Reply to Del Giudice et al., Chekroud et al., and Rosenblatt: Do brains of females and males belong to two distinct populations?

Analysis of Human Brain Structure Reveals that the Brain “Types” Typical of Males Are Also Typical of Females, and Vice Versa

“…Thus, it is not known, and has not been tested in the present study, whether and in what biological sense (structurally or functionally) a brain is more similar to other brains that are similarly classified than to brains from another classification/cluster. In fact, we claim here (see the section “Discussion”) and elsewhere (e.g., Joel et al, 2016 ) that the mosaic nature of the brain makes such classifications functionally meaningless.…”

“…While a failure to find large sex differences in the proportion of females and males in the large clusters indicates that sex category is less important than other variables in determining brain structure, it does not indicate that brains cannot be clustered according to sex category. As has been previously argued ( Joel, 2011 ) and demonstrated ( Chekroud et al, 2016 ; Del Giudice et al, 2016 ; Joel et al, 2016 ; Rosenblatt, 2016 ), the existence of group-level sex differences in the structure of specific brain regions suffices for predicting, with accuracy above chance, whether a brain’s owner is male or female. In this sense, brains can be classified as “male” and “female” ( Chekroud et al, 2016 ; Del Giudice et al, 2016 ; Rosenblatt, 2016 ).…”

Sex on the brain: Are gender‐dependent structural and functional differences associated with behavior?

“…The best option would naturally be to hold a discussion based on convincing (empirical, if possible) arguments challenging or supporting a particular point of view. A recent publication by Del Giudice et al () (http://www.pnas.org/cgi/doi/10.1073/pnas.1525534113) and a reply by Joel et al () can be seen as a well‐guided approach to the problem while also illustrating how important the theoretical approach is, as it often critically influences the methodology and aims of scientific studies. A theoretical approach might also determine the criteria for interpreting the data that are supposed to prove or disprove the existence of sexual differentiation of the brain.…”

Sex and gender affect the social brain: Beyond simplicity

“…Whether the human brain possesses substantial morphological and functional sex differences is currently the focus of heated debate (see, e.g., Joel, 2011; Cahill, ; Fine, ; Hyde, ; Ingalhalikar et al, ; Joel and Tarrasch, ; Joel and Yankelevich–Yahav, ; Klein et al, ), the essential part of which (Chekroud et al, ; Del Guidice et al, ; Glezerman, ; Joel et al, ; Rosenblatt, ) has been elicited by an article entitled Sex beyond the genitalia: the human brain mosaic by Daphna Joel and colleagues (2015) that appeared in the Proceedings of the National Academy of Sciences of the United States of America . With enormous ambition, it has been argued that the human brain (unlike the genitalia) is intersex (Joel, 2011) and that “brains are better described as belonging to a single heterogeneous population rather than two distinct populations” (Joel and Fausto‐Sterling, , p. 1). It has been reported that magnetic resonance imaging (MRI) analysis of about 1,400 human brains revealed extensive overlap among the distributions of females and males for gray matter, white matter, and brain connectivity (Joel et al, ).…”

“…The available scientific data as to the crucial effect of testosterone on the developing male brain is overwhelming” (Glezerman, , p. E1971). There is a hazard that the ambitious new approach for thinking about sex variations in brain structure and function (Joel and Fausto‐Sterling, ) may be misinterpreted, serving for justification and legitimation of a further use of primarily “male brains” in neuroscientific, pharmacological, and biomedical research. Although sex differences represent a rather delicate topic (for debates on neurosexism see, e.g., Fine, ), underestimation or exaggeration of possible effects retards progress in the field.…”