Exploring the Dynamics of Diversifying Selection- A Case Study in Evolutionary Adaptation

Which situation is an example of diversifying selection?

Diversifying selection, also known as disruptive selection, is a type of natural selection that favors the extreme phenotypes over the intermediate ones, leading to an increase in genetic diversity within a population. This process occurs when environmental conditions change, creating new selective pressures that favor individuals with traits at both ends of the phenotypic spectrum. One classic example of diversifying selection is the case of the Galápagos finches, as studied by Charles Darwin.

The Galápagos finches are a group of bird species that inhabit the Galápagos Islands. These finches exhibit significant variation in beak shape and size, which is closely linked to their feeding habits. During the 19th century, Charles Darwin observed that the finches on different islands had different beak shapes, which were adapted to the specific food sources available on each island. This observation provided strong evidence for diversifying selection.

Background and Context

The Galápagos Islands, located in the Pacific Ocean, consist of 13 major islands and numerous smaller islets. The climate and vegetation of these islands vary significantly, creating diverse habitats for various species. The finches on these islands are believed to have originated from a common ancestor that colonized the islands over millions of years. As a result, the finches on different islands have diverged genetically and phenotypically, leading to the formation of numerous species.

Environmental Changes and Diversifying Selection

One of the most notable examples of diversifying selection in the Galápagos finches is the case of the ground finch (Geospiza fortis). This species has experienced significant changes in its beak shape and size over the past century due to environmental fluctuations.

During the 1930s, a severe drought struck the Galápagos Islands, leading to a scarcity of large, hard seeds, which were the primary food source for the ground finches. The finches with smaller beaks were at a disadvantage, as they were unable to crack open the hard seeds. However, the finches with larger beaks were able to exploit the remaining food resources, leading to a higher survival rate and reproductive success.

As the drought subsided, the availability of large seeds increased. This change in environmental conditions favored the finches with smaller beaks, as they were more efficient at cracking open the seeds. Consequently, the population of finches with smaller beaks expanded, while the population of finches with larger beaks decreased.

Long-Term Consequences

The diversifying selection acting on the Galápagos finches has led to a remarkable increase in genetic diversity within the population. Over time, this genetic diversity has allowed the finches to adapt to various environmental conditions, ensuring their survival and reproductive success.

The case of the Galápagos finches is a powerful example of diversifying selection, illustrating how environmental changes can drive the evolution of species by favoring extreme phenotypes. This process has played a crucial role in the formation of new species and the maintenance of genetic diversity within populations.