lation from which the mate is selected. The dominance deviation value is the difference of the genotypic values and additive values, and is caused by the effects of one allele over another in the classic Mendelian dominant/recessive sense. Interaction deviations occur when there are nonadditive relationships between loci. Broad sense heritability is an estimate of the extent to which the genotype determines the phenotype. Narrow sense heritability is used to predict the outcome when selecting for a specific trait in a population, and is estimated as the ratio of additive to phenotypic variance. Stoltenberg and Hirsch caution that heritability is not the same as inherited: while heritability is an estimate of the degree of relationship between genotype and phenotype, it does not give us the proportion of a trait that is genetically determined. Environmental factorsNo one argues for genetics alone in shaping behavior. Lewontin, Rose, and Kamin (1984) "cannot think of any significant human social behavior that is built into our genes in such a way that it cannot be shaped by social conditions." Environment includes a broad array of effects on intelligence; some influence whole populations while others contribute to individual differences. These influences include biological as well as social and cultural factors. Biological factors such as malnutrition, exposure to toxic substances, prenatal and perinatal stressors may result in lowered intelligence. Prolonged malnutrition during childhood has negative long-term intellectual effects, but interestingly, in a study on prenatal malnutrition, Stenin, Susser, Saenger, and Marolla studied the test scores of 19-year-old Dutch males born during a wartime famine (Neisser et al., 1996), and found that exposure to famine had no effect on adult intelligence. Exposure to lead can have a negative effect on intelligence: Neisser et al. (1996) administered IQ tests to children with high blood lead levels ...
