AMNH / Denis Finnin.

Live green iguana (Iguana iguana) on exhibit

At the beginning of his voyage, Darwin saw animals like this green iguana as unique marvels. But by the end, he was looking at species in a different way: He was becoming interested in how species might be related to one another.

Green iguanas were common on the mainland, but they were absent on the Galápagos; instead these islands had their own unique species. Why? Where had these species come from? Eventually Darwin would wonder: Could species from the mainland have reached the Galápagos and somehow changed into the species he found there?

An Island Relative

The Galápagos is not the only place where new species have arisen on isolated islands. If Darwin had visited the Caribbean, for example, he would have found another intriguing iguana to ponder.

The lesser Antilles iguana looks very similar to its larger relative, the green iguana, but it has no tail bars. Once its ancestors became separated from the mainland, it became a distinct species. Yet unlike the Galápagos, where iguanas had to adapt to a rocky, volcanic environment, the forests of the Antilles were similar to the mainland, so fewer new adaptations evolved there.