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Environmental factors including lead exposure,[85] breast feeding,[87] and nutrition[88][89] can significantly affect cognitive development and functioning. For example, iodine deficiency causes a fall, on average, of 12 IQ points.[90]
Such impairments may sometimes be permanent, sometimes be partially or wholly compensated for by later growth.

Окружение:

Different aspects of the Socioeconomic environment in which children are raised have been shown to correlate with part of the IQ gap, but they do not account for the entire gap.[79] Generally the difference between mean test scores of blacks and whites is not eliminated when individuals and groups are matched on SES, suggesting that the relationship between IQ and SES is not simply one in which SES determines IQ. Rather it may be the case that differences in intelligence, particularly parental intelligence, may also cause differences in SES, making separating the two factors difficult.[47] Hunt (2010), p. 428 summarises data [clarification needed] showing that, jointly, SES and parental IQ account for the full gap (in populations of young children, after controlling parental IQ and parental SES, the gap is not statistically different from zero). He argues the SES-linked components reflect parental occupation status, mother's verbal comprehension score and parent-child interaction quality. Hunt also reviews data showing that the correlation between home environment and IQ becomes weaker with age.

И гены:

Geneticist, Alan R. Templeton argues that the question about the possible genetic effects on the test score gap is muddled by the general focus on "race" rather than on populations defined by gene frequency or by geographical proximity, and by the general insistence on phrasing the question in terms of heritability.[111] Templeton points out that racial groups neither represent sub-species nor distinct evolutionary lineages, and that therefore there is no basis for making claims about the general intelligence of races.[111] From this point of view the search for possible genetic influences on the black-white test score gap is a priori flawed, because there is no genetic material shared by all Africans or by all Europeans. Mackintosh (2011) points out that by using genetic cluster analysis to correlate gene frequencies with continental populations it could possibly be the case that African populations had a higher frequency of certain genetic variants that contribute to an average lower intelligence. Such a hypothetical situation could hold without all Africans carrying the same genes or belonging to a single Evolutionary lineage. According to Mackintosh, a biological basis for the gap thus cannot be ruled out on a priori grounds.