The model species

At Molecular Ecologist, Jacob Tennessen asks whether people are the unsung model species of molecular ecology:

Non-invasive genetics and “natural experiments” are employed to make inferences about evolutionary history, behavior, fitness, and other aspects of natural history. These same restrictions also apply to humans: breeding humans in the lab is as ethically fraught as it is logistically challenging. But, the difference between studying humans and, say, elephant seals is that the established knowledge base for humans is much greater. The combined size of available population genetic datasets in humans is a billion-fold larger than for most species, even some that have already been the target of molecular ecology studies, and these human data are much better annotated and validated…

So, what are the most important things we have learned from studying our own molecular ecology? Perhaps the primary lesson from human population genetics is that intergroup differences that seemed substantial to our subjective brains, like between Africans and Europeans, turned out to be minor. There are few if any fixed autosomal differences between continental groups, and the phenotypic markers we are inclined to use, like skin color, are encoded by some of the most divergent loci, making them a poor proxy for overall evolutionary distance. A related major lesson is the surprising ubiquity of “soft sweeps,” or positive selection acting on standing variation. Unlike the classic model of a newly arisen mutation rising quickly to fixation, most geographically local adaptation in humans comes from more subtle changes in the frequency of existing alleles, hence the dearth of fixed differences. A third lesson is that the most genetically diverse human populations are found in our ancestral homeland in sub-Saharan Africa, with basal populations such as the San showing particularly high polymorphism.

These are all excellent and under-appreciated points. In cognitive neuroscience, is there any better model organism than the human brain? One of the limiting factors in incorporating genetics into human neuroscience is the paucity of relevant biological data. We know, roughly, that certain SNPs in genes like DRD4 or SERT can change dopamine or serotonin function, kind of, but it’s very non-specific, and regulation of individuals genes varies across brain region. It’s difficult but I’m highly optimistic about the future of humans as a model organism in molecular neuroscience!

I also wonder whether the lessons of evolutionary ecology are sufficiently well-known among theorists of neural function, especially the influence of ‘soft sweeps’. I get the sense that the answer is definitely no.

More importantly, though, five points to gryffindor for the first comment: ‘the speaker (Lawrence Hurst, I think) started with “humans are an excellent model system for understanding Drosophila’.

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