A couple of days ago James Watson, the maverick scientist who shared the Nobel Prize for medicine with Francis Crick and Maurice Wilkins in 1962 for their work on the structure of DNA, caused outrage by asserting that black people were less intelligent than white.
Strangely, for such an eminent scientist making a verifiable pronouncement, he adduced no evidence for his assertion. Instead he said that he expected such evidence to become available in the next decade; in fact specifically that genes for intelligence would be found. He may or may not be right about that - my uninformed guess is that such genes will indeed be discovered - but it is seriously bad science to assume the results before doing the experiments, and here he is assuming not just that genes for intelligence will be discovered, but that they will be found to be less numerous, or flawed in some way, in black people compared with white.
Of course, there are racial differences, and it is perfectly possible that IQ is one of them. It certainly seems that black people can run faster than whites, and they also have greater or lesser risk of certain diseases such as sickle cell anaemia. There was, indeed, a study some years ago which showed that white Americans had higher IQ than black ones, but the explanations for this are many and various: familiarity with IQ tests was one - over time since IQ tests were first introduced average scores have gone up, showing clearly that part of what such a test measures is a learnable ability to do IQ tests; nutrition was another: during the years of slavery the nutritional input of blacks was far below that of whites, and things have improved only slowly since - blacks are still, on average, poorer than whites and are likely, on average, to have a worse diet, albeit less so than when they were slaves. Nutrition certainly affects IQ, so it is reasonable to suppose that black people were originally just as intelligent as white. A study of Africans who stayed in Africa might be interesting, but has never, so far as I know been done, and there too there would be drawbacks: they may not have been enslaved, but they were colonised, and nutritional standards there are not so good either.
There are also different kinds of intelligence, of which the one measured by IQ is only one. Emotional intelligence for instance, where my (alas evidence-free) guess would be that black people would score higher than whites.
The real question is what Dr Watson was hoping to achieve by his contentious statement. He must have known that, however scientifically it was cloaked, it would be seized upon by racists. Maybe he just likes to cause trouble - he has done it before.