Reconciling Strong Genetic and Strong Environmental Influences on Individual Differences and Deficits in Reading Ability

Abstract

Reading is a uniquely human activity that is strongly dependent both on our shared genetic endowment that distinguishes us from other primates and on the environment, typically through universal and formal reading instruction in modern societies. Thus, strong genetic and strong environmental influences are both apparent when we think of reading as a species-specific and culturally dependent skill. It is less obvious how genes and the environment influence individual differences and deficits in reading ability within modern societies that support universal reading education. Recent studies with identical and fraternal twins from Australia, England, Scandinavia, and the United States have provided evidence for strong genetic and relatively weak environmental influences on reading disability (RD) and on individual differences in reading across the normal range. These results may seem to suggest that the educational environment for reading is of little importance, but there is evidence from remedial training studies for RD (see Foorman & Al Otaiba, this volume), and from whole-school or district-wide reading reforms (see Siegel, this volume) that experimentally demonstrate strong environmental influences on reading development. One of the goals of this chapter is to work toward a reconciliation between the evidence for both strong environmental and strong genetic influences on deficits and individual differences in reading development. This is important because as Sherman and Cowen (this volume) point out, children with RD, their parents, their teachers, and educational policymakers might draw the wrong conclusions regarding the etiology and remediation of RD unless we are clear about the implications of our genetic and neurological research. It is also important that we understand the implications of genetic research for individual differences across the normal range when considering broad public educational policies such as No Child Left Behind (NCLB; 107th Congress, 2002) that often seem to ignore the possibility of genetic and other biological influences on reading ability.