Friday, April 17, 2009

Darwin and Malthus, evolution in good times and bad

Yesterday, again in the NY Times, Nicholas Kristof reported on studies of the genetic basis of IQ. This has long been a sensitive subject because, of course, the measurers come from the upper social strata, and they design the tests to measure things they feel are important (e.g, in defining what IQ even is). It's a middle-class way of ranking middle-class people who are competing for middle-class resources. Naturally, the lower social strata do worse. Whether or not that class-based aspect is societally OK is a separate question and a matter of one's social politics: Kristof says no, and so do we, but clearly not everyone has that view and there are still those who want to attribute more mental agility to some races than to others.

By most if not all measurements, IQ (and 'intelligence', whatever it is, like almost anything else) has substantial 'heritability'. What that means is that the IQ scores of close relatives are more similar than the scores of random pairs of individuals. As everyone who talks about heritability knows (or should know), it's a measure of the relative contribution of shared ancestry to score similarities. It is relative to the contribution of other factors that are referred to as 'environmental.'

Kristof's column points out that IQ is suppressed in deprived circumstances of lower socioeconomic strata. And so is the heritability--the apparent relative contribution of genes. That makes sense, because no matter what your 'genetic' IQ, if you have no books in your house etc., your abilities have little chance of becoming realized. How you do relative to others who are deprived is largely a matter of chance, hardly correlated with your genotype. Correspondingly, there is evidence that scores and heritability rise when conditions, including educational investment, are improved. The point is that when conditions are bad, everyone suffers. When conditions are good, all can gain, and there are opportunities for inherited talent to shine.

Can we relate this to one of the pillars of evolutionary biology? That is the idea, due to both Darwin and Wallace, that natural selection works because in times of overpopulation (which they argued, following Thomas Malthus, was basically all times), those with advantageous genotypes would proliferate at the relative expense of others in the population. That fits the dogma that evolution is an endless brutal struggle for survival, often caricatured as 'survival of the fittest'.

Such an idea is certainly possible in principle. But, hard times might actually be less likely to support innovation evolutionarily. When there is a food shortage, it could be that everyone suffers more comparably, so that even what would otherwise be 'better' genotypes simply struggle along or don't make it at all. By contrast, good times might be good for all on average, but might provide the wiggle room for superior phenotypes, and their underlying genotypes, to excel.

This is not at all strange or out in left field. Natural selection can only select among genetically based fitness differences. If hard times mean there is little correlation between genotype and phenotype, selective differences have little if any evolutionary effect, and survival is mostly luck.

In this sense, from Malthus to the present, this central tenet of evolutionary theory may have been wrong, or at least inaccurate. Adaptive evolution may actually have occurred most in plentiful times, not under severe overpopulation. In most environments, competition is clearly not all that severe--if it were, most organisms would be gaunt and on the very thin edge of survival, which manifestly is not generally true.

The IQ story only reflects some here-and-now findings, not evolutionary ones per se. But it may suggest reasons to think about similar issues more broadly.

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