When the HMS Beagle dropped anchor off the Galápagos archipelago in 1835, Charles Darwin was struck by the fact that each small island seemed to be home to a unique finch. The birds he collected—later found to belong to 15 distinct species of the subfamily Geospizinae—helped shape his ideas on evolution and became a textbook example of how species can adapt to new environments. That’s because each finch had a beak optimized for its own island’s most abundant food source, from cactus pulp to flowers or insects. Now, researchers have nailed the genetics behind these iconic beak shapes. When the team sequenced the genomes of 120 individual birds, it discovered a gene, ALX1, that varies between species with large or small, pointy or dull beaks. But the gene also had slight variations even between some birds of the same species, the researchers report online today in Nature. Medium ground finches (Geospiza fortis), like the bird shown above, were known to have undergone rapid genetic changes in the mid-2000s in response to a new, larger finch setting up house in their territory. And the genetic study revealed that they had different versions of ALX1 depending on their beak's exact shape. In humans, mutations in the same gene have been linked to frontonasal dysplasia, a birth defect that can range in severity from distinctly wide features or a cleft palate to more serious skull and brain malformations. The researchers hypothesize that smaller variations in ALX1 could be responsible for the diversity of face shapes among people.