Whether there is scientific evidence or not I think it'd be safer to say "on average" as there are some immensely intelligent black people?
Sure, but the numbers are small.
Currently MESA membership qualifies at 2SD above mean 130 (Lower than I had assumed actually, just checked it)
Now that means that around 1:50 "White" people are likley to qualify for membership (More Men than Women as I mentioned before), If we look at the USA (I am not sure whether the position is different in the UK or other western countries) then the "Mean" IQ for "Black" people is shifted a full SD to the left. This means that only around 1:1000 Black people are likley to qualify for MENSA membership.
Overall, this is still quite a large number of people when you have a population of many millions.
But It also means that proportionally you wont get to see many Black people at MENSA meetings. And nor will you at the top unis or boards of directors for big companies either unless they are pushed there as part of "Affirmative Action" programs
Which sometimes work out quite well, showing that a good education can actually make a big difference. There was a UK documentary a while ago I recall where some inner city Black kids were sent to a private boarding school. and you know what, they actually did really rather well for themselves.
There was a time when Local authorities would actually send "Problem " children to boarding school (Note, NOT Borstal) as a matter of routine. There were a few at mine back in the 60/70's. They did rather well too.
Shame everybody cant have the same opportunity early in their lives. It is very hard to go back after one has reached a certain point!
Whilst I support the idea of selective education (Grammar Schools) I have always felt that for a truly comprehensive and egalitarian education system one needs to have state boarding schools (Of all types) from secondary level onward (Possibly even later primary like Prep schools) with the schools being well away from the child's home patch.
Only that way can children from poor backgrounds have a real opportunity to escape their intellectual poverty. (And it wont cause any harm for the children from "Good" backgrounds because they would likely relish in it anyway)