Pick a bone, any bone

Evolution works its magic

Ethan Hill


It’s one thing to imagine evolution driving gradual changes in anatomy — for instance, limbs lengthening over generations bit by bit. It’s quite another to imagine a hole opening up on the top of a whale’s head. Or is it?

According to David Kingsley, PhD, professor of developmental biology, apparently novel structures are rarely as unusual as they seem. Take the whale’s blowhole. Looking at a whale skeleton you see that the blowhole is an oddly placed nostril. The bone between the upper lip and the nostril is greatly lengthened whereas bones between the nostril and the top of the head have shortened. All the skeletal pieces remain in place — they’re just configured differently.

Kingsley’s genetic studies have shown one way this can happen: They’ve uncovered a relatively minor mutation that can dramatically alter bone growth. “When you break them down, most novel structures can be explained by simple evolutionary steps,” he says.

In fact, Kingsley and his lab have discovered anatomical antecedents to every seemingly unique structure they’ve analyzed. And they’ve analyzed hundreds. Their lab meetings all include a “bone of the week” discussion, which now includes other structures in addition to bones. The goal is to expand people’s appreciation for the diversity and beauty of life, and to get them thinking about functional changes and disease mechanisms in many different organisms, he says. People have had fun with all sorts of interesting topics over the last decade. One of the main lessons? It’s very hard to find a truly novel structure, one that has no precursor in the animal’s ancestors.

The group has found that whale fins, narwal tusks, turtle shells, bird wishbones and bone itself, which is absent in sharks, all have origins that make sense when you look at the fossil record, comparative anatomy or developmental genetics. One apparent stumper: the glowing lure an anglerfish dangles above its mouth to entice prey. But upon closer examination, this clever looking fishing lure turns out to be a modified skeletal spine, greatly lengthened so it dangles, and now serving as a home for glow-in-the-dark bacteria. Human designers are free to invent from scratch. In contrast, evolution always builds on what came before, nipping and tucking to produce a wonderful diversity of living forms.

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