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Brain’s blood appetite grew faster than its size

Evolution of hominid mental abilities demanded more fuel, study finds

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7:05pm, August 30, 2016
skull

BLOOD FLOW The internal carotid arteries pass into the skull through two tiny holes (shown with arrows on this human skull). Scientists measured these openings in hominid fossils to estimate changes in blood flow rates to the brain across human evolution.

The brains of human ancestors didn’t just grow bigger over evolutionary time. They also amped up their metabolism, demanding more energy for a given volume, a new study suggests.

Those increased energy demands might reflect changes in brain structure and organization as cognitive abilities increased, says physiologist Roger Seymour of the University of Adelaide in Australia, a coauthor of the report, published online August 31 in Royal Society Open Science.

Blood vessels passing through bones leave behind holes in skulls; bigger holes correspond to bigger blood vessels. And since larger vessels carry more blood, scientists can use hole size to estimate blood flow in extinct hominids’ brains. Blood flow in turn indicates how much energy the brain consumed. (In modern humans, the brain eats up 20 to 25 percent of the energy the body generates when at rest.)

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