Why choose?
An old male has lived long and survived life's pitfalls. Thus, he should have good genes that grant him good health. By choosing him, the hen provides her offspring with good genes, and, thereby, good fitness.
Right or wrong
Thus, hens make good choices among the courting cocks. Why is that? A hen that selects the right cock gives her daughters the ability to choose a good mating partner, if this ability is inherited.
Heritage and selection
A character that is inheritable and gives the bearer a high fitness will be transferred to many individuals in the next generation. After many generations, most individuals will have acquired the character. Through this natural process, the character has been "selected" and spread among the individuals.Scientists call this course of events "evolution by natural selection".
