The last refuge of the educational romantics is the extremely high proportion of children of the professional classes who do well in school. Surely that must be explained by affluence and access to the best schools. Or as Adonis put it: "There is no genetic or moral reason why the whole of society should not succeed to the degree that the children of the professional classes do today." Actually, there are both genetic and moral reasons, along with environmental ones.

The genetic reason arises from two politically unfashionable but empirically irrefutable truths.

The first is that IQ, which is nearly coincident with academic ability as I defined it, is somewhere around 40 per cent to 60 per cent heritable. The evidence for the substantial heritability of IQ has become so overwhelming that it is no longer a subject of serious debate, except over the exact figure. The second is that people in the professional classes are, on average, far above the rest of the population in IQ.

Presenting evidence for the high IQ of professionals is superfluous for successful physicians, engineers, barristers, scientists or university lecturers. Possession of an IQ in at least the top 10 per cent is virtually guaranteed by the nature of the academic filters required to finish the professional training. But such evidence is plentiful even when we move to occupations such as business executive. There are many thick people working in business, but studies of the relationship of tested IQ to career success indicates that the overwhelming majority of successful executives are somewhere in the top 10 per cent of IQ.

And so it comes to pass that when a man and woman in the professional classes set out to have a baby, it is extremely likely that at least one gene contributor has a high IQ. In today's society, it is ever more likely that both contributors will be in that category. Think of all the couples you know who consist of two professionals, or ones in which perhaps only one works outside the home but the other has an advanced academic degree. Given this kind of genetic background and a heritability of 40 to 60 per cent for IQ, the children of the professional classes have a meaningful academic advantage at the moment of birth (as a group - individual exceptions abound).