Some people refer to intelligent persons as “big brains”. They imagine those with bigger brains are more intelligent, a simple idea which is very probably right. School children, who are able to observe how the entire class deal with the same problems they are set, soon work out which children are “brainy”. The general principle that larger brains have greater power holds for many species, not just within humans.
Buried in a recent paper in Molecular Psychiatry (2016), 1–9, which itself contains a full library of publishable findings, is a little gem,:
Yes, right at the bottom of this list (and the actual table is much longer) is an indication that infant head circumference is genetically related to later educational attainment.
Here are the results in heat map format:
As you can see, the sample sizes are healthy, which gives us reassurance that the findings are very probably real. Infant head circumference shows a link not only to educational attainment but also to verbal-numerical reasoning.
The authors conclude:
For example, the genetic associations between infant head
circumference and intracranial volume with educational
attainment and verbal-numerical reasoning are important in
themselves, as are many other cognitive–mental health and
cognitive–physical health associations. Taken all together, these results provide a resource that advances the study of aetiology in cognitive epidemiology substantially.
For new readers, cognitive epidemiology is a developing field of health research, in which intelligence is measured and evaluated as an explanatory variable in health outcomes. Once included, it turns out to account for sizeable amounts of the variance. In my view, failure to account for intelligence renders much of ordinary epidemiology questionable.
From the point of view of chronology alone, it is likely that having a bigger brain leads to greater ability. For once, the Press paid attention to this finding, and gave it wide publicity. Slowly, genetic research is coming to public attention.
Here is a link to the full paper from which the above section from Table 2 is drawn.
In summary: cognitive epidemiology now has a new problem: it is generating so many interesting results that it is hard to keep up with them. A nice problem to have.