Is Global Warming Shrinking Our Brains?

There are many theories trying to explain our big brains, from an alimentation rich in protein (meat) to a prolonged childhood in humans.

Now a team from the University at Albany claims that early humans grew larger brains as a response to colder climates. The researchers show that human cranial capacity (which marks brain size) increased dramatically during our evolution, and that climate changes during the Pleistocene (from 2 million years ago till 10,000 years ago), characterized by successive global coolings and glaciations, induced as much as 50 % of the increase in our cranial capacity.

The team employed several measures of paleotemperatures and a sample of 109 fossilized hominid skulls dated down to 2 million years. "By paying close attention to the geographic origin of each of the fossilized skulls it became clear that seasonal variation in climate may also have been an important selective force behind the evolution of human cranial capacity. Specifically, we found that as the distance from the equator increased, north or south, so did brain size," said Gordon G. Gallup Jr., professor of evolutionary psychology.

The researchers believe that cold climate started an evolution towards larger brains as a necessity to stand the cold season, when people were confronted with the cold and food shortage.

Other mammals adapted to the cold season in cooler climates by behavioral, physiological and anatomical mechanisms like hibernation (rodents, hedgehogs), winter torpor (bears) and migration (reindeer), development of fur or/and isolating fat deposits.

But these types of adaptations could not have been made by humans, so they adapted by developing progressively more refined cognitive strategies, cooperative hunting techniques and more sophisticated tools and weapons.

Larger brain capacity enabled people to use fire for keeping warm and for cooking, and to make clothing and shelter.

While how human brain evolved so large is still a puzzle, this research points out the role of climate and movement away from the equator as selective forces in promoting human intelligence and brain capacity.

So, may the current global warming be reversing the trend that gave us big brains?