Sexual selection occurs because there is a correlation between the gender of an individual and its parental investment in each offspring. By investing in the production of current offspring a parent will reduce the likelihood that it will be able to invest in future offspring. Costs can be the energetic demands of parenting, increased predation risk, etc. One important component of parental investment is the investment in gametes . This serves as one means of distinguishing the sexes.
Females are the sex with a large parental investment per gamete .
Example are eggs which have the nutrients to promote the development once fertilization occurs. This difference in investment in gametes has important consequences for how these resources are invested and hence how selection might act differently in the two sexes. Another important component of parental investment is parental care , care of the zygote after fertilization. The amount of parental care is also frequently quite different in males and females. In many species the female also cares for the young after they hatch.