In a population of birds on an island, the average beak size reduced over one generation. A researcher estimated the association between beak size and relative fitness, shown in the graph. The estimated slope was \(-0.05\) with a 95% confidence interval of \(-0.15\) to \(0.09\).
Show Hint
Genetic drift can cause random changes in traits, especially in small populations, leading to changes such as a reduction in beak size.
Step 1: Understand the context of the graph.
The graph shows a negative association between beak size and relative fitness, meaning that smaller beak sizes may confer higher fitness. The slope of \(-0.05\) indicates a weak negative correlation, but with a confidence interval that includes zero, suggesting the effect could be small or negligible.
Step 2: Evaluate the evolutionary processes.
Option (A): Genetic drift is the most likely cause of the observed reduction in beak size. Genetic drift can lead to random changes in traits, including a decrease in beak size, especially in small populations.
Option (B): Group selection is not a likely explanation in this context, as the focus is on individual fitness rather than the group level.
Option (C): Kin selection could involve relatedness but does not directly explain the observed reduction in beak size.
Option (D): Natural selection would typically result in an adaptive change in beak size, but the confidence interval suggests the reduction might not be strongly linked to fitness, making genetic drift more likely.
Hence, the correct answer is (A).
