In most cases, therefore, shared genes and shared environments seem
hopelessly confounded. Can we peel one of these influences away from the
other? Fortunately, there are ways. The most popular procedure for separating
the role of genetics from the role of environment is the twin-study method.
This method takes advantage of a naturally occurring phenomenon: the twoIN THE NEWS
Genetics and Intelligence
A large amount of research indi-
cates that, as with personality traitsand psychological disorders, a sig-nificant portion of intelligence isdetermined by our genetic inheri-
tance. Although at first glance thisconclusion hardly seems surprising,it is in fact at the heart of a con-troversy that flares up periodicallyamong psychologists and those who
debate social policy. Several decades
ago psychologist Arthur Jensen(1969) considered the research onintelligence and the finding that
Black Americans typically scorelower on standard intelligence teststhan Whites. He suggested fromthese observations that Blacksmight be genetically less intelligentthan Whites. Richard Herrnsteinand Charles Murray rekindled thedebate in 1994 when they publishedThe Bell Curve: Intelligence andClass Structure in American Life .
These psychologists also began bypointing out that intelligence islargely inherited. They argued thatany gains from educational inter-vention programs such as HeadStart will be short-lived because achild’s genetically determined apti-
tude will ultimately determine his orher success. Herrnstein and Murraythen touched a social and politicalnerve when they tied their analysisto the question of race. They arguedthat if Black Americans on averagescore lower on IQ tests than WhiteAmericans, perhaps efforts toprovide educational opportunities
for African Americans are a wasteof time. More recently, racistgroups seized on the findings ofgenetics researchers who identified
recent (within the past 40,000years) evolutionary changes inbrain-related genes (Regalado,2006). Because differences werefound between European and
African samples, these individuals
drew the scientifically inappropriateconclusion that the research verifiedclaims of genetically based differ-
ences in intelligence among racialgroups.
In each of these situations, re-
action was strong and swift. Newsanalysts, political commentators,and political leaders were quick tochallenge the interpretations.Reaction from academic psycholo-gists was equally intense. Not onlydo the vast majority of psycholo-gists find the suggestion of inherentracial differences in intelligence of-fensive, they also maintain that sucha conclusion is simply not sup-ported by research findings (Flynn,1999; Neisser et al., 1996; Nisbett,2009; Sternberg, Grigorenko, &Kidd, 2005). Moreover, it is incor-rect to say that intelligence level isfixed by nature and is not amenableto environmental influence (Nisbett,2007). Psychologists are quick topoint out that Black children oftengrow up in an environment that isless intellectually stimulating thanthat of the average White family
(Zernike, 2000). Indeed, researchersfind that Black children adopted byWhite families of reasonable socio-economic means develop IQ scores
no different from those of adoptedWhite children (Nisbett, 2007). Notsurprisingly, as preschool and othereducational opportunities have be-come more available to children of
all backgrounds, the gap between
White and Black students ’IQ
scores has narrowed considerably(Dickens & Flynn, 2006).
Beyond this, critics have raised
the issue of culture-bound intelli-
gence tests. They argue that thequestions asked on most intelligencetests reflect what White, middle-class Americans consider important.One subtest on the widely usedWechsler intelligence tests asksabout general knowledge. The as-sumption behind these questionsis that although all children are ex-posed to this information, the moreintelligent ones will attend to andretain it. But clearly a child growingup in an African American culture isexposed to different informationfrom one growing up in a White,middle-class culture. Because of thisproblem, many psychologists havebeen working to develop “culture-
free” intelligence tests, and recent
versions of the adult and children ’s
Wechsler tests have been revisedto account for some of theseconcerns.Heritability of Personality Traits 253