IQ

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  • Nathan Cofnas (2020) is a recent discussion of group differences in IQ.

"The adult Black–White IQ gap has remained stubbornly constant at approximately one standard deviation (15 IQ points) among cohorts born since around 1970 (Murray, 2007).

Dickens and Flynn (2006, Figure 3) indicate that, in 2002, the Black–White IQ gap in among 20-year-olds was approximately one standard deviation, or 15 points. Nisbett (2017) writes that “Dickens and Flynn found [the Black–White gap in IQ to be] around 9.5 points,” but this is only the gap if we include children (as R. Nisbett confirmed in a personal communication, December 24, 2018). ... Frisby and Beaujean (2015, Table 8) find a Black–White IQ gap of 1.16 standard deviations among a population-representative sample of adults used to norm the Wechsler Adult Intelligence Scale IV in 2007. Intensive interventions can raise IQ substantially during childhood when the heritability of IQ is low. But despite some misleading claims about the success of early intervention programs, gains tend to dissolve by late adolescence or early adulthood (Baumeister & Bacharach, 2000; Lipsey, Farran, & Durkin, 2018; Protzko, 2015). Adoption by white families – one of the most extreme interventions possible – has virtually no effect on the IQ of black adoptees by adulthood. Black children adopted by middle- and upper-middle-class white families in Minnesota obtained IQ scores at age 17 that were roughly identical to the African American average. Adoptees with one black biological parent obtained IQ scores that were intermediate between the black and white means (Loehlin, 2000, Table 9.3).2

Environmentalists never predicted that the Black–White IQ gap would, after reaching one standard deviation, remain impervious to early education, adoption, massive improvements in the socioeconomic status of Blacks, and the (apparent) waning of overt racism and discrimination.

Unlike heritability studies, GWAS can uncover specific genetic variants – or single-nucleotide polymorphisms (SNPs) – associated with IQ. In just the last couple years, GWAS has identified hundreds of such SNPs (Davies et al., 2018; Savage et al., 2018; Sniekers et al., 2017), which together explain around 11% of the variance in IQ (Allegrini et al., 2019).

"Siblings differ among themselves by an average of 12 IQ points; strangers differ by an average of 17 IQ points."

There is no persuasive evidence that the IQ bell curves for different racial-ethnic groups are converging over time, and they differ as much when children leave high school as when they enter kindergarten.

A large, longitudinal study of ex-servicemen in Australia found that safe driving relates to IQ level. Rates of death from motor vehicle accidents doubled and then tripled across three ranges of normal IQ: In the 100-115 IQ range, there were 51 deaths per 10,000 men; at IQ 85-100, there were 92 deaths; and at IQ 80-85, there were 147 deaths.

The shared effects of a family environment on intelligence disappear with age. ...The heritability of intelligence fairly rapidly becomes the dominant influence, rising from 40 percent of the explanation of differences in IQ scores in the pre-school years, to 60 percent by adolescence, to 80 percent in old age.

Studies of children who have become siblings through adoption illustrate this counterintuitive discovery. They become less like one another as they get older, but more like their biological parents and biological siblings, whom they have never met. By adolescence, adopted siblings tend to be no more alike in IQ than complete strangers. On the other hand, identical twins reared apart are almost as similar as identical twins reared together and considerably more similar than fraternal twins reared together.

Special interventions to raise low IQ’s are somewhat successful with young children, but the effects of these interventions almost always fade out as children approach early adolescence.