Answer :

Final answer:

Peter and Rosemary Grant documented natural selection in Galapagos finches, where drought favored larger beaks able to eat hard seeds, increasing average beak size, while an El Niño event favored smaller beaks, shifting the population towards a smaller average beak size.

Explanation:

An example of natural selection involving beak size in Galapagos finches is the study conducted by Peter and Rosemary Grant on the Galápagos island of Daphne Major.

During a period after the 1977 drought, which affected the availability of seeds, large-billed birds that could eat larger, harder seeds had a survival advantage. As a result, the average beak size in the population increased within a span of two years, demonstrating evolution by natural selection due to environmental changes.

However, the situation can reverse. For instance, an El Niño event caused higher than normal rainfall, leading to an abundance of small soft seeds, favoring finches with smaller beaks.

This led to an increased survival rate of the small-beaked birds, causing a shift towards a smaller average beak size in the population. Both events underscore the inherent variability and responsiveness of finch beak size to environmental pressures, which is a cornerstone characteristic of natural selection.

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