Adapting to Island Variation
During his time on the Galapagos, Charles Darwin observed that the Galapagos Tortoise, Chelonoidis nigra, showed variation in form and behavior. On the larger islands with lush highlands and abundant vegetation, the tortoises had domed shells, short necks, foraged closer to the ground and grew much larger than those on the smaller islands.
By contrast, on more arid islands with less available food, the tortoises were smaller and their shells resembled saddles. They also had long necks which they used to reach vegetation higher off the ground. Darwin used variation in tortoise behavior and morphology to support his theory of natural selection.