Intelligence as a biological and racial construct.

The genetic contribution to intelligence is widely acknowledged. Estimates of heritability of intelligence are much larger than for other human traits. Heritability of intelligence has been established in research with estimates of around .75. The effects of the genes increase with age as the influence of family fades away around adolescence. As children age they become more independent of environmental influences and fit their intellectual activities to their genetic potential (Loehlin, Horn, & Willerman, 1989). Children as they get older score more closely to their genetic potential, and become more independent of family influences (Loehlin, Horn, & Willerman, 1989). The evidence of heritability is generally observed from twin studies where some live together and others apart. Regardless of living conditions results demonstrate that the closer the genetic relationship the more alike the IQ scores (Bouchard, Lykken, & McGue, 1994). The genetic component is typically estimated from differences in correlations between those who are closely related like twins compared to those that are less related or complete strangers. Comparisons have been made between identical and fraternal twins also supporting heritability. As noted the heritability estimate is .51 for identical twins (Loehlin, 1992), suggesting a significant genetic contribution to the variability of intelligence.

The construct of intelligence and its genetic component has been hotly argued over the past decades. In the past differences between races in intelligence estimates occupied much attention of researchers and the results has been used as justification to evaluate social policy (Jensen, 1985). Herrnstein and Murphy (1994) argued that intelligence is the main factor predicting success in the United States, and African Americans are found at the lower end of the bell curve for intelligence. Herrnstein and others have argued that social interventions and special education will not make much difference in the intellectual achievements of Blacks since intelligence is assumed to be primarily genetic. The fixedness of intelligence in turn places limits on achievements of Blacks, Jensen, Herrnstein and Murphy argues, and social programs for these minorities are largely a waste of resources. For these researchers the evidence is clear-cut that intelligence is largely an inherited genetic capability. However, the categorization of race is quitе arbitrary, particularly in the U.S. where the research was conducted. Racial categorization is typically based on self identification of skin color that is probably the least meaningful criteria of “race” since in the U.S. the genetic heritage of most people derive from a variety of racial and ethnic backgrounds.

Other investigators have also observed that intelligence often shift drastically under varying social and environmental conditions. Unfortunately, this nature-nurture debate has also become ideological as vested interests have argued that the research cited above supports the higher intelligence of some groups or “races” when compared to others. However, it should be remembered that the heritability estimates of intelligence were derived from studies of individuals to make the argument of differences between populations (Rushton, 1988). Population differences in estimates of intelligence are impossible to ascertain since there is always an interaction effect between the genetic components and the environment. There is no logical basis to infer from the heritability estimates of individual differences that the observed differences between populations are likewise determined by the genetic contribution as the observed differences could be the result interaction with the cultural environment. Genetic inferences for individual differences in intelligence do not allow us to assume that differences at the group or national level are based on inherent factors (Sternberg, 2004). Observed differences (whether between national or “racial” groups) can be totally attributed to environmental advantages or disadvantages.

Limitations to individual achievement based on genetics are not supported by other research. For example improvement in diet over one generation had a profound influence on IQ scores with increases in the range from 15-20 points in Western nations (Flynn, 1987). Since we know that advantageous mutations could not occur at that rapid rate the environmental changes, including improvement in nutrition, is the more likely causal contributor. At any rate IQ scores do not appear to be stable over time therefore making populations comparisons problematic in terms of both reliability and validity. Nevertheless that the hereditary genetic component determines significant parameters of intelligence are supported by nearly all scholars (Snyderman & Rothman, 1998).

Finally, in evaluating the heritability of intelligence it is important to make a distinction between actualized genetic potential and non-actualized intelligence. Heritability estimates are made exclusively from actualized potential and offer no information on non-actualized potential caused for example by adverse environmental conditions. Measured actualized potential is a result of gene-environment interactions and is the basis of any heritability estimates. Further, there are many socio-economic differences that impact actualized potential and therefore impact scores on intelligence tests that are not controlled in studies on group differences. In fact we have no way of evaluating non-actualized intelligence. From the perspective of cross-cultural differences there is an even broader range of socio-cultural environments that are not measured by IQ tests. Finally, we need to emphasize that although group differences in intelligence is reported in research we cannot assume that these have a genetic basis. Racial and other group differences in intelligence can in fact all be accounted for by measurement problems including not utilizing constructs and terms familiar to participants in all racial groups. The heritability of intelligence issue is only important because intelligence testing has been used in the debate over social policy.

Date: 2015-01-11; view: 1062