Complex cultural and social behaviors exhibited by chimpanzees are being lost as humans continue to encroach on wild areas, according to a new study published in Science. 

From the types of tools used to communication strategies, the behaviors of chimpanzees vary dramatically across different groups. Previous research shows that chimps acquire this information socially from other members of their group – how they act depends greatly on who they are surrounded by similar to humans (just like that annoying habit your sister picked up from your brother). But as human population growth continues to increase, deforestation, hunting, and diseases are further pressuring chimpanzee communities in the wild, causing them to alter, change, or altogether lose their unique behavior.

"Chimpanzees are highly intelligent and adaptable creatures," said Kevin Lee in a statement. “And there have been various reports of chimpanzees, both in captivity and in free-living conditions, that have relatively more frequent contact with humans exhibiting some 'novel' behaviors not observed in more remote populations, but it was not clear how overall behavioral diversity would be affected."

Chimps in areas with high human impact are showing an 88 percent loss of their behaviors when compared with populations with less human influence. It’s a trademark of what scientists have described as the Anthropocene era as humans influence Earth’s biological processes and, as a result, the wildlife that once thrived on them. In particular, four chimpanzee subspecies are “severely threatened” by deforestation and poaching resulting in major population declines, regional extinctions, and reduced genetic diversity.

Over the course of a decade, researchers described 31 distinct behaviors displayed in 144 social groups across 46 locations in 15 countries, including the extraction and consumption of termites, ants, algae, nuts, and honey; use of tools for hunting or digging for tubers; and the use of stones, pools, and caves. They then compared the rates of these behaviors against human impact indicators, such as population density, roads, rivers, and forest cover.

"The analysis revealed a strong and robust pattern – chimpanzee behavioral diversity was reduced by 88 percent when the human impact was highest compared to locations with the least human impact,” explained co-author Kevin Langergraber.

We know from our own experience that population size plays a role in what cultural traits we keep and throw out. It’s very likely that highly intelligent chimpanzees are doing just that, learning to avoid old behaviors that could attract hunters, such as how they consume nuts, or finding new ways to hunt and look for food. Under this “disturbance hypothesis”, the researchers say that chimpanzees’ social learning is disrupted as humans deplete their resources, further cutting back on learning opportunities and restricting local traditions from being passed down between generations.

However, some studies suggest that chimps living in human-dominated landscapes may spur new inventions to compensate for and modify to their environment. Regardless, the authors note that the cultural significance of impacted species should be considered and integrated into wildlife conservation practices.