Apparently blacks do tend to score above whites on working memory tests though, I see someone cited this claim as originating in Nijenhuis et al., 2004 , however I do not feel like downloading and digging through that pdf to verify the claim. I know that blacks tend to score closer to whites on visuospatial tests though, and these are thought to be much less culturally biased than tests of verbal intelligence. IQ tests are generally based on four criteria, short and long term verbal and visual memory. The scores from each of the subtest categories influences the overall giq (general IQ) to various degrees. Some people might not be able to remember a sentence they just heard, others could remember it enough to repeat it forwards (a test of verbal short term memory) and others enough to repeat it backwards (which would likely test visual short term memory as an efficient strategy would be to visualize the sentence mentally and then read it backwards orally). Some people are able to remember larger sentences than others , others are able to remember smaller sentences than others but for longer, etc. The overall performance on tests like this is used to determine the persons general IQ score. The point I am trying to make is that it is naive as hell to think that genetics could cause a person to be taller or shorter than another, but that it is entirely culturally determined how many digits from a series a person can repeat backwards before they start to make mistakes or forget, or how well a person can find consistent patterns in series of shapes or numbers.