A Population Geneticist’s Apology

9780981519425_1Brian Charlesworth, co-author of the magisterial Elements of Evolutionary Genetics, won the Thomas Hunt Morgan Medal from the Genetics Society of America this year. An open access copy of his speech, What Use Population Genetics?, is now online at Genetics. In the speech he makes the case toward a broader audience, which includes people working in molecular and developmental areas far removed from population genetics, as to why his field is important and critical to the broader scholarly enterprise.

First, he argues that without a good intuition for population genetic dynamics, one can not model evolutionary process very well. Of course that intuition only comes over time absorbing population genetics and gnawing on problem sets. But you have to put the work in to talk cogently about evolutionary biology in its broadest scope. Charlesworth suggests that those who don’t know population genetics “run the risk of making mistakes such as asserting that rapid evolutionary change is most likely to occur in small founder populations.” The issue here is that selection is powerful in very large populations. Not so much in smaller ones. I’ve personally encountered this confusion many times from biologists who are not population geneticists. But, I do want to also admit that genetic drift can cause rapid allele frequency changes, so even here I would say that some people might quibble a bit with Charlesworth on the specific details (I am not one to dispute this particular assertion, for the record; I know what he meant).

Second, he addresses the nature of transposable elements (TE) in the genomes of organisms, and why they are so common, and where they are so common, as well as the role of PRDM9 in recombination. Pervasive features of the genome may, or may not, have adaptive origins. That means evolutionary genetics has to step into the fray and address the long term dynamics. Intersecting the frameworks of evolutionary genetics, and the structural constraints of molecular genetics, Charlesworth illustrates how population genetics sheds light on the biophysical character of genomic features, as well as the distribution of those features. If evolutionary biology is the science of why. Population genetics is how. Molecular genetics may be thought of in this schema as the is.

Finally, though Charlesworth alludes to it in passing only at the end of his speech, I think it is critical to remember that the post-genomic era is upon us, and it is incumbent upon us to think in in population terms. The style of analysis which is common in population genetics lends itself easily to big data analyses. I recall a conversation with a young researcher last year at ASHG where he told he was moving from population, to medical, genetics. And yet when his most recent publication came out I had to observe that it was fundamentally a work of medical population genomics. You can take the geneticist out of the population, but you can’t take the population out of the geneticist.

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