Nature-Nurture? No: Moving the Sciences of Variation and Heredity Beyond the Gaps
Almost every day we hear that some trait “has a strong genetic basis” or “of course it is a combination of genes and environment, but the hereditary component is sizeable.” To say No to Nature-Nurture is to reject this relative weighting of heredity and environment. Such weighting derives from researchers in the relevant sciences—quantitative and behavioral genetics—partitioning the variation in a trait into a heritability fraction and other components. Little clear or useful information about the genetic and environmental influences is provided by this partitioning. It does not provide a reliable basis for genetic research that seeks to identify the molecular variants associated with trait variation, for asserting that genetic differences in many traits come, over people’s lifetimes, to eclipse environmental differences, for believing that the search for environmental influences and corresponding social policies is unwarranted, or for sociological research that focuses on differences in the experiences of members of the same family.
Saying No is a positive move. When the persistent formulation How much is nature, how much is nurture? is put behind us, interesting scientific and policy questions about heredity and variation can be brought into focus, reframed, and taken in new directions. Or, to be more precise, interesting questions emerge as a result of assembling, step-by-step, a toolbox of conceptual themes that depart from the persistent How much is nature, how much is nurture? formulation. In explicating the concepts, the book draws on examples and perspectives from my earliest research—the analysis of data from large plant breeding trials, in which many cultivated varieties were tested in each of many locations around the world. This background led me to puzzle over the positions and propositions of others that did not, for me, fit together. In conveying the ways I question what many researchers and commentators take as “settled law,” I have ended up taking a first-principles, pedagogical approach. Although this involves, at times, identifying shortcomings in the work of other authors, that is not the dominant style of this book.
Part I draws readers into puzzles that have not been resolved in the study of heredity and variation then distills issues into eight conceptual and methodological gaps that need attention. Some gaps should be kept open; others should be bridged or the difficulty of doing so should be conceded. Previous researchers and commentators have either not acknowledged the gaps, not developed the appropriate responses, or not consistently sustained their responses. The account of puzzles and gaps, while necessarily centered on the idea of data analysis, is expressed in terms accessible to non-specialists; no equations, mathematical symbols, or data sets are needed to explain the issues. At the same time, the account should be challenging to researchers in the social and life sciences as well as other specialists and commentators who believe that the nature-nurture arena has been exhaustively covered.
Part II employs equations and technical detail to build on Part I. A formulation of quantitative genetics is introduced that makes no reference to genes and the field’s causal claims are circumscribed as forms of rerun predictability. Two more general themes are developed: heterogeneity—when similar responses of different individual types are observed, it is not necessarily the case that similar conjunctions of measurable factors have been involved in producing those responses—and causal claims are grounded in practice, that is, always drawing on the actions possible or proposed on the basis of what is known. These two themes carry over to Part III, in which they help to illuminate the possibilities and problems of research programs in behavior, health, and epidemiology that address genes and environment but leave heritability studies behind.
Along the way, more puzzles and questions are opened up to elicit and guide contributions from others who work in various sciences from quantitative, behavioral, and molecular genetics to epidemiology and agricultural breeding; in history, philosophy, sociology, and politics of the life and social sciences; and in engagement of the public in discussion of developments in science. The book ends in that opening-up spirit by introducing a suggestion that invites further exploration, namely, behind the persistence of the relative weighting of nature and nurture lies a conflation of concerns about family and about populations.
(revised 14 August 2014)
In advance of the book appearing in press, the following references address key points:
Taylor, P. J. (2010). “Three puzzles and eight gaps: What heritability studies and critical commentaries have not paid enough attention to.” Biology & Philosophy 25(1): 1-31.
Taylor, P. J. (2012). “A gene-free formulation of classical quantitative genetics used to examine results and interpretations under three standard assumptions.” Acta Biotheoretica 60(4): 357-378.