Lemurs Group Size Predicts Social Intelligence
June 27, 2013

For Lemurs, Larger Groups Mean A Higher Social IQ

Brett Smith for redOrbit.com - Your Universe Online

Social interaction is highly valuable skill across a broad variety of animal species, particularly primates. Now, a new study in the open access journal PLOS ONE demonstrates that lemurs that live in big groups tend to have higher social IQs.

In a study that involved six different species of lemurs, researchers at Duke University wanted to see if the size of a lemur species group made them more or less likely to steal a bit of food if they were being watched - the idea being that more socialized lemurs would not want to be caught in such an antisocial act as stealing.

In one experiment, a pair of study researchers sat in a room with two plates of food as lemurs were allowed to enter one-by-one. One person faced the food plate and the lemur entering the room, while the other person had his, or her, back turned. In another experiment, the researchers sat in profile, facing either toward or away from the food. In a third experiment, the scientists wore a black band around either their eyes or their mouth, and both faced the plates and entering lemurs.

To determine whether they were witnessing social intelligence or simply generally higher cognition levels, the scientists also performed a non-social intelligence test that required the lemurs to retrieve food from transparent tubes.

The research team found that lemur species that tend to form large social groups, such as the ring-tailed lemur, appeared to be more sensitive to social cues, according to study co-author Evan MacLean, an evolutionary anthropologist at Duke.

Meanwhile, lemur species that form smaller groups, such as the mongoose lemur, tended to be more oblivious the observations of humans. The blindfolds did not appear to influence lemur behavior, researchers said.

All lemur species performed equally in the non-social test - indicating that the primates all had roughly the same cognitive ability.

According to the researchers, this study was the first to examine the relationship between peer group size and social intelligence across several species. Previous studies have shown that primates' evolution of cognitive skills correlate with life in increasingly larger social networks, and relative brain size in some primates has also been linked to group size.

However, lemur brain size has not been found to correlate with the size of their social group. According to the study authors, their results with these smaller primates supports the "social intelligence hypothesis," which states that living in ever larger social networks helped push for the evolution of more complex social cognition in primates.

"Being socially savvy doesn´t make you brainy in every domain," MacLean said. "Our data suggest that for lemurs, living in large social networks favored the evolution of social intelligence without changing other cognitive abilities for solving nonsocial problems."

"Interestingly these cognitive changes don't seem to have been accompanied by increases in brain size because species with smaller brains actually performed better than species with bigger brains when it came to social reasoning," he added.

MacLean noted that behavioral experiments are necessary to test these abilities because assumptions about primate brain size with respect to intelligence often do not hold up in real-world observations.