In 2014, American criminologists Callie Burt and Ronald Simons published a critique of twin, adoption, and other “heritability” studies in their field, and in the process challenged the validity of studies of twins reared together (the classical twin method), and of twins reared apart.1 They also challenged the behavioral genetic position that observed behavior is the result of the additive influences of genes, the “shared environment,” and the “unshared environment.”2 They concluded that their fellow criminologists should abandon heritability studies because they are “methodologically flawed,” and because they are based on the “biologically unsound” practice of “partitioning genetic versus environmental influences on variance in phenotypes.”3 Burt and Simons’ article was followed by responses from a group of leading biosocial criminologist twin researchers.4 Burt and Simons responded to these and other critics in a subsequent article.5
A group of critically minded writers and I decided to enter this debate, and to weigh in on the validity of the twin method’s controversial MZ-DZ “equal environment assumption.” Our article was published online August 9th in the journal Logos, and is very relevant to twin studies in medicine, psychiatry, psychology, and all areas of human behavior.
I encourage readers to take a look at this article.6 A previously unpublished summary of it can be found below:
“The long-running debate on the validity of twin research recently resurfaced in American criminology, and has major implications for behavioral and medical twin research. We review the twin method’s controversial ‘equal environment assumption’ (EEA), and challenge biosocial criminologists’ claim that the assumption is well supported, and that computer simulations prove that twin method heritability estimates are valid. We also challenge the claim that the false assumptions underlying the twin method cancel each other out in favor of genetics. Most twin researchers and their critics agree that reared-together monozygotic (MZ) twin pairs experience more similar environments than experienced by same-sex dizygotic (DZ) pairs, and we argue that the twin method is therefore unable to disentangle the potential influences of genes and environment on human behavioral differences, a conclusion supported by the failures of molecular genetic research. Finally, we comment on a call to end twin (and other ‘heritability’) research in criminology.”
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1. See also Joseph, J., (2004), The Gene Illusion: Genetic Research in Psychiatry and Psychology under the Microscope, New York: Algora; Joseph, J., (2015), The Trouble with Twin Studies: A Reassessment of Twin Research in the Social and Behavioral Sciences, New York: Routledge.
2. Burt, C. H., & Simons, R. L., (2014), Pulling Back the Curtain on Heritability Studies: Biosocial Criminology in the Postgenomic Era, Criminology, 52, 223-262.
3. Burt & Simons, 2014, p. 250.
4. Barnes et al., (2014), Demonstrating the Validity of Twin Research in Criminology, Criminology, 52, 588-626; Wright et al., (2015), Mathematical Proof is Not Minutiae and Irreducible Complexity is not a Theory: A Final Response to Burt and Simons and a Call to Criminologists, Criminology, 53, 113-120.
5. Burt, C. H., & Simons, R. L., (2015), Heritability Studies in the Postgenomic Era: The Fatal Flaw is Conceptual, Criminology, 53, 103-112.
6. Joseph, J., Chaufan, C., Richardson, K., Shultziner, D., Fosse, R., James, O., Latham, J., & Read, J., (2015), The Twin Research Debate in American Criminology, Logos, 14 (Nos. 2-3), Published online 8/9/2015.
Mad in America hosts blogs by a diverse group of writers. These posts are designed to serve as a public forum for a discussion—broadly speaking—of psychiatry and its treatments. The opinions expressed are the writers’ own.