War, migration helped in evolution of human social behaviour

June 5th, 2009 - 1:27 pm ICT by ANI  

London, June 5 (ANI): Wars and migration may explain how humans started cooperating as groups and ultimately colonise planets, according to two studies.

The studies claim that demography - the size, density and distribution of populations - has played the biggest role in the evolution of human behaviour.

Samuel Bowles, a behavioural scientist at the Santa Fe Institute in New Mexico, has dealt with the puzzle of how humans acquired such unrivalled altruistic behaviour towards unrelated individuals, indicating that the answer, paradoxically, could turn on war.Adam Powell and his colleagues at University College London propose that demography could account for the emergence of modern human behaviour - sophisticated tools, art, bodily ornamentation and other culturally transmitted expressions of symbolic thought.

Bowles says that when everyone in a group is altruistic, the group does better as a whole.

However, such groups are vulnerable to invasion and exploitation by free riders who selfishly accept the altruists’ benevolence while giving nothing back. Thus, selfishness pays off, and finally replaces altruism.

But earlier theoretical work showed that within-group altruism could co-evolve with between-group conflict - warfare.

For his research, Bowles drew on demographic data from the archaeological and ethnographic records, which, according to him indicate that inter-group conflict would have been common among our hunter-gather ancestors.

He also drew on estimates that it accounted for roughly 14 percent of all deaths - much higher than the mortality rate seen in wars of recent history.

Under these conditions, he showed that even costly group-beneficial altruism and cooperation could be favoured.

“It’s possible that a genuinely altruistic human nature could have evolved, and that it depended in part on the tendency to engage in inter-group conflict,” said Bowles.

Bowles’ model is based on genetically transmitted altruism and, more controversially, genetic group selection - selection for traits that are passed on because they benefit the group, even at a cost to individuals.

However, Bowles thinks genetic data from hunter-gather groups shows that they meet this criterion, and are compatible with genetic group selection.

On the other hand, Powell and his colleagues examined the role of demography on the emergence of modern human behaviour.

“The tendency has been to look for a genetic magic bullet that suddenly made humans flower into modern culture,” said a co-author on the paper.

Challenging this inference, the study argued that demography, particularly population density and migration, could be the key determinant of when and where modern behaviour develops.

As populations need to reach and maintain a certain density for modern behaviour and culture to emerge and persist, the authors looked at historical population densities and migration.

They drew on genetic analyses that have used mitochondrial DNA to estimate human populations at different times and in different regions of the world.

Such rough genetic estimates have suggested comparable population densities in both regions at the relevant dates, which meet the demographic requirements for supporting modern behaviour.

The studies have been published in two papers in Science. (ANI)

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