Our conclusion, that the Black–White IQ difference is partly heritable, ac-
cords with previous analytic reviews of this literature. Loehlin et al. (1975)
concluded that Black–White IQ differences “probably” reflected “genetic differ-
ences among the groups” (p. 238). P. E. Vernon (1979) tabulated 30 main topics,
each scored on a 4-point scale, and concluded that “although the total number of
items favoring genetic influences (G and G?) is roughly balanced by the number
of environmental points (E and E?), more of the highly convincing items are G
rather than E” (p. 319). The survey of over 1,000 experts in behavioral genetics
and psychometrics by Snyderman and Rothman (1987) also found that a plurality
believed the Black–White IQ difference “to be a product of both genetic and
environmental variation” (p. 141). However, there are also notable statements to
the contrary. The APA Task Force on intelligence, for example, concluded
“[t]here is certainly no support for a genetic interpretation” (Neisser et al., 1996,
p. 97). Likewise, Nisbett (1998) reached the conclusion that “the most relevant
studies provide no evidence for the genetic superiority of either race” (p. 101).
In our opinion, the present review, similar to those of Loehlin et al. (1975) and
Vernon (1979) earlier, should be given greater weight because they surveyed a
greater range of evidence. Examining all the documentation allows a greater
chance of finding accurate explanations than does selecting a few items from the
whole. The 10 categories of predictions reviewed in Table 5 were derived from
the “hard core” assumptions of the two competing research programs, each of
which tries to explain the Black–White IQ difference (see Section 2). Based on
Lakatos’s (1970, 1978) criteria for evaluating research programs, and a philoso-
phy of science methodology that evaluates rival theories by generating multiple
strong inferences and assessing the preponderance and the consilience of many
lines of evidence, we believe the hereditarian theory has satisfied the criteria for
a “progressive” research program, whereas the culture-only program has not. Both
have drawn implications to make numerous, testable, novel predictions, but we
found the hereditarian predictions were mostly confirmed, whereas those from
culture-only theory mostly were not.
Some attempts to salvage the culture-only theory have been problematic.
Suggestions that “White flight” undermined desegregation and busing programs
so that “true” integration has not yet been properly tried, that Head Start programs
278 RUSHTON AND JENSEN
still have not been fully funded, that culture-fair tests were not really fair, that the
sensory deprivation and race-of-examiner hypotheses were of only minor signif-
icance, or that being Black in America is really a matter of caste, not class or race,
fall short of being strong inference. Urbach (1974b, p. 237) dismissed such
claims, and that the mean Black–White IQ difference is a system problem, and
that caste and class differences are complex, subtle, and attitudinal rather than
grossly econometric, as “pseudo-scientific maneuvers,” noting that “it is intellec-
tually improper to obscure facts by continually retreating behind the trivial truth
that the world is complex [italics added]”.
We believe the burden of proof must shift to those who argue for a 100%
culture-only position. For example, they need to address why, if important
minority-specific developmental processes such as stereotype threat (Steele, 1997)
and racial stigma (Loury, 2002) exert such a powerful influence on school
achievement, the correlation matrices representing developmental processes can
be so similar across ethnic and racial groups (Section 5). They need to explain
why, if gene– environment interactions are as widespread and difficult to disen-
tangle as often claimed (e.g., Block, 1995), identical twins reared apart grow to be
so similar (Bouchard, 1996; Bouchard & Loehlin, 2001). Some culture-only
hypotheses are too ambiguous to be tested.
A conundrum for theorists of all persuasions, however, is that there is too little
evidence of any environmental effects. The hereditarian model of Black–White IQ
differences proposed in Section 2 (50% genetic and 50% environmental), far from
precluding environmental factors, requires they be found. Although evidence in
Sections 3 to 11 provided strong support for the genetic component of the model,
evidence from Section 12 was unable to identify the environmental component.
On the basis of the present evidence, perhaps the genetic component must be
given greater weight and the environmental component correspondingly re-
duced. In fact, Jensen’s (1998b, p. 443) latest statement of the hereditarian model,
termed the default hypothesis, is that genetic and cultural factors carry the exact
same weight in causing the mean Black–White difference in IQ as they do in
causing individual differences in IQ, about 80% genetic–20% environmental by
adulthood.
One current challenge, therefore, is to identify significant sources of nonge-
netic variance. It is hoped that the recent models of gene– culture correlation put
forward by Dickens and Flynn (2001, 2002) to explain the paradox of large
heritability estimates and large environmental effects mark a new trend in the
race–IQ debate. Their models accept the empirical reality of both genetic and
environmental influences. Within Whites, most of the nongenetic variance ap-
pears to result from a small number of random adverse effects such as prenatal
problems, complications in the birth process, maternal health, and childhood
disease and trauma (Jensen, 1997).