A Genetic Need for Sex?

Different fare at the LA Times this morning. The gist: sexual procreation helps us beat disease. Excerpts:

Lots of living things reproduce by parthenogenesis (the development of unfertilized eggs) or simply by sending out shoots or buds. Not only does asexual reproduction avoid the many direct hassles of sex – the need to find a suitable mate, the time and effort of courtship, the risk of being injured or infected during the act – it also gets around a huge genetic drawback: Genes within a sexually reproducing creature enjoy only a 50% chance that they will be transmitted to any given offspring, whereas asexual reproduction guarantees that each gene has a 100% certainty of being projected into the future. And projecting genes into the future is what evolution is all about.

This 50% cost imposed by sexual reproduction had long troubled evolutionary scientists. Until, that is, British biologist William D. Hamilton came up with the idea that sexual reproduction might be a tactic in an evolutionary arms race between hosts and their diseases. . .

[T]here are many more of them (pathogens and parasites) than us (free-living organisms). After all, every multicellular critter is home to thousands, often millions, of internal free-loaders. Considering just one group of worms, invertebrate biologist Ralph Buchsbaum has suggested that "if all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable. Trees would still stand in ghostly rows representing our streets and highways. The location of the various plants and animals would still be decipherable."

Nematodes and all the rest seek to live at our expense; we, in turn, seek to thwart them. If we, the unwitting and unwilling hosts, stay genetically the same from one generation to the next, then we are sitting ducks, easy targets for "them."

Enter sex. By mixing and matching our genes, sexually reproducing creatures bob and weave, creating new genetic combinations with every bout of reproduction, confounding – or at least challenging – our pathogens and parasites by creating moving targets instead of sitting ducks. Because of their generally short life spans, pathogens can evolve rapidly compared with ourselves; via the diversity-creating mechanism of sex, we level – somewhat – the evolutionary playing field. At least some bacteria, worms and viruses are unable to draw a bead on our descendants.

I don't know much about biology, but I wonder: What does this say about artificial insemination, test tube babies, and the rest? What does it say about single women who go to the sperm store and select the baby they want to have? Does all this planning, efficiency, and control mitigate the "mixing and matching," the "bob and weave"? Throughout history, the coupling of the genes was wholly random. Is that going to change as genetic screening improves more and more?

These are just questions; I don't know the answers. But I believe nature "will out." If we're meant to procreate in a fun way, all these attempts to bypass it will bite us at some point. Maybe this little LA Times op-ed shows us how the bite will happen.