Theory and Review

Two primary theories of heredity and development are prevalent in biology and psychology today. They may be summarized in terms of the symbols G for genotype, H for heredity, and E for Environment.

1. HE. Heredity consists of more than Mendelian genes and includes cytoplasmic organelles such as the mitochondria. Depending on the design of the experiment, heredity may also include the maternal environment. The organism's environment, being all things external to the organism that impinge on it, comes into existence at conception. During development, heredity and environment form an interactive and interdependent system that can be analysed with experiments. H and E do not act separately during development and cannot be separated statistically, however.

2. G + E. Heredity consists solely of genes present in the cell nucleus. The genes and the environment act separately and independently during development of an organism. Consequently, their effects on behaviour are additive and separable statistically. Algebraic methods can partition variance into components, and heritability represents the percentage of variation among individuals in a population that is attributable to genetic differences.

A concise description of theoretical perspectives on heredity, development, and behaviour is given in the entry on behaviour genetics in the forthcoming Encyclopedia of Psychology. A preliminary draft of this article may be obtained from the author by submitting an email request.

Wahlsten, D. Behavior genetics. Encyclopedia of Psychology (American Psychological Association). New York: Oxford University Press, in press.

Carlier, M., Roubertoux, P.L., and Wahlsten, D. Maternal effects in behavior genetic analysis. In P. Mormede and B Jones (Eds.), Cellular and Quantitative Methods in Neurogenetics. CRC Press, in press.

Wahlsten, D. Single-gene influences on brain and behavior. Annual Review of Psychology, 1999, 50, 599-624.

Gottlieb, G., Wahlsten, D., and Lickliter, R. The significance of biology for human development: a developmental psychobiological systems view. In R. Lerner (Ed.), Handbook of Child Psychology, Vol. 1, Theory. New York: Wiley, 1998, pp. 233-273.

Wahlsten, D., and Gottlieb, G. The invalid separation of effects of nature and nurture: Lessons from animal experimentation. In R. J. Sternberg and E. L. Grigorenko (Eds.), Intelligence, Heredity and Environment. Cambridge: Cambridge University Press, 1997, pp. 163-192.

Wahlsten, D. The malleability of intelligence is not constrained by heritability. In B. Devlin, et al. (Eds.), Intelligence, Genes & Success. New York: Copernicus (Springer Verlag),1997, pp. 71-87.

Wahlsten, D. Advances in genetic analysis of IQ await a better understanding of environment. In D. K. Detterman (Ed.), Current Topics in Human Intelligence, Vol. 5. Norwood, NJ: Ablex Publishing, 1996, pp. 185-190.

Wahlsten, D. Evaluating genetic models of cognitive evolution. Behavioural Processes, 1996, 35, 183-194.

Wahlsten, D. The intelligence of heritability. Canadian Psychology, 1994, 35, 244-258.

Wahlsten, D. Probability and the understanding of individual differences. In J. Brzezinski (Ed.), Probability in theory-building. Amsterdam: RODOPI, 1994, 39, pp. 47-60.

Wahlsten, D. Insensitivity of the analysis of variance to heredity-environment interaction. Behavioral and Brain Sciences, 1990, 13, 109-120. (Target article)