Matthew Syed in The London Times
The reluctance of liberals to engage in real debate has left the impression that there is an inconvenient truth about IQ differences that is being suppressed by political correctness. This has bolstered the phenomenon of black skin being used subconsciously as an information-bearing trait, so that blacks are judged as a group rather than as individuals. This has prejudiced blacks in finding jobs and amounts to de facto affirmative action for whites.
The unwillingness to engage with the IQ controversy is based upon the fear that an exclusively environmental explanation is difficult to sustain. It is generally accepted that the variation in IQ within the white population is largely heritable, as is the variation within the black population. But if white-white and black-black IQ differences are predominantly heritable, how could it be that the black-white difference is exclusively environmental? This argument was first put by Arthur Jensen in 1969 in his seminal paper, How Much Can We Boost IQ and Scholastic Achievement?
But it rests upon a confusion. To see how, imagine a sack of genetically diverse seed that is randomly divided into two bunches. Bunch A is grown in a field with good lighting and Bunch B in a field with poor lighting. The differences in height between the seedlings in Bunch A will be exclusively genetic since they have all been subjected to the same environment. The same is true of Bunch B. But the difference in the average height between Bunch A and Bunch B is exclusively environmental � caused by the difference in lighting conditions.