Now that Christmas is just around the corner, thoughts inevitably turn to an expectant Mary in the stable. However, she is not alone in the sphere of life-giving without the involvement of both sexes. In the animal kingdom, there are many species that engage in immaculate conception.
What we refer to as virgin birth means that an unfertilized egg can develop into a new individual. The technical term for this reproductive phenomenon is parthenogenesis. Almost all types of animals - with the notable exception of mammals - have species that can reproduce asexually through parthenogenesis: insects, crustaceans, spiders, fish, amphibians, reptiles, and even birds.
"There are pros and cons to asexuality. Reproduction is faster and no energy is wasted on unnecessary males, but because all individuals of the same clone are genetically identical, there is a reduced ability to adapt. This means a higher risk of accumulating harmful mutations over time," says Jessica Abbott, evolutionary biologist at Lund University.
In the animal kingdom, there are several different variations of virgin birth that yield different results. Asexual, virgin turkeys are not uncommon. However, their eggs can only produce males, which thus creates an evolutionary dead end. Aphids and water fleas alternate between sexual and asexual reproduction depending on the season.
"Wasps use virgin birth to produce sons. The females have two sets of chromosomes, which is normal for all animals, while the males only have one set, indicating that they are produced from unfertilized eggs," explains Jessica Abbott.
Among mammals, there are no examples of spontaneous virgin birth. However, Chinese researchers have recently succeeded in having mice reproduce through parthenogenesis. This was done artificially by reprogramming the genetic material in a polar body - a type of cell produced during egg cell formation - to resemble the genetic material of a sperm cell. The polar body was then able to fertilize the egg cell, allowing the creation of an embryo with only one parent.
"The cloning of the sheep Dolly can also be seen as a step towards virgin birth in mammals. A cell nucleus was taken from a skin cell of an adult individual and inserted into an egg cell from which the nucleus had been removed. Dolly was then a clone of the donor, like a twin born much later," says Jessica Abbott.
If we consider the genetic leap to humans, is there any chance that women in the future could give birth without the involvement of the opposite sex?
"It's incredibly unlikely. Even if the egg cell is not fertilized, a sperm cell is still needed for it to divide. And that's not something that happens on its own. There are examples of salamanders and fish that mate with males from a closely related species just to trigger cell division and then discard the sperm. But for this to happen spontaneously in humans is extremely unlikely," concludes Jessica Abbott.
