May 29 2009
Human Brain Size Still a Mystery
Why did our kind evolve such large, energy-expensive brains? Early theorizing targeted tool use. But there was very little change in hominid tool kits over thousands and millions of years. Over those same years the hominid brain kept changing. Hmm.
More recent reasoning has focused on social living. Maybe our kind experienced selective pressure to be able to live and work in complex groups. But that may not be the full reason, either. At least not according to the analysis of evolutionary biologists John Finarelli and John Flynn. After looking at living and fossil carnivore species they -
found that increased brain size is not routinely associated with sociality.
I imagine they focused on carnivores because while many herbivores live in large groups, like cattle and sheep, but, to use scientific lingo, “they aren’t too bright.” Perhaps hoofed vegetarians are social in a very rudimentary fashion, but not as rudimentary, no doubt, as, say, schooling fish.
Still, the conclusion does raise serious questions.
“The universality of the Social Brain Hypothesis does not apply,” says Finarelli. “When you look at relative brain size from the point of view of the entire evolutionary history of the clade, the story starts to fall apart—at least in carnivores. This study shows that, almost assuredly, brain size is increasing for different reasons in different groups of carnivores.”
What we have is a puzzle wrapped in a enigma being chased by a pack of hungry scientists. So to speak. I don’t know about you, but I love puzzles.
