Diversifying selection is responsible for this outcome.
c) Diversifying selection
Step-by-step explanation:
Diversifying selection is also known as Disruptive Selection that explains the changes in population genetics and favors individuals at both ends of the phenotypic spectrum. The diversifying selection causes increase in variance of the trait which led to division of the population into two distinct groups.
The disruptive selection helps in evolution of new species from the surviving inherited species. The disruptive selection causes organisms exhibiting intermediate traits to reproduce less, and organisms exhibiting extreme traits to reproduce more.