Parthenogenesis or Virgin Birth

Parthenogenesis (from the Greek παρθένος parthenos, "virgin", + γένεσις genesis, "birth") is a form of asexual reproduction found in females, where growth and development of embryos occurs without fertilization by a male. It is a form of reproduction in which the ovum develops into a new individual without fertilization by a male.

Parthenogenesis occurs naturally in some invertebrate animal species (e.g. water fleas, aphids, nematodes, some bees, some Phasmida, some scorpion species, and parasitic wasps) and some vertebrates (e.g. some reptiles, fish, and very rarely birds and sharks). Komodo dragons and the hammerhead- and blacktip sharks have recently been added to the list of vertebrates that exhibit differing forms of asexual reproduction.

The phenomenon of parthenogenesis was discovered in the 18th century by Charles Bonnet. In 1900, Jacques Loeb accomplished the first clear case of artificial parthenogenesis when he pricked unfertilized frog eggs with a needle and found that in some cases normal embryonic development ensued. Artificial parthenogenesis has since been achieved in almost all major groups of animals, although it usually results in incomplete and abnormal development. Numerous mechanical and chemical agents have been used to stimulate unfertilized eggs. In 1936, Gregory Pincus induced parthenogenesis in mammalian (rabbit) eggs by temperature change and chemical agents. No successful experiments with human parthenogenesis have been reported.

Parthenogenesis has been studied extensively in the New Mexico whiptail, of which 15 species reproduce exclusively by parthenogenesis. These lizards live in the dry and sometimes harsh climate of the south-western United States and northern Mexico.

A parthenogenetic baby Komodo dragon, Chester Zoo, England

Recently, the Komodo dragon, which normally reproduces sexually, was found also to be able to reproduce asexually by parthenogenesis. A Komodo dragon at London Zoo named Sungai laid a clutch of eggs in late 2005 after being separated from male company for more than two years. Scientists initially assumed that she had been able to store On December 20, 2006, it was reported that Flora, a captive Komodo dragon living in the Chester Zoo in England, was the second known Komodo dragon to have laid unfertilized eggs: she laid 11 eggs, and 7 of them hatched, all of them male. Scientists at Liverpool University in England performed genetic tests on three eggs that collapsed after being moved to an incubator, and verified that Flora had never been in physical contact with a male dragon. After Flora's eggs' condition had been discovered, testing showed that Sungai's eggs were also produced without outside fertilization.

A bonnethead, a type of small hammerhead shark, was found to have produced a pup, born live on 14 December 2001 at Henry Doorly Zoo in Nebraska, in a tank containing three female hammerheads, but no males. The pup was thought to have been conceived through parthenogenic method.

It has been hypothesized that this reproductive adaptation allows a single female to enter an isolated ecological niche and by parthenogenesis produce male offspring, thereby establishing a sexually reproducing population. Despite the advantages of such an adaptation, zoos are cautioned that parthenogenesis may be detrimental to genetic diversity.