Final answer:
The few ancestors of the Galápagos finches who colonized the islands exemplify the founder effect, a form of genetic drift that occurs when a small number of individuals from a larger population establish a new population.
Step-by-step explanation:
The few ancestors of the Galápagos finches who colonized the islands serve as an example of the founder effect. The founder effect occurs when a new population is established by a very small number of individuals from a larger population, leading to a decrease in genetic variation and potentially different allele frequencies in the new population compared to the original. Both the bottleneck and founder effect are forms of genetic drift, where the former involves a large population being drastically reduced in size, often due to a catastrophe, while the latter involves the establishment of a new colony by a few members, as seen with the Galápagos finches.
The Galápagos finches originated from a common ancestor and have undergone adaptive radiation, evolving into different species to fill various ecological niches available on the islands. Scientists like Peter and Rosemary Grant have studied these finches and demonstrated natural selection in action, observing changes in beak sizes among different finch populations in response to environmental pressures such as food availability. Nevertheless, the initial colonization by the few ancestors is specifically an example of the founder effect, not natural selection directly.