The determination of many traits can be considered from the perspective of nature versus nurture. A 2006 study (Visscher et al) found that adult height has a heritability estimated at 0.80 (correlation coefficient) for families where the environments are very similar. There can be no “absolute” coefficient of heritability of a trait, for as the environmental variation encountered by a group increases then, the heritability figure for that group would decrease. Therefore, the heritability of height in a study such as Visscher’s where the environments were matched for similarities is likely to be an upper estimate. On the other hand, where environments are very diverse (in developing nations) the heritability figures will be correspondingly lower.
A 1996 statement by the American Psychological Association, seeking to establish facts about intelligence (Intelligence: Knowns and Unknowns) estimated heritability between .45 and .8. This statement followed Herrnstein and Murray’s (1994) book “The Bell Curve” , which while academically rigorous has been perceived as inflammatory for its controversial emphasis on the heritability of intelligence and race differences in IQ. Herrnstein and Murray stirred controversy by suggesting that:
» Educational and environmental intervention efforts targeted at disadvantaged populations are largely a waste of time and money
» Increasing population of ‘lower caste’ intelligences is lessening the nation’s ‘genetic capital because the less intelligence, lower class is reproducing at a greater rate than high IQ classes
Richard Lynn (born 1930) is Professor Emeritus of Psychology at the University of Ulster. His latest book (The Global Bell Curve: 2008) again discusses the challenging topic of race and intelligence. Lynn, like Herrnstein and Murray, presents controversial evidence for significant differences in IQ between races:
* East Asian (Chinese, Japanese, Koreans) (Average IQ of 105)
* Europeans (Average IQ 100)
* South East Asians (Average IQ 87)
* North African (Average IQ of 84)
Lynn’s presentation of the evidence above has been both praised as brave and criticised as over-simplistic. Does the Flynn effect not highlight the role of environmental effects and development of culture over-time? Sternberg (1997) has presented extensive evidence that appropriate stimulation (neither poor nor overenriched) maximises the realization of a person’s intelligence. What about Feldman’s (1986) argument that genes create an appetite rather than an aptitude? If one is of a mechanical bent one will seek our mechanical challenges; if one is a bookworm, one will seek out books. But these appetites may not lead to aptitudes without the appropriate environment.
For many it seems that IQ testing and by extension other standardised tests such as SAT’s are politically damaged. For a contemporary political perspective on the issue of standardised testing consider the words of Barrack Obama about testing below.
“One thing I never want to see happen is schools that are just teaching the test because then you’re not learning about the world, you’re not learning about different cultures, you’re not discovering science… all you’re learning about is how to fill out a little bubble on an exam and little tricks that you need to do in order to take a test and that’s not going to make education interesting.” Barrack Obama: Bell Multicultural High School in Washington, D.C: 27 March 2011
Dodging the controversy I find the following facts provide some useful pointers:
1. As populations have got more educated they have got significantly better at doing the things measured by tests. This suggests a substantive role for environmental factors. (Ref Flynn)
2. There is a heredity factor in intelligence however in more diverse environments factors such as mental stimulation, nutrition, education and family circumstances will substantially interact with hereditary factors to contribute to intelligence.
3. Tests measure what they measure. It is true that general ability tests and IQ tests measure a particular type of intelligence (Ref Gardner and Goleman on the following pages). However, the type of intelligence tests measure is still relevant to many demands encountered in life.
4. A blinkered focus on academic intelligence will tend to create a vicious circle. If we only value the differences which we can measure then we will ignore more interesting less definable individual differences.
5. The term bias is emotive and needs to be used with precision. Psychometricians reserve the term “test bias” for situations where tests are biased against a group but these differences are not relevant to real world performance but are artefacts of how we are testing people.