The etiology of giftedness

Abstract

Many theories of giftedness either explicitly or implicitly acknowledge the role of genetic influences; yet, empirical work has not been able to establish the impact that genes have specifically on gifted behavior. In contrast, a great deal of research has been targeted at understanding the etiology of individual differences in general and specific cognitive abilities across the entire range of ability and to a lesser extent, high cognitive ability. This paper attempts to outline what we know and what we don't know about the etiology of giftedness as operationally defined as high g. We review studies selected to represent a variety of approaches that each address a different question about genetics and giftedness. These studies include quantitative genetic research which estimate heritability, shared and nonshared family environment – at the high and low ends of intelligence – as well as the heritability of group differences for general cognitive ability and specific cognitive abilities. We discuss the molecular genetic methods and mechanisms contributing to cognitive ability and suggest how epigenetic factors may operate. Quantitative and molecular genetic studies that include endophenotypes representing intelligence at a level closer to the genotype, are also included. This last group of studies represent a relatively new area of work that builds on and extends the extensive groundwork established by classic quantitative genetic studies of behavior.

Introduction

Robert Sternberg and Janet Davidson published the second edition of Conceptions of Giftedness in 2005, a volume authored by a panel of researchers, educators and practitioners with a wide array of expertise on giftedness and talent. Each of the authors was asked to address 5 basic questions beginning with, “What is giftedness?” To advance, the scientific study of giftedness must be grounded on well defined behaviors and measurement of these behaviors (Mayer, 2005); however, a consensus definition has proven elusive and disagreement continues on how to rigorously assess giftedness. In the book's final chapter, Richard E. Mayer holds that understanding the etiology of giftedness or in Mayer's words, answering the question “Is giftedness learned or innate?” is critical to knowing what giftedness is. Mayer summarizes the evidence provided and concludes that giftedness is the result of both innate ability and experiences that allow and/or cultivate this ability to flourish. Mayer's conclusion is empirically supported by the behavioral genetics literature on the etiology of individual differences in general cognitive ability; however, the underlying complexity of how genes and environment affect the development of giftedness will continue to challenge researchers for some time to come.

Galton, called the father of behavior genetics by many (Plomin, DeFries, McClearn, & McGuffin, 2008), conducted what is credited as the first behavioral genetic study of giftedness (Galton, 1869). Lacking a detailed understanding of genetics, and without a way to empirically measure intelligence or giftedness, Galton substituted social eminence as a proxy for genius. He discovered that eminence ran in families leading him to claim that genius is the result of nature more than nurture. Although Galton's claim was overstated and premature because familial resemblance is due to shared genes and shared environments and social eminence is not synonymous with high intelligence, Galton's study set the stage for many future behavioral genetic studies of general cognitive ability, perhaps the most widely studied behavioral trait in the field of behavioral genetics (Plomin, 2002).

Although the definition and measurement of giftedness is still debated (Sternberg & Davidson, 2005, Sternberg, 2005), most genetic studies of giftedness have used standardized measures of cognitive ability with an index of general cognitive ability or g the most common indicator of giftedness. While some may argue that g too narrowly defines the construct of giftedness, this definition has several advantages. The ubiquity of g, especially when formed through factor analysis of a battery of diverse cognitive tests, allows the results of different studies to be compared to each other. Quantitative genetic studies using families, twins and adoptees require large samples to attain the power necessary for reliable estimates of heritability (h²), shared (c²) and nonshared (e²) environmental influences. Cognitive tests are easy to administer and many studies have used tests that can be administered in groups and/or over the telephone (Petrill, Rempell, Oliver, & Plomin, 2002) allowing large samples to be efficiently assessed. Finally and perhaps most important from a theoretical perspective, regardless of the definition of giftedness, g is likely to be involved as a central characteristic of giftedness (Detterman and Ruthsatz, 1999, Sternberg, 2005).

This paper attempts to outline what we know and what we don't know about the etiology of giftedness as operationally defined as high g. We review studies selected to represent a variety of approaches where each addresses a different question about genetics and giftedness. These studies include quantitative genetic research which estimate heritability, shared and nonshared family environment – at the high and low ends of intelligence – as well as the heritability of group differences for general cognitive ability and specific cognitive abilities. We discuss the molecular genetic methods and mechanisms contributing to cognitive ability and suggest how epigenetic factors may operate. Quantitative and molecular genetic studies that include endophenotypes representing intelligence at a level closer to the genotype, are also included. This last group of studies represents a relatively new area of work that builds on and extends the extensive groundwork established by classic quantitative genetic studies of behavior.