A hermaphrodite is any organism with both male and female reproductive organs which produce both male gametes (sperm) and female gametes (ova). In some animals, the simultaneous hermaphrodites, both male and female organs are functional at the same time. In other animals, the sequential hermaphrodites, one sex develops at one time, which later develops into the other sex. Examples of both strategies are found naturally, especially in invertebrates, and for many creatures, hermaphrodism is the only method of reproduction.

True hermaphroditic humans do not exist, but pseudohermaphrodism does, where an individual has both male and female external genital organs, sometimes at the same time. Female embryos exposed to high levels of androgens (the male hormones) develop female internal reproductive organs but male external genitalia. Alternately, genetic defects cause children to be born with female external genital organs, which change at puberty, with the development of a penis and...