Are Humans Still Evolving?

Of course. Sometimes, the idea pops up that the human species has stopped evolving because of better healthcare and its corollaries. But this is a serious misconception. For evolution (through natural selection, I’ll come back to this later) to occur, basically three things are needed:

1. Variation, (Check. Just look at the people around you.)
2. With a heritable component, (Check. Our environment matters. But so do our genes.)
3. And an effect on fitness (Check. Put simply, not everyone has children, and those who do, don’t have equal amounts of them. These differences can have their origin  in the above mentioned variation.)

What can we say, then? Human beings still evolve. Even through natural selection. Proof? Why, I’m glad you asked. A new study (Courtiol et al., 2012) presents evidence that natural selection could have occurred in a Finnish population of almost 6000 individuals born between 1760 – 1849. By analyzing a dataset obtained through church records, the researchers focused on four ‘targets’ for selection: survival to reproductive age, mate access (or, in this study, getting married), mating success (or, having kids), and fertility per mate (or having kids with more than one spouse). They found that most variation in fitness could be explained through individual differences in early survival and fertility. Furthermore, differences in mating success also contributed. Thus, plenty of opportunity for selection to take hold. Overall, results that, in the words of the authors:

… emphasize that  the demographic, cultural and technological changes of the last 10,000y did not preclude the potential for natural and sexual selection in our species.

However, that was a few centuries ago in a preindustrial community, you say? Indeed. A lot has changed since then. But we haven’t stopped evolving and natural selection hasn’t been abolished. A study conducted a few years ago (Byars et al., 2010) demonstrated natural selection in a contemporary human population in Massachusetts. Using data from the Framingham Heart Study, traits analyzed were total cholesterol, blood pressure (both systolic and diastolic) and blood glucose levels. And indeed, it was found that natural selection was causing slow, gradual evolutionary change. The traits showed variation, with a heritable component, and affected fitness. The three requirements mentioned above were present. In the words of the authors:

Natural selection is acting slowly and gradually on traits of medical importance and on life history traits in the FHS population.

But surely, our modern way of life must have an influence on our evolution? Of course, but that influence need not be an evolutionary stop-sign. In what ways and to what degree modern life affects human evolution is a very interesting question, and surely more research is needed. A few brief points to keep in mind:

• Natural selection is not the only mechanism behind evolution. For some more information, check this page at Evolution 101 (a site which I would highly recommend to anyone who wants a correct, yet understandable, introduction to evolution). So, even if modern life should diminish the influence of natural selection, evolution certainly wouldn’t come to a grinding halt.
• The fact that, through science and technology, traits that would have been ‘weeded out’ by natural selection in other circumstances, are allowed to persist, doesn’t mean that there is no selection. In other words, what we are affecting, are selection pressures. That is, to what extent and in what way selection acts. But we’re not eradicating selection (it seems unlikely we could, actually…). Besides, things needn’t be as subtle as in the above studies. After all, there are still a lot of parasites, diseases and environmental factors that affect human reproduction and survival and, as such, represent clear selection pressures.  
• Perhaps one might even argue that, through the persistence of more traits, or, phrased otherwise, more genetic variation, we are providing more ‘raw material’ for evolution? After all, selection could potentially be seen as a filter that gets rid of ‘bad variation’?

So, natural selection still occurs in human beings. And even if we diminish its grip, that doesn’t mean that evolution will slow down. Mankind still evolves (and that’s a good thing).

Evolve on!

(Adapted from Wikipedia’s human evolution scheme. Wikimedia Commons, author M. Garde)

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Byars, S.G., Ewbank, D., Govindaraju, D.R. & Stearns, S.C. (2010). Colloquium Paper: Natural selection in a contemporary human population, Proceedings of the National Academy of Sciences, 107 (suppl_1), 1787. DOI: 10.1073/pnas.0906199106

Courtiol, A., Pettay, J.E., Jokela, M., Rotkirch, A. & Lummaa, V. (2012). Natural and sexual selection in a monogamous historical human population, Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1118174109

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