The popularized view is that hormones create and regulate an invariant sequence of biological reproduction characterized by the production of sperm and ova, followed by heterosexual mating behavior of two distinct sexes, followed by genetic cross fertilization, gestation or incubation. In fact, there are numerous exceptions to even the most fundamental assumptions about the basics of biological reproduction.
Reproduction does not require courtship or mating (physical joining), and for that matter, does not necessarily involve an exchange of the genetic material that is definitive of sexual reproduction. There are many species that thrive and function quite well by reproducing in an asexual format, that is, parthenogenesis. For example, in some hermaphroditic species such as earthworms and sea bass, individuals are both male and female, and simultaneously produce both egg and sperm (Crews, 1992). Other hermaphrodites, including many tropical reef fish, produce gametes in sequence, and are actually male and female individuals at respective times. Hermaphroditic species can be first male then female later in life (protan — drous), and others, as in many varieties of the teleost fishes, are protogyn — ous, being first female and subsequently male (Demski, 1987). Still other species are parthenogenic reproducers that do not rely on the genetic combination of sperm and ova, and all individuals in the species are female. For example, the Amazon Molly, a popular aquarium fish, engages in mating behavior with males from similar species who actually deposit sperm, but there is no genetic contribution of DNA from the donor males. Although the mere presence of sperm may be necessary for the development of the eggs, it is the social behavior associated with mating rituals that stimulates the reproductive biological cycle. Still other parthenogenic species, such as whiptail lizards, require no sperm at all (Crews, 1992).