A Peek Into the Mind of Darwin

Review: The Flight of the Iguana by David Quammen

Imagine a moment in the history of ideas: A young man stands on the corner of a tropical island, throwing an oversized lizard into the sea.

The lizard swims back to shore. The young man follows this animal,… catches it by its long muscular tail, and throws it back again into the sea… Always the lizard swims straight back to that same stretch of rocky shoreline where the young man waits to catch it again, throw it again. The lizard is a strong swimmer but seems stubbornly disinclined to try to escape through the water. The young man takes note of that fact and, despite his homesickness, wonders why.

The young man is Charles Darwin, approaching the end of his trip to the Galapagos Islands. The lizard is the Galapagos marine iguana, an animal adapted to swimming and feeding in the sea. Darwin spent the better part of a day repeatedly tossing the lizard into the sea, asking himself, “Why does it continue to return to me on the shore, when it has the ability to escape by water?”

The nature of this lizard’s food, as well as the structure of its tail and feet, and the fact of its having been seen voluntarily swimming out at sea, absolutely prove its aquatic habits; yet there is in this respect one strange anomaly... they will sooner allow a person to catch hold of their tails than jump into the water… Perhaps this singular piece of apparent stupidity may be accounted for by the circumstance, that this reptile has no enemy whatever on shore, whereas at sea it must often fall a prey to the numerous sharks. Hence, probably, urged by a fixed and hereditary instinct that the shore is its place of safety, whatever the emergency may be, it there takes refuge. —Charles Darwin, Voyage of the Beagle, Ch. 17.

We know all about The Beagle, all about giant tortoises and finches and the theory they spawned in Darwin’s mind. But this tale of the tossed lizard, which Darwin recounted in The Voyage of the Beagle, is rarely mentioned.

David Quammen, visiting the Galapagos himself, explores in The Flight of the Iguana what the later-famous theorist was like at the time: boundlessly curious, unsentimental about nature, doggedly systematic, “and yet in some measure still just a wealthy young remittance-man off on a round-the-world lark.” In addition to these insights into Darwin’s development as an observer and scientist, Quammen gives us his own picture of the application of Darwin’s theories to island ecologies.

The Flight of the Iguana is just one of a collection of essays (most from Outside magazine). Many of them espouse Quammen’s concept of the “fragile island” that supports diversity, and the impact of “island ecologies”—and their fragility—on evolution, extinction and the richness of living things on Earth.

Even with Quammen’s perspective and bias in mind, each essay is enjoyable on its own; collected in one volume, they sound a warning for those complacent that we are “saving enough”. If Quammen is correct that the islands are more fragile than we think, where will a future Darwin observe the variation to inform his inspiration?