Left-brain / right-brain split ain’t what it used to be

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As you might remember from anatomy class, the left side of your body is controlled by the right side of your brain, and vice-versa. For decades scientists assumed that only human beings had these specialized hemispheres in the brain, but they’re starting to realize that — like speech, tool-making, homosexuality, and just about everything else “uniquely human” — the left-brain / right-brain split in humans isn’t unique, or even that special.

Among the lower orders, scientists (see, e.g., this Scientific American article) have found evidence of species-wide left-right specialization not only with limbs but with jaws (whales prefers to eat with one side of the mouth), beaks, and eyes. The eye finding was especially significant. Unlike mouths or appendages (which largely react to what the brain wants them to do), eyes are sensory tools that provide information to the brain. Lose your left eye, and it turns out you’re less ready to dodge attacks by predators, since the right side of the brain is better at responding to novel stimuli. You’ll also have more trouble recognizing individual faces, like those of friends.

On the other, well, hand, losing the right eye could interfere with routine tasks like feeding, since the left side the brain controls how (and how well) we carry out everyday tasks. The left side of the brain also seems to control and interpret communication signals, so the lack of a right eye would delay the understanding of those signals.

Now, all that’s not to say your brain, after losing one eye, would be incapable of interpretting signals. Information from the left eye will still get to the left brain — it just takes longer, and the process is less efficient. But it’s still fun to thing about what you’d rather sacrifice: The ability to carry out everyday tasks efficiently? Or the ability to react instantly to startling new phenonmena? (Even more interesting would be to see if left-handed or right-handed people have a preference for one or the other.)

In any case, the delays would affect your chances of survival only in the jungle wilds. Indeed, one thing that does separate humans from all other animals is that we’ve built environments where deficiencies like losing one eye doesn’t matter that much.