can ever reach any conspicuous magnitude, because it would make itself felt at the very first step, by rendering existence difficult and extinction almost sure soon to follow."

Should this be mentioned in the article? Vultur (talk) 07:24, 9 March 2011 (UTC)

I have just read Wallace's paper where he makes that comment (On the Tendency of Varieties to depart indefinitely from the Original Type 1858). His definition of a balanced deficiency is "a deficiency in one set of organs always being compensated by an increased development of some others". One example he gives is "powerful wings accompanying weak feet". He likens the "acting cause to account for that balance so often observed in nature" to the "centrifugal governor of the steam engine". Stablilizing selection would act to prevent feet or wings from varying beyond certain limits in a population. It would not result in feet becoming weaker and wings becoming stronger in compensation. Therefore I do not think Wallace was talking about stabilizing selection here.

The first sentence of the last paragraph of that same paper does seem to hint at a recognition of stabilizing selection. The sentence starts by stating the role of natural selection in "varieties [progressing] further and further from the original type" and then goes on to say "that same principal [ie. natural selection ...] will also explain why domestic varieties have a tendency to revert to the original type". It seem to me there is an implicit recognition here that natural selection is responsible for maintaining the original type when departures from it occur. I think Patrick Matthew makes a much better job of explaining stabilizing selection. Darwin makes a huge mess of it as the first two sentences of the Origin of Species and many other sentences in that book demonstrate. Gourdiehill (talk) 10:07, 11 April 2024 (UTC)

Graph

Hi! The graph shown on this page along with the associated pages concerning directional and disruptive types of selections lacks both axes and could be more intuitive. I'll make them and update them on the pages. This will be my first edits, so if there's anything I should know - tell me (: — Preceding unsigned comment added by Epitoke (talk • contribs) 11:00, 9 December 2014 (UTC)

Patrick Matthew

Patrick Matthew explains stabilizing selection in his 1831 book, Naval Timber and Arboriculture, where he points out as does Darwin in the Origin that domesticated varieties show more variation than the varieties or species they are derived from living under nature. Darwin comes up with an incorrect explanation for this phenomenon while Patrick Matthew explanation is what is now called stabilizing selection. The relevant passages are:

Matthew: Man’s interference, by preventing this natural process of selection among plants, independent of the wider range of circumstances to which he introduces them, has increased the difference in varieties, particularly in the more domesticated kinds; and even in man himself, the greater uniformity, and more general vigour among savage tribes, is referrible to nearly similar selecting law—the weaker individual sinking under the ill treatment of the stronger, or under the common hardship.

He is pointing out here that preventing natural selection increases variation. The corollary is that natural selection decreases variation. That is stabilizing selection.

Darwin (first 2 sentences of the Origin): When we look to the individuals of the same variety or sub-variety of our older cultivated plants and animals, one of the first points which strikes us, is, that they generally differ much more from each other, than do the individuals of any one species or variety in a state of nature. When we reflect on the vast diversity of the plants and animals which have been cultivated, and which have varied during all ages under the most different climates and treatment, I think we are driven to conclude that this greater variability is simply due to our domestic productions having been raised under conditions of life not so uniform as, and somewhat different from, those to which the parent-species have been exposed under nature.

Here Darwin is attributing the phenomenon to the conditions of life of domesticated populations being "not so uniform as, and somewhat different from" natural populations.

It is interesting to note the phrase in the Matthew passage, "independent of the wider range of circumstances to which he introduces them". This clearly shows that Matthew could see the same thing as Darwin (domestic population's "conditions of life [are] not so uniform as, and somewhat different from" natural populations). It also shows that unlike Darwin he thought these factors were independent of the phenomenon ie not causally linked to it.

It is rather remarkable that despite Darwin reading Matthew's book in 1860 he did not amend subsequent editions of the Origin to incorporate this (stabilizing) aspect of natural selection for explaining the phenomenon of greater variability in domestic populations. Also one might have thought his colleagues would have suggested it to him. I wonder if there was a worry that had he done so it would have elevated Matthew's status and diminished his own?

I would like to add the fact that Patrick Matthew explained stabilizing selection in Naval Timber and Arboriculture to the History Section including the passage I quoted from him above. It is rather nice that the passage includes his coining of the term "natural process of selection". Let me know if you have reasons against this and if not I will put it in. Gourdiehill (talk) 10:25, 20 March 2024 (UTC)

• I'm not sure that I see how Matthew's remark is about stabilizing selection. The latter is the kind of selection where both extremes of a distribution are unfavorable. Whether that leads to more or less variation within a population is debatable. --Randykitty (talk) 11:10, 20 March 2024 (UTC)

  I am not quite clear from your comment whether you are saying it is debatable whether stabilizing selection leads to more or less variation within a population. If so then I would argue it is not debatable. Stabilizing selection leads to less variation in a population. Wikipedia's article on Directional Selection contains the sentence: "Stabilizing selection favors the middle phenotype, causing the decline in variation in a population over time". It contains a reference for the statement the abstract for which does not look promising and the full paper costing $9.99 and therefore even more unattractive as a proposition.

  If both extremes of a distribution for a trait are selected against, it will lead to the population having a smaller range of values for the trait ie. less variation for that trait. I think Matthews is describing this mode of operation of natural selection in the passage I quoted and I think it is what is now called Stabilizing Selection.

  I actually think the figure in the main article which shows a graph of frequency in the population on the y axis vs the value of some trait on the x axis with red before and blue after stabilizing selection is quite misleading. I think it would make more sense if the red curve was a normal curve like the blue curve because in the absence of some stated reason one would normally assume that the distribution would conform to a normal curve. If it is drawn as a normal curve, and I have seen that in other explanations of stabilizing selection, then it would illustrate the reduction in variation that occurs after stabilizing selection has operated. As the curves are presented it is true to say that the extreme values for the red curve are the same as for the blue curve and so you could say the extent of variation is the same before and after stabilizing selection although extremes are less frequent after stabilizing selection. The Khan Academy has a section called Natural selection in populations (https://www.khanacademy.org/science/ap-biology/natural-selection/population-genetics/a/natural-selection-in-populations) which has a graph for Stabilizing Selection which shows the situation quite clearly.

  Hope I didn't misunderstand your comment! Gourdiehill (talk) 19:28, 20 March 2024 (UTC)

• Your OR graphs are incorrect: the phenotypical range of a population under stabilizing selection doesn't usually get smaller, but the distribution becomes a narrower bell curve (see, e.g. [1]). In fact, stabilizing selection works to maintain genetic variation in a population ([2]). Having a narrower bell curve means that the variance in a population gets smaller, but not necessarily the range. So you replacement image is incorrect and the previous version is better. --Randykitty (talk) 16:07, 23 March 2024 (UTC)

  Sorry not to see your reply earlier (I thought Wikipedia would notify me but it did not seem to). I have not really been able to consider your comments properly or read the references you have given although I do intend to do so. I just want to say here that if the graph I added is wrong then it would make a lot of sense to first address this in the article on Natural Selection which is where I got the graph from. I think it is very desirable the graphs in the different articles should be the same as if they are different it is confusing for readers. I hope to come back to this topic soon. Gourdiehill (talk) 09:42, 11 April 2024 (UTC)

  I have had time to give this more thought. If we assume for the purposes of explanation that the frequency distribution before and after stabilizing selection both conform to bell (normal) distributions then if the central portion of the curve becomes narrower then the range must be reduced. By range I am talking about the range of values between a given number of standard deviations from the mean. I can not think of another meaningful definition of range.

  Your first reference to the article written by Heather Scoville in thoughtco.com contains the following statement: "Stabilizing selection is often shown on a graph as a modified bell curve where the central portion is narrower and taller than the normal bell shape". I think this is either suggesting stabilizing selection changes a bell (normal) curve into a curve that is no longer a bell (normal) curve which I think is unwarranted and unhelpful. If it is not saying that and the author is suggesting we start and end with bell (normal) curves (as I am sure should be the case for the explanation to be sensible and useful) then if the "central portion is narrower" then the range must be smaller as that is a property of the normal distribution.

  Your second reference (Genetics. 2013 Aug; 194(4): 955–971) contains the following statement: "Subsequently, Fisher (1930b, pp. 105–111) showed that mutation could maintain variability in a trait under stabilizing selection". Perhaps you have interpreted this to mean that somehow the range is unaffected though the variation nearer to the mean is affected? It does not say that and I could find nothing in the paper to support your inference. I note the authors stated that: "Stabilizing selection on genomic traits is, however, likely to be very weak [...]". It would be better to choose examples where stabilizing selection acts strongly if you are trying to explain core features associated with such selection.

  If you want to see a clear explanation of stabilizing selection from someone who has a string of peer reviewed papers, books, prestigious academic positions, awards and honors I would look at the lecture by Stephen C. Stearns on YouTube called 3.Adaptive Evolution: Natural Selection hosted by YaleCourses in the series Evolution, Ecology and Behavior with Stephen C. Stearns (https://www.youtube.com/watch?v=WJayMGhZxO0&list=PL6299F3195349CCDA&index=3). It starts at 30:50 (Chapter 4. Types of Selection). As part of the excellent presentation there is a slide where you can see his version of the frequency distribution before and after stabilizing selection. It shows that the whole curve is narrowed not just the central portion.

  Content of the quality of Yale University's (and other centres of excellence) free lectures is very much more suitable for informing Wikipedia articles than "science writers" who have no particular reasons to be taken seriously or very highly specialized scientific papers which are likely concerned with very specific aspects of an area of science rather than a balanced overview which is what Wikipedia should be aiming for. Gourdiehill (talk) 17:35, 11 April 2024 (UTC)

Selection Diagrams

The stabilizing and directional selection diagrams are misleading because the extremes before and after selection are at the same points on the x-axis. The diagrams shown in the Natural Selection article have got it correct.

It would seem like a good idea to just use the same diagram as the Natural Selection article mainly because it is correct but also because it makes sense if the four selection articles (Natural Selection, Directional Selection, Disruptive Selection and Stabilizing Selection) are consistent with each other. The other three articles all use the same diagram. The Disruptive Selection article additionally has a misleading diagram that should be removed. I will put a comment on that talk page.

If anyone can do this it would be great but if not I am happy to have a go but it may take me a while as I have not used image or other files when editing Wikipedia yet. Gourdiehill (talk) 23:10, 21 March 2024 (UTC)

I have now replaced the selection diagrams and corresponding legend with those from the article On Natural Selection. Gourdiehill (talk) 20:21, 22 March 2024 (UTC)