Human hunter-gatherer group structure is unique among primates, according to new research by anthropologists who studied data from 5,000 individuals in 32 present-day foraging societies.
One of the most complex human mysteries involves how and why we became an outlier species in terms of biological success.
Research findings published in the March 11 edition of the journal Science by an international team of noted anthropologists who study hunter-gatherer societies, are informing the issue by suggesting that human ancestral social structure may be the root of cumulative culture and cooperation and, ultimately, human uniqueness, according to SMU anthropologist Thomas N. Headland and his co-authors on the study.
“We are not saying here that present-day hunter-gatherer societies are fossilized remnants from the stone age,” said Headland, an adjunct professor in SMU’s Department of Anthropology. “We are suggesting, however, that 20th-century foraging societies may give us a keyhole glimpse into how our ancient ancestors may have lived in prehistory, and how they even thrived under a foraging lifestyle.”
Humans have lived as hunter-gatherers for 95 percent of the species’ history, so current foraging societies provide the best window for viewing human social evolution, according to the authors. Given that, the researchers focused on co-residence patterns among thousands of individuals from present-day foraging societies around the globe. Those societies include the Gunwinggu, Labrador Inuit, Mbuti, Apache, Aka, Ache, Agta and Vedda.
“We are also suggesting,” Headland said, “that the unique style of co-residence we find in so many hunter-gatherer societies today may provide clues into some aspects of early human cultural evolution – certain adaptive behaviors that helped Homo sapiens to be so biologically successful because of a unique group structure that emphasized cooperation among band groups.”
Lead authors on the study were Kim Hill, Arizona State University, and Robert Walker, University of Missouri. Other researchers included: Miran Bozicevic, James Eder and Ana Magdalena Hurtado, Arizona State; Barry Hewlett, Hawassa University, Ethiopia, and Washington State University; Frank Marlowe, Durham University, U.K.; Polly Wiessner, University of Utah; and Brian Wood, Stanford University.
Their findings showed that across all groups, adult brothers and sisters frequently live together, making it common for male in-laws to co-reside. They also found that it was equally common for males or females to move from or remain with family units. This is in contrast to other primate species, where either males or females move to another group at puberty.
A major point in the study is that foraging bands contain several individuals completely unconnected by kinship or marriage ties, yet include males with a vested interest in the offspring of daughters, sisters and wives. This organization mitigates the group hostility frequently seen in other apes and also promotes interaction among residential groups, thereby leading to the development of a large social network.
“The increase in human network size over other primates may explain why humans evolved an emphasis on social learning that results in cultural transmission,” said Hill. “Likewise, the unique composition of human ancestral groups promotes cooperation among large groups of non-kin, something extremely rare in nature.”
The group’s findings appear in the paper “Co-Residence Patterns in Hunter-Gatherer Societies Show Unique Human Social Structure.” It is the first published analyses of adult co-residence patterns in hunter-gatherer societies based on census data rather than post-marital residence typologies, Hill noted. – Arizona State University