Darwin's Finches

Darwin's finches are the iconic example of adaptive radiation and natural selection in action. Eighteen species descended from a single ancestor that arrived on the Galapagos Islands from South America two million years ago. Each species evolved beaks specialized for different food sources: the large ground finch with crushing beaks for hard seeds, the cactus finch with sharp beaks for piercing cactus pads, the woodpecker finch that uses twigs as tools, and even the vampire finch that drinks seabird blood.

The Grants' 40-year study on Daphne Major documented natural selection in real time: after the 1977 drought, average beak depth increased 4% in a single generation as small-beaked finches died and large-beaked survivors reproduced. This demonstrated that fitness landscapes shift with environmental conditions - what's optimal during wet years (small beaks for soft seeds) becomes fatal during drought (when only hard seeds remain).