According to The Bell Curve, Black Americans are genetically inferior to Whites. That's not the only point in Richard Herrnstein and Charles Murray's book. They also argue that there is something called "general intelligence" which is measured by IQ tests, socially important, and 60 percent "heritable" within whites. (I'll explain heritability below.) But the claim about genetic inferiority is my target here. It has been subject to wide-ranging criticism since the book was first published last year. Those criticisms, however, have (...) missed its deepest flaws. Indeed, the Herrnstein/Murray argument depends on conceptual confusions that have been tacitly accepted to some degree by many of the book's sharpest critics. (shrink)

Causation has multiple distinct meanings in genetics. One reason for this is meaning slippage between two concepts of the gene: Mendelian and molecular. Another reason is that a variety of genetic methods address different kinds of causal relationships. Some genetic studies address causes of traits in individuals, which can only be assessed when single genes follow predictable inheritance patterns that reliably cause a trait. A second sense concerns the causes of trait differences within a population. Whereas some single genes can (...) be said to cause population-level differences, most often these claims concern the effects of many genes. Polygenic traits can be understood using heritability estimates, which estimate the relative influences of genetic and environmental differences to trait differences within a population. Attempts to understand the molecular mechanisms underlying polygenic traits have been developed, although causal inference based on these results remains controversial. Genetic variation has also recently been leveraged as a randomizing factor to identify environmental causes of trait differences. This technique—Mendelian randomization—offers some solutions to traditional epidemiological challenges, although it is limited to the study of environments with known genetic influences. (shrink)

A central thesis of this paper is that understanding the nature of child maltreatment is so complex that no one disciplinary specialty is likely to be sufficient for the task. Although life history theory is the guiding principle for our analysis, we argue that an evolutionary explanation adds precision by incorporating empirical findings originating from the fields of anthropology; clinical, developmental, and social psychology; and sociology. Although evolutionary accounts of child maltreatment have been largely limited to the role of the (...) coefficient of relatedness, the prospective reproductive value of a child, and the residual reproductive potential of parents, a case is made for expanding this basic application. An explanatory model is presented that describes how ecological conditions as well as parental and child traits interact to influence the degree of parental investment. As shown in the model, these various “marker variables” alter parental perceptions of the benefits and costs associated with child care and promote low-investment parenting, which leads to disrupted family management practices and to a downward-spiraling, self-perpetuating system of coercive family interaction, increased parental rejection of the child, and even lower parental investment. Child maltreatment is the ultimate outcome of this downward trajectory of family relations. (shrink)

The target article is skeptical of the heritability concept while maintaining an old-fashioned point of view about it. As a descriptive statistic, it is to be expected that heritability goes up and down in different circumstances, but the relationship between heritability coefficients and the biological processes that underlie them is difficult to specify, and may be impossible in humans.

Several new molecular findings and concepts furnish evidence in support of geneneogenomicsclassical” behavioral genetics modeling.