War and Population in Human Social Evolution

While travelling in Scotland and England, it has been good to read some articles in the June 5th issue of SCIENCE on human social evolution. One article by Samuel Bowles argues that group selection through warfare created the conditions for social cooperation and morality. Another article by Mark Thomas et al. argues that increases in population density have fostered technological and symbolic complexity in human cultural evolution. In the same issue of the journal, Ruth Mace has a "perspectives" article on these two papers. The June 6th issue of THE ECONOMIST has an article on these papers.

Bowles claims that human morality--concern for the well-being of others and the willingness to sacrifice for them--arises from group selection in warfare among foragers in the late Pleistocene and the early Holocene. He reaches this conclusion by surveying the archaeological evidence for ancient warfare and the ethnographic evidence for warfare among historic foraging groups. He also formulates his reasoning in a formal model.

This argument that human beings evolved to cooperate in order to compete in war with those outside their group was set forth by Darwin as a key factor for the evolution of the moral sense. Later, people like Richard Alexander have elaborated the reasoning for this. But the Bowles article is one of the best surveys of the evidence from the most recent archaeological and ethnographic research.

This warfare hypothesis has a long history in political philosophy from Aristotle to Hume. But this Darwinian view of militaristic evolution now allows us to see how this emerged in the deep history of politics.

This history of Scotland and England provides plenty of illustrations of how human history has been shaped by warfare. Touring the castles of Great Britain reminds us of the history of warfare. And in some cases--for example, Edinburgh Castle--there is archaeological evidence that the site of the castle has been fortified for 6,000 years or more.

The Thomas article raises the question of why the material artifacts of culture--such as tools, weapons, and art--wax and wane in the archaeological record. The answer set forth in the article is that this reflects fluctuations in the density of population. A more dense population makes it more likely that cultural knowledge will accumulate over time through the exchange and transmission of information.

The invention of agriculture creates dense human populations and thus more cultural learning. Modern commercial and industrial societies have created an explosive density of population that fosters cultural evolution. As David Christian has shown, the whole history of human social evolution can be seen as the progress in collective learning associated with increases in population density and global exchanges of information. This explains why the emergence of philosophy and science is associated with urban centers.

Hume developed this point in suggesting that the expansion of population in modern commercial societies would have a civilizing influence. One of the most salient features of the modern commercial and industrial revolution is the huge increase in the global human population, which is associated with increases in collective learning that foster ever more complex mechanisms in channeling the flow of energy to sustain human social life.