Metamorphosis: A Natural and Human History

A search for the meaning of one of nature's greatest riddles: why do so many creatures transform?

“How many creatures walking on this earth / Have their first being in another form?” the Roman poet Ovid asked two thousand years ago. He could not have known the full extent of the truth: today, biologists estimate a stunning three-quarters of all animal species on Earth undergo some form of metamorphosis.

But why do tadpoles transform into frogs, caterpillars into butterflies, elvers into ee...