Heritability and Heterogeneity: The Limited Relevance of Heritability in Investigating Genetic and Environmental Factors
- 33 Downloads
Many psychometricians and behavioral geneticists believe that high heritability of IQ test scores within racial groups coupled with environmental hypotheses failing to account for the differences between the mean scores for groups lends plausibility to explanations of mean differences in terms of genetic factors. I show that heritability estimates and the statistical analysis of variance (AOV) on which they are based have limited relevance in exposing genetic and environmental factors operating within any single group or population. I begin with agricultural investigations, where replication of genetic types and control over environmental factors are possible, and highlight the difficulties of moving from AOV of observed traits to investigation of measurable genetic factors. The difficulties can only be exacerbated for human data sets, which are equivalent to a crop trial in which each variety is replicated in only one or two of the locations.
The possible heterogeneity of factors is an important consideration here. In analyzing crop trials, the AOV is most useful for generating hypotheses about measurable factors when genetic varieties can be grouped so as to make it more plausible that the factors underlying the similar responses of varieties within a group are homogeneous. Even then, this does not imply that in other groups the same set of genetic factors are being modulated by the same set of environmental factors to produce the varieties’ responses, or, by extension, the same set of factors produces the differences between the mean responses for groups. This article and its companion (Taylor in press 2006 Biological Theory 1) seek to open more conceptual space for the challenge of deriving empirically validated models of developmental pathways whose components are heterogeneous and differ among individuals at any one time and over generations.
Keywordsagricultural crops analysis of variance causes heritability heterogeneity hypothesis generation measurable factors models observational trials rerun predictability
Unable to display preview. Download preview PDF.
- Jencks C, Phillips M, eds (1998) The Black-White Test Score Gap. Washington, DC: Brookings Institution Press.Google Scholar
- Jensen AR (1969) How much can we boost IQ and scholastic achievement? Harvard Educational Review 39: 1–123.Google Scholar
- Jensen AR (1970) Race and the genetics of intelligence: A reply to Lewontin. Bulletin of the Atomic Scientists 26: 17–23.Google Scholar
- Lewontin RC (1970a) Race and intelligence. Bulletin of the Atomic Scientists 26: 2–8.Google Scholar
- Lewontin RC (1970b) Further remarks on race and the genetics of intelligence. Bulletin of the Atomic Scientists: 23–25.Google Scholar
- Lewontin RC (1974) The analysis of variance and the analysis of causes. American Journal of Human Genetics 26: 400–411.Google Scholar
- Lewontin RC (1982) Human Diversity. New York: Freeman.Google Scholar
- Lynch M, Walsh B (1998) Genetics and Analysis of Quantitative Traits. Sunderland, MA: Sinauer.Google Scholar
- Miele F (2002) Intelligence, Race, and Genetics: Conversations with Arthur Jensen. Boulder, CO: Westview Press.Google Scholar
- Parens E (2004) Genetic differences and human identities: On why talking about behavioral genetics is important and difficult. Hastings Center Report (January–February): S1–S36.Google Scholar
- Pearl J (2000) Causality: Models, Reasoning, and Inference. Cambridge: Cambridge University Press.Google Scholar
- Plomin R, Defries JC, Craig IW, McGuffi P, eds (2003) Behavioral Genetics in the Postgenomic Era. Washington, DC: American Psychological Association.Google Scholar
- Taylor PJ (in press 2006) Heritability and heterogeneity: II. The irrelevance of heritability in explaining differences between means for different human groups or generations. Biological Theory 1(4).Google Scholar
- Woodward J (2003) Making Things Happen: A Theory of Causal Explanation. New York: Oxford University Press.Google Scholar