ABSTRACT
The assumption of fixed intelligence so pervades our culture that, like freeway noise, it recedes from conscious attention to form a life-drama backdrop that is seldom noticed, let alone scrutinized (Hunt, 1961). To test that assumption requires that attention be directed to evidence bearing on the plasticity of intelligence—to whether intelligence can and does change. We will see that intelligence is indeed plastic; even so, genetics is not irrelevant. On the contrary, genetic heritability makes a “significant and substantial” contribution to intelligence (Pederson, Plomin, Nesselroade, & McClearn, 1992, p. 346). The finding is robust and acknowledged by virtually all who have read the relevant research; some call it “indisputable” (Bouchard & McGue, 1981, p. 1058). A more debatable question is: How much of a contribution does heredity make? That is, what is the heritability of intelligence? A follow-up question, and one that bears more directly on the polemic of this volume, is whether a genetic contribution to intelligence places a cap on the level of intelligence attainable by an individual.
