Biological Sex Categories

A cave insect species has a role reversal in which the egg-producing individual has a penis-like structure and inserts it into the sperm-producing individual's vagina-like structure. Animal biology demonstrates that a male does not necessarily have a penis, and having a penis does not make an animal male. Animal biology does not consistently fit a two-sex binary; some animals show continua of structures and behaviors that humans label masculine or feminine. Some genetically female pigs in Vanuatu naturally develop structures typically associated with males, showing that these structures are not strictly male. Some reptiles and fish can reproduce through parthenogenesis without sperm, as demonstrated by a zoo anaconda that produced offspring without a male present.