The size of a primate's social group can predict cognitive skills related to social abilities, according to research published June 26 in the open access journal PLOS ONE by Evan MacLean and colleagues from Duke University.
The authors compared six lemur species' performance on two tests, a social cognition task that required understanding a competitor's actions and a second test where animals tried to retrieve food placed in a transparent tube, testing their non-social cognitive skills.
A lemur species that usually lives in large, 15 member- groups performed significantly better on the social cognition test than another species that usually lives in smaller groups of approximately five members. On the second test, all the species tested performed on par with one another, regardless of the size of their social groups. Based on these results, the authors conclude that the size of a lemur's social network correlates with their social cognitive skills.
Previous research supports the idea that primates evolved complex cognitive skills as they adapted to life in large social networks. Relative brain size has been correlated with social group size in some monkeys and apes, but the size of lemurs' social groups are not correlated with their brain size. According to the authors, their results reveal the potential for cognitive evolution without a change in brain size.
MacLean elaborates, "Being socially savvy doesn't make you brainy in every domain. 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."
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