Showing posts from June, 2020

It’s Time to Abandon the “Classical Twin Method” in Behavioral Research

Note: Many more articles on twin research and behavioral genetics can be found at .  My 2020 analysis of reared-apart twin studies can be found HERE (First revision 8/17/2020. Second revision 12/23/2020, based on small stylistic changes, and adding a new introductory paragraph and a paragraph about a 2018 study by Segal and colleagues) By Jay Joseph, Psy.D. In this article I will argue that studies using the "classical twin method" should be abandoned in the social and behavioral sciences. I will attempt to show that the main assumption these studies are based on is false — an argument I have developed in books, peer-reviewed articles , and online articles since 1998 .  Twin studies supply the "scientific evidence" most often cited in support of the claim that human behavioral differences are strongly influenced by heredity. Yet genetic interpretations of twin studies of behavior, including areas such as I