ferent heterotic effects on the various tests are specifically related to the tests' g loadings. The column vector of the heterosis index on each of the fifteen tests and the column vector of the tests' g loadings show a rank-order correlation (with tests' reliability coefficients partialed out) of +.52 (p < .05). This finding for heterosis, along with the findings for inbreeding depression, leaves little doubt that a significant part of the genetic basis of psychometric g is attributable to dominance of the alleles that to some degree enhance phenotypic mental abilities.
My own ( Jensen, 1981 a, Chapter 3, pp. 74-127) attempt to explain the genetics of mental ability as clearly and simply as possible for readers with no technical background whatsoever in this field begins with the earliest study by Galton, introduces the basic concepts of Mendelian and quantitative genetics, and succinctly reviews the main findings regarding the various sources of genetic and environmental variance in IQ. For those who have no prior knowledge of how behavioral genetics "works," this chapter may serve as an essential prerequisite for any of the other items listed below. Another good introduction to behavior genetics methodology, briefer but slightly more technical than Jensen ( 1981 a), is by Eysenck ( 1984a). Plomin ( 1990) offers a more extended elementary treatment. The reading level in Plomin ( 1994) presents no real technical difficulty for the uninitiated, but its main theme is somewhat specialized and would probably be more appreciated by readers who have some familiarity with the standard material presented in the previously mentioned references. Plomin, DeFries, & McClearn ( 1990) provide one of the standard introductory textbooks of behavioral genetics. There are also several fairly comprehensive reviews of genetic research on human abilities that assume some knowledge of the terminology and methodology of quantitative genetics (but do not make them absolutely essential for understanding the main conclusions): Bouchard, 1993; Bouchard et al., 1996; Plomin, 1988; Scarr & Carter-Saltzman, 1982; and Vandenberg & Vogler, 1985. A book edited by Plomin & McClearn ( 1993) presents elementary accounts of specialized topics in human behavioral genetics, although the first two chapters introduce the most basic general principles of quantitative genetics. Accounts of the historical and controversial aspects of the so-called "nature-nurture" debate