Thick headed people

Children with thicker skulls by the age of twelve tend to be smarter, as this interesting study reported by BBC News tells us. This study was conducted by the US Institute of Mental Health on 307 children. A thicker skull means a longer thime for the children to develop higher level brain circuitry (whatever that means, I am not sure). However, the interesting question is what triggers the skull thickening? Genes or the activities the child was engaged in?

Time to take out those callipers...