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October 17, 2004

Dawkins on Kin Selection

In writings on Kin Selection there are often references to Richard Dawkins’s article ‘12 Misunderstandings of Kin Selection’, in Zeitschrift für Tierpsychologie, 51 (1979), 184-200.

Alas, the Zeitschrift für Tierpsychologie is not on every bookshelf, and I don’t know of any more accessible reprint. But I recently looked up a library copy, and it may be useful to list the ‘misunderstandings’ with a few comments.

The ‘misunderstandings’ follow Dawkins’s numbering and are quoted verbatim. In most cases Dawkins gives references for examples of the ’misunderstandings’, but I will omit these. Of course, some of Dawkins’s points are familiar from other sources, such as the endnotes to the second edition of The Selfish Gene, or Chapter 10 of The Extended Phenotype.

Misunderstanding 1: Kin selection is a special, complex kind of natural selection, to be invoked only when ‘individual selection’ proves inadequate.
Dawkins argues that in principle the theory of kin selection is more parsimonious than ‘individual selection’, which requires additional special assumptions to exclude the fitness effect of actions on relatives other than offspring.

Misunderstanding 2: Kin selection is a form of group selection
This is largely a matter of definition. Dawkins follows Maynard Smith’s definition of group selection as ‘the differential survival or extinction of whole groups of organisms’, and in this sense it is clear that there can be kin selection without group selection, or without distinct ‘groups’ existing at all. But there are other defensible definitions of the term: see my discussion here.

Misunderstanding 3: The theory of kin selection demands formidable feats of cognitive reasoning by animals.
A crude misunderstanding found only among the biologically ignorant: see the endnotes to the second edition of The Selfish Gene.

Misunderstanding 4: It is hard to imagine a gene ‘for’ anything so complex as altruistic behaviour towards kin
Dawkins explains what is meant by a gene ‘for’ a form of behaviour, and argues that kin selection could easily evolve by a slight modification of existing behaviour, for example by a change in developmental timing leading to maternal care being extended to siblings.

Misunderstanding 5: All members of a species share more than 99% of their genes, so why shouldn’t selection favour universal altruism?
This is ‘Washburn’s Fallacy’: see the endnotes to the second edition of The Selfish Gene.

Misunderstanding 6: Kin selection works only for rare genes
See the endnotes to the second edition of The Selfish Gene. Under ‘Misunderstanding 6’ Dawkins also makes some comments on Hamilton’s 1975 essay on ‘Innate social aptitudes of man’, where Hamilton suggests that in remote, semi-isolated communities, all individuals will eventually be closely related to each other, and may therefore be expected to show high levels of altruism within the community. Dawkins disputes this, as individuals will still be more closely related to their actual close relatives than they are to the general population of the community. They would not be genetically inclined to be notably ‘altruistic’ to inhabitants in general, with whom they and their relatives are competing for food and other resources. Dawkins appears however to accept (or at least not to reject) Hamilton’s suggestion that the inhabitants would show innate ‘xenophobia’ towards outsiders. I see a difficulty with this: organisms can only evolve a trait by natural selection if it is beneficial in circumstances which are commonly encountered, and there is a conflict between the suppositions (a) that the inhabitants interact with ‘outsiders’ often enough to evolve a trait of xenophobia, and (b) that they are isolated enough from outsiders for a sharp difference of genetic relatedness to arise. This is not to say that there is no innate basis for xenophobia, but if there is, I think it is more likely to be a by-product of some other adaptation, rather than an adaptation in itself. As someone suggested in discussion of this point, people might evolve the capacity to distinguish close relatives from more distant relatives (e.g. by smell), and such a capacity might then be triggered by the even larger differences between close relatives and ‘outsiders’, even though outsiders were rarely encountered. (This would be what ethologists call a supernormal stimulus.) This does seem a possibility worth exploring, though of course there are other possible explanations for xenophobia.

Misunderstanding 7: Altruism is necessarily expected between members of an identical clone.
Dawkins points out that clonal organisms (like some lizards) are often descendants of a single mutant female. Since the founder of the clone presumably did not have altruistic genes, neither will her clonal descendants. Of course, the descendants might acquire mutations promoting altruism, but in that case they would no longer be clones of their neighbours! The new genes would only spread if they helped the actual close relatives of the mutant forms. Of course, clonal organisms may be altruistic towards each other, but the fact that they are clonal is not a sufficient reason for this.

Misunderstanding 8: Sterile worker insects propagate their genes by caring for other sterile workers who are especially closely related to them.
Dawkins points out that only help given directly or indirectly to fertile relatives would be favoured by kin selection.

Misunderstanding 9: Because full siblings are no less valuable to an individual than his own offspring, Trivers’s theory of parent/offspring conflict does not apply to monogamous species
Trivers’s theory maintains that there is a conflict of interest between parents and offspring, because the parent has an equal interest in all its offspring (ceteris paribus) whereas each offspring values its own fitness more highly than that of its siblings. The offspring will therefore try to get more than an equal share of parental resources, while the parent will resist this. According to Dawkins the theory has been criticised on the grounds that each offspring would value its full siblings as highly as its own future offspring, since their relatedness is equal; therefore if all siblings are full siblings the parent/offspring conflict of interest does not arise. Dawkins points out that this is the wrong comparison of relatedness to make: the comparison should be between relatives in the same generation, e.g. between the offspring’s own offspring and its siblings’ offspring, in which case the relatedness is not equal.

Misunderstanding 10: Individuals should tend to inbreed, simply because this brings extra close relatives into the world
This is a tricky one. A gene which causes its bearer to mate with his or her sibling would on average be passed on to ¾ of the resulting offspring, instead of only ½ of them. [This assumes that one sibling definitely carries the gene, and has a ½ probability of passing it on, while the other has a ½ probability of carrying it, and a ½ x ½ = ¼ probability of passing it on.] If there is no strong disadvantage to inbreeding (such as expression of harmful recessives) it seems that such a gene would be favoured by kin selection.

Dawkins points out that this is fallacious as it stands, because it overlooks the opportunity cost of giving up outbred matings. If each offspring of sibling incest simply replaces an outbred mating, there is no increase in ’genes for incest’. An incestuous couple would have (in a stable population) 2 offspring, with a ¾ probability of passing on the gene to each of them, giving an expected total of 1½ copies. But if the partners mated with unrelated individuals, the expected number of copies would be (2 x ½) + (2 x ¼), giving the same expected total of 1½.

The crucial point is therefore whether incestuous matings would simply replace outbred ones. Dawkins notes this question, but does not mention the likely asymmetry between males and females: females can usually only have a limited number of offspring, whereas males can have a practically unlimited number. A male who mates with his sister (or daughter) is therefore more likely to gain in the number of offspring than she is, and the balance between gain of inclusive fitness (measured by the increase in genes identical by descent) and loss of physiological fitness will be different for the two sexes. Suppose that a brother can mate with his sister and thereby gain 2 extra offspring for himself, while she gains none for herself (since the mating with her brother displaces an outbred one); a gene causing him to mate with his sister will therefore gain on average 2 x ¾ copies, [2 x ½ copies of his own genes, plus 2 x ¼ i.b.d. genes from her] whereas a gene causing her to mate with her brother will gain only 2 x ¼ copies [since she would pass it on to half her offspring anyway, and it is only the possibility of extra copies from her brother that counts]. We might therefore expect males and females to evolve different attitudes towards incest, with females being much more resistant to it.

Misunderstanding 11: There is an important distinction between exact and probabilistic coefficients of relatedness which affects the kind of altruistic behaviour predicted.
Except for parents and offspring, the proportion of genes shared by relatives, e.g. siblings, is only an expected average, not a uniform percentage. In some cases it will be above, and in others below, the average. It might therefore seem that among relatives other than parents and offspring, there would be an advantage in evolving the capacity to detect which relatives had higher than average relatedness, and to direct altruism preferentially towards these.

The difficulty with this, Dawkins points out, is that what matters in kin selection is only the probability of sharing a particular gene for altruism. Other indicators of relatedness, such as physical features, will give no information on this, unless they happen to be linked to the gene for altruism. Your brother may share your big nose, but this does not make him any more likely to share your gene for altruism than your sister with her small nose. For more on this point see chapter 10 of The Extended Phenotype.

[In practice, it is often uncertain what the genealogical relationships between relatives really are, e.g. whether a sibling is a full sibling or a half-sibling. In this context a ‘relatedness-detection’ ability could be beneficial to kin selection, but whether the ability could itself evolve by kin selection is a tricky point. The mere ability to identify degrees of relatedness does not in itself appear to confer any fitness benefit on anyone. It would have to be correlated with some kind of discriminating behaviour.]

Misunderstanding 12: An animal is expected to dole out to each relative an amount of altruism proportional to the coefficient of relatedness.
This is a serious error, and one that Dawkins himself committed in the first edition of The Selfish Gene - see the endnotes to the second edition. It arises from a misinterpretation of Hamilton’s Rule. This states that altruism towards relatives can evolve if br > c, where b is the fitness benefit to a relative, c is the cost to the altruist, and r is the appropriate coefficient of relationship between them. It does not imply that the amount of altruism given to relatives should be proportional to their degree of relationship. As Dawkins points out in his retraction, ceteris paribus any altruistic benefit should be given to the closest relative available, and none at all to any more distant relatives. It may be that diminishing returns or other special circumstances would make it worthwhile to divert some benefit to the latter, but there can be no general rule for this.

I think this point deserves more prominence than Dawkins gives it. It tends to undermine Dawkins’s own case for the general importance of kin selection.

Related posts:
Ethnic Genetic Interests: Part 2
Ethnic Genetic Interests
Interracial Marriage: Salter's fallacy
Limits to Hamiltons Rule
On Genetic Interests
Dissin' Dawkins
Green Beard and Ethnic Nepotism

Posted by David B at 10:56 AM