Painting of Sierra Miwok at the Mariposa Indian Encampment, Yosemite Valley by Albert Bierstadt, ~1872

People from different societies eat different foods, use different technologies, follow different social norms, and believe in different gods. The behavioral variation exhibited by the human species is unmatched in the animal world. 

For more than a century, scholars have debated whether this span of behavior is due to the unusually wide range of environments we humans inhabit or to our unique reliance on social learning, which enables members of different societies to inherit different cultural traditions.

At stake in this debate is to what extent human uniqueness is driven by our large brain and the intelligence that allows us to adapt to different environments or by our capacity for culture. 

In a new paper, largely researched at the Santa Fe Institute, SFI Omidyar Fellow alum Charles Perreault and Sarah Mathew (both with the School of Human Evolution and Social Change and the Institute of Human Origins at Arizona State University) ask whether behavioral variation among 172 Native American tribes was due to the varied environments they lived in or their different cultural histories.

Their results suggest that cultural history is more important than environment in determining a tribe’s behavior. The richness of our behavioral repertoire may thus be due to our capacity for culture, not our intelligence and cognitive flexibility. 

The researchers also demonstrate that behaviors can persist in cultural lineages for millennia. In other words, the behavior of a particular tribe (e.g. whether a tribe uses baskets or follows a certain marriage practice) largely traces to their ancestors having practiced the behavior hundred or even thousands of years ago. This suggests that a large part of human behavior is cultural inertia. 

The effect of cultural inertia may persist for up to 15,000 years. For instance, societies that speak a Na-Dene language are behaviorally more similar to each other than they are to societies speaking an Amerind language, although it may have been 15,000 years since languages in the Na-Dene phylum last branched from a common ancestor.

The researchers say their results might prompt a rethink of why we in the U.S., for example, eat bread, wear pants, use surnames, carry an umbrella when it rains, live in nuclear households, or choose our own spouses. These behaviors may not necessarily be the “best” or most “optimal” behaviors today and may instead result from cultural inertia.

In other words, we do these things because our parents’ generation did them. This does not mean that cultural inertia is disadvantageous, says Perreault. In fact, learning from one's parents' generation could be beneficial because it allows for the accumulation of information through time. 

Perreault and Mathew speculate that the capacity for cultural learning may explain why modern humans were able to thrive in virtually every terrestrial habitat on the planet, and why human societies vary to an extent unmatched in the animal world.

Read the paper in Proceedings of the Royal Society B (June 17, 2015, subscription required)