Yesterday, I blogged about the misuse of the word “proof” by science journalists. Wouldn’t you know it, later, I came across this blog post, which tells us:
“Now, a new study proves that people who are good at reading are also quite naturally talented at math.”
Actually, not really. The study, in and of itself, is quite interesting, but this blogger, apparently relying on an LA Times piece rather than the original paper, gets a number of the details wrong.
You can read the original paper here. The abstract reads:
“Dissecting how genetic and environmental influences impact on learning is helpful for maximizing numeracy and literacy. Here we show, using twin and genome-wide analysis, that there is a substantial genetic component to children’s ability in reading and mathematics, and estimate that around one half of the observed correlation in these traits is due to shared genetic effects (so-called Generalist Genes). Thus, our results highlight the potential role of the learning environment in contributing to differences in a child’s cognitive abilities at age twelve.”
One of the big confusions that accompanies a study like this is the misunderstanding of the concept of heritability. Heritability is not a measure of the percentage of a trait is caused by genes. It is not even an individual level measure of a trait, it is a measure of how much of the variance in a population is genetic.
One of the consequences of this is that heritablity is not fixed, it will be affected by the level of environmental variance. We can see this by a simple thought experiment. Imagine a society with total absolute equality between individuals. In that circumstance, since there would be no difference in environment, heritablity would be one hundred percent. This conclusion, strikes many as counterintuitive but if you contemplate it for a while you will see that this must be true.