#groupselection

Kin Selection: This hypothesis argues that all individuals of species serve only to propagate their own genes and compete with those of all others proportionally to the degree that those genes differ. This is prescribed by the role of reproduction in preserving the same genes in close relatives including collateral ones, such as uncles or cousins, while more distant relatives are treated as competitors. It appears superficially to be a pure expression of Darwinian evolution. It is ingenious, but that is about all that can be said for it. Darwin himself never made such a proposal and indeed gave great emphasis to the role of emotions in guiding animal and human behavior. Although kin selection has become a dogma, experience gained over the last half century has failed to find support for it either intuitively or through observation. Group Selection: This hypothesis proposes that genes adapt to the group of social species rather than to each individual. Certainly, mutations that are favorable to multiple animals can diffuse throughout the herd by promoting cooperation. However, the limitation of this interpretation is that it does not explain how the genes cause this action and therefore does not advance our understanding of sociality in the real world. Emotions: It has become customary in some circles to evaluate animal actions as being precisely directed towards favorable outcomes, but that is not how nature works. Their and our brains are instead guided towards anticipated or realized pleasurable feelings and away from aversive or painful ones. These are expressed as emotional signals which are controlled by hormones. Sociality itself is no more complicated than a pleasurable sensation of the presence of other familiar animals nearby, which may extend to close or distant relatives as well as unrelated individuals and is evidenced by the formation of herds. Hormones: The two hormones that control sociality in mammals and birds are testosterone and estradiol. These are well recognized for contributing to the attraction of opposite genders, but their decline or absence causes them to reward proximity to the same sex. So these sex hormones account for competitive reproduction during the mating season and for collegiality in the rest of the year. The latter property is essential for animals to collaborate and undertake tasks that would otherwise be beyond their reach. The evidence that sociality correlates inversely with the output of androgens or estrogens is very strong since it is precisely observed in many different species of mammal or bird, many types of association and in both genders. Human Sociality: A special case is that of species such as humans who breed at any time during the year, because both their sexual and social qualities need to be expressed simultaneously. Sexual orientation develops initially in the maturing brains of embryos. There is good evidence that individuals of either gender may elicit reverse sexuality at this stage which leads to homosexuality. It is very likely that individuals of each gender exhibit their own biased continuum of sexual orientation. In this way, both sexuality and sociality may coexist in all individuals at different levels which benefits the whole population and is the essential component of human civilization. Read the full article

Despite the long history of the theory of kin selection, it has never been confirmed through unambiguous observation or experiment. Neither of the two authors in the previous blog seems to have had much interest in testing their ideas. In order to understand kin selection theory, one must recall the effect of the degree of separation of pedigree of two related individuals on the degree of identity of their genes. The basic rule is that for each degree of separation it drops by a factor of 2. Parents, progeny, and siblings are all, on average, half-identical, while uncles, nieces, grandparents, and grandchildren are a quarter, and cousins an eighth identical. The general effect of this exponential decline should be to give preference to small compact herds. Kin selection is not a feasible explanation for massed herds of species such as reindeer, wildebeest or emperor penguin. Moreover, Kay Holekamp has reported that hyena colonies are also generally only loosely related. Coltman et al have used genetic profiling to show that female wild sheep herds are related only to the extent of second cousins, while the males are unrelated1—and so it goes on. The Limit of Kin Selection in Animal Sociality Kin selection is a possible explanation for small herds of deer, sheep, and bovines. But, they all present a problem for males who may not even recognize their offspring, since they are absent at the time of their birth; when the two genders meet at the mating season in the next year they are more interested in sex than in their progeny. In this and in many other cases, in which the hypothesis has been challenged, partisan commentators have responded by modifying the theory with untested explanations. Edward Wilson has expressed his frustration with this unscientific practice in “The Social Conquest of the Earth”. Some animals act generously to those in distress by assisting them even to their own detriment. A good example of this is the adoption by macaques, chimps, hyena, and humans of orphaned infants and nursing them for long periods. Genetic profiles have shown that many of them are not related to the surrogates, which is a direct breach of the rules of kin selection. Hyenas nurse the infant orphans for more than a year and eventually incorporate them into hyena society, while receiving no tangible benefit to themselves.2 Among the chimp surrogates are some males, who do not normally engage in rearing.3 These observations contravene the “ruthless selfishness” of Dawkins. Some male baboons, who move into a new colony, team up with nursing mothers to protect the offspring from rough treatment by other members of the community, even though they receive no reward for this.4 What is Group Selection? An alternative to kin selection, called ‘group selection’, has been championed by the Wilsons (David and Edward); as its name implies it argues that genes may be propagated that benefit the whole society rather than the individual.5 This may indeed be a more realistic description of animal societies. However, it suffers from the drawback that it does not really advance our understanding of sociality. Asocial species do not benefit from group selection, because they do not form groups. Social species do receive a benefit, since this is an evolutionary requirement for the propagation of a trait, but where is the mechanistic explanation of how group selection arises? The time has come to abandon evolutionary explanations which have proved so unsatisfactory, and to turn to physiological approaches for understanding animal interactions: The Social Gene (blog #3. Social Genes). 1Coltman, D. W., Pilkington, J. G., & Pemberton, J. M.. Molecular Ecology, 12, 733-742. (2003) 2East ML, Höner OP, Wachter B, Wilhelm K, Burke T, Hofer H. Behavioral Ecology. 20:478-83. (2009) 3Boesch, C., Bole, C., Eckhardt, N., & Boesch, H. PLoS One, 5, e8901. (2010). 4Nguyen, N., Van Horn, R. C., Alberts, S. C., & Altmann, J. Behavioral ecology and sociobiology, 63, 1331-1344. (2009) 5Wilson DS, Wilson EO. American Scientist.;96:380-9. (2008) Read the full article