There are mountainous piles of evidence to show that there are IQ differences between races based on biology, this evidence is probably best detailed in the Bell Curve.

I think you are probably referring to the Eyferth study, which showed only slight differences between children born to American service men who were black, and service men who were white, when they had children with German women after WW2.

The thing is, far more black men were denied service into the US Army for IQ reasons than white men, meaning that the black men in Germany would have been the cream of the intellectual crop. Also, the German women would probably have been more likely to sleep with the smartest black men not the dumbest, further invalidating the data. The Eyferth study is counteracted by a huge amount of easily observable facts about life.