Question

Peter and Rosemary Grant conducted a 25 year study of the medium ground finch on Daphne Major Island in the Galapagos. They observed and recorded data that clearly

showed a shift in the average population beak size to a shorter beak size being more prominent after periods of severe droughts occurring from 1976-1978 and again in
1981-1982. This example of the change in beak depth demonstrates -
Group of answer choices
A. directional natural selection that evolution occurs so slowly that it is not possible to determine if the change has happened in less than a million years.
B. the environment in the Galapagos Islands has always favored bigger and bigger beaks in the medium ground finch.
C. disruptive natural selection.

Answer 1

The Grants' long-term study of the medium ground finch on Daphne Major reveals directional natural selection, where drought conditions favored finches with larger beaks, illustrating evolution in response to environmental pressures.

Step-by-step explanation:

The study conducted by Peter and Rosemary Grant on the medium ground finch, specifically on the island of Daphne Major in the Galapagos, demonstrates directional natural selection. During periods of severe drought, there were fewer small, soft seeds available, which led to the decline in survival of finches with smaller beaks. Finch individuals with larger beaks, which could consume the remaining larger, hard seeds, survived and reproduced. As a consequence, the average beak size within the population increased.

This change in beak size was directly related to the environmental conditions and the availability of food sources, which exerted selection pressures on the finch population. After the drought, when the environment again favored smaller seeds, a shift towards smaller beak size was observed. This fluctuation in beak size over the years due to environmental pressures illustrates how natural selection can lead to evolution in response to changes in the environment.