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9:47am on Friday, 5th May, 2006:
My brother-in-law gave me a book for Christmas, Does Anything Eat Wasps?. It's answers from readers of New Scientist to questions posed by other readers of New Scientist. It was this year's unexpected Christmas best-seller.
One of the questions asked in it is representative of a whole class of questions that are regularly asked (especially on TV), to which the answers given annoy me more than somewhat. Here's the question:
Why do people have eyebrows?
There are two answers given. One is that eyebrows divert sweat away from the eyes. The other is that eyebrows allow us to express emotions.
Neither of these is the correct answer. The correct answer is: because we evolved that way.
We don't have to have eyebrows for a reason. If there's a reason for them, then that suggests there's someone doing the reasoning. "If we didn't have them, sweat would run into our eyes" is no answer, because if we had bony ridges instead then sweat wouldn't run into our eyes either. If our eyes were on stalks we wouldn't have the problem. Besides, not everyone does "need" them to divert sweat anyway: oriental eyes, with the extra fold of skin, are less susceptible to it, and some people have eyes deep-enough set that their eyes wouldn't even get wet in the shower. Eyebrows are just an accident of evolution. If we didn't have them then the chances of survival in the past for some of us would have been slightly reduced, but lots of other mutations could also have given the same edge; eyebrows just happened to win out.
As for having eyebrows "because" they show emotion, I'm stunned at this suggestion. Yes, they can be used to show emotion, but how can that be why we have them? Millennia ago, eyebrowless beings were more attracted to those with eyebrows because they expressed their emotions better? But that would mean they'd need to understand the language of eyebrows — that raising them was a question, for example. How could that happen if the eyebrows didn't come first? And again, why eyebrows and not some other way of expressing emotion, say a vein that visibly throbbed on the forehead if you were angry?
No, the implication is that "someone" decided that we needed to be able to express ourselves more, so gave us eyebrows. Science is replaced by theism.
In any case, how do either of these answers explain bats? Many varieties of bat have eyebrows. They have them to show emotion? When they primarily "see" each other by sonar that couldn't pick up that level of detail? And they need to divert sweat from their eyes? When they spend much of their time hanging upside down?
Why do we have 32 teeth? Why do fingernails grow? Why do we have tonsils? All these questions have the same answer: because we evolved that way.
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