Our Big Brains Have Shrunk. Scientists Might Know Why.  – WSJ

The development of bigger brains has long been considered a hallmark of our species increased intelligence and subsequent dominance on this planet. The last two million years of our evolution were marked by a nearly fourfold increase in brain volume.

But a growing body of evidence suggests our brains recently changed in an unexpected way: They diminished in size sometime following the end of the last Ice Age.

Most people think of brain evolution happening in this linear way. It grows, plateaus and stops, said Jeremy DeSilva, a professor of paleoanthropology at Dartmouth College. But we ve lost brain tissue equal to the volume of a lime it isn t a tiny little sliver we re talking about.

The precise timing of that post-Ice Age brain shrink has remained a mystery until now. A group of researchers led by DeSilva used a mixture of fossil and modern specimen data to pinpoint that this loss of gray matter happened between 3,000 to 5,000 years ago, according to research published in June in the journal Frontiers in Ecology and Evolution.

Many anthropologists had initially posited the changes coincided with the advent of agricultural practices around 10,000 years ago, and a global shift away from hunting and gathering.

The more-recent dates from DeSilva s group point to booming eras for ancient civilizations in North Africa, the Middle East and South America complex societies that they think may have played a role in the shrinkage.

via www.wsj.com

This explains a lot.