Lemurs that live in large groups are better thieves than their more introverted relatives, researchers reported in a study last week. The findings suggest that communal living is tied to greater social intelligence, the researchers said.
Evolutionary anthropologists have hypothesized that primates evolved big brains in response to the demands of living with others. There is some debate, however, over whether the corresponding increase in cognitive ability involved just those skills necessary for dealing with social situations, or if it extended to other aspects of intelligence as well.
To answer that question, researchers from Duke University set up two experiments using six different species of lemurs from social groups of varying size. The study was published online in the journal PLoS One.
In the first experiment, the researchers presented the lemurs with two plates of food and observed if they would approach when someone was watching. During trials with about 60 lemurs, one researcher would sit at eye level with one plate, while another researcher would sit with his or her back turned away from the other. The lemurs that came from larger social groups were more inclined to take food from the researcher who wasn’t looking at them, displaying a kind of social intelligence that they may have developed from competing with their group members for food in the wild, the researchers said.
In different trial conditions, one researcher would cover his eyes with a black band, while the other would cover his mouth, but the lemurs’ choice of food was not affected by the presence of the blindfold. The results indicate that while lemurs may use social cues like physical orientation to decide which piece of food to go after, unlike some other species, they are not sensitive to more subtle signals like eye movement.
For the second experiment, the researchers administered a cognitive test to establish whether the lemurs from bigger groups also had more intelligence overall. Though there were species differences in the lemurs’ ability to problem solve, those differences were not correlated with group size. In addition, brain size was not correlated with performance in either of the experiments.
While the results provide support for the idea that living with others increases social smarts, they also suggest that total intelligence is the product of a variety of factors, the researchers wrote.