How Did the Zebra Get Its Stripes?

 

We've been discussing the adaptationist approach to biology on another thread and this is a good example to illustrate the issues. If I were to ask you how the zebra got its stripes, what would you think?

Would you immediately assume that it could be an evolutionary accident with no adaptive significance then start to wonder if you could rule out such an explanation? Can random genetic drift of neutral alleles explain the zebra's stripes?

Or would you immediately start thinking of adaptive explanations for why all three extant species of zebras have stripes but no other large mammals in the same environment are striped. Most other horses don't have prominent stripes but many have faint stripes on some parts of their bodies (Darwin, 1859).

I argue that you have to rule out the null hypothesis (drift) before invoking adaptationist explanations. In other words, the first question you need to ask is whether zebra stripes are adaptive. But that's not the adaptationist approach. Adaptationists begin with the assumption that stripes are adaptive, then they start looking for adaptive explanations.

What if the favorite adaptive explanation is refuted? What does an adaptationist do next? Gould and Lewontin (1978) provide the answer ...
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