The “Secret Recipe” of Galápagos

Galápagos tortoises demonstrate the special “creative force” of evolution in the archipelago, having radiated into 15 species—each with a characteristic shell shape—within the last 3.2 million years. Formed over an active mid-ocean volcanic hotspot, Galápagos islands have also changed dramatically in the same period, providing new and diverse “petri dishes” for tortoise evolution. In these new homes, which are low, dry islands, where the tortoise’s main food is prickly pear cactus (which has concurrently evolved a protective treelike stature), tortoises evolved impressive new features, including saddlebacked shells and extra-long limbs. On all the islands where they occur, tortoises serve as “ecological engineers,” building suitable niches for themselves (and incidentally for other species). In the case of domed-shell tortoises, those niches include tortoise-maintained wallows, meadows, and migration trails. Heavily hunted in Galápagos history, most tortoise species are rebounding today, some from tortoises rediscovered in the novel places they had been carried by early mariners in their quest for food.