Explain how the graphed data of beak size and weather conditions is evidence for natural selection.

Question

What will be an ideal response?

Answer 1

This graph depicts the relationship between beak size and weather conditions. This population of birds is "changing" in response to environmental changes. It is obvious that beak size is greater in drier years and less in wet periods. One might assume that weather conditions affected the food source of the ground finch and thereby favored a particular beak size that best used the food sources that were more plentiful in wet, as opposed to dry conditions. In fact, Peter and Rosemary Grant collected this data in 1973 as further evidence of natural selection. Under normal conditions, the finches prefer small, tender seeds that require a smaller beak size. Therefore, in wet years, the small-beaked birds are more successful reproductively. In drier weather, the finches must eat larger, drier seeds which are harder to crush. Therefore, larger birds are favored during this time and have more offspring. This is evidence of differential reproductive success in a changing environment.