By Vidya Rajan, Columnist, The Times
December seems a good time of year to bring up the topic of virgin births. Religion aside, this is actually an interesting and significant biological topic. Curiously, virgin births have been documented in all vertebrates with jaws with the exception of mammals. To be clear, the majority of organisms on this planet – single celled bacteria and protists – normally demonstrate virgin birth. Dramatically, each organism cleaves itself into two, and each goes on its merry way. There is no sex that occurs before the production of such offspring. Then there is the complication that the majority of life’s forms are neither male or female, some are hermaphrodites (like plants and most worms and many fish). Some fish conveniently change genders. Some test the imagination – the everyday baking yeast has 2000 dissimilar mating types. When “sex” or the fusion of nuclei from two genetically different individuals does happen, it is not dramatic and involves a cytoplasmic bridge being made between two individuals whose nuclei fuse and then divide into new individual offspring. But this is such a big subject I am going to stop there and move on to what we actually mean when we talk of “virgin births”.
What we mean by the term is the unusual situation where a female who is not known to have engaged in sexual intercourse shows up pregnant. Many of us who like to cook have sliced open a bell pepper and found a second, developing, pepper inside, or a seed in an apple that appears to be germinating. People seem to accept plants as more primitive than animals, such that such occurrences are acceptable. (It might surprise you then to know that animals are evolutionarily about 300 million years older than plants as a group.) Many plants also are hermaphroditic, with both male and female sexual parts, and it is only the biologically uninformed that don’t know this is the case for many animals as well. Sufficiently isolated, many animals can quite happily mate with themselves, a condition termed parthenogenesis, specifically automixis. Typically out-crossing is preferred because it leads to more genetic diversity and better future outcomes for coming generations. In-breeding is not a good evolutionary decision.
Although queen honeybees and other bees appear to lay eggs in the absence of a male, the uninitiated do not know that the queen stores sperm from drones in her body for application when diploid workers eggs are produced, but not when haploid drone eggs are produced. This mechanism is called haplodiploidy. By contrast, female Cape honeybees – both queens and workers – from South Africa can undergo parthenogenesis by a process called thelytoky in the absence of males. The gene for thelytoky is controlled by the presence in the queen/worker of the same gene (homozygous condition.) But these autonomously replicating females are spreading – to other bee colonies where, like the brood-parasitic cuckoo bird, lay eggs for the host hive to raise. But, unlike the cuckoo, these fertile workers also live off the foraging of the host colony, but do not participate in the foraging. A bit like drones, I guess. Then the host colony, stressed by additional mouths to feed dies off and the Cape honeybees fly off looking for other hives to support them.[1]
Animals, like the Caucasian rock lizard in the genus Darevskia, many geckos, and whiptail lizards in the genus Aspidoscelis from the southwestern United States, all of which are not hermaphroditic, have survived quite happily without any males ever being born in their society generation upon generation.[2] Even in this complete absence of males, the female babies that result do have some genetic diversity. This is because in ALL animals, the diploid cell determined to become an egg actually divides into 4 genetically dis-similar gamete cells by a process called meiosis. Only one survives to become the egg, and the other three become tiny polar bodies, which more or less resemble what sperm are – genetic packets without much cytoplasm. One of those three polar bodies fuses with the egg – the process of automixis mentioned above – and the zygote then develops normally. However the embryo’s genome is dissimilar to the mother’s. There is a laundry-list of snakes,[3] lizards, fish (including sharks)[4] with parthenogenetic development. There are still questions about how specific types of parthenogenesis occurs, so more research is needed.
Back in 2018, a lady crocodile who had been living alone in a Costa Rican zoo laid a clutch of eggs.[5] Thing is, this was a long-time solitary lady. Being located in a zoo, the ingress and egress of potential suitors was somewhat complicated, given that crocodiles cannot fly. So…she laid eggs. And one of the eggs had an embryo in it. Sadly, it did not survive to hatch out, but it still it was a surprise to the zookeepers. Similarly, at the Omaha Henry Doorly Zoo in Nebraska in December 2001, a bonnet shark which was placed with two other females gave birth to the surprise of the staff. Sadly, the baby did not live long. Considering the size of the ocean (fish and crocodiles) or expanse of desert (snakes and lizards), and the low probability of coming across a suitable mate, particularly for solitary species, it is not really surprising that evolution has provided a mechanism for persistence of the species. Had it not been for the fact that these individuals had been known to not have mated, it would not have even come to light.
Going back to religion, not just Christianity, but many other belief systems (some now obsolete), have a parthenogenetic event in their mythology.[6] This includes the following: The Babylonian belief resulting in the birth of Madruk, as well as many other events within the Babylonian mythology; The Hittite mythology of the birth of Kumarbi (which has the explanatory foreshadowing where the mother of Kumarbi bites off the genitals of Anu, another god after defeating him), and apparently itself foreshadowing the mythology of the Greek god Uranus’s castration and the birth of Aphrodite); The conception of Horus by Isis in Egyptian mythology; The birth of the Egyptian Pharoah Queen Hatshetpsut (who was unusually a woman Pharaoh and probably needed to have something to elevate her as exceptional and so devised her mother, Queen Ahmose being impregnated by the god Amun); The Hindu mythology of the birth of Krishna by immaculate conception by his mother Devaki; The birth of the heroic twins Hunahpu and Xbalanque from the spittle of their decapitated father landing on his mother’s hand; The birth of Isaac from the aged Sarah who was infertile due to her old age…frankly there are so many stories I will leave you to read the rest of the stories for yourself 6 or this paragraph will be three pages long.
Life does find a way. Mythology then elevates it.
References:
[1]. Wikipedia. (2023). Cape honey bee. [online] Available at: https://en.wikipedia.org/wiki/Cape_honey_bee [Accessed 18 November 2023]
[2]. Wikipedia Contributors. (2019, March 10). Parthenogenesis in squamata. Wikipedia; Wikimedia Foundation.
https://en.wikipedia.org/wiki/Parthenogenesis_in_squamata [Accessed 18 November 2023]
[3]. Booth, W. and Schuett, G.W. (2015). The emerging phylogenetic pattern of parthenogenesis in snakes. Biological Journal of the Linnean Society, [online] 118(2), pp.172–186. doi:https://doi.org/10.1111/bij.12744
[4]. Holtcamp, W., 2009. Lone parents: parthenogenesis in sharks. BioScience, 59(7), pp.546-550. https://doi.org/10.1525/bio.2009.59.7.3
[5]. Greenwood, V. (2023). Scientists Discover a Virgin Birth in a Crocodile. The New York Times. [online] 6 Jun. Available at: https://www.nytimes.com/2023/06/06/science/crocodile-virgin-birth-parthenogenesis.html
[6]. Wikipedia Contributors (2019). Miraculous births. [online] Wikipedia. Available at: https://en.wikipedia.org/wiki/Miraculous_births [Accessed 18 November 2023]
