“I think I’m so educated and I’m so civilized
cos I’m a strict vegetarian
But with the over-population and inflation and starvation
And the crazy politicians
I don’t feel safe in this world no more
I don’t want to die in a nuclear war
I want to sail away to a distant shore and make like an ape man
I’m an ape man…”
-The Kinks - “Apeman”
Most folks agree that the brain is what separates us from the rest of the beasts. The human brain is about three times larger in volume than our closest relatives, the great apes. What’s a little puzzling about this is that the brain is an expensive organ to keep running. Most of biology is about efficiency, particularly in energy expenditure. The brain is like the SUV of organs - requiring ten times as much energy by weight as other tissues. So, from an evolutionary point of view, a big brain must provide advantages that overcome the excess fuel required to run it. And there’s little doubt that our big brains have served us well. Humans have cognitive abilities - the capacity for complex thinking - well beyond even our closest living relatives, the great apes. But, the evolutionary puzzle is how and why.
Science Tuesday is running a week behind as Baby Z began to make his presence felt last Tuesday. In last weeks Science magazine, work done in collaboration by researchers from the Max Planck Institute for Evolutionary Anthropology in Germany, Duke University in America and the Universidad Complutense de Madrid in Spain addressed this puzzle. Their approach was to test the two leading hypotheses used to explain the big human brain. The general intelligence hypothesis states that the bigger human brain grants us better thinking across the board - better memory, faster learning and better planning ability. The alternative is the social intelligence hypothesis which states that humans have evolved sophisticated social interactions which allow information to be passed on from generation to generation and this is what the extra brain is for. To test which of these hypotheses is more accurate, the researchers compared the performance of human children before formal education begins (around 2 1/2 years old) with chimpanzees and orangutans on a variety of tests designed to distinguish between the two. The rationale for the species used is that chimpanzees are our closest living relative and thus a good comparison whereas orangutans are a bit more evolutionarily distant and should perform differently.
The researchers used two categories of tests to test the two hypotheses. Physical cognition, which essentially tests an individual’s memory, ability to use tools and ability to do simple addition, and social cognition, which involves testing an individual’s ability to learn from another person. For example, one of the physical cognition tests is a scientific version of a shell game, using food as the prize. One of the social cognition tests involves solving a problem after being shown how to do so. Humans and chimpanzees performed about the same on physical cognition tests and better than orangutans. In fact, chimps performed better than toddlers in simple addition and in tool use. What this means is that humans are not more intelligent across the board than our more “primitive” relatives. However, on the tests for social cognition, human toddlers outperformed both ape species on nearly every test.
If the general intelligence hypothesis were valid then humans should have outperformed apes on every test given. This would mean that humans are just smarter in general. However, since this is not the case, the social intelligence hypothesis looks more reasonable. The surprising implications of these results is that humans use their massive and energy inefficient brains primarily to interact with other humans. From an evolutionary standpoint, there are many ways in which this social intelligence would have been useful. Humans were able to form complex societies that allow for division of labor and protection from predators. Social intelligence allowed for “behavioral flexibility” so if the environment changed, human societies could change with it to avoid extinction. What I think may be the biggest advantage is that this social intelligence may have allowed us to learn from previous generations - from old wives tales to the lessons of history.
There are a couple of flaws in this work. The biggest is that while the researchers used human children of the same age for all the experiments, the chimpanzees and orangutans were from a variety of ages, mostly adult. Certainly there is a significant amount of social learning that occurs in these species that may have skewed the results one way or another. In addition, this research doesn’t address other hypotheses that have been proposed to explain the big human brain. But, their work does suggest that part of the reason that we’ve got so much going on upstairs is to allow us to play well with others. It appears that Marx may have been right about at least one thing - man is a social animal - without society we are animals . So the next time your boss busts you messing around on Facebook, just explain that it’s an evolutionary imperative.
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2 responses so far ↓
1 Matthew // Sep 18, 2007 at 9:48 am
About 3 or 4 years ago, I read a theory that I thought was quite creative. The argument was that we have a big brain through run away sexual selection (similar to the peacock tail). That women would select for men that were cleaver or wittier or what have you for mating purposes. I did a quick Google search, but didn’t find much. I can’t remember the person who came up with this, but the results mentioned above kind of fits in with that hypothesis.
2 Jason // Sep 18, 2007 at 4:57 pm
As I’m sure you’ve heard many times before, its not actually the size that matters. If it was truly the size of the brain that dictates intelligence, then I’d imagine that whales would be the smartest creatures on earth, and perhaps dinosaurs would have been smart enough to survive (although I think I’ve heard that their brains were pretty small. Its all relative though). There are two main things to consider when reading such information.
First, its easy to equate the brain with intellect or cognitive ability but this would be inappropriate. Like most other organs, the brain has many parts with specialized functions. Only a fraction of the brain is actually devoted to cognition and higher-order processing, or “smartness”. Other areas of the brain are largely involved in maintaining the overall functioning of the body, to describe it very simply, and can be broken down into dozens upon dozens of jobs. So, just using brain size to determine smartness isn’t really fair.
Secondly, since brain size doesn’t seem to matter in comparison to whales, elephants, etc., the big difference between a human brain and other brains is the “wrinkling” that is typical on the surface of the cortex. Other species don’t have this feature, or at least not nearly to the same extent. Its this wrinkling feature that greatly increases surface area. The surface of the brain, or the “gray matter” is where most cognitive ability takes place and with exponentially increased surface area comes exponentially increased cognitive ability.
I should probably read the article you mention. I’m sure I could have something to say about it and it sounds like an interesting study, but I think I’d rather spend my time on deciding whether or not to pick up DeShawn Wynn for my fantasy team.
On a related note, in response to Matt’s statement above about women selecting for men that were clever or wittier, that topic always seems to come up in evolutionary discussions but I can’t see how its really true these days. When someone like Kevin Federline has already spawned 5 kids yet most of the smartest people in the world never come even close to this number in their lifetime, doesn’t it seem like we’ve evolved to a point where we are (as a society) working AGAINST evolution?
And finally, this post reminded me of when I was in high school and I was on a visit to Cornell. I recall walking through one of the science buildings on a tour and we walked past this display of human brains preserved in large jars. The interesting thing about that tour was that I learned that the largest human brains ever examined at Cornell belonged to serial killers and other deranged sociopaths. Now what does that tell you about brain size?
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