DID shrinking guts and high-energy food help us evolve enormous, powerful brains? The latest round in the row over what's known as the "expensive tissue hypothesis" says no. But don't expect that to settle the debate.
The hypothesis has it that in order to grow large brains relative to body size, our ancestors had to free up energy from elsewhere - perhaps by switching to rich foods like nuts and meat, which provide more calories and require less energy to break down, or possibly by learning to cook: cooked food also requires less energy to digest.
Kari Allen and Richard Kay of Duke University in Durham, North Carolina, turned to New World monkeys to explore the hypothesis. Previous studies offer a wealth of data on the monkeys' diets and show that their brain size varies greatly from species to species. But when the pair controlled for similarities between related species, they found no correlation between large brains and small guts (Proceedings of the Royal Society B, DOI: 10.1098/rspb.2011.1311).
As Robin Dunbar at the University of Oxford points out: "It is one thing to say that the hypothesis doesn't apply to New World monkeys, and another to extrapolate that to humans."
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