Why is your brain huge?

In the last, oh, about two and a half million years, the human brain exploded in size and we became big old smartypants. Scientists are trying to figure out why.

A new study says that it might have to do with temperature. Brains, as you know, are busy all the time, cells constantly buzzing and electrical signals flying. As they work, brains get really hot! And it's hard to cool off, especially since they are encased in bone.

Before the last Ice Age, when temperatures were higher than today, humans had brains about half our size. That was about as big as they could get in the warm temperatures without overheating and frying themselves to a crisp. But as the Ice Age came along and temperatures fell, the problem of overheating brains eased up. Now brains could get bigger without getting too dang hot. Bigger brains came with all kinds of benefits, like outsmarting the neighbors, figuring out how to keep warm, and generally surviving better.

If bigger brained people survived better and had bigger brained kids, and then if those kids went on to have bigger-brained kids, and so on, then a couple of million years later -- voila! -- your huge brain!