Final answer:
The selection described, where a male develops a trait making him more attractive to females, is known as sexual selection, a form of natural selection affecting reproductive success. the correct option is b.) Sexual .
Step-by-step explanation:
The type of selection occurring when a male develops a trait making him a more attractive mate to females is sexual selection. This is a specific case of natural selection that impacts an individual's ability to mate and subsequently produce offspring, therefore influencing the evolutionary path of a species.
Sexual dimorphism often results from this type of selection, leading to distinct differences between males and females beyond just reproductive anatomy. In the case presented, females selecting males based on an attractive trait exemplifies intersexual selection, a component of sexual selection where the mate choice is a critical determinant of reproductive success.
In the case of the more attractive male mentioned in the question, the trait that makes him more attractive is being selected for by the females, contributing to the mating success of the male with the trait.