Our Shrinking Gray Matter

Over the last 20-30 thousand years the human brain has shrunk by about 10%—from 1500 cc to 1350 cc. No one knows why, and few scientists seem to be aware of the fact or even want to look further into the issue. Maybe it challenges one of humanity’s most cherished beliefs: that we humans are the smartest and it’s all due to our big brain. Could it be instead that we are dumbing down? If you take a look at what we humans are doing today, you could make a strong case for our actions being pretty dumb.

We know when our brain began to grow: around two million years ago, when Earth’s environment changed. Vegetation grew drier, and our deep ancestors came down from the trees and also changed. Their brains grew rapidly. It’s not clear why their cranial volume grew, however. The debate continues.

There’s been a tendency for us to think that we need this big brain—else why have it?—as well as to think that we’re most special, just because we have it. After all, aren’t we in charge here? Don’t we pretty much get our way in this world, primarily due to our being so smart? We rule!

Scientists have created a simple measure of an animal’s intelligence that tends to work in most cases: the Encephalization Quotient, or EQ. It’s the ratio of the brain’s weight to body weight. It’s a rough but helpful measure of intelligence, especially when we’re examining the skull sizes of various extinct species and trying to guess how smart they were and what their capabilities might have been. The idea behind EQ is that the larger an animal is, the larger its brain needs to be, just for basic survival skills. Any surplus gray matter presumably can be then used for higher cognitive skills.

Our immediate ancestors—the Cro-Magnon peoples of 20 to 30 thousand years ago—had bigger bodies and bigger brains than we do, so they had about the same EQ as we do. Both our bodies and our brains have shrunk since then. Will this brain-shrinking trend continue—maybe even as our bodies hold steady—and thus make us dumber? Nobody knows.

A big brain has a major advantage: the owner is smarter (in general) and more adaptable—thus is more likely to survive. But a larger cranial volume comes at a cost: the large human brain, for example, hogs about 20% of the food energy that we consume. So having a smaller brain has its own advantage: it requires less food and thus makes life easier.

Other studies suggest that we humans no longer need to be as resourceful as we once had to be—back when we were chasing down gazelles and dodging lions. Our culture has advanced so much that we can be dumber and survive just fine today, since our complex and interdependent societies can provide food and safety beyond what our ancestors knew. Additionally, our computers do a lot of brainwork for us, and machines provide the brawn, so we don’t need either the larger brain or body.

It may also be that we’ve not really lost any intelligence with our smaller brain, just that it has evolved to become more efficient. If so, we could have our brain shrink, require less food, and still be smart enough. We haven’t used but a fraction of our mental capability so far, so we might do just fine with a smaller cranial volume.

Studies also show that creatures with smaller brains tend to be less aggressive. Hmmm… Has our big brain been the thing that has led us to be so violent? Might our species even benefit from a little brain shrinkage?

Domesticated animals—pigs, cattle, goats, dogs, cats—have smaller brains than their wild counterparts. We have bred them for tame qualities, so they are more docile and less aggressive, but that has also made them dumber. It may be that the same is true for us. If smaller brains really do cause us to be more peaceful, then I say let ‘em shrink! We sure could stand to shed a few ounces of aggression.