Given he said it in 2007, pretty much no evidence to back it up. Genetic differences between races are small compared to those within races, so much so that the concept of races does not really stand up scientifically.
He seemed to have been basing the comments on IQ tests, which are not really a good way of comparing groups of people with different cultures or education. They score an individual within a group of comparable individuals.
It is worth noting that if he had made the same statement in the first half of the 20th century it would have been mainstream science, but even then it was not so much supported by evidence but supported by a lack of evidence showing otherwise.
He seemed to have been basing the comments on IQ tests, which are not really a good way of comparing groups of people with different cultures or education. They score an individual within a group of comparable individuals.
It is worth noting that if he had made the same statement in the first half of the 20th century it would have been mainstream science, but even then it was not so much supported by evidence but supported by a lack of evidence showing otherwise.