Research NewsEvolution

Solving the Brain's Energy Crisis

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Science  29 May 1998:
Vol. 280, Issue 5368, pp. 1345-1347
DOI: 10.1126/science.280.5368.1345

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Last month at the annual meeting of the American Association of Physical Anthropologists, researchers debated two solutions to the problem of energetic constraints on brain size and how humans may have evolved a way around them: the expensive tissue hypothesis, which holds that big brains in adults are fueled by the energy saved in humans' relatively small gastrointestinal tracts (which we can afford because of our high-quality diet), and the maternal investment hypothesis, which proposes that most of the extra energy comes early in life--from mom, through the placenta during pregnancy and through breast milk between birth and age 4, when the human brain reaches 85% of its adult size. Either way (and it may very well be that both play a role at different times in development), a growing number of anthropologists and neuroscientists are analyzing the potential constraints on brain evolution, testing their ideas with data from genetics, neuroscience, and comparative physiology.