Barbed bone harpoons from the site of Katanda, Democratic Republic of Congo, dating between 110,000 and 80,000 years ago. [Image © Science/AAAS]
Population growth, migration, and other demographic changes among our hunter-gatherer ancestors may have played a major role in the evolution of modern human social behavior, as these changes affected how groups fought, traded, and shared ideas with each other, a pair of studies suggests.
In one of two articles appearing in the 5 June issue of Science, Samuel Bowles of the Santa Fe Institute and the University of Siena in Italy reports that warfare could have favored the survival of groups containing altruistic individuals who were willing to risk their own lives in order to fight on behalf of their groups.
Bowles used a theoretical model of conflict between groups of humans to measure the benefits and costs of altruistic behavior, for individuals and their groups. Then, he incorporated ethnographic and archaeological evidence from around the world, about adult mortality due to warfare in prehistoric and modern hunter-gatherer populations. His results suggest that prehistoric warfare was sufficiently common that altruistic behaviors could have evolved because they improved a group's chances to win lethal conflicts.
The second study proposes that population size and migration patterns can explain why modern human behavior appeared in Africa about 90,000 years ago but much later across Europe. Such behavior includes the development of advanced tools, musical instruments and art. The earliest hints of this behavior have been found in Africa and are about 70,000 to 90,000 years old. Other evidence from Europe is 45,000 years old.
Adam Powell of University College London and colleagues analyzed a population model in which individuals live in groups and learn skills from others in the group or by contact due to migration between groups. The authors found that the symbolic and technological complexity that appeared in Africa and later in Europe could have arisen because populations were mixing enough at those times to spread cultural innovation effectively, and not necessarily because of biological changes in cognitive capacity.