Friday, March 07, 2008

The social brains of Hyenas

There is a correlation between brain size, particularly the newer frontal lobes, and the size of the social group an animal lives in. This rule works for our primate lineage and, it turns out, also for hyenas: those with the simplest social systems have the tiniest frontal cortices. The spotted hyena, which lives in the most complex societies, has far and away the largest frontal cortex. The brown and striped hyenas, with intermediate social systems, have intermediate brains. It appears that primates are not unique in the complexity of their social lives. An article by Zimmer describes the work of Holekamp and colleagues, who have found an array of complex social behaviors in spotted hyenas that are as complex as those of baboons. The groups are comprised of 60 to 80 individuals who all know each other individually. There are alliances, rivalries, and social hierarchies headed by an alpha female. Cubs undergo an education period. Hyena clans patrol their territory borders together against neighboring clans, kills near these borders can provoke clan conflicts. These behaviors are accomplished by brains with frontal lobes that are as easily distinguished as those of social primates (see figure.)

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