The theory of evolution has its origins in the Galápagos.

Now climate change is rapidly heating the ocean here.
Darwin’s creatures are threatened.

ALCEDO VOLCANO, Galápagos — When the clouds break, the equatorial sun bears down on the crater of this steaming volcano, revealing a watery landscape where the theory of evolution began to be conceived.

Across a shallow strip of sea lies the island of Santiago, where Charles Darwin once sighted marine iguanas, the only lizard that scours the ocean for food. Finches, the product of slow generational flux, dart by. Now, in the era of climate change, they might be no match for the whims of natural selection.

In the struggle against extinction on these islands, Darwin saw a blueprint for the origin of every species, including humans.

Yet not even Darwin could have imagined what awaited the Galápagos, where the stage is set for perhaps the greatest evolutionary test yet.

Marine iguanas on Fernandina Island.

As climate change warms the world’s oceans, these islands are a crucible. And scientists are worried. Not only do the Galápagos sit at the intersection of three ocean currents, they are in the cross hairs of one of the world’s most destructive weather patterns, El Niño, which causes rapid, extreme ocean heating across the Eastern Pacific tropics.

Research published in 2014 by more than a dozen climate scientists warned that rising ocean temperatures were making El Niño both more frequent and more intense. Unesco, the United Nations educational and cultural agency, now warns the Galápagos Islands are one of the places most vulnerable to the impacts of climate change.

“You can see them laying one or two eggs and being attacked by the ants,” said Christian Sevilla, a conservationist at the national park here. “They’re just throwing off the rest of the eggs as they walk off trying to escape, with the ants still biting at their legs.”

(Not without irony, Darwin was a predator of the tortoises well before the ants were. “The young tortoises make excellent soup,” he wrote in 1839.)

Mr. Sevilla and other workers at the park are now considering mitigation efforts to try to protect threatened species from the more frequent El Niño events that have come with climate change. The park already has a program to breed giant tortoises in captivity.