It appears that the most common method of mate selection has been by arrangement. Typically, the parents, often with the aid of certain relatives or professional matchmakers, have chosen the spouse for their child. This form of mate choice is more common when extended kin groups are strong and important.

What is the main underlying factor for mate selection?

There are two general circumstances leading to sexual selection. One is the preference shown by one sex (often the females) for individuals of the other sex that exhibit certain traits. The other is increased strength (usually among the males) that yields greater success in securing mates.

What is a good example of intrasexual selection?

Intrasexual selection, on the other hand, occurs between members of the same sex. For example, male sea lions compete for dominance over rookeries of females. Here, intrasexual selection acts on the physiology of the sea lion, to make it large enough to compete with other males for a group of females.