Humans are the only primate species in which mammary glands (breasts) remain large and prominent throughout adulthood. other primates’ mammary glands swell only when they are nursing offspring; scientists are not sure why human females have noticeable breasts on a permanent basis. one hypothesis is that they increase a female’s ability to attract mates. if so, this would be an example of a trait favored by…?

Sexual selection.

Explanation:

Natural selection may be defined as the reproduction of individuals and survival reproduction due to difference in their phenotype. Natural selection acts as the main driving force for evolution.

Sexual selection is one of the mode of the natural selection in which one species develop attracting characters that helps in the process of breeding. The human females breast size has been developed in such a way that attract its mate and provides the example of sexual selection.

Thus, the answer is sexual selection.