The Incredible Shrinking Brain

Source: Decline of the Empire

I like to have fun on Sundays, and today is no exception. At the library, I stumbled upon a thought-provoking article in the September, 2010 issue of the popular science magazine Discover. Called The Incredible Shrinking Brain, this article gets right to the point.

John Hawks is in the middle of explaining his research on human evolution when he drops a bombshell. Running down a list of changes that have occurred in our skeleton and skull since the Stone Age, the University of Wisconsin anthropologist nonchalantly adds, “And it’s also clear the brain has been shrinking.”

“Shrinking?” I ask. “I thought it was getting larger.” The whole ascent-of-man thing.

“That was true for 2 million years of our evolution,” Hawks says. “but there has been a reversal.”

He rattles off some dismaying numbers: Over the past 20,000 years, the average volume of the human male brain has decreased from 1,500 cubic centimeters to 1,350 cc, losing a chunk the size of a tennis ball. The female brain has shrunk by about the same proportion. “I’d call that major downsizing in an evolutionary eyeblink,” he says. “This happened in China, Europe, Africa – everywhere we look.”

If our brain keeps dwindling at that rate over the next 20,000 years, it will start to approach the size found in Homo erectus, a relative that lived half a million years ago and had a brain volume of only 1,100 cc. Possibly owing to said shrinkage, it takes me a while to catch on. “Are you saying we’re getting dumber?” I ask.

Hawks, a bearish man with rounded features and a jovial disposition, looks at me with an amused expression. “It certainly gives you a different perspective on the advantage of a big brain,” he says.

For me, it doesn’t get any better than this. Are you saying we’re getting dumber? I don’t want to be culture-centric, but it sure does explain a lot of what we’ve observed in the United States! But of course that doesn’t apply, for it appears the brain has been shrinking for the last 20,000 years, not just in Washington D.C. or Anytown, U.S.A, but everywhere Homo sapiens (“wise man”) lives and breathes.

It was thought that this might be simply due to a reduction in body size, and thus the size of the brain, proportionally speaking, is the same in modern people as it was in Cro-Magnons. This is called our Encephalization Quotient (EQ).

But the routine dismissal [of this shrinking brain trend] is not as weird as it seems at first blush, Stringer suggests, due to the issue of scaling. “As a general rule,” he says, “the more meat on your bones, the more brain you need to control massive muscle blocks.” An elephant brain, for instance, can weigh four times as much as a human’s. Scaling is also why nobody seems too surprised by the large brains of the Neanderthals, the burly hominids that died out about 30,000 years ago.

The Homo sapiens with the biggest brains lived 20,000 to 30,000 years ago in Europe. Called the Cro-Magnons, they had barrel chests and huge, jutting jaws with enormous teeth. Consequently, their large brains have often been attributed to brawniness rather than brilliance. In support of that claim, one widely cited study found that the ratio of brain volume to body mass – commonly referred to as the encephalization quotient, or EQ – was the same for Cro-Magnons as it is for us. On that basis, Stringer says, our ancestors were presumed to have the same raw cognitive horsepower.

Click to enlarge. Note that a Log/Log scale is used on the left, meaning that the difference between a human and a baboon or a wolf is much higher than it might appear at glance. I’ve provided a simplified view on the right. At no point during the Phanerozoic Eon (543 million years ago to the present) did an animal with such a proportionally large brain appear on Earth.

 Unfortunately, the EQ explanation of the shrinking brain problem does not hold up.

Now many anthropologists are rethinking the equation. For one thing, it is no longer clear that EQs flatlined back in the Stone Age. Recent studies of human fossils suggest the brain shrank more quickly than the body in near-modern times. More important, analysis of the genome casts doubt on the notion that modern humans are simply daintier but otherwise identical versions of our ancestors, right down to how we think and feel.

Over the very period that the brain shrank, our DNA accumulated numerous adaptive mutations related to brain development and neurotransmitter systems – an indication that even as the organ got smaller, its inner workings changed. The impact of these mutations remains uncertain, but many scientists say it is plausible that our temperament or reasoning abilities shifted as a result.

It is plausible that our temperament or reasoning have shifted. Think about that. The writer Kathleen McAuliffe offers up three theories to explain what that shift means. Of the three, only two are worth considering. The third, the “we use our brains more efficiently and are smarter as a result” theory can be dismissed out of hand. This view, taken by John Hawks, who was quoted at the top, seems to be based on obligatory, delusional optimism. There is has no evidence to support it, it depends on a set of improbable positive genetic mutations having occurred, and doesn’t address the problem of how we came to have such big brains in the first place. That leaves us with the other two theories—humans are dumber or humans are tamer. Both have merit.

Dumbing Down — The Idiocracy Theory

This quote says it all.

“You may not want to hear this,” says cognitive scientist David Geary of the University of Missouri, “but I think the best explanation for our brain size is the idiocracy theory.” Geary is referring to the eponymous film by Mike Judge about an ordinary guy who becomes involved in a hibernation experiment at the dawn of the 21st century. When he wakes up five hundred years later, he is easily the smartest person on the dumbed-down planet. “I think something a bit like that happened to us,” Geary says. In other words, idiocracy is where we are at now.

A recent study he conducted with a colleague, Drew Bailey, led Geary to this. Bailey and Geary found population density did indeed track closely with brain size, but in a surprising way. When population numbers were low, as was the case for most of our evolution, the cranium kept getting bigger. But as population went from sparse to dense in a given area, cranial size declined, highlighted by a sudden 3 to 4 percent drop in EQ starting around 15,000 to 10,000 years ago. “We saw that trend in Europe, China, Africa, Malaysia – every – where we looked,” Geary says.

The observation led the researchers to a radical conclusion: As complex societies emerged, the brain became smaller because people did not have to be as smart to stay alive. As Geary explains, individuals who would not have been able to survive by their wits alone could scrape by with the help of others – supported, as it were, by the first social safety nets.

Makes sense to me. Certainly the docile idiots we find in contemporary America could not survive 5 minutes as hunter-gatherers, who would not doubt ask “who are these dummies?” before kicking them out of the band because they were heavy drag on the group’s survival.

A Tamer Breed Of Humans — The “Sheeple” Theory

Harvard anthropologist Richard Wrangham is the leading proponent of the theory that humans have become more domesticated. Think cows or sheep. Sheeple!

Other researchers think many of their colleagues are barking up the wrong tree with their focus on intelligence as the key to the riddle of our disappearing gray matter. What may have caused the trend instead, they argue, is selection against aggression. In essence, we domesticated ourselves, according to Richard Wrangham, a primatologist at Harvard University and a leading proponent of this view.

Some 30 animals have been domesticated, he notes, and in the process every one of them has lost brain volume – typically a 10 to 15 percent reduction compared with their wild progenitors. Domesticated animals also have more gracile builds, smaller teeth, flatter faces, a more striking range of coloration and hair types – and, in many breed, floppy ears and curly tails. Except for those last two traits, the domesticated breeds sound a lot like us.

“When you select against aggression, you get some surprising traits that come along with it,” Wrangham says. “My suspicion is that the easiest way for natural selection to reduce aggressiveness is to favor those individuals whose brains develop relatively slowly in relation to their bodies.” When fully grown, such an animal does not display as much aggression because it has a more juvenile brain, which tends to be less aggressive than that of an adult. “This is a very easy target for natural selection,” Wrangham argues, because it probably does not depend on numerous mutations but rather on the tweaking of one or two regulatory genes that determine the timing of a whole cascade of developmental events. For that reason, he says, “it happens consistently.” The result, he believes, is an adult possessing a suite of juvenile characteristics, including a very different temperament.

Unfortunately, the”evidence” Wrangham uses to support this view makes little sense, at least to me. Here’s an example where Wrangham is talking about our increasing “peacefulness” (non-aggressiveness) as a species.

“The story written in our bones is that we look more and more peaceful over the last 50,000 years,” Wrangham says. And that is not all. If he is correct, domestication has also transformed our cognitive style. His hunch is based on studies – many done by his former graduate student Brian Hare – comparing domestic animals with their wild relatives. The good news, Wrangham says, is that “you can’t speak of one group being more intelligent than the other.”

Hare, now an assistant professor of evolutionary anthropology at Duke University, agrees. “All you can say is that wild types and domesticates think differently.”

All I can say about this silly view is that if we’re more “peaceful” now than we were 50,000 years ago, I certainly wouldn’t want to run into a gang of paleolithic humans. If we had more broken bones then, surely it was due to hunting injuries, or the other pitfalls of the daily life of hunter-gatherers, not our warlike nature. In fact, most anthropologists think we became less peaceful after about 10,000 years ago. And why? Because with agriculture comes surplus, and with surplus comes wealth, specialization and cities. In short, for the first time in human history, there was stuff to steal.

The Meaning Of It All

In the past I’ve said that Homo sapiens is a species, so what you see is what you get, which means don’t expect to see significant change in human behavior. Each new generation is basically the same as the last, excluding trivial cultural differences.

However, perhaps I was wrong to exclude the possibility of the physical/cognitive changes which are making the situation even worse than it appears to intelligent, conscious people today. In fact, I think human beings are both dumber and tamer than they were even 100 years ago. And considering Americans, it appears that they are much dumber and tamer than they were just 30 years ago.

The “domestication” theory can be saved by considering surplus, which I mentioned above.

In hierarchical societies, like all human societies (excluding vestigial hunter-gatherer societies) since the invention of agriculture, a very large majority of people live at the bottom of the pyramid, with only a relatively few, more aggressive people at the top. If brain sizes (EQ) on average have been falling, it is not surprising because worker bees don’t need such large brains to survive. And large brains are, from an energy consumption standpoint, very expensive. Which is why it is a total mystery as to why they evolved in our species in the first place.

So what is the meaning of it all? God only knows, but the best evidence available to us says that human societies will go downhill from here. For this and lots of other reasons I could mention, we might conclude that maybe the evolutionary experiment which gave rise to us wasn’t such a hot idea after all.

Bonus Video — from Mike Judge’s Idiocracy. Don’t worry about the glitch in the first few seconds.

Read more at Decline of the Empire