Which type of selection indicates that individuals with intermediate trait values have the highest fitness?

Stabilizing selection is the process that favors individuals with intermediate trait values over those with extreme values. This form of selection typically occurs in stable environments where the average phenotype has a selective advantage. For example, in a population of birds, those with an average body size might possess the optimal traits for survival and reproduction, such as better foraging efficiency or enhanced thermoregulation, compared to very small or very large individuals that may face disadvantages related to their size.

In populations experiencing stabilizing selection, the extremes are selected against, leading to a decrease in the variance of the trait over generations as the average phenotype becomes more prevalent. This mechanism helps maintain the existing traits within a population, reinforcing the idea that intermediate traits confer the best fitness benefits in a consistent environment. The focus on maintaining a balance in traits through stabilizing selection contrasts with other forms of selection, where the fitness landscape encourages shifts toward extremes or specific adaptive traits.