Field of Science

Humans are still evolving, especially right now

I had sworn that I would find time during my postdoc to blog as much as during my PhD. But I was wrong. So, for the first time ever on Pleiotropy, here's a repost of a post from February, 2009 - the month of Darwin's bicentennial. The question is one that I find interest many layman, namely whether humans are still evolving. Of course, what they mostly mean is whether we can expect to see significant morphological changes any time soon - wings, tails, x-ray vision. Probably not, but I would argue that if ever, this is the time to do it, because the larger a population is, the bigger the chance that mutations happen, and therefore the more genetic variation. Genetic variation leading to phenotypic changes is the stuff that natural selection acts on, so the fact that most people survive to reproduce actually means that evolution can happen faster. Just wait for the next big environmental change, and then we might see natural selection taking humans in a new direction.

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Yes, we are still evolving

On I learned that BBC has published a magazine celebrating Darwin's bicentennial. It's in the February issue of Focus, the BBC’s award-winning science and technology magazine.

Dawkins wrote the editorial, Carl Zimmer a piece on Rich Lenski, who studies the evolution of E. coli as it happens, among other things, someone wrote some stuff about artificial selection, and someone wrote about what we have learned since Darwin, and then... Then there's Steve Jones and PZ Myers, two "leading evolutionary biologists," who each give their answer to this question: "Has our species's evolution comes to a halt?" In other words, are humans still evolving? I don't know Steve Jones, Professor of Genetics and the University College London, in any other context (but see this older post on the same subject), but I am a frequent reader of Pharyngula. Neither professor is a leading evolutionary biologist. Jones is a geneticist, and PZ is a developmental biologist. It's a small quip, but since they are discussing evolution, perhaps it is worth taking into account.

Steve Jones says 'yes', and PZ says 'no'. Jones' answer is the controversial one. It is also the stupid one. He clearly does not understand evolution very well. Just trust me. Okay, don't trust me. Here's what he says and why it's wrong.

Jones' claim is that because mortality before the reproductive age has almost vanished, there is no selection going on in humans anymore, and as a result we are not evolving. He gives examples of men in the past who had hundreds of children while other men had none. This is selection: differential reproductive success.

Now, he says, variation in reproduction has all but disappeared. Most people have between zero and four offspring. Thus, he expounds, the variation that selection could favor among is gone, so we are done evolving.


First of all, zero or four offspring makes a big difference for evolution. In fact, if everyone had one child, except one man who had two (and his children had two each, etc.), then his lineage would soon dominate completely. Zero vs. four makes a huge difference.

Secondly, it is a common misunderstanding that natural selection is a prerequisite for evolution. It is not. All that's needed is heritability and variation. Neutral evolution due to random sampling will take care of the rest (also named genetic drift). Neutral evolution will result in a lot more variation in the (human) population compared to the case with selection. The effect of selection is to reduce variation within a population (but increase it between different populations), so as long as there is no selection, any genotype/phenotype is as good as the other and the population will become more and more diverse.

In humans today there is a great deal of neutral evolution going on, but selection obviously still has a large effect. Just think of genetic diseases. Cystic fibrosis, Tay-Sachs, and Huntington's disease are examples of horrible, heritable diseases, and the unfortunate people who have them are strongly selected against. Additionally, spontaneous abortions happen all the time, and it is likely that many of them are caused by deleterious mutations in the either one of the parents or in the fetus. Additionally, sexual selection may be at work. The more attractive specimens may in fact end up having more children. And then there's the fact that some groups of humans have more children than others (at the moment), such as the Quiverfull, the Congolese, and the Malagasy (source). Selection for reproductive strategy, as in 'the Lord tells me to keep churning them out.'

Another important point to make is that people have different things in mind when they think about evolution. For instance, recalling the notorious micro/macro-evolution dichotomy, in which microevolution is (merely) a change in allele frequencies, whereas macroevolution is speciation and the origination of new traits, such as exoskeletons, blindness, and telepathy. If you mean only the latter, then you might have a point, because right now we don't see these big changes in humans. No one seems to be getting new abilities X-men style or less.

Evolutionary biologists generally agree today that the micro/macro distinction is invalid, in the sense that they are not separated by different mechanisms. A lot of small changes in at the genomic level (micro) accumulates and can eventually result in significant morphological/physiological/anatomical changes and the birth of new species (macro). (Creationist will frequently make this distinction saying that microevolution is possible, but that macroevolution does not follow.) The problem is just that these things naturally take a very long time. 'Millions of years' is an oft quoted span of time necessary for such events (though there is recent evidence in other species that much, much less time is needed). Since humans live and have recorded their own history for a very, very short time compared to a million years, we should not expect to see major changes happen in our lifetimes. The fact that we then don't should not lead us to conclude that we aren't evolving. Have a little patience!

As for selection, it is an unstoppable process. PZ Myers nearly ends his essay in the Darwin 200 magazine thus:
Selection is a subtle force, and you cannot escape it.


  1. The timescale is the sticking point for me when people make the silly argument that human evolution is "done". Even if we buy that selection pressure has been essentially eliminated in the present (and there's strong evidence against this) (and it had not even occurred to me that, as you point out, removing selection pressure does not necessarily halt evolution anyway), then my question is, so what? Does anyone really assert with confidence that our civilization will be more or less the same in 100,000 years? 500,000? A million?

    Let's just say, hypothetically, that at some point in the distant past, a magical elf waved a magic wand and made evolution "stop" for 6000 years or so. We wouldn't have the slightest inkling. It would not show up in the fossil record. The species we see today would not be directly affected (I'm ignoring the fact that contingent events could create huge changes in the eventual outcome of evolution, butterfly/hurricane-style). A few thousand years just doesn't matter.

  2. Very true. Expecting visible human evolution on a time-scale we can expect to observe is silly, and that is really what some people mean when they ask that question. 6000 years is indeed nothing.


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