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Proc Natl Acad Sci U S A. 2015 Dec 15;112(50):15468-73. doi: 10.1073/pnas.1509654112. Epub 2015 Nov 30.

Sex beyond the genitalia: The human brain mosaic.

Author information

1
School of Psychological Sciences, Tel-Aviv University, Ramat Aviv, Tel-Aviv 6997801, Israel; Sagol School of Neuoroscience, Tel-Aviv University, Ramat Aviv, Tel-Aviv 6997801, Israel; djoel@post.tau.ac.il.
2
Sagol School of Neuoroscience, Tel-Aviv University, Ramat Aviv, Tel-Aviv 6997801, Israel;
3
Department of Neurobiology, Faculty of Life Sciences, Tel-Aviv University, Ramat Aviv, Tel-Aviv 6997801, Israel;
4
School of Mathematical Sciences, Tel-Aviv University, Ramat Aviv, Tel-Aviv 6997801, Israel;
5
School of Psychological Sciences, Tel-Aviv University, Ramat Aviv, Tel-Aviv 6997801, Israel;
6
School of Psychological Sciences, Tel-Aviv University, Ramat Aviv, Tel-Aviv 6997801, Israel; Sagol School of Neuoroscience, Tel-Aviv University, Ramat Aviv, Tel-Aviv 6997801, Israel;
7
Max Planck Research Group for Neuroanatomy & Connectivity, Max Planck Institute for Human Cognitive and Brain Sciences, 04103 Leipzig, Germany;
8
Max Planck Research Group for Neuroanatomy & Connectivity, Max Planck Institute for Human Cognitive and Brain Sciences, 04103 Leipzig, Germany; Division Neuropsychology, Department of Psychology, University of Zurich, 8050 Zurich, Switzerland.
9
Division Neuropsychology, Department of Psychology, University of Zurich, 8050 Zurich, Switzerland.
10
Sagol School of Neuoroscience, Tel-Aviv University, Ramat Aviv, Tel-Aviv 6997801, Israel; Department of Neurobiology, Faculty of Life Sciences, Tel-Aviv University, Ramat Aviv, Tel-Aviv 6997801, Israel;

Abstract

Whereas a categorical difference in the genitals has always been acknowledged, the question of how far these categories extend into human biology is still not resolved. Documented sex/gender differences in the brain are often taken as support of a sexually dimorphic view of human brains ("female brain" or "male brain"). However, such a distinction would be possible only if sex/gender differences in brain features were highly dimorphic (i.e., little overlap between the forms of these features in males and females) and internally consistent (i.e., a brain has only "male" or only "female" features). Here, analysis of MRIs of more than 1,400 human brains from four datasets reveals extensive overlap between the distributions of females and males for all gray matter, white matter, and connections assessed. Moreover, analyses of internal consistency reveal that brains with features that are consistently at one end of the "maleness-femaleness" continuum are rare. Rather, most brains are comprised of unique "mosaics" of features, some more common in females compared with males, some more common in males compared with females, and some common in both females and males. Our findings are robust across sample, age, type of MRI, and method of analysis. These findings are corroborated by a similar analysis of personality traits, attitudes, interests, and behaviors of more than 5,500 individuals, which reveals that internal consistency is extremely rare. Our study demonstrates that, although there are sex/gender differences in the brain, human brains do not belong to one of two distinct categories: male brain/female brain.

KEYWORDS:

behavior; brain connectivity; brain structure; gender differences; sex differences

PMID:
26621705
PMCID:
PMC4687544
DOI:
10.1073/pnas.1509654112
[Indexed for MEDLINE]
Free PMC Article
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