Over time, natural selection causes changes in features.

In 1976, one of the Galápagos Islands was struck by a drought, killing many of the small soft plants such as grasses. There was an increase in the plants with larger, harder seeds, as these survived the drought better.

The change in vegetation caused the population of Geospiza fortis finches to drop from about 1400 individuals to only 200, and most of those survivors tended to have a particular body and beak size.

What finch body and beak size was favored as a result of the change in diet? Click on the graph that best shows the change in body and beak size.

Graphs © UCMP.