Conflict and social evolution

Last week’s edition of Science has an interesting article by Sam Bowles on the role of conflict on human social evolution. Bowles covers some familiar ground on the debate around the role of group selection in shaping human altruistic preferences:

[F]or most animals, gene flow (due to migration) would minimize genetic differences between groups, and hence nullify the genetic effects of group competition. But recent evidence suggests that this may not be the case for a number of species, including recent human foragers, whose population structures may resemble those of our Late Pleistocene ancestors. Others may have doubted Darwin’s conflict-based account because they believe warfare to be a postagricultural revolution corruption of our naturally peaceful disposition. But hunter-gatherer burials with smashed skulls, broken or missing forearms (taken as trophies), and stone points embedded in bones tell a different story, as does ethnographic evidence that warfare was a leading cause of death among some recent hunters and gatherers.

I have shown that we can plausibly infer from these data that the degree of mortal conflict and extent of genetic differences among ancestral forager groups were jointly sufficient to have allowed the evolution of a genetically transmitted predisposition to contribute to common projects (including defense and predation vis a vis other groups), even when one’s individual fitness would have been enhanced by free riding on those who would “aid and defend each other.”

Bowles cites his theoretical models that show this point, but is there any society whose warlike behaviour against other groups extended to elimination of the women of their vanquished rival? If any of the women of the defeated group are absorbed into the victor, there will be substantial gene flow. Add exogamy to the mix, and I struggle to see how a human group could maintain the required level of genetic differentiation.

Bowles has a number of other interesting threads in the article. The most novel of these is the manner in which he links conflict with the modern liberal state. Bowles writes:

Seven centuries ago, in what is now Italy, there were more than 200 distinct independent governing entities. Europe was governed by about 500 sovereign bodies: “empires, city states, federations of cities, networks of landlords, religious orders, leagues of pirates, warrior bands”. By World War I, fewer than 30 remained. A single political form had survived: the national state, a centralized bureaucratic structure maintaining order over a defined territory, with the capacity to mobilize substantial resources by taxation and borrowing and to deploy permanent armed forces.

What explains the competitive success of this novel form of rule? The simple answer is that national states won wars.

This battle then continued within the state:

American high school students are taught that their democratic constitution was the gift of the landed and commercial elites of the 13 former colonies. James Madison and the other authors of The Federalist Papers, the story goes, convinced the haves that the have nots would never be able to unite sufficiently to redistribute wealth. The elites could safely take a chance on democracy. But that is just one of America’s national myths. The United States would wait more than a century and a half to meet the elementary standard of democratic rule by extending suffrage to virtually all adults (with the Voting Rights Act of 1965), a process propelled by the victories of abolitionists, slaves and their descendants, workers, and women demanding the vote .

A natural corollary to the argument that group conflict was important in shaping human traits and our institutions is the question about whether that must necessarily have negative implications for conflict today. Bowles is optimistic on this front:

It seems likely, too, that conflict will remain important for human progress. But does this require the violence, suffering, bigotry, and waste characteristic of the conflicts of the past along with the cultural inheritance of this dismal trajectory, an unpleasant nexus of predispositions that Choi and I call “parochial altruism,” marked by generosity toward those we call “us” and hostility and intolerance toward “them” ?

I do not think so: Our legacy need not be our fate. We could not have become what Gintis and I call a cooperative species  were we not, par excellence, a cultural animal. Among the lessons of our past are not only the grisly truths on which I have dwelled but also the fact that our us’s and them’s are not primordial. On world historic time scales, we make and unmake these pronouns of exclusion at lightning speed. For ancestral humans, making peace was no less essential than surviving wars [as Boehm points out in his contribution to this issue].

As is often the case, the whole article is worth a read.


  1. The problem about warfare and genetic differentiation is interesting. There will be gene flow, but it still gives the dominant group (and their presumably more dominant men) an advantage for passing on their genes compared to the defeated groups. Given the probably small number of captured women and the relatively small number of offspring mixing with other group members will not pose a major threat to the group gene pool. Another question is whether offspring of such matings actually survived long enough to pass on these mixed genes. 

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