Thursday, December 21, 2006

The December 8th edition of Science Magazine (Vol. 314, Issue 5805), the journal of the AAAS, has three very interesting articles on the evolution of cooperation. Two are specifically related to human sociability and one is a general theoretical piece on the evolution of cooperation. This blog explores the first article of the eponymous title in the 'Perspectives' section of the magazine (pp1555-1556). Further entries will explore the other articles.
Robert Boyd has written an overview of an article by S. Bowles in this issue of Science. The subject is the "evolutionary puzzle" of the wide range of human cooperation as compared to other animal species. As the author says,
"Division of labour, trade and large-scale conflict are common. The sick, hungry and disabled are cared for, and social life is regulated by commonly held moral systems that are enforced, albeit imperfectly, by third party sanctions. In contrast, in other primate species, cooperation is limited to relatives and small groups of reciprocaters. There is little division of labour or trade, and no large scale conflict. No one cares for the sick or feeds the hungry or disabled. The strong take from the weak without fear of sanctions by third parties".
(Molly note: This introduction overstates the case greatly !!!. Of all the presumably human-only attributes cited above only "trade" is absent in other social species. This is not just confined to the primates. Other social species exhibit ALL the behaviors cited, though with specific items in each species. Third party sanctions, as the author calls them, are actually a fertile field of research in primatology and other fields. There they are called "altruistic punishment" , and anyone familiar with the behavior of domestic animals sees these agonistic actions on a routine basis. Ah, well it's a review, and the author is allowed to overstate his case.)
The author goes on to explain the disproportionate levels of cooperation between humans and other primates by proposing that the small size of primate societies means that kin selection provides a reasonable explanation of the behavior. The reviewer then goes on to point out that Bowles proposes that competition between genetically differentiated groups of proto-humans led to evolutionary selective pressure that favoured prosociality genes. He says,
"Limited migration between groups can lead to the buildup of genetic relatedness...among group members. This means that group membership can also be a clue that allows assortative interaction-genes that cause you to help members of your group can be favoured because other group members are disproportionately likely to carry the same genes, even though you do not share a recent common ancestor."
The author does point out that this idea, originally found in Darwin's 'The Descent of Man' has never been very popular. It's called "group selection". It was a theory held by Kropotkin amongst others (and Kropotkin took it to the extreme of species level selection). The reviewer points out that Bowles meets the standard objections to group selection with both data and theoretical considerations. First of all, data are presented about the level of genetic differentiation between hunter gatherer groups that present a different picture from the standard view. Hunter gatherer groups are much more different genetically than has usually been assumed and, therefore, intragroup cooperation has a basis of genetic similarity greater than what is usually assumed.
(Molly Note: watch out, there's a "weasel word" contained in Boyd's summary. He states that the level of differentiation between groups is the same as "the level of relatedness within such groups". That is not necessarily true. The two are NOT synonyms. It is easily conceivable that another human group can be widely different in a genetic sense while a competitive group can have all sorts of different levels of similarity)
The level of costs and benefits according to these articles is that cooperation will be favoured if the benefits are about 10 times the cost. The ability of cooperative groups to colonize the territories of competitors means that competition amongst relatives does not attenuate the benefit of cooperation. It is finally pointed out that intergroup competition is common in hunter gatherer societies (Molly Note: unlike the fantasies entertained by primitivists) so that benefits from cooperation are substantial.
Finally and perhaps most importantly, according to Boyd, Bowles notes that foraging groups have culturally transmitted norms such as food sharing and imposed monogamy that "reduce fitness differences within groups. he makes the original and interesting argument that such 'levelling mechanisms' act like redistributive taxes to reduce the disadvantage of engaging in costly prosocial behavior".
(Molly Note: These behaviors are themselves genetically influenced in humans and are not pure examples of cultural transmission. They also vary between groups, but, in general, they hover about a norm that is a clue to our evolutionary sociobiology)
The reviewer goes on to argue that the article by Bowles is not a group selection hypothesis because it merely presents an alternative mathematical framework that works out to the same sums as viewing the matter within kin selection lenses. This may or may not be true. Boyd then poses the questions of whether the levels of genetic variability observed in today's foragers are the same as those in Pleistocene hominids, whether the benefits were the same then as now (Molly Note: a questionable assumption given a much ! lower population density) and whether the "leveling mechanisms" were the same in ancestral populations.
The reviewer opines that "there is little dominance among human foragers" in contrast to other social species, an opinion that is not a settled matter. He goes on to suggest that, "It is certainly fair to invoke reproductive levelling to explain the stability of extended altruism among humans, but whether it is sufficient to explain its origin is not yet clear."(Molly Note: I am of the opinion that they are NOT for many reasons, not the least because research on altruistic punishment suggests that this mechanism which appears in other social species has a broader effect than 'reproductive levelling'. This is the old "proximate cause" and "ultimate cause" argument. Altruistic punishment can evolve via mechanisms in a social species that are very much removed from "reproductive levelling" and still be perpetuated in the species because they happen to serve the "ultimate cause" of reproductive levelling. Concentrating on one cause may lead to an ignoring of more fruitful areas of research.)
The author concludes with speculations on what he sees as the "competing explanations" for human sociality ie "the theory of mind, spoken language and other cognitive mechanisms" As he notes all these explanations are not mutually exclusive. Molly feels that the explanation of human cooperation will be a multi-faceted "complex" one rather than a "chaotic" one of one evolutionary pressure reaching some sort of "tipping point". Genes will interact with each other in a full "genetic environment" that is, in turn, influenced by the "memetic environment"-itself complex- of a learning animal. At its best this is what anarchism posits as an explanation for social evolution in contrast to the unidimensional theories of traditional Marxism and present day primitivism.
The other two articles in this issue of Science will be reviewed later.
Til then,

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