Why are females often more selective than males when choosing mates?

In zoology, the tendency for females to be more selective than males regarding mates is primarily explained by the theory of differential parental investment.12

Because eggs are nutritionally more costly to produce than sperm, females typically make a higher initial investment in their offspring. In many species, this investment is further compounded by the demands of internal gestation and nursing. Consequently, females have more to lose from a poor mating choice and are incentivized to be more selective, often preferring males who demonstrate high fitness, provide resources, or offer direct parental care.12

This selectivity creates a conflict of interest, as males—who produce relatively inexpensive sperm—can often increase their reproductive success by mating with multiple females. This dynamic drives sexual selection, where males compete to prove their quality through displays, ornamentation, or strength to satisfy female preferences.123

While this pattern is common, it is not universal. In species where males provide the majority of parental care, such as certain pipefishes or phalaropes, sex-role reversals occur, and males become the more selective sex.12