IQ, Age and Race

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Peter Frost says:

Intellectual capacity is much more malleable in children than in adults. This is well known in the IQ literature, including studies on African and Euro Americans. When Dickens and Flynn (2006) analyzed the results of the 2002 standardization sample for the WISC (Wechsler Intelligence Scale for Children), they found that IQ starts off high in African American children and then declines with age:

African-American WISC scores
Age — IQ
4 — 95.5
12 — 90.5
15 — 88.8
24 — 84.5

Dickens and Flynn (2006) similarly note that these scores show a gain of 5-6 points over the scores of black children thirty years earlier. But the decline of black IQ with age has remained stable. This decline also shows up in the Minnesota Transracial Adoption Study —a longitudinal study of black, biracial (black/white), and white children adopted into white middle-class Minnesota families (Scarr and Weinberg, 1976; Weinberg, Scarr, and Waldman, 1992). The children’s IQs were measured at 7 years of age and again ten years later:

——————- Age 7 Age 17
Black children –—- 97 — 89
Biracial children – 109 — 99
White children –– 112 – 106

Finally, we see this age effect in a study of children fathered by soldiers stationed in Germany and then raised by German mothers (Eyferth 1961). One third of the children were between 5 and 10 years old and two thirds between 10 and 13 years old. The study found no significant difference in IQ between children with white fathers (83 subjects) and those with black fathers (98 subjects), the mean IQ being about 97 for both groups.

So Chanda has discovered what many IQ researchers have long known: if you place children in an enriched learning environment, they will do much better on IQ tests. Unfortunately, this improvement will not last. It will “wash out” and disappear by adulthood. This was pointed out by Franz Boas (yes, the same Franz Boas!) in a speech delivered in 1894 under the title “Human Faculty as Determined by Race”:

“When we compare the capacity for education between the lower and higher races, we find that the great point of divergence is at adolescence and the inference is fairly good that we shall not find in the brains of the lower races the post-pubertal growth in the cortex to which I have just alluded.” (Boas, 1974, p. 234)

Among humans in general, intellectual capacity seems to decline with age. Indeed, there are statements in the literature that IQ declines from one’s twenties onwards (presumably among European Americans). Is this decline due to natural aging processes? Or is it prewired into the human organism?

Perhaps the ability to acquire new information became less useful with age in ancestral humans. What we call ‘intelligence’ may have originally been an infant trait that humans lost as they grew up. With the expansion of our cultural environment, natural selection would have progressively extended this infant trait into older age groups, and more so in some populations than in others.

By way of analogy, lactose tolerance was originally an infant trait and is still so in most human populations. It has become an adult trait in those populations that have long practiced dairy farming and adult consumption of milk.


Boas, F. (1974). A Franz Boas Reader. The Shaping of American Anthropology, 1883-1911, G.W. Stocking Jr. (ed.), Chicago: The University of Chicago Press.

Dickens, W.T., and J.R. Flynn. (2006). Black Americans reduce the racial IQ gap. Evidence from standardization samples. Psychological Science, 17, 913-920.

Eyferth, K. (1961). Leistungen verscheidener Gruppen von Besatzungskindern in Hamburg-Wechsler Intelligenztest für Kinder (HAWIK). Archiv für die gesamte Psychologie, 113, 222-241.

Scarr, S., and Weinberg, R.A. (1976). IQ test performance of Black children adopted by White families, American Psychologist, 31, 726-739.

Weinberg, R.A., Scar, S., and Waldman, I.D. (1992). The Minnesota Transracial Adoption Study: A follow-up of IQ test performance at adolescence. Intelligence, 16, 117-135.

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