Human evolution has been marked by two major developments—increases in brain size and the development of social groups. Many scientists have assumed that one cannot live without the other to solve sophisticated social cognitive problems.
But a Duke University study shows that, among lemurs, larger social networks were the best predictor of how well an individual could perform cognitive tasks. Moreover, the sizes of lemur networks did not correlate with brain size. The study, led by anthropologist Evan MacLean, appears in the June 2013 issue of PLoS ONE, and suggests that cognition can evolve without an increase in brain size, and that measuring intelligence purely by brain size will not show the evolution of cognition.
MacLean and his colleagues tested several species of lemurs; each species belonged to varying sizes of social groups, and all had relatively small brains compared to humans and other primates. First, the lemurs were required to steal food from two humans who were perceived as competitors for the food. Each time they had to pilfer food, the lemurs dealt either with a human experimenter who faced the lemur, or one who did not. This way, the researchers knew they were testing a lemur’s ability to read social cues (the human face) while performing a task (stealing food). This first experiment was, then, the test of social cognition. Lemurs that belonged to larger social groups performed the best in this experiment. In fact, the species that performed the best, Lemur catta (pictured), also form the largest social groups of any of the species tested (they usually live in groups of 15).
In the second experiment, lemurs were forced to find alternate ways to grab food that was in a transparent container, usually by reaching around the container. Unlike in the first experiment, performance of this decidedly un-social cognitive task did not correlate with the lemur’s social group size. Therefore, the scientists concluded, it was the social abilities, and not some special ability unique to a species, that determined how well social cognition went.
“These data provide the first demonstration of a link between group size and experimental measures of social cognitive skills in animals,” the researchers wrote. “Being socially savvy doesn’t make you brainy in every domain. Our data suggest that for lemurs, living in social networks favored the evolution of social intelligence without changing over cognitive abilities.”
The researchers also show that since changes in social cognitive abilities do not necessarily depend on brain size, then it’s not possible to assume that larger brains automatically translate into superior social cognition. One of the hallmarks of sophisticated social interaction is flexibility, using a multitude of social tools to respond to a large number of situations. It could be, as this study suggests, that lessons learned from dealing with many peers is more important than excelling at one particular task.
Photo: Wikimedia Commons
MacLean, E., et al. (2013). Group size predicts social but not nonsocial cognition in lemurs PLoS ONE, 8 (6) DOI: 10.1371/journal.pone.0066359
cognition problems,evolution of the human brain research, social cognitive theory constructs