By favoring acts of battlefield selflessness, Stone Age warfare might have accelerated the development of altruism.
A computer model of cultural evolution and between-group competition primed with data taken from studies of mankind's hyperviolent early years suggests a bloody origin for a celebrated modern behavior.
"Altruism will be strongly favored if it leads groups to win wars," said Sam Bowles, a Santa Fe Institute economist and institutional theorist, and author of the study, published Thursday in Science. "That would counteract the way that selfish individuals usually dominate the altruistic ones in their groups."
That the ability to put others' well-being ahead of one's own could have such brutal origins seems counterintuitive. Then again, so is altruism. Genes are supposed to be selfish, not self-sacrificing.
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Cultural Complexity as Function of Networks, Not Biology____
__The first anatomically modern humans appeared about 200,000 years ago, but it took another 100,000 years for abstract art, instrumental music, sophisticated hunting techniques and other modern behaviors to emerge.Those behaviors arose first in Africa and appear to have disappeared 25,000 years later, only to re-emerge 40,000 years ago, about the same time as the first evidence of modern culture shows up in Europe. It took another 20,000 years for modern behaviors to show up in northern Asia. This chronologically and geographically staggered evolution of cultural complexity is one of the great mysteries of anthropology.
Some scientists have suggested that modernity required a genetically based change in our cognitive powers. That's possible, but there's no evidence for it in the fossil record. The requisite mutations would have had to evolve at multiple times in different places — again possible, but complicated and speculative.
Other researchers posit a social as well as biological change. Communities of growing size and complexity may have favored more sophisticated linguistic communication, which strengthened human minds and provided a cognitive framework for modern behaviors.
In a paper published Thursday in Science, archaeologists have proposed another demographic explanation: population density. With enough people in a given area, the transfer of skills and knowledge between individuals and groups could have been sustained and eventually reached a critical point, rather than petering out in isolated pockets.
Using a Stone Age-customized version of a cultural evolution model developed by University of British Columbia anthropologist Joe Henrich, researchers have shown that the population density of humans when modern behaviors emerged in Europe would have been ideal for spreading and maintaining modern skills. The researchers then showed that population densities were similar in northern Asia and Africa when modernity appeared.
"We've probably had the same cognitive capacity from the time of our species' origin," said study co-author Adam Powell, a University College London anthropologist. "This model demonstrates that you don't need to invoke regional genetic change."
Indeed, nearly every non-human example of altruism in the animal world can be explained in terms of kin selection, with individuals sacrificing themselves for genetically similar relatives. Only humans routinely care for total strangers, with no expectation of reward.
Such behaviors might be explained as particularly complex forms of self-interest, with apparent altruism actually satisfying social demands or gratifying a conscience weaned on generosity. But even so, they require some initial spark of altruistic possibility. How that came to be is a mystery.
In addition to its animal rarity, altruism fares poorly in computer simulations of group interaction. When altruistic individuals emerge in a community characterized by self-interested behavior, selfishness triumphs. Freeloaders fare better than cooperators.
The original spark seems doomed — unless, perhaps, something else can coax that spark to life. One plausible candidate is the evolutionary dynamics of combat between small groups, which appears to have been a fundamental part of life for most of human history.
"The selfish gain on the altruistic, but once in a while, the groups composed of selfish guys get clobbered in competition with groups that have altruistic individuals," Bowles said.
Bowles is hardly the first researcher to propose such a system. In The Descent of Man, Charles Darwin wrote that social virtues could spread when evolution favored groups "with a greater number of courageous, sympathetic and faithful members," who at times of conflict would readily "aid and defend each other."
Despite its pedigree, however, that idea has received little formal attention, in part because it was assumed that altruism would have genetic roots, and that the genetic differences between competing Stone Age groups were insignificant.
But as Bowles showed in 2006, genetic analyses of tribes still living a Stone Age life suggests there was enough variation to make group competition a driver of genetic change. And should cultural memes be more important than genes in producing altruistic behavior, then Bowles' proposed dynamics still apply.
According to his analysis of archaeological evidence from Stone Age sites and and ethnographic studies of remaining tribes, combat between groups accounted for about 14 percent of all deaths in hunter-gatherer societies. Composed of a few dozen people with no social institutions, such groups were the dominant community form for most of human history.
"These were not modern societies. As with chimpanzees going out on patrol, there was no leadership. You could stay home if you wanted," said Bowles.
After estimating the rate that altruism would reduce an individual's chances of reproducing, Bowles plugged the numbers into a model of intergroup competition where an individual's altruism would also improve a group's chances of combat triumph. Groups with selfless individuals eventually predominated, and altruism predominated within those groups.
"Lethal hostility toward other groups could thus underpin cooperation and support within human communities," writes Ruth Mace, a University College London anthropologist who was not involved in the study, in a commentary accompanying the findings.
Asked whether the willingness to participate in battle might be taken for fear of within-group punishment, Bowles said that merely "displaced the question."
"I might hope that someone would punish you, but why should I do it? You might hit back. The idea that I can exert order on you presupposes the idea that someone is altruistic," he said.
A great many assumptions are of course involved in Bowles' calculations, and other rewards, such as immediate access to the spoils of battle, may outweigh the risks of an apparently selfless decision to fight. But the dynamics are at least plausible.
"There are many alternative explanations possible," notes Ruth, but the findings put the hypothesis "firmly up the list of possibilities to be taken seriously."
See Also:
- An Evolutionary Explanation for Altruism
- Chimps Follow the Golden Rule
- Religion: Biological Accident, Adaptation — or Both
Citations: "Did Warfare Among Ancestral Hunter-Gatherers Affect the Evolution of Human Social Behaviors?" By Samuel Bowles. Science*, Vol. 324 Issue 5932, May 5, 2009.*
"Late Pleistocene Demography and the Appearance of Modern Human Behavior." By Adam Powell, Stephen Shennan, Mark G. Thomas. Science*, Vol. 324 Issue 5932, May 5, 2009.*
"On Becoming Modern." By Ruth Mace. Science*, Vol. 324 Issue 5932, May 5, 2009.
Images: 1) Mary Jackes/University of Waterloo.* 2)* Science
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