Ok, sorry for taking so long to get back but I'll help give you the data because you are wholly misusing what IQ data actually means and don't know what you are talking about.
1) IQ:
https://en.wikipedia.org/wiki/Intelligence_quotient
An
intelligence quotient (
IQ) is a total score derived from several
standardized tests designed to assess
human intelligence. The abbreviation "IQ" was coined by the
psychologist William Stern for the
German term
Intelligenzquotient, his term for a scoring method for intelligence tests at
University of Breslau he advocated in a 1912 book.
[1] Historically, IQ is a score obtained by dividing a person's
mental age score, obtained by administering an intelligence test, by the person's chronological age, both expressed in terms of years and months. The resulting fraction is multiplied by 100 to obtain the IQ score.
[2] When current
IQ tests were developed, the
median raw score of the norming sample is defined as IQ 100 and scores each
standard deviation (SD) up or down are defined as 15 IQ points greater or less,
[3] although this was not always so historically. By this definition, approximately two-thirds of the population scores are between IQ 85 and IQ 115. About 2.5 percent of the population scores above 130, and 2.5 percent below 70.
[4][5]
So what this in effect means is that every few years IQ is renormalized, otherwise the current average IQ of Americans would be 130...
2)IQ Black and White gap:
Knowing that IQ is an average means we can rate and understand what this means.
Because IQ is an average adjusted to 100, that means that the average white person pre-1950s would have had an average of a 70 IQ compared to todays black IQ of 85.
Meaning White Americans pre-1950 would be considered MENTALLY RETARDED when compared to today's black Americans...
Further the gap is shrinking, meaning Black IQ rates are INCREASING AT A RATE FASTER THAN WHITE AMERICANS.
This means, if we want to continue with your incorrect interpretation of it being "genetic" rather than environmental, then Black IQs rise at rates FASTER than White Americans and will eventually OVERTAKE WHITE IQs to make WHITE IQs INFERIOR TO BLACK IQS. Again only if your incorrect interpretation persists.
3) IQs rise VERY VERY fast based on environmental factors.
Again, we see where the average IQ has rised almost 30 points in the US since pre-1950s.
Black individuals keeping pace and closing the gap indicates that
1) This is no Average IQ cap.
2) The rate of IQ increase is at least comparable if not faster for black IQs.
Now what all this tells us is that ultimately there is a gap in the environmental variables between black and white.
We see that global variables which would effect both populations such as national education and medicine so that the gap remains constant. Thus your understanding of this concept of IQ is just severely uneducated.