The differing parental investment between males and females together with the differing ease of confirming parentage both tend to encourage a mating preference in males for quantity and a mating preference in females for quality.

There are several reasons why females might find a preference for quantity beneficial. By mating with multiple males, a female can create confusion about the paternity of her offspring, encouraging several males to help feed her and her children. By having children with many males, instead of just one, a female gives her children greater genetic diversity and increases the likelihood of beneficial genetic traits. Also, there is some evidence that sperm may actually compete for egg fertilization, so by mating with multiple males, a female can create a situation where the "best" male is the parent of her child.