Christmas is upon us. While our minds may be focused on finishing up our shopping, the reason for this season (as my good Catholic aunts will remind me) is the birth of Jesus.
The fact that Jesus' mother Mary conceived him while remaining a virgin has long been part of Christian faith. No natural father. No sex. No sperm. Chalk it up as a miracle. Some people don't have "miracle" in their vocabulary, though, so we have to ask: "Are virgin births possible?"
You bet they are! There's actually a lot more "“ or less, really "“ to the birds and the bees than our parents told us.
Hot, Steamy Asexual Reproduction
Reproduction usually follows the same basic blueprint: Boy meets girl; sperm meets egg; congratulations, you have a baby.
Sometimes, though, there's no boy and there's no sperm. There's just a girl, an egg and eventually a baby. This virgin birth is called parthenogenesis (from Greek, meaning "virgin creation"), and it happens when an embryo develops by itself without fertilization of an ovum (egg cell).
The resulting baby is called a parthenogen, and because it results from the inheritance of only a single sex chromosome from the mother, it will always be female in animals where two like chromosomes determine the female sex (the XY sex-determination system), and always male in animals where two like chromosomes make for a male (the ZW sex-determination system, where WZ is female, ZZ is male and WW is inviable).
Scientists have found a number of animals that can reproduce this way, and have also figured out how to induce other animals to perform the trick. Some researchers have even tried to make it happen in humans.
In insects, parthenogenesis is common among honeybees. In a hive of domesticated honeybees, the queen bee is the only fertile female, but the female worker bees, through parthenogenesis, produce male drones to mate with the queen. Additionally, some parasitic bacteria can induce parthenogenesis in insects.
Marmorkrebs, a type of crayfish discovered only a decade ago, produce parthenogens that are genetically identical to their mother.
Fifteen species of whiptail lizard found in the American Southwest reproduce exclusively by parthenogenesis (populations are all female), but still exhibit mating behavior (including one female mounting another that is about to lay eggs) because the sexual behavioral stimulates maximum reproductive success.
The Komodo dragon, the sex of which is determined by the WZ system, has been observed to switch to sexual reproduction after parthenogenetic reproduction. Scientists think this helps the lizard colonize islands.
Several cases of parthenogenesis have been documented in sharks. In each case, pups were born in aquarium tanks that contained only female sharks. The parthenogenetic reproductions concern shark experts and conservationists because, while the population increases, genetic diversity decreases. Additionally, sharks have an XY sex-determination system, so female populations can only produce more females.
While there are no known cases of parthenogenesis occurring naturally in mammals in the wild, scientists have successfully induced it in rabbits, mice and monkeys. The resulting embryos ran into problems, however, because of biological phenomenon in mammals (and some flowering plants) known as genomic imprinting. During the formation of sperm and egg cells, certain genes necessary for embryo development are shut down by chemical marks, or imprints. Some of these imprints are in sperm, others are in the egg. All the key genes are there only when a sperm and an egg meet, so without paternally imprinted genes, a mammalian embryo created by parthenogenesis develops abnormally.
Virgin Birth in Humans?
Because of the problems stemming from genomic imprinting, research into human parthenogenesis isn't focused on reproductive therapy, but the production of embryonic stem cells for medical treatment. Last year, Dr. Elena Revazova and her research team at International Stem Cell Corporation produced the first intentional human stem cells from unfertilized human eggs through parthenogenesis. Intentional is the key word there, because before ISC's achievement, Hwang Woo-Suk, who famously fabricated the results of his attempt to extract stem cells from cloned human embryos, unknowingly produced the first human embryos from parthenogenesis.
Stem cells are one thing, but a bouncing baby is another. Could a human naturally be produced by virgin birth? In theory, yes, if a number of biochemical events occur by chance or genetic defect in close succession and the egg doesn't complete meiosis (when an egg does this, it loses half of its genetic material to make room for the paternal DNA in the sperm. But without the sperm, each half of the divided egg would come up short on genetic material). The chances of all that happening are almost zero. But even if nature found a way, we run into genomic imprinting again, so we wouldn't wind up with a viable embryo.
There is one documented case of a natural half-parthenogenetic birth. In 1995, Nature Genetics reported a child that had some cells (about 50%) that consisted of genetic material only from his mother and some that were normal and consisted of a DNA from both parents. Doctors who studied the child theorized that one of the mother's eggs that had been fertilized by the father fused with an unfertilized egg that was dividing parthogenetically.
Might Jesus been a biological one-in-a-billion like that kid? Not according to Christian belief, which holds that the virgin birth of Jesus was not parthenogenesis, but strictly miraculous and not explainable by science as a natural process.