About Rationally Speaking

Rationally Speaking is a blog maintained by Prof. Massimo Pigliucci, a philosopher at the City University of New York. The blog reflects the Enlightenment figure Marquis de Condorcet's idea of what a public intellectual (yes, we know, that's such a bad word) ought to be: someone who devotes himself to "the tracking down of prejudices in the hiding places where priests, the schools, the government, and all long-established institutions had gathered and protected them." You're welcome. Please notice that the contents of this blog can be reprinted under the standard Creative Commons license.

Wednesday, October 15, 2008

Is human evolution over? Nah.

A recent article in the Times (of London) quotes Steve Jones, a renowned geneticist author of Darwin’s Ghost (nothing less than an updated version of Darwin’s Origin of Species), as saying “Human evolution is over. Quite unexpectedly, we have dropped the human mutation rate because of a change in reproductive patterns.” What’s he talking about?

Jones maintains that older men (35+) contribute most of the new mutations entering the human gene pool, and those people ain’t reproducing as they used to. Really? Perhaps Jones has forgotten that for most of human history people were highly unlikely to live to, let alone reproduce, at that old age (by Pleistocene standards). Besides, what are we to make of cultural trends (in Western societies) that postpone reproduction for both men and women?

Well, Jones says, “In the old days, you would find one powerful man having hundreds of children,” citing the example of Moulay Ismail from 18th century Morocco who (allegedly) copulated with an average of 1.2 women per day for a straight 60 years (without Viagra), thereby producing a whopping 888 children (nicely symmetric number, which probably doesn’t take into account the human tendency for exaggeration and the likely fact that some of Ismail’s concubines were having, shall we say, side jobs). At any rate, these “old days” are just not old enough to be evolutionarily relevant. The appropriate time frame, again, is pre-agricultural time, when most of human evolution took place. And in those old days there simply wasn’t enough food to go around for a single man to maintain dozens of sexual partners and their offspring.

“In ancient times” continues Jones in the Times interview, “half our children could have died by the age of 20. Now, in the Western world, 98 per cent of them are surviving to 21.” The key words here, of course, are “in the Western world,” as infant and child mortality (and hence the opportunity for natural selection to do its work) are still astronomically high outside of Western societies (and a few others, like Japan). Besides, here is an area where I’m going to be glad that natural selection has a little less wiggle room than it would have without modern medicine.

Finally, Jones complains that human populations have become too large (certainly true from the point of view of our environmental impact) and interbreed too much (I will refrain from engaging in ethnic jokes by pointing out that only a Brit could complain about too much sex. Oh, darn, I just did engage in an ethnic joke). The problem here is that this reduces the relevance of the chance factor in evolution, which is associated with random fluctuations in gene frequencies in very small populations. But human populations have probably very rarely been small enough for so-called genetic drift to have a major effect, and Jones seems to be forgetting that the flip side of that coin is that large populations carry more genetic variation, and are thereby better suited to respond to selection.

As for the last comment in the published interview: “History is made in bed, but nowadays the beds are getting closer together. We are mixing into a global mass, and the future is brown.” As in: we will all look the same, because biologically based ethnic differences will be erased by worldwide interbreeding. Well, to begin with, this is just not happening quickly enough for my taste. Talk about a truly color-blind society that would result from it! Second, I’m sure the human ability to arbitrarily define in-group and out-group membership, thereby continuing the self-destructive “us-vs-them” attitude that has characterized us since “the old days” isn’t going to be halted by a simple quirk of demography.


  1. I have been wondering if our "modern" monogamous lifestyle and family planning practices do have an effect in the human evolution. I mean it's not that people are having less sexual contact, but with various contraceptives available we certainly don't go around making as many babies as we would have 10,000 years ago.

    That's not a statement by the way, I am in no way qualified to do that. But it is more of a question. It kind of makes sense that changes in lifestyle and sexual practices would have an effect on evolution, maybe even slowing it down, or maybe not, maybe it just steers it in a different direction, just like the "all brown" example from this entry shows.

    But evolution stopping because less 35 year olds are making babies. Nah, I don't buy that either.

  2. "..but with various contraceptives available we certainly don't go around making as many babies as we would have 10,000 years ago."

    Actually, a foraging subsistence lifeway and a lack of long-term sedentism, the dominant human condition 10,000 years ago, also put some pretty severe limits on making babies also. Remember, population growth didn't really take off until after agriculture and sedentism.

  3. I sure hope human evolution isn't over - I'd hate to think that we're stuck with people like Sarah Palin representing the spex of our species' growth.

  4. Dear Dr Pigliucci, I was upset at having missed your post as it came out 5 days ago (my fault). A few months ago I started a thread in the SGU forum (and did not follow up in my blog for lack of knowledge, I am not a biologist) about how natural selection has been stopped by the human race. I don't think we are done evolving, just that we are cheating the natural mechanisms that ensure survival of the fittest. Not to pin the blame on anyone else, I should not be alive anymore - I had apendicites at 17 and had my appendix removed. Had I been living in a pre-industrial society I would have probably died and my children would not have been born, which would have effectively eliminated my genes from the pool, if not my father's. And then, look at how many births are now caesarean sections, how many of those children and mothers would have died if not for the surgical procedure?
    The point is that many people living and reproducing today are doing so because we have ensured not only the fittest survive but also many others who were not "so fit". My question is, what is this all leading to?

  5. Zarek,

    yes, what you say is correct, which means that human technology has been altering selective pressures, in some cases dramatically reducing them. What this means is that we are gradually taking control of our own evolutionary path. This still does not imply, as Jones maintains, that human evolution has stopped.


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