To explain the biological nature of human beings as political animals, Aristotle compared human beings to other political animals--and particularly, ants, bees, and wasps. The great size and complexity of social insect colonies are comparable to that of human communities.
Darwin saw the same resemblance between human communities and social insect colonies--particularly, in their intricate division of labor. But for Darwin, the existence of sterile female castes of workers among the social insects was "by far the most serious special difficulty which my theory has encountered," as he wrote in the chapter on "Instinct" in The Origin of Species. The obvious problem is that this seems to contradict evolution by natural selection, because the sterile females are sacrificing their reproductive fitness for the reproductive advantage of the queen. Darwin's solution was to propose that "selection may be applied to the family, as well as to the individual, and may thus gain the desired end." He thus implied that natural selection could favor the altruistic sacrifice of individuals for the reproductive good of their group. Moreover, in The Descent of Man, he clearly claimed that human moral and political evolution depended on group selection in war, so that some of the highest moral virtues arose as dispositions that conferred advantages on human groups in violent conflict with other groups. But he left it unclear as to how exactly natural selection could do this.
In the 1960s, William D. Hamilton set out to solve Darwin's problem by developing the ideas of "inclusive fitness" and "kin selection." The basic idea is that individuals can evolve to show altruistic behavior--behavior that is costly to the animal but beneficial to others--if the cost to the actor brings sufficient benefit to sufficiently closely related recipients. Evolutionary selection should favor my acting not only for the sake of benefiting my direct offspring, who share some of my genes, but also for benefiting the offspring of my close relatives, who share some of my genes and therefore might carry my genes for altruistic behavior. In the case of sterile female worker castes, Hamilton argued, this extraordinary altruism could be explained by the fact that the workers are sisters who are more closely related genetically to one another that they are to their offspring, and consequently, it better enhances their inclusive fitness to serve the reproductive activity of the queen in producing more sisters than to have offspring of their own. This happens because among the Hymenoptera, the order of ants, bees, and wasps, the sex-determining mechanism is haplodiploidy, in which fertilized eggs become females, and unfertilized eggs males.
There are serious problems with this theory. One is that some of the eusocial species--such as termites and naked mole rats--don't use haplodiploid sex determination, and therefore Hamilton's theory can't explain the sterility of worker castes among them as it does for Hymenoptera.
But despite such problems, Hamilton's theory of kin selection has been widely accepted among many biological theorists of social evolution over the past 50 years, and especially since the publication of Wilson's Sociobiology in 1975, which adopted Hamilton's theory.
In recent years, however, E. O. Wilson and David Sloan Wilson have been criticizing kin selection theory and defending group selection theory as superior. Most recently, E. O. Wilson co-authored an article with Martin Nowak and Corina Tarnita in Nature (vol. 466, August 26, 2010, pp. 1057-1062) that summarizes some of the reasoning against Hamilton's theory. This article has provoked an intense controversy in the whole community of biologists and psychologists studying the biological evolution of sociality.
Much of the publicity surrounding this controversy turns on the perception that E. O. Wilson has undergone a radical change of mind--from promoting to rejecting Hamilton's theory. But anyone who reads Wilson's Sociobiology carefully (for example, pp. 30, 129) will see that he was never convinced that Hamilton's theory was superior to group selection theory. Over the years, Wilson has given encouragement to proponents of group selection such as David Sloan Wilson; and in recent years, the two Wilsons have co-authored some articles.
It's hard for me to see that one has to choose between kin selection and group selection in explaining social evolution. I suspect that this is a false dichotomy that obscures their complementarity. In fact, one can even argue that kin selection is a form of group selection where the group is constituted by kinship. Here I agree with Samir Okasha, who makes the argument for complementarity in a recent article in Nature (vol. 467, October 7, 2010, pp. 653-55.)
Regardless of whether one favors kin selection, group selection, or some combination of both, there is a deeper moral and political issue here. All of these kinds of Darwinian explanations of social evolution point to the inevitability of tragic conflicts in moral and political life that cannot be resolved by ideal principles of universal love and cooperation.
There is a tendency among modern moral and political philosophers to assume that moral and political life can and should be governed ultimately by some ideal conception of disinterested humanitarianism. One can see this, for example, in John Rawls' appeal to the ideal situation of people agreeing to universal, rational principles of justice in the "original position," where human beings would act as if they were disembodied spirits. One can also see this among religious believers who assume that the teaching of universal love in Jesus' Sermon on Mount is the moral ideal for all human beings, or among secular philosophers like Peter Singer who assume that morality and politics should be guided by an impartial concern for the interests of all sentient creatures.
If our moral and political dispositions have not been created by some cosmic order of the good and the just to conform to some eternal values of love and cooperation, if these dispositions have been created, on the contrary, by natural evolutionary selection, then we can expect that our moral and political lives will be torn by tragic conflicts of interest that cannot be resolved by universal principles of ethics.
E. O. Wilson refers to this as the problem of "moral ambivalency," and it runs through his writing in his book Sociobiology, beginning with the epigram from the Bhagavad Gita. The passage Wilson quotes shows Arjuna doubting the justice of leading his family in a war against another family competing for political dominance, but Lord Krishna (the Lord of the Universe) teaches him that this is his sacred duty. Wilson suggests that an evolutionary theory of social evolution would explain this tragic conflict as arising from a natural history of counteracting pressures on the units of natural selection. Wilson writes:
What is good for the individual can be destructive to the family; what preserves the family can be harsh on both the individual and the tribe to which the family belongs; what promotes the tribe can weaken the family and destroy the individual; and so on upward through the permutations of levels of organizations. Counteracting selection on these different units will result in certain genes being multiplied and fixed, others lost, and combinations of still others held in static proportions. According to the present theory, some of the genes will produce emotional states that reflect the balance of counteracting selection forces at the different levels. (p. 4; cf. pp. 129, 563)
Here, then, is the scientific basis for the tragic realism of evolutionary ethics. We see the evolved moral and political nature of human beings as shaped by countervailing levels of selection, which have created tragic conflicts in our moral emotions that cannot be resolved by rational appeals to universal moral principles. Such moral realism is repugnant to moral utopians who assume that moral and political order must be ultimately guided by universal rules of love and cooperation that can in principle resolve all conflicts.
Oddly enough, while E. O. Wilson accepts this moral realism as a conclusion from his evolutionary account of morality as shaped by group selection, David Sloan Wilson rejects this conclusion while trying to hold on to some utopian vision of universal cooperation.
Some related posts can be found here, here, here, here, and here.