Wednesday, 12 October 2011

Memes and the great brain shrinkage

Coyne (1999) criticises the meme hypothesis for explaining big brains:

First, there is no evidence that brain-size increase had anything to do with memes — there are as many explanations (including language, social grouping, hunting) as there are evolutionists, and no way to judge which theory is best. Indeed, the meme hypothesis seems among the least likely. As others have noted, the serious proliferation of memes began roughly 30,000 years ago when humans commenced their march to larger social groups, writing and complex culture. The human brain, however, stopped enlarging after reaching its present volume nearly 500,000 years ago. Why did brain-size evolution stop so long before the heaviest rain of memes?
Mammal brain size increases can't go on forever - the female pelvis and the human neck act as restraints. That seems to be the most obvious explanation for increases in human brain coming to an end. Such a constraint apples equally well to all theories that posit a selective advantage to large brains - including the meme theory.

The volume average male brain reduced from 1,500 cubic centimeters to 1,350 cubic centimeters over the last 20,000 years. How does the meme theory explain this cranial shrinkage?

That is most likely to have been among the results of the agricultural revolution. Human settlements formed and role-specialisation began. No longer did each member of the tribe have to carry all the tribes memes around in their heads. Bakers, tailors, teachers, managers and priests established their own traditions. Then writing came along - allowing memory storage space to be out-sourced.

In short, humans domesticated themselves. Collective meme-storage took over - and individual meme-storage became less valuable.

Of course, we don't know with much certainty exactly what happened - but the meme hypothesis is at least consistent with conventional explanations for recent changes in human brain size.


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