While the Grants were on the Galápagos, a drought occurred. As a result, fewer seeds were available for finches to eat. Birds with smaller beaks could crack open and eat only the smaller seeds. Birds with bigger beaks could crack and eat seeds of all sizes. As a result, many of the small-beaked birds died in the drought. Birds with bigger beaks survived and reproduced (see Figure below ). Within 2 years, the average beak size in the finch population increased. Evolution by natural selection had occurred.
Mice in the area were born either grey or white. The fur color was completely random at one time. However as people moved into the area and feral cats became a problem the white mice were especially easy for the cats to spot at night.
where the grey and white mice the same or different species?