Animal researchers have long been puzzled why humans have such larger and more complex brains than other animals, “…seven times larger than one would predict for an average mammal of our size. Many of our extra neurons are in a region called the frontal cortex, where much of the most sophisticated thought takes place.”
One potential clue came from apes who also had outsize brains, a large frontal cortex (heavily associated with socializing) and engaged in lots of social activity in groups. Carl Zimmer in the NY Times writes: ” Primates may be pushed into larger groups thanks to predators or to patchy sources of food like fruit trees. As their numbers grow, natural selection may favor social intelligence. The primates form long-term alliances with each other and compete with rivals. They begin to keep track of a larger and larger social network….A boost in social intelligence can lead to an evolutionary edge for primates. Well-connected female baboons, for example, dominate their bands. They have more babies than lower-ranking females, and their babies enjoy better health and faster growth.”
But this frontal cortex-socializing-large brain theory has until now been largely limited to humans and primates. A new important piece of the puzzle has emerged from research by Kay E. Holekamp, who has been observing spotted hyenas on the savannas in southern Kenya. Holekamp said that researchers studied primates because of a bias assuming that other animals weren’t worth studying. In Holekamp’s research she finds that the “social brain” is not limited to primates. Hyenas (with much smaller brains) can differentiate which hyena they are hearing on tape.
Spotted hyenas have a rigid hierarchy. One dominant female rules over a number of hyenas beneath her. Each cub learns exactly where it and all other hyenas fit into this hierarchy. If a kill is made, other clans may fight for the meat, but the first right within the clan goes to the dominant female. But other species of hyenas — striped, aardwol, and brown — lived very different lives.
Were their lifestyles were a function of their brain size? Holekamp’s discovery was that they were: the “social complexity model” fit the data. There was a continuum from the hyenas with the simplest social systems and the tiniest frontal cortices (striped), to brown and striped hyenas, with intermediate social systems and intermediate brains, to the spotted hyena, with the largest brains and frontal cortexes who lived in the most complex societies.
Holekamp is now testing whether the brain size from sociability also influences the innovation and intelligence of hyenas by seeing which of these hyenas can learn new system (like unbolting a gate to get food). This would test whether the brain size that came from socializing led to an intelligence and innovation advantage.
Read the article “Sociable, and Smart“. (3/4/08)
See also a related article about trying to tease out the relationship between brain size and socializing among wasps (“Which Came First, Social Dominance Or Big Brains? Wasps May Tell“, Science Daily, 3/12/08)