Wednesday, March 05, 2008

How to Repopulate a World Without Men?

As I left, Lydia was explaining the difference between parthenogenesis (which is so easy that anyone can practice it) and what we do, which is the merging of ova. That is why Katy's baby looks like me.
~ Joanna Russ "When It Changed"
What would happen to the human race if the male half of the population vanished - taken by a Y chromosome-specific plague, culled by evil aliens, or killed in a tragic accident (not likely on Earth, but possible on a less populous colony world)? Would the remaining women simply let Homo sapiens die out? Of course not! We would use our ingenuity and mad biology skillz to make sure he human race survived. It would take a few years, though, because the technology isn't quite ready for large-scale single-sex reproduction yet.

The all-female world has been a feature in science fiction stories from Poul Anderson's 1959 novel Virgin Planet to the Brian Vaughan and Pia Guerra's recently concluded comic book series, Y: The Last Man. Most of the stories are vague on how reproduction takes place, but usually it's one of two methods: parthenogenesis or cloning. In the past, these methods were equally speculative. Today, however, recent advances in reproductive technologies are taking them from the realm of science fiction into the real world.

Cloning is the reproductive method of choice for many maleless worlds, in addition to making genetically-identical armies or labor forces. Human clones have been generated, but none have been allowed to develop beyond the stage that they could be implanted in a uterus. Ethical concerns make it unlikely that any adult human clones will be produced in the near future. Successful cloning of a number of non-human mammals - including sheep, cows, mice and cats - makes it likely that cloning humans would be technically feasible. There are problems with clones, though, including abnormal gene expression and possibly early aging. Even if those issues are overcome, a population maintained by cloning would lack the biological advantages of sexual reproduction.

So, what about parthenogenesis? In nature, parthenogenesis or development from an unfertilized egg, is rare in vertebrates other than a few species of lizards. Attempts at artificial parthenogenesis in mammals have been almost completely unsuccessful. This is thought to be due to the necessity of genomic imprinting, which causes genes inherited from the mother and father to be expressed differently in the developing fetus. In 2004, a lab in Japan created a single fatherless mutant mouse that lived to adulthood (Kono et al., Nature 428:860-4 (2004)). As a contemporary article notes, the process they used is too inefficient to be used for human reproduction.
Whilst the idea of extending this sort of experimental technique to humans is likely to be eagerly seized upon by some (suggesting, for instance, that it might be used by two homosexual women to create a child genetically related to both of them), in reality such applications would not be feasible. Of 457 mouse embryos created, only one has survived to adulthood, showing that imprinting is not easily bypassed; the laborious procedure is far too unsafe to use for humans and would also be widely considered unethical.
I suspect that further experimentation could eventually overcome the technical obstacles and both improve the success rate, and get parthenogenesis working in mammals besides mice.

The other advantage, as the quote hints, is that artificially-induced mammalian parthenogenesis uses two eggs, allowing the variation of sexual reproduction. Novels that include that are Joanna Russ's The Female Man (1975), which is set on the same world of Whileaway as "When it Changed", Leona Gom's The Y Chromosome (1990), and Nicola Griffith's Ammonite (1994).


Recent work from the laboratory of Karim Nayernia at the University of Newcastle suggests a slightly different approach. He claims that his lab has generated primitive sperm cells from female embryonic stem cells, with the ultimate goal the generation of functioning sperm cells from female bone marrow. His work is in the preliminary stages - the latest results were announced to the press without any accompanying publication - and other scientists are skeptical.

However, Dr Robin Lovell-Badge, a stem cell and sex determination expert at the National Institute for Medical Research, Mill Hill, London, doubts it will work: “The presence of two X chromosomes is incompatible with this. Moreover they need genes from the Y chromosome to go through meiosis. So they are at least double-damned.”

I think that research like this - in the realm of the scientifically almost-but-not-quite-impossible - could be the interesting basis of a science fiction story.

More reading:
Image: "Image depicting in vitro fertilization of an egg in a process similar to the one researchers used to fertilize mouse embryos with the sperm-like cells."

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1 comment:

Athena Andreadis said...

There are also Joan Slonczewski's Sharers in A Door into Ocean.

Making sperm from female bone marrow should theoretically work, if they can make the cells haploid.

It will be interesting to see what happens with the excess mitochondria, normally inherited only from the maternal line. On the other hand, if cell physiology affects imprinting, they will have to pare these cells down so that they do resemble sperm.