Genetic and Environmental Influences on Continuity and Change in Reading Achievement in the Colorado Adoption Project

Abstract

Mastery of reading skills in childhood has far-reaching implications for development. Serving as a foundation for all academic learning, reading performance affects not only educational attainment, but also employment options, interpersonal relationships, and emotional well-being. Although this essential skill continues to develop throughout adolescence and adulthood, measures of reading achievement are highly stable, with correlations ranging from .23 to .96 over intervals of 1 to 8 years (e.g., Bast & Reitsma, 1998; DeFries, 1988; DeFries & Baker, 1983; Shaywitz, Escobar, Shaywitz, Fletcher, & Makuch, 1992; Wadsworth, Corley, Hewitt, & DeFries, 2001; Wagner et al., 1997; Williams & McGee, 1996). Results obtained from both twin and adoption studies have provided compelling evidence for substantial genetic influences on individual differences in reading performance from age 7 to adulthood, with heritability estimates ranging from .18 to .81 (e.g., Alarcon & DeFries, 1995; Cardon, DiLalla, Plomin, DeFries, & Fulker, 1990; Knopik & DeFries, 1999; Stevenson, Graham, Fredman, & McLoughlin, 1987; Wadsworth et al., 2001). Despite the striking evidence for stability and heritability, reading achievement also shows some change as a function of environmental influences. All of these factors – genes and environment, continuity and change – are needed for a complete understanding of the development of reading achievement. The evidence that individual differences in reading achievement are both stable and heritable throughout development suggests that genetic influences contribute to continuity. Genetic influences that are important at an early age may also be important at later ages.