Friday, May 25, 2012

Squirrels, Dawkins, and Evolution

Richard Dawkins doesn't like the new book by Edward O. Wilson [The Descent of Edward Wilson].

This shouldn't be a surprise to anyone since Wilson has become a supporter of group selection and—even more egregious—a critic of kin selection. Dawkins is a big fan of gene centric adaptation so group selection is heresy. Dawkins thinks that Hamilton's discovery of kin selection ranks right up there with Newton and Darwin, so anyone who casts doubt on kin selection is also a heretic.

I'm not an expert on the details of this debate although my instinct is to think that kin selection is vastly overblown1 and there's nothing obviously wrong with the concepts of group selection or species sorting. However, Dawkins mentions something that raises some important questions about evolution and I wonder what people think.
Nobody doubts that some groups survive better than others. What is controversial is the idea that differential group survival drives evolution, as differential individual survival does. The American grey squirrel is driving our native red squirrel to extinction, no doubt because it happens to have certain advantages. That’s differential group survival. But you’d never say of any part of a squirrel that it evolved to promote the welfare of the grey squirrel over the red. Wilson wouldn’t say anything so silly about squirrels. He doesn’t realise that what he does say, if you examine it carefully, is as implausible and as unsupported by evidence.

...

Evolution, then, results from the differential survival of genes in gene pools. “Good” genes become numerous at the expense of “bad.” But what is a gene “good” at? Here’s where the organism enters the stage. Genes flourish or fail in gene pools, but they don’t float freely in the pool like molecules of water. They are locked up in the bodies of individual organisms. The pool is stirred by the process of sexual reproduction, which changes a gene’s partners in every generation. A gene’s success depends on the survival and reproduction of the bodies in which it sits, and which it influences via “phenotypic” effects. This is why I have called the organism a “survival machine” or “vehicle” for the genes that ride inside it. Genes that happen to cause slight improvements in squirrel eyes or tails or behaviour patterns are passed on because individual squirrels bearing those improving genes survive at the expense of individuals lacking them. To say that genes improve the survival of groups of squirrels is a mighty stretch.
The fact that gray squirrels are displacing red squirrels in Great Britain surely has something to do with evolution. The question is, what? It can't be an examples of population-level natural selection acting on individuals through their genes. It seems more like species sorting as advocated by Stephen Jay Gould in The Structure of Evolutionary Theory.

Maybe it's not group selection but surely it's evolution acting at a level higher than individuals in populations? There are currently 30 species of squirrels in the genus Sciurus. Some of these will survive and some will go extinct, especially in areas where the species overlap. What part of evolutionary theory explains this? Don't we look for an evolutionary explanation for why Neanderthals went extinct?

Ryan Gregory is also confused by Dawkin's example [Does Dawkins understand group selection?]. He says ...
That’s not group selection among conspecifics, that’s interspecific competition. And I can easily imagine traits evolving in response to competitive pressure. However, if grey and red squirrels have only recently come into sympatry then this wouldn’t apply and this would be an irrelevant example. It’s curious to see Dawkins make such a silly argument.
Go over to Genomicron is you want to discuss whether this is an example of group selection and whether Dawkins got it wrong.

Stay here if you want to discuss whether the squirrel example is any kind of evolution that can't be fully explained by populations genetics.

UPDATE: Jerry Coyne really liked the Dawkins review [Richard Dawkins reviews Ed Wilson’s new book. He defends inclusinve fitness (kin selection) as; "one of the most productive concepts in modern evolutionary biology." I'm still not clear on why a concept that mostly applies to animals with substantial brains is so important to all of evolutionary biology.


1. For example, it's hard to see how it applies to maple trees, mushrooms, diatoms, and E. coli whereas Darwin's discoveries apply to all living things and Newton's discoveries apply to the entire universe.

65 comments :

  1. For once, I agree with Larry. Too many scientists only believe what they want to believe. Dawkins likes the idea of gene centric evolution and kin selection, and hence is willing to believe in this no matter what the merits of the evidence. Anyone who disagrees with his orthodox view is to be regarded as a heretic. This is where science gives way to a nasty pseudo-religious ideology.

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    1. God, you are insufferable - not all dogmatic thinking is instantly and always equatable to 'nasty pseudo-religious ideology.' But leave it to you to rush straight to the far end of things, cuz, you know, Darwinism is a religion, and all that.

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  2. I'm still not clear on why a concept that mostly applies to animals with substantial brains is so important to all of evolutionary biology.

    Probably still a bit of a 'diplocentric' view, but the concept can be applied to the evolution of multicellularity. It is much the same argument that applies to, for example, the sterile social insects. Genes will forego their own direct reproduction in favour of reproduction of copies in the germ line, provided rB>C. The multicellular bottleneck is typically haploid, so relatedness is 1/2, but without that bottleneck, with r=1, benefit B is unlikely to exceed cost C. Really, each somatic gene is half-related to two gametes, in a sexual species. Kinship is split by meiosis, so the average payoff per generation is determined by (2 x 1/2 x B) > C.

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    1. I see no reason why kin selection could not also act on haploid, clonal organisms, such as bacteria in biofilms. (Of course, a biofilm could be considered as pseudo-multicellularity.) I think that people get very confused by kin selection and assume that the organism involved has to consciously recognise its kin. It doesn't, any more that an immune cell has consciously recognise self versus non-self cells.

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    2. I see no reason why kin selection could not also act on haploid, clonal organisms, such as bacteria in biofilms.

      In principle, no - but there are some mechanistic considerations: – dispersal, mutation rate and clonal reproduction itself can have a bearing on whether a particular asexual reduction in direct reproduction is causally linked to the assistance of allele copies. There is a distinction between simple mutualism between components of a microbial ecology, and the operation of a cost/benefit relationship enabling gene copies to help each other.

      One of the most important factors relates to the presence of a reproductive bottleneck. In a lineage where reproduction is always by asexual replication, cells always have a simple path out of any co-operative setup (as, indeed, have cooperators in a dispersed sexual population). If the arrangement does not suit, they can reproduce on their own account, and sod their r=1 relatives. But if there is obligate meiosis at some point in the life cycle, somatic lineages that have undergone any significant differentiation have shut themselves off from immortality. They can replicate ad lib (see: cancer) but genes cannot get out other than through nurture of the only cells that have retained the meiotic option: the germ line.

      The same applies to arguments about eusocial colonies. When people (eg Genomicron commenters) equate inter-colony selection with group selection, they miss the reproductive element. The genes for making colonies live in the bodies of queens and fertile males. Whatever elaborate phenotypic contrivances they make – including armies of sterile ‘somatic individuals’ – these are no more ‘groups’ than is an individual organism vis a vis its cells. Genes in queens and fertile males compete via the quality of the colonies they build, and ‘allele frequency’ must be reduced to the overwintering fraction, not some midsummer ‘bloom’ of copies. We don’t count the gene copies in all our cells to get allele frequency.

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    3. This is true but, as Dawkins writes in the article: "It is extremely important not to forget B and C and conclude that only r matters in evaluating the success of the theory in particular cases."

      You are saying that B - the benefit - is zero in many/most of these systems. This may be true but kin selection theory - inclusive fitness in other words - still holds. Some biofilms actually seem to have division of labour and may only "reproduce" through a subset of individuals like a multicellular organism. This is all still open to debate and more evidence is needed. The key point, though, is rB > C still holds true even in these systems. It is universal. It just so happens that, often, B=C=0.

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    4. This is true but, as Dawkins writes in the article: "It is extremely important not to forget B and C and conclude that only r matters in evaluating the success of the theory in particular cases."

      This is, I think, what I was trying to get across. It is too easy to look at prokaryote 'relatedness' and conclude that they must be riddled with kinship effects.

      cf this, where a number of different explanations for an apparently altruistic act, cell suicide, are urged for consideration alongside kin selection.

      Additionally, r only = 1 for the first products of fission. Bacteria are 'related' by the number of nodes that separate them on their family tree, and the probability of mutation/recombination intervening between those. One can integrate the inclusive sum, of course, but add in the difficulties of getting a meaningful value for B and C ... while I accept that the fundamental logic is universal, and quite possibly applies to prokaryotes, the mechanistic distinctions - and practical difficulties - are significant (I realise no-one is saying they aren't!).

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    5. cabbagesofdoom says,

      I see no reason why kin selection could not also act on haploid, clonal organisms, ...

      Please give me an example where kin selection has been conclusively demonstrated in any species other than animals.

      I'm not interested in theoretical speculations or models. I'm interested in actual evidence.

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    6. cabbagesofdoom says,

      This is all still open to debate and more evidence is needed. The key point, though, is rB > C still holds true even in these systems. It is universal. It just so happens that, often, B=C=0.

      Please read the thread on The Importance of the Null Hypothesis. It's quite relevant.

      You can't just assume that your magical equation is correct. You have to provide evidence that the results can't be explained by chance or some other process.

      BTW, I was always taught that when you multiply something by zero the answer is always zero. Are you saying that zero is greater than zero (0 > 0) is a valid equation?

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    7. I have been reading that thread. (I even left a comment over the weekend.) It's not relevant. rB > C demonstrably works when the conditions are met. You can model it till the cows come home. No assumption of magic needed, just assumptions of inheritance.

      Yes, for a specific scenario it would be wrong to assume that B>0 or C>0, but this is not what I am doing. The null hypothesis is that B=C=0, i.e. neutral evolution. I would have thought you would like that!

      I think you misunderstand (a) what I am saying and (b) what "equation" means. "Equation" needs an "=". rB > C is a condition to test, not an equation.

      Pedantry aside, I was saying that if B is zero, you will not see any cooperative behaviour even when r means it is theoretically possible, such as a biofilm. (Your math teacher can sleep easy.) I think Alan Miller fully understood what I meant and, as we have in the past, I think we have reached agreement and clarity through constructive posting. My point is that just because r=1 and "kin selection" effects are not seen, does not mean that rB > C is wrong or not universal, just that B and C are usually 0 for all individuals other than the gene-carrier. (The rB term is really the sum over the whole population.) It is kind of trivial but also inescapable and, I would argue, is one of the few "Laws" of biology.

      On purely theoretical grounds, I cannot see how rB > C can be wrong or not universal. Of course, if B is always 0, it is entirely unnecessary, but there is a lot of evidence that B is not always zero, unless you believe that no cooperative behaviour is genetically programmed.

      Am I saying that rB > C can explain every scenario of cooperation we have ever imagined? No. Can it explain every scenario of cooperation we have actually seen or, specifically, where we can actually measure r, B and C? I think so. I don't know of any situations where someone has demonstrated a gene adaptively increasing in frequency despite unequivocal evidence that rB < C. (Obviously, there is also drift and hitchhiking.) If someone knows of such an example, I would love to see it. I am here to learn (and maybe teach), not to preach. I can cope with being wrong.

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    8. Actually, upon reflection, I think that I have also over-stated my position here. A clear, biologically relevant example of evolutionary adaptation that rB > C is demonstrably not able to explain and "Group Selection" is, would probably be enough. I don't think rB < C is necessary, just as negative selection is not necessary to make positive selection unnecessary as an explanation.

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  3. Are organisms not an example of group selection at the gene level? A gene without a context is useless

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    1. No. This is the essence of "The Selfish Gene". (A good book - read it if you haven't.) An allele is successful if it increases its own frequency. This is usually done as part of a whole (an organism) but not always. (Think of a virus or transposable element.) The key thing - the thing that makes it not group selection - is that an allele could not evolve that aids the organism at the expense of itself. For example, a Y-linked allele that somehow made super-fit daughters (or promoted more altruistic behaviour towards daughters) could not evolve as, without benefiting itself, it would not increase in frequency. An X-linked allele that made super-fit daughters would also increase its own frequency and thus could evolve.

      The important thing against group selection is not that regular adaptations cannot benefit the group - they can - it is that adaptations arise for the good of the individual (gene) not for the good of the species.

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    2. cabbagesofdoom says,

      The important thing against group selection is not that regular adaptations cannot benefit the group - they can - it is that adaptations arise for the good of the individual (gene) not for the good of the species.

      Let me rephrase your statement in order to make it clear to everyone else.

      Here's what you meant to say,

      I'm a firm believer in the concept of the selfish gene as proposed by Richard Dawkins 35 years ago. According to that speculation, the only kind of adaptations allowed are those that benefit the gene or the individual that carries them. No other level of evolution is allowed, according to what I believe. Therefore, group selection is wrong.

      Is that a fair summary of your belief?

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    3. No, that is a very churlish and unfair summary of my position. ("Belief" is also a very loaded term.) A fair summary would be:

      The only known mechanism by which a mutation/allele/"gene" can reach (near) fixation through Natural Selection (i.e. not drift or hitch-hiking) is by having an effect that, on average, increases its frequency in the next generation. (The only mechanism known to me.) That it can happen is not speculation, it is obvious and demonstrated. That it is the only kind of adaptation "allowed" is not proven but I am not aware of any others that have been "unequivocally" demonstrated.

      Given the concept of inclusive fitness (a.k.a. kin selection), a "gene" does not need to act through direct benefit to "itself" (i.e. the physical copy that is expressing some kind of phenotype) as long a a particular condition is met: rB > C, where C is the cost to the “self” copy for a given phenotype, B is the benefit to potential gene-copy-carrier X and r is the probability that X actually carries a copy of the “gene”. In the “standard” model of selection, where X is the host/vehicle/organism carrying the “self” copy, r=1 (it is definitely carrying itself) and C is 0 (it does not harm itself) and so it will spread so long as B>0, i.e. it has a selective advantage. (Actually, I think B needs to exceed 1/4Ne for a sexual diploid population but you get the gist. When r=1 and C=0, B is just the basic selection coefficient, s.)

      Given that these things are quite obviously true, there is no need to invoke any additional mechanism all the time that these things are able to explain observations. In particular, it would be wrong to invoke something with no demonstrated mechanism – Group Selection – to explain something that is already explained by something with a demonstrated mechanism – inclusive fitness (a.k.a. Kin selection).

      If you can direct me to a demonstrated mechanism by which a “gene” can spread by benefiting the “group” but not itself – in other words, you can demonstrate that rB > C is violated and yet the “gene” still spreads because the population benefits – then I will admit that I am wrong and welcome Group Selection into the fold of plausible explanations for evolutionary events. Until I see such a mechanism, I think it is neither unreasonable nor “speculation” to reject it.

      That is a much more accurate representation of my views. Next time, perhaps you can just ask for the reasoning behind my statement, rather than trying to tell me what I “meant to say”? I know this is your site but I do not see the need to be so hostile all the time.

      For the record, and in the interest of full disclosure, “The Selfish Gene” was one of the most influential books I have ever read and was largely responsible for me becoming an evolutionary biologist (and an atheist) and, yes, I do have a certain fondness for Dawkins as a result. However, I like to take each of his arguments on its own merits and am far from agreeing with everything he thinks/writes. (He's a bit too animal-centric for me. I was also very disappointed with “The Greatest Show on Earth”.) I don't just hold these views on a whim and strongly resent the implication that its some kind of irrational belief system to which I subscribe. I am just yet to be convinced that it is wrong.

      I won't assume it but I will ask: are you anti-Dawkins and out to try and pick holes in everything he writes/thinks?

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    4. Cabbagesofdoom said:

      The important thing against group selection is not that regular adaptations cannot benefit the group - they can - it is that adaptations arise for the good of the individual (gene) not for the good of the species

      Adaptations don't arise for the good of the individual or the group (or the general level of adaptation of the species). A mutant in a gene might give rise to a trait that has a positive covariance with the fitness of an individual or of a group in a subdivided population. Depends on how one tallies fitness in any particular case. In both cases, individual fitness and group fitness, the mutant allele has to have on average over all its individuals in all its groups a higher average fitness if it is going to stay in the population. That is, even if group selection works by the existence of different fitnesses for groups of different genetic composition, the alleles concerned still can be described as 'selfish genes'. What rather shows that 'selfish genes' have nothing to do with the argument. The argument is about how to compute fitness if the population is structured.

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    5. Correction noted. I should have said "spread" not "arise" and made it more explicit that "individual (gene)" meant "allele".

      I'm not really sure what "group fitness" is, though. Is it not just mean individual fitness? If not, why not?

      I am also worried that there are different definitions for "Group Selection". I grew up with the "for the good of the species" definition, which is clearly wrong - the squirrels example. The essence of this was that the individual's fitness was of no consequence as long as the group would benefit. This is clearly wrong (to me) as if the group benefits only at the (average) expense individual bearing the relevant alleles, it will disappear. (rB > C again)

      Is there a new, contemporary definition of Group Selection that recognises that the individual fitness of allele-carriers is still important? Is this all just semantics and definitions? (Is the new Group Selection just rB > C redefined using different words?)

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    6. In a subdivided population groups of different genetic composition might have different prospects.
      (Suppose alleles additive in their effect; many locally restricted yearly food supplies; one generation per year).Allele 1 might lead to higher dispersal but lower local efficiency in food conversion. Allele 2 might lead to less dispersal but higher carrying capacity due to more efficiency in food conversion. In computing fitness averaged for the alleles the total population, it is not such a good idea to neglect the population structuring.
      Another idea is considering say ant colonies as individuals - a case of group selection if one insists on ants as the individual. That example shows too that group selection and kin selection are highly connected.

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  4. The argument itself seems almost (almost!) semantic. Maybe I've been hanging around a few too many systems biologists, but on the surface this argument is almost a "big picture" versus "fine details" argument, or perhaps a "component" versus "emergent" picture would be more accurate.

    We have two unique (and non-interbreeding?) populations, each with a unique gene pool which is a product of their evolutionary past. These two populations are now competing for the same niche. At one level, selection is very much at the level of the individual and his/her genes - individual red squirrels are being out-competed, while individual grey squirrels are enjoying high reproductive success. If one looked close enough, specific genes that account for the difference in fitness between the individuals in the two populations would be found, thus giving you Dawkins "selection at the gene level".

    However, you can also look at it from the point of view of the populations - one population is, on average, more fit than the other. As a result we see a net gain in one population, and a net loss in the other - selection very much seems to be occurring at the level of an entire population, independent of variation within one population or the other.

    But, at least to my (fairly uneducated in this area) eyes, it is simply two metrics measuring the same thing. No matter how you slice it, group selection requires events impacting individuals in the population, while the events impacting individuals in the population have an emergent property (that being the "group" selection) due to shared characteristics within the individuals comprising each population.

    Or am I missing something?

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    1. Bryan: However, you can also look at it from the point of view of the populations - one population is, on average, more fit than the other. As a result we see a net gain in one population, and a net loss in the other - selection very much seems to be occurring at the level of an entire population, independent of variation within one population or the other.

      I think the point may be that it is artificial to change one’s ‘level’ above that of the individual simply because of the presence or absence of recombination. Recombination does affect matters, and turns a whole-genome competition into a set of subgenome competitions, but if Red and Grey were simply two alleles of a coat-colour gene, the close ecological competition between conspecifics would lead us to talk of the Grey allele substituting the Red in a single group. We would not talk of the Grey Group outcompeting the Group of Reds – it is true, but it happens due to individual fitness.

      So when we have no interbreeding, but still have close ecological competition, the arena is the same. We have a combined population of individuals all of whom are, more or less, after the same resources, and Greys are producing more offspring per capita than Reds (due to more than just the one ‘gene’). The whole genome is the evolutionary allele – just as in the prokaryote case.

      By the same token, competitive exclusion - the inability of close competitors to coexist indefinitely, even with no average fitness differential - is closely related to the within-population fixation of a neutral allele.

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  5. I'm really struggling to understand how to attach any sensible interpretation to what Dawkins is saying.

    "But you’d never say of any part of a squirrel that it evolved to promote the welfare of the grey squirrel over the red.": To say this would be to ascribe purpose to chance events, which of course we don't do. But leaving purpose aside, it is clear that some parts of gray squirrel phenotype _do_ promote the welfare of the gray squirrel over the red and when the two populations share the same niche, this certainly affects the evolution of the combined population. If a beneficial allele arises in either of the two populations while they are sharing a niche, its fitness advantage will make it more likely to rise to fixation not only in its red/gray population, but also in the combined population.

    "To say that genes improve the survival of groups of squirrels is a mighty stretch." - Huh? How could genes _not_ improve the survival of groups of squirrels? The gray squirrels are outcompeting the red ones precisely because they have better genes - this is just natural selection at work, eliminating less fit genes in favour of more fit ones. Eventually, we expect the gray phenotype to become fixed in the combined red and gray squirrel population, following the usual laws of population genetics. The relevant fact is that the red and gray squirrels share the same space and resources; the fact that they are different species (i.e. cannot interbreed) is completely irrelevant.

    The above is hardly rocket science - would Dawkins argue against it? What exactly is he thinking?

    Part of the explanation may just be a small issue of semantics: when Dawkins says "evolution", he seems to be referring to intra-species evolution only. So if two species coexist in the same niche and one drives another to extinction by having a more fit genotype, Dawkins simply does not call this evolution, even though the results of population genetics apply in exactly the same way as it does for two alleles in a population of same-species organisms. For some reason, Dawkins is happy to call the latter situation "evolution", but not the first. Does anyone know why?

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    1. I don't consider evolution the result of any dynamical system either.

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    2. The point is that the grey squirrels evolve because individual grey squirrels are good at surviving and pass on their "genes". What Dawkins is saying is that at no point did any of the adaptations of grey squirrels evolve for the benefit of all grey squirrels. Individual grey squirrels are not sacrificing themselves to take out red squirrels so that other grey squirrels can prosper. The fact grey squirrels as a group are out-competing red squirrels as a group is merely a by-product of them evolving to be individually better. This is not necessarily true - individuals could evolve to be more successful than other members of their species but to the overall detriment of that species - you only have to look at runaway sexual selection (peacock feathers etc.) to see examples of that.

      The squirrel example is a key lesson of evolution versus design. Red squirrels just needed to be better than the competition to survive and thrive. They have not been designed as a "perfect" fit to their niche, nor have they necessarily evolved the maximum possible fitness. Therefore, when grey squirrels came on the scene they were able to out-compete the indigenous species that, in theory, should be "better" adapted.

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    3. Let me see if I understand this:

      In the context of a single-species population, a beneficial phenotype may rise to fixation by outcompeting the other phenotypes in the population (this may have a beneficial, detrimental, or no effect on the overall fitness of the population, which could be important if the species is competing with other species or enters such competition at a later stage, but is not relevant to discussions about evolution _within_ the single-species population). This is _not_ referred to as group selection, and is the description that applies in the squirrel case if we consider evolution in the two single-species populations separately (the relevant phenotypes have already been fixed in the respective populations).

      In the context of a multi-species population, a beneficial phenotype may rise to fixation by outcompeting the other phenotypes in the population (this may have a beneficial, detrimental, or no effect on the overall fitness of the population, which could be important if the population is competing with other populations or enters such competition at a later stage, but is not relevant to discussions about evolution _within_ the original population). This _is_ referred to as group selection, and is the description that applies in the squirrel case if we consider evolution in the combined population (fixation of the relevant phenotype in the combined population is still an ongoing process).

      I have two questions:

      1) Is it feasible to accept the first while rejecting the second description?

      2) To me, the two descriptions look essentially identical, to the extent that I wouldn't even know where the squirrel case fits in if I didn't know the seemingly irrelevant detail of whether red squirrels mate with gray ones. Why bother inventing a separate term to describe the second case?

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    4. I would answer (1) No, and (2) Exactly. It is no special case. There is nothing different happening. There is no need to invent a term.

      I struggle to see what "Group Selection" claims to offer but that might be due to a lack of a good, clear definition for it. According to a different review of Wilson's book by someone who liked it (in the WEIT comments), apparently Wilson himself fails to clearly define it.

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  6. Um.... What makes you think kin selection theory can't be applied to prokaryotes?

    Quorum sensing for example?

    http://www.ncbi.nlm.nih.gov/pubmed/18004383

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  7. I completely agree with the last comment. Kin selection has been shown to occur in asexual, unicellular organisms, from prokaryotes to microeukaryotes. In asexual organisms r is equal to one, and cooperation and altruism can evolve much easier. Take a look at the literature on Bacteria cooperation, Dictyostelium sociobiology and program cell death in ¨protozoan¨ parasites.

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    1. Sergio Muñoz says,

      Kin selection has been shown to occur in asexual, unicellular organisms, from prokaryotes to microeukaryotes.

      I'm not familiar with this literature. Please give me your very best example of kin selection in unicellular organisms. Be sure to pick an example where all other possibilities have been eliminated and kin selection has been unequivocally shown to be operative.

      Models don't count.

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  8. Kin selection is ordinary gene-centered evolution. It just uses better accounting than in the usual individual-based formulation. It is practically a mathematical law; it has to happen, when Hamilton's rule is satisfied.

    It is far from ranking with the theory of evolution itself; it seems a minor (and in retrospect obvious) footnote to Darwin's formulation. It is even farther from ranking with Newtonian theory.

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    1. I agree that it is not of Darwinian nor Newtonian magnitude but I think that kin selection is more that a minor footnote. The fact that it now seems obvious is an indicator of what a great idea it was - it is like Natural Selection in that sense. Without kin selection, there is a lot of biology that simply cannot be explained in an evolutionary framework. We take it for granted now but, at the time, it was a pretty big step forward. Were it not for kin selection, we'd still be having uncomfortable conversations with Creationists about altruism. It was also the final nail in the coffin of the "good of the species" Group Selectionists. (Even if, perhaps, they have not all yet realised it.)

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  9. Plants also have been observed to recognize kin and not compete for resources as aggressively. Sorry I don't have time right now to find the reference, but the research was done in sea rockets.

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    1. Now that _is_ rocket science :-P

      (sorry, couldn't resist)

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  10. "Stay here if you want to discuss whether the squirrel example is any kind of evolution that can't be fully explained by populations genetics."

    I must admit to being very confused by this. As far as I am aware, population genetics has no problem with extinction. There are two different things going on here: (1) the population genetics within each squirrel population as different genotypes compete and gene frequencies change through time through selection and drift; (2) the overall population dynamics determined by birth/death rates in each population. Yes, the latter is influenced by competition, which in turn is influenced by the former, but I fail to see why it needs any special explanation. I feel like I must be missing something but I cannot see the problem.

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    1. Speciation and extinction cannot be fully explained by population genetics. That's why you don't find much discussion of meteors in a population genetics textbook. Can you explain why Neanderthals went extinct using only population genetics? Can you explain why there are several species of ground finches in the Galapagos using only population genetics?

      I feel like I must be missing something but I cannot see the problem.

      I also feel like you're missing something and I can't see why. It seems perfectly obvious to me that microevolution is necessary but not sufficient to explain macroevoltuion.

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    2. It's easy to explain extinction in general - you include rates of mortality and reproduction and model a finite population size. If mortality exceeds fecundity from, say, competition for resources from another species, you go extinct. It's not rocket science. Likewise, for speciation, you need to model two or more populations with gene flow, some kind of reproductive incompatibility factor and a reduced fitness for hybrids.

      Of course, with models you can load the dice to get the desired outcome. You can investigate what might have happened but not what actually did happen – almost by definition, these events tend to be historical and we do not have access to the right parameter values. Even for contemporary extinction/speciation “in action” I am not sure that we can accurately measure such things.

      How do you explain a specific extinction or speciation? Well, I don't. Explanations of past events are always going to have an element of just-so about them, that's just a fact of life. They will never be “fully explained” nor can they be. It doesn't mean there's anything wrong with the models, just that we don't have enough data and/or a time machine to check that we're right. It is enough for me to know that we can explain them in principle.

      Once this year's exam load is over, I will check out the micro/macroevolution post. (It will be too distracting to do it now!) Personally, I have never been convinced that there is a need for those terms. To me, evolution and evolutionary change are continua and micro/macro is a false dichotomy. That said, one is never too old to learn and it will be interesting to see what I am missing.

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    3. It's easy to explain extinction in general - you include rates of mortality and reproduction and model a finite population size. If mortality exceeds fecundity from, say, competition for resources from another species, you go extinct. It's not rocket science.

      LOL

      Thanks for injecting a bit of humor into the thread.

      For a minute I actually thought you were being serious.

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    4. Having just re-read your post, are you simply saying (without actually simply saying) that you also need external factors for a lot of extinction and speciation? That "population genetics" does not occur in a vacuum? Well, obviously. No one branch of science explains everything.

      Can PopGen explain a meteor? No! How could it? Can it explain gene flow in an expanding population colonising a new island or an open niche following a meteor? Yes! Can it explain specific past events? Theoretically, I think it could but in reality I doubt it - we just don't have the necessary data.

      (I don't see what this has to do with squirrels or Group selection, though. I think you can model interspecific competition and, if the parameters were set right, result in extinction of one species.)

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    5. I'm with cabbagesofdoom here. Unless you are using a version of popgen that assumes constant or monotonically increasing population size, popgen predicts that population size will sometimes become zero (when the population in question is an entire species, this is known as extinction). Since population size is obviously affected by external factors (such as metereorites that drastically reduce the carrying capacity of a particular niche), popgen predicts that extinctions will happen under the influence of external factors. So what part of extinction does popgen fail to explain? Naturally we don't have the data to answer specific questions about unobserved past events, but that doesn't mean that we don't know the general mechanism.

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  11. Yeah, I agree with you here. Of course it's evolution. The squirrel thing is species selection, though for some reason you want to call it species sorting. Interspecific competition in which there is no selection happening within either population is clearly species selection.

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    1. It's not species selection! Species selection requires an analogue of a birth/death process, above the level of the individual species.

      Different collections of species differing in internal or external factors that directly impinge upon their rates of speciation and extinction behave (theoretically) like collective 'individuals'.

      This is not at all the same thing as a contest between just two overlapping reproductively isolated species.

      I'm a bit dubious about how useful species selection is - but it relates to more than just a pair of 'evolutionary individuals', one of which survives without 'reproducing' and the other 'dies'!

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    2. The squirrel thing is species selection, though for some reason you want to call it species sorting.

      That's because I'm aware of something called "the null hypothesis." We see that one species survives and another goes extinct but we don't know whether that's due to chance or selection.

      If you call all of these events "species selection" then you are making an assumption about the process. In most cases you have no evidence that your assumption is correct so it's better to use a neutral term ("species sorting") until you have collected that evidence.

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    3. I posted a response to these posts, but it has been eaten by the Internet ...

      The squirrels are not an example of species selection - but this is not because there may be some kind of "species drift" in operation! I doubt you would find a reputable source that supported either of your usages. Eg see Futuyma Evolutionary Biology 3rd Ed p352, or here. Or see the original coinage by Stanley

      SS relates to speciation as a birth analogue and extinction as a death analogue, giving possible patterns above the level of single species, analogous to patterns in asexual individuals. When an internal or external character causes a greater level of cladogenesis/reduced extinction rate among species in possession of it than related species lacking it, the conditions for species selection are met. From an SS perspective, there are precisely two evolutionary ‘individuals’ in the squirrel scenario. Neither has ‘reproduced’ (speciated), and one is on the back foot but has not yet ‘died’ (gone extinct). Two evolutionary 'individuals' do not a selective arena make.

      This is just competition, and it is mediated, just like within-species competitions between alleles, by individual fitness. I think there is excellent reason to reject the ‘null hypothesis’ that the red just happened to be unlucky, and drift is in charge – or, it is ‘unlucky’ in just about every habitat where the two co-exist.

      It is evolution, true. You can readily, and legitimately, view it as a single population of squirrels, which happens to contain two non-recombining ‘haplotypes’. Allele frequency of these (diploid!) haplotypes is changing, apparently as a result of higher fitness of one ‘evolutionary allele’ – whole Grey genomes – vs the other – whole Red genomes.

      There is no rule that says the evolutionary allele must map onto something lower than the genome (or that evolution only occurs when it is lower). In the case of asexuals, and reproductively isolated species, it can’t.

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    4. Thanks for that post. I am still trying to get my head around why such a big fuss was being made over Dawkins using interspecific competition rather than conspecific group competition. I know the latter can potentially mate but surely there's a continuum of gene flow between populations and different species are just an extreme case where gene flow is fixed at zero? Again, I feel that I must be missing something! (And I'm not too proud to admit it. Marking second year coursework leaves my brain feeling fuzzy.)

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    5. Alan Miller:

      We can agree that Larry's "drift" analogy is pointless here, since the problem with red squirrels is clearly competition, not just that there happens by chance to be fewer of them.

      So is competition species selection? I agree that my take on this is non-standard, but I don't think there are good reasons to reject it. Certainly an artificial lumping of two species into one for purposes of making it a within-species phenomenon is bizarre and unjustified. They aren't one species, but two. And within each species there is no selection going on, at least none that has any likely effect on the result, which is extinction of one species. Can we grant that an extinct species is less likely to speciate than a non-extinct one? If so, there's your birth-death process.

      We are left with your objection that this involves only two species rather than many at once. I don't see its force. If there were a population of two asexually-reproducing individuals and one of them outcompeted the other, that would be natural selection, and thus evolution. Same here.

      So what do we have? We agree it's evolution, and it isn't evolution through allele frequency change within a population. What do you want to call it? I claim that if we have interspecific competition that results in no significant selection within species but that results in extinction of one species, we might as well call that species selection.

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    6. I definitely see what you are saying, I'm just not sure if it is relevant to the Group Selection/Kin Selection thing or, if it is, it highlights another situation where people may be arguing past each other. (Or, where I am being naive.)

      Extinction and speciation (as a birth/death model) happen on a very different timescale to allelic evolution. Regular Natural Selection is a cause of evolutionary change. "Species selection" is a consequence. Natural Selection (including kin selection) is about how/why/when an adaptation spreads. Species selection would be about how/why/when it persists long-term. (Obviously, Natural Selection is also acting long-term because lots of short-terms add up to long-term.)

      Extinction and speciation can happen in single generations, such as a meteor killing an entire population, or polyploidy in plants, but these rare events are not to do with group competition.

      The other thing that makes me squirm a bit about "Species Selection" is that, above 1, there is no reason why more species is better/fitter. Clearly extinction is less fit than life but that is simple individual fitness. Why is two species better than one? What if a tiny population of red squirrels on the Isle of Wight end up speciating from a small population of red squirrels in Scotland due to reproductive isolation and drift? How would these two "species" be better in any way to the massive rampant grey squirrel population that fills the rest of the country? Lastly, capacity for speciation is still not an indication of really long-term survival. You might spawn a load of different specialist species but then a big climatic upheaval drives them all extinct, while the generalist rats and cockroaches of the world just carry on their merry way. Specialist niche adaptation can evolve despite the long-term risks because Natural Selection and "species selection" occur on different timescales.

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    7. The other thing that makes me squirm a bit about "Species Selection" is that, above 1, there is no reason why more species is better/fitter.

      We can turn your question around: Why are more individuals or haplotypes better for fitter? In the latter case, it's just because we assess fitness that way within species. Even if speciation is random, differential extinction will result in different characteristics becoming more prevalent in the biota. That is, the distribution of characters in the biota can depend on differential extinction, quite aside from selection within populations. That's evolution.

      There are at least two possible responses to competition: adaptation or extinction. Species selection would occur when adaptation doesn't, presumably because there is no relevant variation within the population for selection to create adaptation from. I see this as being a fairly common response. We can see it in space more easily than in time, when one species competitively excludes another from some habitat (or when two species mutually exclude each other).

      Whether the environment changes over time, thus causing different characters to make a species subject to extinction, is irrelevant, just as changing environments are irrelevant to whether individuals are subject to selection. Nor do time scales seem all that relevant.

      Whether species are equivalent to one another as units of diversity is another question too, one that also doesn't seem relevant.

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    8. I think I see what you are getting at. (I'm about 10% of the way toward being convinced, which is more than I was!)

      As far as I can tell, though, there is a cause/effect difference here. Individual haplotype fitness is important because it is the cause of evolutionary change. Species selection as described is the consequence of evolutionary change. It is still evolution and interesting and wonderful etc. but I still think that it is the individual/haplotype fitness that is driving the whole show, and that's an important difference. (And why the different timescales are very relevant.)

      I would also say that you can replace "differential extinction will result in different characteristics becoming more prevalent in the biota" with "differential death will result in different characteristics becoming more prevalent in the biota", i.e. regular Natural Selection.

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    9. What makes fitness a cause of evolutionary change? Shouldn't the cause be mutation, which creates the haplotypes that are then selected? This is similar to your argument. All selection does is sort existing variation, changing the distribution of characteristics in the population; all species selection does is sort existing variation (some of which presumably arose by natural selection acting on mutations), changing the distribution of characteristics (in species) in the biota. The causes are different, certainly, but they're also analogous. Selection can be considered a cause or a consequence, depending on how you look at it, regardless of level.

      Of course you can replace extinction in a biota with death in a population. They're analogous phenomena. But are analogous phenomena therefore the same phenomenon? Your last paragraph would seem to support my point.

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    10. "What makes fitness a cause of evolutionary change? Shouldn't the cause be mutation, which creates the haplotypes that are then selected?"

      I don't think so, no. Selection can act on alleles that are already in the population. Mutations add to the raw materials for evolution but they do not really cause evolutionary change as normally defined. I don't think anyone would claim that a mutation that lasted one generation before disappearing was causing evolution. Differential fitness does cause evolutionary change, through selection. It is not the only form of evolutionary change - there is also random genetic drift - but it is definitely a cause. (RGD is also an effect - a form of evolutionary change; the cause of RGD is random segregation of alleles and/or random selection-independent differential reproduction.)

      "Selection can be considered a cause or a consequence, depending on how you look at it, regardless of level."

      Selection is the consequence of different phenotypes with different fitness but it is still the cause of evolutionary change. Extinction is not. It is the consequence of evolutionary change. I don't think they are analogous at all.

      "...all species selection does is sort existing variation (some of which presumably arose by natural selection acting on mutations), changing the distribution of characteristics (in species) in the biota."

      But what does this really mean? Species is a very woolly term and often arbitrary. Claiming that something has "changed its distribution ... in the biota" just because it now exists in two reproductively isolated populations rather than two reproductively compatible populations seems like a very odd claim to me. It hasn't changed at all. Any changing distribution is to do with the relative success of individuals, not speciation.

      Extinction and speciation are not two sides of the same coin. They are not birth/death processes that are analogous to actual birth and death. Extinction IS death - they are the same phenomenon, not analogues. Speciation is not an analogue of birth. It is not a species reproducing, it is a group of individuals becoming reproductively isolated. It is the consequence of evolutionary change that prevents gene flow, which is possibly preceded by a geographic barrier to gene flow. (Evolutionary change that itself is often driven by the individual fitness effects of mating and producing sterile or otherwise low fitness hybrid offspring.)

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    11. I think you're arbitrarily resisting the analogy out of habit. Extinction can be a cause of evolutionary change just as much as individual selection can, in that it removes particular variations from the biota. As Dave Jablonski is fond of saying, species selection never built an eye or a wing, but that doesn't prevent it from being a force in evolution. It may in fact be a minor force, but we aren't arguing relative importance here. If the extinction of alleles is evolution, why isn't the extinction of species?

      I agree with you that speciation isn't a perfect analogue of reproduction. But it's close enough for our purposes. Mere separation isn't all that much like reproduction, but it does give an opportunity for variation, growth, geographic spread, and further diversification, and so has the potential to be analogous to reproduction, eventually. Sure, speciation is probably most often driven by selection. So what? How species come to be isn't relevant to species selection.

      The relative success of individuals in different species, in which there is no change in allele frequencies within species, isn't plain vanilla natural selection. What do you want to call it?

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    12. John: I agree with you that speciation isn't a perfect analogue of reproduction. But it's close enough for our purposes

      Nnnnngh!!! Whose purposes? In essence, speciation is a 'vegetative' process. Vegetative processes can be reproductive, or not, but the choice would involve something a bit more positive that "well, it's branching ...!".

      Species Selection (as formally defined) is IMO a poor analogy, which I would resist on mechanistic grounds.

      The relative success of individuals in different species, in which there is no change in allele frequencies within species, isn't plain vanilla natural selection. What do you want to call it?

      Natural selection, please. What makes an 'allele' solely a subgenome unit? I think you are 'arbitrarily resisting out of habit'! Consider prokaryotes with no LGT, or differential reproduction between the individuals of any asexual lineage of your choosing. What do you call it then?

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    13. John: We are left with your objection that this involves only two species rather than many at once. I don't see its force. If there were a population of two asexually-reproducing individuals and one of them outcompeted the other, that would be natural selection, and thus evolution. Same here.

      There are two issues here. One is that Species Selection as per Stanley et al is specifically predicated on a differential in speciation/longevity/extinction rates between clumps of species. There are more survivor species in Clade A than Clade B, because of differentials in some fundamental and differential character. But if Clade A has 1 species, and Clade B also has 1, this is not SS sensu Stanley.

      The other matter is that selection is a consistent bias for one type vs another over numerous 'rounds' of competition - the signal of selection emerges from the stochastic noise of individual lives. With a sample size of 2, stochastic effects would swamp any selective differential.

      I would simply call this Evolution (change in allele frequency, the 'alleles' being whole genomes), by Natural Selection (consistent reproductive differential on the 'conventional' per-capita basis). 'Higher-level' phenomena appear to be absent in this case, beside a certain 'diplocentric' bias coming from members of a sexual species arguing that evolution by individual-output NS only happens inside collections delimited by their reproductive mode! :0)

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    14. @John: I think we should just agree to disagree (I'm back to 0%) as this could run and run. Like Allan (I think), I see no utility to what you propose. I will however answer your questions, briefly.

      "The relative success of individuals in different species, in which there is no change in allele frequencies within species, isn't plain vanilla natural selection. What do you want to call it?"

      How about "inter-specific competition"? It is still vanilla Natural Selection unless "plain vanilla" = "pure 19th Century Darwinian".

      If the extinction of alleles is evolution, why isn't the extinction of species?

      I don't think anyone said that extinction is not evolution. They are the consequence of evolutionary change, not the cause. They are the essentially same thing - the failure of all individuals carrying that genetic variant to pass it on. So?

      We have moved on a long way from Natural Selection being straight Darwinian struggles with other members of your own species. Genes can even have their primary phenotype through members of other species. So what? At the basic level, it really isn't any different. "Species" are a convenient but pretty fake unit of biology and certainly not a unit of selection. I am not resisting the alternative out of habit - I am resisting it because it makes no sense and only has the potential to confuse, in my considered opinion. (And I have considered it.)

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  12. I'm not a scientist... just a fan. But what I'm seeing here reminds me just a little of the polemics of religion. I know science requires ideas to clash, in a way like religion, but the difference is that in science, if one's right and the other's wrong, that can be demonstrated. In the finest sense, religions are incapable of this.

    But here it looks like dogma. I think the problem may be that BOTH ideas are valid, not one or the other. I can't see a reason why evolution has to be driven by just ONE overarching principle, much less that it is. I'm fine with the idea that different dynamics can drive aspects of evolution in different ways in various circumstances. I really admire Richard Dawkins and I'm grateful to him for opening so much up to me as a teenager reading The Blind Watchmaker, but this comes across as being a little too hidebound, and I'd like to see him mumble a Saganesque "Well, maybe...".

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    1. From what I can understand/see, it is definitely not dogma. What is happening here is that (mostly) experts in the field are discussing subtle (and maybe not so subtle) distinctions between their respective points of view.

      Nobody in this discussion has said that evolution has to be driven by just one overarching principle. Rather, at least some of them seem to be making the VERY DIFFERENT POINT that at least the aspect of evolution under discussion seems to be driven/explained by one principle.

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    2. Okay, all you're doing is taking my point and moving it down a level from overall theory to supporting instance. It still stands. I get the impression Dawkins is being intractable not because of evidence but because he's personally invested in his view. Again, I don't see why both principles can't be at work and what implies they're necessarily mutually exclusive. Dawkins seems to, but even with my limited understanding, I find the conclusion suspect.

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  13. Just one comment, and on the North American version of the "competition", so may not be applicable to the UK version..

    I remember in my grad-student days seeing a few seminars by a woman pushing the idea that the grey squirrels (in British Columbia) favour disturbed habitats, while the reds prefer undisturbed conifer forest. She was asserting that what looked like out-competition by the greys is actually them filling the new "residential habitat" niche. As the land is being developed, it give the appearance that they greys were out competing the reds, when it was in fact another factor.

    See, for example
    http://www.canadianfieldnaturalist.ca/index.php/cfn/article/viewFile/143/143 (not the primary article that I saw her discuss, but this is the only free article discussing it that I could find).

    -The Other Jim

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  14. It seems to me that the reality on the ground (or in the trees) is individual Gray Squirrels (or pairs) outcompeting individuals (or pairs) of European Red Squirrels. That's enough to explain the loss of European Red Squirrels.

    It seems to me that individual competition would be the null hypothesis. Group selection might happen, but you'd have to have evidence that groups form among the Gray Squirrels (or both species), and that interactions at the level of these groups explain the disappearance of European Red Squirrels. At least in my informal observations, Gray Squirrels don't actually cooperate in groups. (A mere failure to fight while scarfing down the surplus of food at a bird feeder doesn't qualify as cooperation, in my opinion.) I doubt European Red Squirrels do, either, but I haven't seen them.

    If we humans think Gray Squirrels as a group replace European Red Squirrels as a group, that's because we tend to think of these squirrels collectively, not because they act collectively.

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  15. @cabbagesofdoom,

    Yes, I wonder why there is so much of a fuss about this, and I think it reflects a number of biases, and the degree to which people expert in some areas of biology grasp other topics – or the degree to which people think other people grasp topics they think they themselves grasp well! Dawkins gets things wrong (see “random”). He is also prone to metaphors that have the potential to mislead (see: “Selfish”, “Gene”, “Blind” and “Watchmaker”). But does Dawkins understand group selection? I’d say so. Do people understand Dawkins? Despite his general clarity, not always.

    The unfortunate part of this particular issue is that he (or an editor) omits to show the precise viewpoint of Wilson which he is equating with the squirrels, which renders it something of a ‘take-my-word-for-it’. But as regards what it ‘is’ and ‘isn’t’, critics seem to be espousing a view of evolution that places recombining alleles in a different category from nonrecombining ones. The evolutionary allele itself is not a ‘gene’, but simply a particular genetic linkage unit, potentially encompassing any fraction of the genome from all of it down to fragments of a ‘gene’ – or even to a ‘gap’, a complete absence of DNA at a locus where other members possess something. Some genetic units can be split, partitioning fitness effects more finely among the bodies they successively occupy - and some cannot. And some can be split in some arenas, but not others. I think Dawkins is pretty clear on this.

    The ultimate reductio(nism) ad absurdum would be consideration of the fate of every individual DNA base pair. It is the only truly indivisible unit, but impractical to treat as such. It happens to be physically linked to others, and that linkage tends to be retained more often than broken, leading to evolutionary persistence of sequence. That persistence can be extended – indefinitely in the case of asexuality, or nonrecombining chromosomes, for a long time in inversion-boxed segments or regions of crossover repulsion, or those where the population tends to be dominated by homozygotes in the region of interest … it is a bit of a moving target, in short.

    But the important point is that very little linkage exists above the level of the organism - there is a discontinuity. People who see a nice neat hierarchy from chromosome fragment to chromosome to genome to cell to organism to group to population to species to higher taxa are slipping almost unnoticed from homologous systems to analogous ones, at the point at which reproductive linkage breaks down. It’s often the organism, conceivably the pair, but rarely higher – even those cases (eg eusocial insects) where it seems higher are explicable through individual selection. Queen genes simply have a complex phenotype that extends beyond her body. The elements of the colony don’t reproduce; the queen does – it is individual selection on queen genes via emergent effects through her non-germline progeny. IMO the debate isn’t just a matter of dogmatic Weltanschauung, but the extent to which the rival viewpoints have a mechanistic basis.

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    1. "...consideration of the fate of every individual DNA base pair. It is the only truly indivisible unit, but impractical to treat as such." - But that's exactly what we do, much of the time. Treating whole genes as units means one cannot investigate the point mutations individually in a population genetic or phylogenetic framework - the linkage makes it computationally intractactable. But in many cases it is possible and informative to ignore linkage and study point changes individually (or with only pairwise linkage), which we can do in detail.

      Of course linkage is important in evolution, but I don't understand why it needs to be emphasized in this debate, and hence why you are drawing a line at the organism level. If you think about one allele at a time, the way it spreads in populations of genes, chromosomes, cells, organisms and species is the same.

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    2. Konrad: Of course linkage is important in evolution, but I don't understand why it needs to be emphasized in this debate

      I bring it up because people are saying that Dawkins is talking crap because his example is interspecific. Linkage defines the extent of the evolutionary allele, and nonrecombining alleles are still legitimate evolutionary units (else how would prokaryotes evolve, absent LGT?).

      ... and hence why you are drawing a line at the organism level.

      The mechanism changes at the organism level. Instead of direct fitness (the number of copies different rival linkage units can churn out by direct replication), we have a slightly more mysterious 'something else'.

      Kin selection would have it that that 'something else' relates to the ability of a gene copy in one body to assist gene copies in other bodies. Group selection would have it that something emergent takes over - individual fitness effects notwithstanding, the Group is a legitimate 'evolutionary unit'. The problem with that - going back to Williams's "Adaptation and Natural Selection" is to explain how an individually detrimental allele can spread to realise its emergent effect, and persist in the face of 'cheating' individuals. I'm not sure how the modern Group-Selectionists deal with that issue, but I don't think it has just gone away. There is no problem with emergent effects from neutral, or only mildly detrimental, alleles. Emergent effects can increase selective advantage.

      If you think about one allele at a time, the way it spreads in populations of genes, chromosomes, cells, organisms and species is the same.

      Which is back to my point - what is the 'allele'? The evolutionary allele is somewhat different from the geneticist's, and a given bit of DNA can take part in multiple competitions simultaneously. Recombination does affect, quite dramatically, the nature of the competition. Whole Grey genomes compete with whole Red ones - GGGGGG competes with RRRRRR for representation in the space available. But GGGGGG is itself a set of smaller alleles, each with an evolutionary 'half-life' dependent on the length of DNA you pick and the amount of crossover that occurs within that subunit in a given unit time. Depending on length of persistence, the selective advantage of a particular unit is that of the whole unit, not the individual protein-coding parts of it.

      But what is the 'reproductive unit' of a group of organisms? There is simply replication of individuals, potentially (but not necessarily) subdividing smaller evolutionary units by recombination, with important consequences. But there is no 'composite replicator' at the higher level, which introduces a mechanistic discontinuity.

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    3. Alan: Thanks for taking time with tihs - your responses are very informative.

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    4. @Allan: I think you are right. I also think a lot of people don't try to understand Dawkins because they really want him to be wrong. Often, it seems, for no greater reason than scientific snobbery - he hasn't published much in peer-reviewed literature. I also agree that it was a very bad move on someone's part (presumably his) not to be more explicit out the Wilson/squirrel comparison. The benefit of hindsight, maybe.

      The one thing that I am not sure that I agree about but is important to highlight for it definitely fuels the debates in this area is the statement: "The evolutionary allele itself is not a ‘gene’".

      Regrettably, I do not think this is always true because there are so many definitions of "gene" kicking around. (Without defining it each time you use it, or adding qualifiers such as "protein-coding", it is a useless term.) In particular, my understanding of "The Selfish Gene" is that "gene" is precisely defined in that context to mean exactly that. My memory is a bit hazy now but I think there is quite a lot in the book discussing the very issue of alleles and what the evolutionary unit is, and settles on "gene" as a convenient (and widely used e.g. in "gene pool") catch-all term for the underlying unit.

      People may criticise Dawkins for defining gene in this way but they should be clear to recognise that it is defined in this way before attacking the rest of the argument. Before they criticise this definition, they should also remember that it was done in the '70's, long before we really knew much about physical genetics. (And I say "we" in the global sense, for I was not even born!)

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    5. cabbagesofdoom,

      Just noticed your response, and I agree, even with the bit where you disagree with me ... ! Anything that can have alleles must itself be a gene, so I wouldn't say the evolutionary allele is not a gene ... just that it is not always what people typically think of as a gene. I think Dawkins is clear with his definition (in which I think he is following Williams), and he goes into further detail in The Extended Phenotype.

      Even gene-selectionists can confuse levels, however. My teeth grate whenever I read treatments of the Paradox of Sex (TM) that start "imagine a gene for asexuality ... ". Maynard Smith did this, and Williams; both seem to overlook the fact that you cannot meaningfully apply a subgenome model to asexuality. People who equate the 'Twofold Cost of males' in a gendered species with the gene-level segregation cost in meiosis are making a similar error.

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  16. Er, kin selection is *not* confined to animals. See, for example:

    Gilbert, O. M., Strassmann, J.E., & Queller, D.C. 2012. High relatedness in a social amoebae: the role of kin discrimination.

    Kuzdzal-Fick, J.A., Fox, S.A., Strassmann, J.E. & Queller, D. C. 2011. High relatedness is necessary and sufficient to maintain multicellularity in Dictyostelium.

    Even things like plants giving resources (e.g. fats in nuts) to their sexual offspring is covered by kin selection theory.

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