Final answer:
Sexually selected traits, like the bright plumage of male peacocks, can lead to increased reproductive isolation and fitness among sympatrically diverging populations.
Step-by-step explanation:
Secondary traits, such as sexually selected traits, can lead to increased reproductive isolation and ultimately increase the fitness of individuals among sympatrically diverging populations. This is because these secondary traits enable individuals to more effectively discriminate between potential mates of their own population and those of the other population.
A typical example of a sexually selected trait is the bright plumage of male peacocks, which is preferred by females of the species. If females of one population show a strong preference for bright plumage, while females of the other population do not, this can lead to reduced interbreeding and increased reproductive isolation.
Over time, this can result in the evolution of distinct populations with higher fitness within their own respective environments.