In directional selection, the highest fitness is associated with:

In directional selection, the highest fitness is indeed associated with extreme trait values at one end of the spectrum. This type of natural selection occurs when individuals at one extreme of a trait distribution have greater reproductive success than those at the average or the other extreme. As a result, over time, the population's trait distribution shifts in the direction of that extreme, favoring those individuals with the advantageous trait.

For example, if we consider a population of bears where larger size provides an advantage in terms of survival and reproduction due to competition for food or mates, directional selection would favor larger bears. This leads to an increase in the frequency of larger size in subsequent generations.

This process contrasts with stabilizing selection, which favors intermediate trait values and reduces variation around a mean, or disruptive selection, which favors extremes at both ends of the spectrum while selecting against the average trait. Directional selection emphasizes one end, reinforcing the traits found in that extreme, which drives evolutionary change in a specific direction.