Immaculate Conception in Nature
“The Birds and the Bees”. We all know it as a euphemism for baby-making between members of the opposite sex. But, did you know that both female birds and bees are capable of reproducing without a baby-daddy altogether? A phenomenon known as parthenogenesis gives “single mum” a new meaning.
What in the world is parthenogenesis?
Derived from the greek words parthenos and genesis, meaning “virgin” and “creation”, parthenogenesis is the naturally-occurring phenomenon by which a female is able to produce offspring independently of a male counterpart. More technically, it refers to the development of an embryo from an unfertilised egg.
While parthenogenesis, a.k.a. “virgin birth”, might seem miraculous, it’s actually common as dirt in nature. Indeed, some 2000 species are capable of doing it, including snakes, ants, turkeys, chickens, amphibians, Komodo dragons, and sharks.
That’s right, even your Christmas lunch can do it.
The Komodo Dragon by Adhi Rachdian via Flickr
Go on then, how is this possible?
Eggs and sperm are produced by a special process called meiosis, which makes them genetically unique from their parents. In general, these reproductive cells are “haploid”. In other words, they each carry only half the genetic material of an adult and form a full set during fertilisation.
In parthenogenesis, however, a haploid egg can either double its own genetic material, or fuse with another egg to form an embryo with a complete suite of genetic information.
But wait, there’s more…
There are multiple mechanisms of virgin birth which have evolved independently across different organisms. In some animals, like bees, adults can exist as haploids. In other animals, such as crayfish, embryos don’t have to come from eggs, and can just be identical genetic clones of their mother.
Why does parthenogenesis exist in nature?
While some species only reproduce by parthenogenesis, other nifty organisms are capable of switching between regular sexual reproduction and parthenogenesis. In aphids and crustaceans, this switch is triggered by a change in season and favourable growth conditions. Komodo dragons and snakes change tack when male suitors are lacking.
Is this possible in mammals?
The egg-laying animals that can partake in solo conception don’t have to worry about genomic imprinting, chemical modifications to genes which cause them to act differently depending on which parent they’ve come from. Without a copy from mum and a copy from dad, mammalian development is out of kilter and doesn’t happen normally.
However, on 11 October 2018, researchers from the Chinese Academy of Sciences chemically induced parthenogenesis in mouse eggs. Haploid stem cells were then collected from the activated, dividing eggs. By deleting problematic imprinted genes, the scientists were able to fuse two haploid stem cells from two different female mice to bring to life 29 live pups. Astoundingly, these pups went onto mate with male mice and have pups of their own.
This female mouse was born of two mums, and is pictured here with pups of her own. Photo by Leyun Wang via Nature.
Can same-sex couples have biological kids then?
Only if they are female and also mice! While this research has helped us to understand how imprinted genes affect embryo development, this nascent technology is still far from use in humans, and raises valid safety and ethical concerns.
The 29 pups that were healthy came from an original pool of 210 embryos – that’s a 14% success rate. Pups from two mums can genetically only be female. Meanwhile, pups from two dads died within 48 hrs of birth because of more complicated imprinting issues. There are additional concerns about the long-term effects of deleting imprinted genes on the health of these engineered mice.
While artificial parthenogenesis has provided invaluable insight into developmental biology, we should keep in mind that it is a natural phenomenon that has been perfected through evolution over millennia and not be too hasty in recreating it.