Human quality control

Human reproduction is a highly uncertain business. Even trying hard, a woman may take many months to achieve pregnancy. Of her ova that manage to get fertilized, about 70% are likely to be miscarried — mostly so rapidly that she notices nothing but a missed or delayed period.

This, says Daedalus, shows evolution at work. Stable creatures like cats and cows can reproduce easily and unfailingly; but human beings are a recent and hasty evolutionary lash-up. Like a new generation of microprocessors, they push the state of the art so far that 100% yields cannot be expected. Flawed specimens are inevitable, and must be identified by rigorous quality-control tests. They are rejected rapidly, allowing their owner to try again.

So DREADCO biochemists are seeking to understand the ‘dialogue’ of tests between mother and fetus. It may be a strategic contest, like many other inter-generational genetic struggles; or it may be entirely honest. A set of genes trapped in a sub-standard fetus may prefer to be aborted, to give an identical set a better chance next time. One clue is that many drugs — among them alcohol, nicotine, caffeine and aminopterin — increase the spontaneous abortion rate. The conventional wisdom is that they may damage the fetus, so that it fails the mother's quality-control tests. On the other hand, they may sabotage the tests themselves, and trigger rejection by giving falsely low readings. Daedalus muses that they may even raise the tests' acceptance threshold. Mediocre fetuses, which might otherwise have just scraped an undistinguished pass, are then rejected; only the best are retained to term.

With luck, DREADCO's biochemical investigations and epidemiological studies will soon elucidate the testing process. Presumably the mother challenges the fetus with a chemical signal; the fetus releases, or fails to release, a competent hormonal response; and a chemical ‘reject’ signal triggers spontaneous abortion.

When identified, the ‘reject’ signal will be the ideal, natural, abortifacient. It will not damage the mother — evolution will have seen to that. It will be the perfect morning-after (or even month-after) contraceptive. And if it works by raising the acceptance level to some lofty peak of human perfection, then its occasional failure may be no bad thing. The mother will know that she is carrying an exceptional baby, well worth the inconvenience.


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Jones, D. Human quality control. Nature 393, 525 (1998). https://doi.org/10.1038/31119

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