Beyond Heritability: Twin Studies in Behavioral Research

It's possible to get past the pay wall on this brand new article

Johnson, W., Turkheimer, E., Gottesman, I., and Bouchard, T. (2009). Beyond Heritability: Twin Studies in Behavioral Research. Current Directions in Psychological Science, 18, 4. 217-220.

here:

http://www.psychologicalscience.org/journals/cd/18_4_inpress...

The article, by some of the leading researchers on behavioral genetics, corrects common misconceptions about what "heritability" means. Contrary to much opinion of persons who have not studied genetics, heritability has nothing to do with what Sandra Scarr or William Angoff called "malleability," how much a trait can be influenced by environmental factors:

"Moreover, even highly heritable traits can be strongly manipulated by the environment, so heritability has little if anything to do with controllability. For example, height is on the order of 90% heritable, yet North and South Koreans, who come from the same genetic background, presently differ in average height by a full 6 inches (Pak, 2004; Schwekendiek, 2008)."

Using twin studies to look for discordant traits between monozygotic twins provides some surprising controls on assumptions of genetic determinism in human behavior:

"In a related vein, intelligence and education are often associated with healthier lifestyle choices (Deary, Whalley, Batty, & Starr, 2006; Gottfredson, 2004). Controlling for genetic and shared-environmental influences, however, Johnson, Hicks, McGue, & Iacono (in press) found that both higher IQ and greater education were associated with more alcohol and nicotine use in both sexes at age 24. This suggests that the generally lower substance use among brighter and better-educated young adults results from selection on genetic and family influences contributing to an environment emphasizing both educational attainment and reduced substance use, rather than from direct application of intelligence and/or education in substance-use choices."