I know some fine, upstanding black people.
Its the culture or the discipline of the people that makes the difference.
I have relatives, lilly white, that are welfare rats and trailer trash.
The purpose of the bell curve was to get away from the individual anomalies on both sides of the curve and show the main body of what ever was being evaluated.
You also state it is not race that makes the difference but as every single person who ever used that line you offer no proof.
There is proof positive that race not only can change the color of the skin (on average) but can, change the average height, can change the shape of the eyes, can create unique genetic medical conditions, can change the average athletic capability of the group...yet there are still those who CLAIM race cannot change the type of person ON AVERAGE, hence the bell curve to cut through all the prejudice of those who want to hate and of those who want to make excuses.
At least in the USA we are all supposed to be equal in the eyes of the law as it should be. Don't try to tell those of us who can see, hear, read, count that we are all equal.
You denialist, you!
(I don't do sarcasm tags, and when I start wondering if one of my posts really needs one to avoid misunderstandings, it's a bit of a sad day for me.)