WTF Fun Fact 12581 – The Shrinking Human Brain

All jokes about human intelligence these days aside, it’s true that humans have smaller brains than ever before.

The human brain has been shrinking in size for tens of thousands of years (so we can’t blame video games or reality TV or politics). According to anthropologists, the brain volume of Homo sapiens has decreased by about 10% over the last 40,000 years.

We’re used to hearing about the increasing size of brains as humans evolved, but that is a trend that goes back millions of years in human evolution.

And to be fair, our brains may be smaller today, but they are still about 3x bigger than other primates based on body weight.

Anthropologists estimate the brain sizes of our ancestors by measuring the amount of room in the skull. The oldest ancestors of humans had brains the size of a modern chimp’s. The skull cavity could hold about 1.5 cups (to put it in quantities that are easier to picture).

Then, between 2 and 4 million years ago, craniums (and therefore brains) got bigger, distinguishing humans from other primate ancestors. They could hold about 2 cups.

If you go back “just” 1 million years (to our ancestors Homo erectus), their brains could hold 4 cups. And Neanderthals and Homo sapiens (going back about 130,000 years) had craniums that could hold 6 cups.

So if you go back far enough, you see that brain size did increase, up to a point. After that, they began shrinking in size.

Today, the average human brain holds around 5.7 cups. But why? We can only make assumptions.

For starters, human bodies got smaller once the Ice Age was over, and so did skulls and brains.

But Discover Magazine claims that the most convincing hypothesis comes from anthropologist Brian Hare, which he calls “survival of the friendliest.”

This hypothesizes that Stone Age societies valued different, more domestic traits – specifically, ones that made humans more social. Social behavior is regulated by hormones that also affect brain and body size. So when we selected for these behaviors (by breeding with more social humans), we also chose genes that made bodies and brains smaller.

A reduction in skull and brain size isn’t necessarily a bad thing. It may be that we needed less brain volume as we began to live in collectives, cooperate, and rely on our communities. In other words, now we share the burden of survival with others, so our brains don’t have to hold every element of survival. – WTF fun facts

Source: “The Human Brain Has been Getting Smaller Since the Stone Age” — Discover