'Wassup, Sheep?' He Asked : Krulwich Wonders... How come so many species of domesticated animals — dogs, pigs, cows, ducks, geese, rats, horses — have smaller brains than their wild ancestors? Oh, and humans too!
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'Wassup, Sheep?' He Asked

One man is facing a few hundred sheep. He has questions. When he shouts to them, the sheep — surprisingly — answer back. It's a very lively back and forth, with one obvious problem. I don't trust these sheep. Their answer to his "Are you happy?" question seemed oddly, even suspiciously, short. Are they hiding something? Or are they — and I mean this with the greatest respect — a little dim?


I'm going with "dim" here. These sheep are domesticated animals. They live to be shorn or eaten by humans. In 2005, zoologist Dieter Kruska described changes in various mammalian brains over time, and found that domesticated sheep brains are smaller than wild sheep brains.

This is not just a sheep thing; it's a trend in domesticated animals. Domesticated pigs have smaller brains than wild boars. Lab rats have smaller brains than wild rats. Dog brains are smaller than wolf brains. Same for domesticated ducks, domesticated geese, domesticated horses — when you get bred for gentleness, for human uses, apparently you get stupider.

Well, "stupider" may not be fair. Brain size doesn't always correlate with intelligence. On some tests, laboratory rats outperformed wild rats, and domestic guinea pigs did better than wild cavies. But most of the time, writes evolutionary biologist and science blogger Christie Wilcox, when the test is about puzzle solving, wild animals win:

Dogs, for example, appear to be a few crayons short of the box when compared to wolves. A study in 1985 found that wolves vastly outperformed malamutes in getting a food dish from a series of complex puzzle boxes. And while one study had found that dogs are better able to pick up human social cues than wolves, they were criticized for using wild wolves that had little interaction with people. Indeed, when another set of researchers did the same kind of study using wolves that had been raised by humans, the wolves beat the dogs hands down.

The Price Of Nice

These changes don't happen instantly. When a wild pigeon gets captured, its brain doesn't shrink. The transition is gradual, across generations, in the animal's DNA. Presumably, domestic beasts are selected for certain qualities — tameness, friendliness, cooperativeness. Which may (or may not — scientists are still arguing about this), lead to a slightly duller animal, like the ones bleating in our video.

Interestingly, this development seems to include us.

NPR reported a couple of years ago that human brains have gotten smaller over the past 10,000 years. About 10 percent smaller. Our skeletons are also a little lighter, our foreheads a little flatter. Duke University's Brian Hare told my colleague Jacki Lyden that these changes — and smaller brains — are a "signature of selection against aggression," meaning we may, on the whole, be less brutish than we used to be. The most violent among us are more likely to be culled (bye-bye, Saddam, Osama, Idi, Adolph; hello, Alan Alda). We have begun, Hare thinks, to domesticate ourselves. That's nice to hear, but going back to the sheep video: What if the price of getting nicer is that we turn a wee bit duller?

I like the niceness. But I want the brightness. Will nature make us choose?