Tuesday, 4 January 2011

Where have all the birdies gone?

One of the frustrations I find with watching birds in our back garden is that quite often, there's very little activity at all.  I've just spent about 20 minutes peering out of a back window and seen only a couple of collared doves, a wood pigeon, a blackbird feeding on fallen apples, and that's about it.

Then suddenly, I realised why that was.  I'm reading an excellent book called Catching Fire by Richard Wrangham, in which he proposes the theory that our brain size increased rapidly, starting a couple of million years ago, as a result of our starting to cook our food.  I'll go into why I'm (moderately) convinced in  a minute, but first, how does this help with the birds?

In the book, Wrangham describes how chimpanzees (and lots of other animals, of course) eat until their stomachs are full, then have to go and have a rest while the stomach processes the food, before they can go back to stuffing themselves.  I expect you're way ahead of me here, but of course, this is exactly what's happening with the birds.  They eat until their crops are full, then have to go for a little lie down while the crop empties itself.  I've noticed before that the small birds in our garden all tend to feed at the same time, which I take to be a defence mechanism, but it neatly explains why so often there's bugger all happening out there.

So why am I convinced by Wrangham's argument that cooking food gave us bigger brains?  First, he says that cooked food is more easily digested than raw, and supports this with quite a bit of evidence, not least how poorly people who subsist on an entirely raw diet fare.  Then he reports that there is evidence (albeit circumstantial) for the use of fire by Homo erectus starting about 2 million years ago and that at that time, anatomical changes occurred which fit neatly in - the teeth start to get smaller and weaker, the jaw and jaw musculature is reduced, the rib cage and pelvic girdle become more slender, implying they guts they're holding are shrinking, all of which are consistent with eating cooked food.  And at that time, the 450cc Australopithecine brain expands to 6 or 700 in H. erectus, then to 1200 in H. erectus heidelbergensis about 600,000 years ago and finally to 1400cc when anatomically modern H. sapiens comes on the scene 200,000 years ago.  It turns out that reducing the size of your gut saves you a hell of a lot of energy, which can be diverted to the brain. Soft, easily-digested, cooked food permits a reduction in the size of the gut, freeing off energy to make you smarter. 

The later brain expansion episodes don't have the supporting evidence relating to cooking that the 2 Myo episode does, all of which I find quite persuasive.  Until someone comes up with a better idea, of course.

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