Adaptive radiation: one ancestor, many species

0:00How can one species of bird give rise to dozens of others?

0:05Millions of years ago, finch-like birds reached the Hawaiian Islands. Their species is the ancestor, the one all the others came from.

0:14The islands had habitats with different foods: nectar from flowers, seeds, and insects.

0:22Groups of birds settled in each habitat. Each group is a population: birds of one species living in one area.

0:30In each population, beaks vary a little, and young birds tend to inherit their parents' beak shape.

0:37Birds with beaks that suit the local food are more likely to survive and breed. This is natural selection.

0:45Generation after generation, the beaks changed: long and curved for nectar, thick and strong for seeds, thin and pointed for insects.

0:56Eventually they became too different to breed with each other, so each is now a separate species.

1:05These species did not appear in a single step: small changes built up over many generations.

1:13One ancestor giving rise to many species, each adapted to its own way of life, is called adaptive radiation.

1:21The Hawaiian honeycreepers formed dozens of species this way, though many are now extinct.

1:28Cichlid fish in Africa's Great Lakes did the same, forming hundreds of species, and so did Darwin's finches in the Galápagos.

1:37So adaptive radiation is one ancestor becoming many species, each adapted by natural selection to its own food.