structural:scholar_edition
Sex determination

The sex of a particular organism may be determined by a number of factors. These may be genetic or environmental, or may naturally change during the course of an organism's life. Although most species have only two sexes (either male or female), hermaphroditic animals, such as worms, have both male and female reproductive organs.

Not all species share a common sex-determination system. In most animals, including humans, sex is determined genetically; however, species such as Cymothoa exigua change sex depending on the number of females present in the vicinity.