No 10 furore is latest chapter in long, dark history of racist science

Idea that members of one race are intellectually superior has had to be confronted regularly

The notion that members of one race are inherently more intelligent than members of another - brought back into circulation by the appointment of Andrew Sabisky, who claims that black Americans have a lower average IQ than white people, as a Downing Street adviser - is an idea with a deep and disturbing history.

In modern times, the study most often rolled out as supporting "evidence" is a 2006 work from the English psychologist Richard Lynn. In the publication, Lynn concluded that black Africans had an average IQ of less than 70, compared with the average western IQ of 100. This, he claimed, explained the low level of economic development in sub-Saharan Africa.