Animal species

Animal species

Main articles: Animal sexuality and Mating system

Animal sexual behavior takes many different forms, even within the same species. Researchers have observed monogamy, promiscuity, sex between species, sexual arousal from objects or places, rape, necrophilia, sexual orientation (heterosexuality, homosexuality, bisexuality and situational sexual behaviour) and a range of other practices among animals other than humans. Related studies have noted diversity in sexed bodies and gendered behaviour, such as intersex and transgender animals.

The study of animal sexuality (and primate sexuality especially) is a rapidly developing field. It used to be believed that only humans and a handful of species performed sexual acts other than for procreation, and that animals' sexuality was instinctive and a simple response to the "right" stimulation (sight, scent). Current understanding is that many species believed monogamous have now been proven to be promiscuous or opportunistic in nature, a wide range of species appear to both masturbate and to use objects as tools to help them do so, in many species animals try to give and get sexual stimulation with others where procreation is not the aim, and homosexual behavior has now been observed among 1,500 species, and in 500 of those it is well documented.^{[citation needed]} A few species have particularly complex sex determination systems. Although two sexes is the official maximum, these complex species could reasonably be said to have 3, 4 or 5 sexually distinct phenotypes. For example:

• the clam shrimp Eulimnadia texana has no females, but two types of hermaphrodite and one male phenotype, a system call androdioecy.^[8]
• harvester ant genus Pogonomyrmex has two types of female and two types of male, with an acknowledged claim to these being considered as constituting at least three distinct sexes,^[9] or possibly four.^[10]
• the reptile tuatara might have four sexes^[11]
• Coprinus macrorhizus (Pers.) Rea might have three or four sexes^[12]
• Coprinus lagopus has four sexes^[13]
• A notable minority view regarding humans has been put forward by Anne Fausto-Sterling, who suggested various disorders of sexual development could be classified into an additional three human sexes.^[14][15] Despite mainstream opposition, including the Intersex Society of North America, Fausto-Sterling and others still maintain this view in current publications.
• Other species have exhibited evidence of 5 sexes^[16]