Can of worms. The book "The Bell Curve" by by Richard Herrnstein and Charles Murray is seriously politically incorrect, and so various leftist "scientists" have tried to "correct" it. Who knows, maybe some of their claims are true.
FWIW I tend to believe Charles Murray and to distrust everyone else.
Here is Wikipedia's entry on Race and intelligence:
In reading the comment thread under the article link I bumped into this video - sums up Progressives to a tee:
https://www.youtube.com/watch?v=fonSqHNoWkQ&feature=youtu.be
How important is cultural diversity at your school?