March 4 (UPI) -- As hunter-gatherers settled down and took to farming the land, groups of people began gathering in larger numbers and cooperating. But new research suggests the adoption of agriculture encouraged violence between humans populations, too.
"We were interested in understanding why people would make the shift from hunting and gathering to farming," Elic Weitzel, doctoral student in anthropology at the University of Connecticut, said in a news release. "Then I started to get interested in what happened in society after they made that shift and started farming on a larger scale."
Weitzel and his colleagues used "ideal free distribution" to simulate the distribution of farmers in in eastern North America between 7,500 and 5,000 years ago, as well as to locate the most coveted land -- the acreage with the most food, water, raw materials and shelter.
Scientists graded different land parcels with a "net primary productivity" score. The most productive pieces of land tended to host the largest concentration of people, and thus, host the greatest amount of conflict and violence.
"If you are living in a suitable area, you can lay claim and keep others from accessing what you have," Weitzel said. "That becomes a cooperative process, because one person is not as effective as a whole group is at defending a territory."
But scientists also found evidence of the so-called Allee's Principle, which posits increases in individual fitness boost the density of the population through cooperation.
"The transition from a hunting and gathering society to an agricultural society is dependent on collaboration," said co-author Stephen Carmody, an anthropologist at Troy University. "The development of agriculture appears to only have happened in nine places around the world so Eastern North America is a unique part of the world to study. Agriculture was one of the most consequential transitions that happened in the past. It changed our whole economic situation."
The concentration of valuable resources could only be accessed via cooperation and coordinated protection, but coveted land and resources also inspired jealousy and violence.
"When a resource like domesticated crops is dense and predictable, that is when we expect that it would be defendable," Weitzel said. "Other groups may want access to your crop in case their crop failed, for example. There is cooperation and there are aspects of competition. Harvesting and defending."
During the time period studied, scientists identified archaeological evidence of larger, more dense population centers, a sign of growing levels of cooperation among groups of humans. But researchers also found evidence of increased violence and trophy taking in the archaeological record.
"Of course there are signs of violence throughout history, but trophy-taking is a different type of violence," Weitzel said. "The victor removes a part of the loser as a signal they won. They took scalps, hands, feet, heads -- that first evidence appears to have happened at the same time as plant management."
Scientists were also able to see patterns predicted by Allee's Principle playing out in the archaeological record. As concentrations of humans grew, the land's suitability declined and groups began to disperse once more. A decline in trophy-taking violence declined during the period of dispersal.
Researchers suggest their findings -- published this week in the journal Environmental Archaeology -- could be used to better understand the effects of modern pressures, like climate change and economic inequality, on human behavior.
"This is one of the ways archaeology is relevant to contemporary and future society," Weitzel said. "The modeling of human behaviors in society and our relationships can help us overcome current collective action problems. We are all better off if we cooperate."