The Trouble with Twin Studies (2015)

The Trouble with Twin Studies: A Reassessment of Twin Research in the Social and Behavioral Sciences

Available from Taylor & Francis and (including Kindle Edition).

We have now reached a pivotal moment in the history of the social and behavioral sciences. Although researchers have argued for decades that twin studies show that genetic factors exert an important influence on human behavioral differences, for the most part, despite decades of attempts, they have failed to produce confirmed evidence of specific genes that underlie differences in IQ, personality, socially disapproved behavior, and the major psychiatric disorders. Dramatically conflicting results of this type can lead to the overturn of scientific paradigms—eventually, something has to give in light of these ongoing gene discovery failures.     

Cover of The Trouble with Twin Studies by Jay Joseph

Most twin studies compare the behavioral resemblance of identical (MZ) and same-sex fraternal (DZ) twin pairs reared together in the same family home, while a tiny yet influential handful have studied what researchers call “reared-apart” twins. The author shows that in addition to important methodological flaws, both types of twin studies are based on highly questionable or outright false assumptions about twins and their behavior-influencing environments. He places special emphasis on problems with reared-apart twin studies because they are widely—yet wrongly—put forward as the ultimate test of the relative influences of “nature” and “nurture.” 

The Trouble with Twin Studies is an interesting and thought provoking work, and is based on the author’s comprehensive 15-year evaluation of behavioral twin research. It provides a thorough critical analysis of the main research methods used to support genetic determinist theories, and is sure to be widely discussed by social and behavioral scientists, and many others, for years to come.


Joseph (a practicing psychologist) presents a meticulously detailed albeit polemical critique of behavior genetics in general and the twin studies technique in particular. … Though complex, the material is carefully presented and should be accessible to students of psychology and biology. The book is particularly valuable for bringing together political and scientific issues. Summing Up: Highly recommended. Upper-division undergraduates through faculty and professionals.

J. Mercer, emerita, Stockton University, in CHOICE, July 2015

The Trouble with Twin Studies significantly adds to Jay Joseph’s impressive record of scholarship critiquing the conceptual and methodological flaws of research claiming to document a genetically-determined basis of human behavior and development. This book provides an insightful and important analysis of the flaws of claims derived from twin research that, independent of coactions with the environment, genes alone or in large part determine human psychological and social attributes. This title is essential reading for basic and applied scholars interested in understanding the inadequacies of simplistic, genetic-reductionist accounts of human development.

Richard M. Lerner, Director, Institute for Applied Research in Youth Development, Tufts University

Jay Joseph exposes the fundamentally flawed assumptions held by researchers who use twins to study the genetics of human behavior, bolstering his criticisms with the words of the researchers themselves. This is a must-read for biology teachers, geneticists seeking genes for human behaviors, psychiatrists, and all of us who learned in school about nature’s supposedly “perfect experiment” – the study of identical twins.

Jonathan Beckwith, Harvard Medical School, Department of Microbiology and Immunobiology

This book is an astonishingly detailed and comprehensive dissection of the results of all the major twin studies, and the vaulting claims of twin researchers. It reveals the simplistic notions about genes and environments and the preposterous idea that their effects on human variation can be separated. Joseph then exposes the often-shoddy, corner-cutting methods through which that impossible dream has been pursued. This book will be an invaluable resource to those who suspect that twin studies are too good to be true, and want to articulate the arguments that encourage wider views of the causes of human variation.

Ken Richardson PhD, Former Lecturer, Open University

Joseph’s analysis of the twin studies is a masterpiece in both breadth and depth. If you have always been skeptical of claims about genes for mental illness then you owe Joseph a debt of gratitude. The Trouble with Twin Studies shows that often made claims about genes and mental health are laid bare.

Jonathan Leo, PhD, Professor of Neuroanatomy, Lincoln Memorial University