In stabilizing selection, the fitness of individuals is greatest when they possess:

In stabilizing selection, the fitness of individuals is greatest when they possess intermediate trait values. This phenomenon occurs because stabilizing selection favors traits that are well-suited to the environment, which typically means moderate or average traits. Populations that exhibit extreme trait values, whether they are at the high or low end of the spectrum, are less likely to survive and reproduce successfully because they may be less adaptable to varying environmental conditions. For example, in a species of birds, individuals with average-sized beaks might be best suited to access the type of food available in their habitat, while those with very large or very small beaks may struggle.

Conversely, trait variability does not directly contribute to increased fitness in the context of stabilizing selection; rather, it is the consistency of specific advantageous traits that enhances survival. Additionally, dominant traits represent a genetic dominance in inheritance but do not inherently correlate with the fitness advantages emphasized in stabilizing selection. Thus, the focus on intermediate trait values accurately reflects the mechanism of stabilizing selection and its impact on evolutionary fitness over time.