Hamilton on inclusive fitness and social behavior in humans

In his "admittedly speculative outline of certain cultural and genetic processes in tribal evolution", Hamilton emphasizes selection at a level higher than that of the individual. From "Innate social aptitudes of man: an approach from evolutionary genetics" (text; pdf):

[. . .] The other point concerns the distribution of gene frequencies. The apparent variability of colonies is expected to change rather sharply at certain critical levels of migration. These are M=.5 for the island model and M=1 for the two-dimensional stepping-stone model with close migration predominant. This means that at about the point where the colony members are related to each other like outbreds sibs it should become relatively easy for individuals to detect a fairly clear difference in appearance when comparing fellow colony members with outsiders. Actually, in the stepping-stone model the possibilities with regard to patchiness and cline-like effects are complex, but, considering simultaneously several traits which are independently inherited and at most weakly selected, the complex overlap of patterns should make possible fairly accurate separation of 'us' and 'them' at the level of colonies. We shall shortly see why natural selection might favour motivation and ability so to discriminate.

What is happening to the ordinary families embedded in these supposedly endogamous colonies? Sibilings, parents, and offspring will still be the individual's closest relatives. Owing to the inbreeding, their relatedness will be above the value of 1/2 that applies under outbreeding. Thus an individual should be more altruistic than usual to his immediate kin. But other neighbours who are not immediate kin are now also closely related, and it is this reduced contrast between neighbours and close kin that will give what is probably the most striking effect: we expect less nepotistic discrimination and more genuine communism of behavior. At the boundary of the local group, however, there is usually a sharp drop in relatedness. If migrants (or whole groups) are very mobile, leading to an 'island' rather than a 'stepping-stone' situation, this drop may be such as to promote active hostility between neighbouring groups.(Note 3) Even though these groups have some relatedness, as practical limitations to distant migration naturally ensure, the contrast is still such that a minor benefit from taking the life of an outsider would make the act adaptive. Recent studies on hunting dogs (Kuhme 1965; Lawick-Goodall & Lawick-Goodall 1971) and hyenas (Kruuk 1972), show strangers sometimes being killed, while within-the-group relations are usually amicable and even communistic. The most serious wounding which Lawick-Goodall (1971) recorded in her study of chimpanzees occurred when two males combined to attack a male of another group. Bygott (1972) witnessed a fierce attack by a group of male chimpanzees on a stranger female. The female escaped but the males caught and ate her infant. Trespassers may sometimes be killed in wolves (Mech 1972), and in rats (Lorenz 1966). In lions (Schaller 1972), langurs (Sugiyama & Parthasanathy 1969), and probably in rats and mice there is also killing of strange young, but this is probably in a rather different category because it is done only by males whose aim seems to be to sire new offspring on the mothers they bereave. [. . .]

Roughly, as we currently see it, a cunning ape-like creature once pushed boldly out from near niches now held by baboon and chimpanzee. Whether or not (as one quite plausible view holds) it first left its less enterprising cousins to take a holiday on the seashore, eventually it reappears on the African savannah participating in the Pleistocene wild-life bonanza as a group-hunting carnivore. In spite of the now-not-so-prehensile foot which it kept all the while in the door of an omnivorous diet, it seems likely that this creature would have needed the same population structure as the other group-hunting carnivores and for the same but more urgent reasons. It is difficult to see what was the first factor in the escalation in cunning of this particular primate line, but the choice seems mainly between tools and language. The great benefits that these could confer to a cooperative hunter through improved technique and organization would ensure rapid selection for their development. But they would also affect the social situation in significant ways and indirectly this might escalate their selection: (a) both would provide extra cultural clues to group identification; (b) tools (and later other valued artefacts) would give further scope for parasitical behavior, first intragroup but later between groups as well. Tools and possessions could be appropriated instead of made. With language in rapid evolution, learning experience, and even intelligence would become increasingly open to parasitism. Meanwhile, increasing intelligence would make possible a very plastic approach to parasitical and altruistic behavior, which in turn would increase the complexity of the semi-serious deception and coalition games which are so characteristic of behavior within primate groups. Real rewards in food and mating are the incentive to this activity and thus escalate the selection for skill in play. The main point is that intelligence, plus (a) and (b), plus what has been explained about the real differentiation of genetical relatedness suggest the development of an explosive situation. Close frontiers to migrants a little more, or slightly increase group mobility, and it is possible to imagine the sudden success of a policy which makes any frontier incident an occasion for an attempt at violent incursion by the more populous group with losers killed, enslaved, or driven off. Successful occupation of the captured territory would soon bring the victors into contact with still less related 'stones' of the 'stepping-stone' lattice, which they could attack adaptively with even less reason for restraint. Increasing foresight would mean that a group would not necessarily wait until large enough to _need_ neighbouring territory, if attacking a weak group while it is weak helped to ensure that space could be occupied as needed. Increasing ability to abstract and generalize would enable groups to reanimate their intragroup coalition games in the more serious intergroup context. The usual and firmest coalitions would be between related groups, as is the case with the coalitions of individuals (usually males) in wild turkeys (Watts and Stokes 1971), lions (Schaller 1972) and chimpanzees (Lawick-Goodall 1971). Are group fights necessarily more serious for the species if, on the analogy of the super-organism, we are allowed to equate a few deaths to a minor wound? Perhaps not, and of course it is possible that making groups more aggressive would not 'melt' the lattice structure to the extent suggested. Moreover, groups might be units in super-groups that are themselves in a 'stepping-stone' lattice. In such class warfare -- for that is the behavior we now survey -- might carry over from intragroup behavior (or itself spontaneously develop) quite orderly restrained procedures involving little loss of life.

In developing this admittedly speculative outline of certain cultural and genetic processes in tribal evolution, I confess a bias towards discovering the patterns of coalitions, warfare, language, contempt, and so on that are documented in certain remote peoples of the present day, for example the Yanomamo (Chagnon 1968) and various New Guinea highlanders (Matthiessen 1962; Rappaport 1971). Admittedly in these cases there is agriculture; it is possible to claim that most hunter-gatherers are more peaceable. For example why not aim to derive the customs of the Kalahari Bushmen? But most hunter-gatherers are certainly less peaceable than Bushmen. The record of human violence goes back far indeed, even if the earliest attributions (Dart’s cases in Australopithecus_: Ardrey 1961) are doubtful. A trace of homology with the sporadic violence of chimpanzees, actual violence towards outsiders would contrast with restrained violence, or mere threats, used within the group, while within the group too there would be much sharing and cooperation. One neanderthal skeleton of Shanidar Cave had bone damage suggesting a stab wound (Solecki 1971). Another skeleton also had bone defects but of quite different implication: one forearm was lacking, perhaps from birth, certainly for a long time, and a healed injury to the skull showed that one eye was blind. Goodall’s chimpanzees were part hostile, part sympathetic, and part indifferent to comrades sudddenly crippled with polio: they did nothing positive to support them. In contrast, the neanderthals of Shanidar evidently supported a cripple, and on his death they buried him in a cave where, in other graves, they also sometimes buried their dead with flowers. These hints of violence and loyalty and (perhaps most purely human) of incipient love of things for themselves evoke a startlingly familiar and sympathetic portrait. Considering only the same affectional attributes in the present-day tribal and pastoral Kurds (as opposed to attributes connected to the ever-accelerating change in material culture), a recording angel perhaps notes today much the same events in Shanidar Cave as he noted an ice age ago (Hamilton 1937; Solecki 1971). [. . .]

The rewards of the victors in warfare obviously increase for peoples past the neolithic revolution. There are tools, livestock, stores of food, luxury goods to be seized, and even a possibility for the victors to impose themselves for a long period as a parasitical upper class. Hunter-gatherers, on the other hand, at most win only mates and land. It might seem that these things would not repay the expected cost of the fighting, but it has to be remembered that to raise mean fitness in a group either new territory or outside mates have to be obtained somehow. The occurrence of quasi-warlike group interactions in various higher primates(Kummer 1968; Sugiyama & Parthasanathy 1969; and references in Bigelow 1969) strongly suggests that something like warfare may have become adaptive far down in the hominid stock. These primate examples suggest the prototype war party as an all-male group, brothers and kin, practised as a team in successful hunting and at last redirecting its skill towards usurping the females or territory of another group. Out of such cells can be built the somewhat less stable organism of the post-neolithic army. The Homeric Illiad gives a vivid inside view of the process of coalition, while the siege it describes emphasizes the existence of economic surpluses supporting the warriors on both sides (something hunter-gatherer warriors would never have). If the male war party has been adaptive for as long as is surmised here, it is hardly surprising that a similar grouping often reappears spontaneously even in circumstances where its present adaptive value is low or negative, as in modern teenage gangs (Patrick 1973).

Whether or not the neolithic revolution brought an increase in the per capita incidence of violence it does seem that from then on warfare looms larger in the affairs of men. The situation seems reflected in the fact that only one of various series of pre-neolithic cave paintings depicts warfare (Pericot 1961), whereas for most early civilizations the earliest known written records are records of warfare, booty, captives, and the like. [. . .]

The incursions of barbaric pastoralists seem to do civilizations less harm in the long run than one might expect. Indeed, two dark ages and renaissances in Europe suggest a recurring pattern in which a renaissance follows an incursion by about 800 years. It may even be suggested that certain genes or traditions of pastoralists revitalize the conquered people with an ingredient of progress which tends to die out in a large panmictic population for the reasons already discussed. I have in mind altruism itself, or the part of the altruism which is perhaps better described as self-sacrificial daring. By the time of the renaissance it may be that the mixing of genes and cultures (or of cultures alone if these are the only vehicles, which I doubt) has continued long enough to bring the old mercantile thoughtfulness and the infused daring into conjunction in a few individuals who then find courage for all kinds of inventive innovation against the resistance of established thought and practice. Often, however, the cost in fitness of such altruism and sublimated pugnacity to the individuals concerned is by no means metaphorical, and the benefits to fitness, such as they are, go to a mass of individuals whose genetic correlation with the innovator must be slight indeed. Thus civilization probably slowly reduces its altruism of all kinds, including the kinds needed for cultural creativity (see also Eshel 1972).


James Neel and early human population structure:

We believe that the level of inbreeding that we encountered in the Yanomama was not a recent development, but one that goes far back in time. Accordingly, aided by the computer program, we could ask the question, if this pattern of inbreeding was in place when the Indian entered the Americas, just how inbred had these populations become by now? Our best estimate was that the average marriage in an Indian village represented a level of inbreeding at least five times as large as the inbreeding in a first-cousin marriage. This is, in fact, greater than the inbreeding in a brother-sister union. This conclusion was so surprising that we have gone back to reexamine it from every possible vantage point, and from every possible vantage point it seems to hold.

Mechanisms of sexual selection in humans : Male coalitions and between-group competition. The tendency of males to form alliances may have evolved in the common ancestor of humans and our closest living relatives, Pan, as a means of cooperative female capture and defense (Fig. 3), although coalitions may also have evolved independently in these lineages for this purpose (Geary & Flinn, 2001; Wrangham, 1999). Male coalitions are rare among primates but common in humans and Pan, especially common chimpanzees (P. troglodytes), and are strengthened by kinship (Nishida & Hiraiwa- Hasegawa, 1987). The capture of women was a primary objective of early warfare (Darwin, 1871; Hrdy, 1997; Lerner, 1986; Spencer, 1885), and among foragers, groups of men commonly raid other villages and abscond with women (e.g., Chagnon, 1988). Such raids may also function in mate defense by deterring future attacks. These behaviors would tend to favor not only aggression and physical prowess, but also social intelligence for negotiating alliances (e.g., Alexander, 1989; Geary & Flinn, 2002; Mueller & Mazur, 1996; Wrangham, 1999).


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