Thursday, April 2, 2009

When natural selection works as advertized

We and others have written quite a bit about the nature of natural selection and how it is detected (or how hard it is to detect) by various means. Darwin based his ideas of the origin of species on the extrapolation over long evolutionary time periods, of the kinds of effects seen in agricultural breeding. He assumed that eventually, such gradual changes would be adaptive, because nature (like breeders) chose only subsets of individuals for successful reproduction, and because adaptive differentiation would lead to speciation.

It is routine to assume that a trait of interest is the result of adaptive natural selection, and then suggest (guess at) what the selective force might have been. This is a highly problematic enterprise and, we think, scenarios are often asserted with very little to support them....which we think is a mistake and can be dangerous when applied to humans. That's because searches for and studies of selection in humans can easily lead to group generalizations about inherent value, including many forms of racism. So spending research money on such searches should only be done when the evidence is actually strong enough, and the likely societal penalty low enough, to justify it.

But there are instances when classical ideas of natural selection seem to work more or less as advertized, and do have great importance. Our posting today is triggered by a story in the news as a meeting convenes on the risk of global epidemics of multiple drug resistant tuberculosis.

The evolution of antibiotic resistance may not always be simple at the pathogen's gene level, but it does seem to be clearly a genetic adaptation phenomenon due to intense selection imposed by widespread, or excessive, use of too-few antibiotics. The problem can be exacerbated by population crowding, poverty leading to large numbers of unvaccinated people (for some diseases), with rapid global travel, and so on.

Many other initiatives, such as genetically personalized medicine, are clearly less urgent than preventing or containing global epidemics. The latter are clear genetic, evolutionary problems that warrant substantial scientific investment even in tight economic times. There, too, investment in social aspects of group dynamics could be actually effective, unlike much of social science research, whose payoff is modest and indirect at best.

If the genomics industry is too politically powerful or too large to fail (like, for example, AIG and General Motors), then at least funds should be shifted to problems that really are genetic and that ought to be susceptible to molecular technologies -- even if the challenge to do that is great.

So, while we think excessive genetic determinism and selectionism are misplaced relative to what we actually know about genes and about evolution, control of infectious diseases (and similar issues in relation to agricultural pest and disease control) are a totally appropriate application of biological theory and modern biotechnology.

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