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A Critical Review of the Research on the Extreme Male Brain Theory and Digit Ratio (2D:4D)

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Abstract

Boys are more likely than girls to be diagnosed with an autism spectrum disorder (ASD). The extreme male brain (EMB) theory of ASD suggests that fetal testosterone (FT) exposure may underlie sex differences in autistic traits. A link between the organizational effects of FT on the brain and ASD is often drawn based on research using digit ratio (2D:4D), a putative biomarker, without a full survey of the findings. This paper critically and quantitatively reviews the research on the relationship between 2D:4D and ASD as well as autism spectrum, empathizing, and systemizing measures in neurotypical populations. Overall, there is some support for the EMB theory in all four areas, particularly the 2D:4D–ASD relationship. Recommendations for future research are provided.

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Notes

  1. de Bruin et al. (2006) in Table 1 herein corresponds to de Bruin et al. (2009) in Table 1 of Hönekopp (2012). de Bruin et al. (2009) did not report on differences in 2D:4D as a function of ASD diagnosis but rather the correlation between 2D:4D and the autism diagnostic observation schedule-generic (ADOS-G) in a mixed-diagnosis clinical sample. It is possible that Hönekopp (2012) contacted the corresponding author for the former information. However, the data presented in Table 1 of Hönekopp (2012) are consistent with that from de Bruin et al. (2009) and the ASD subsample sizes in de Bruin et al. (2006) and de Bruin et al. (2009) do not match. Also, it should be noted that the de Bruin et al. data for left and right 2D:4D are inverted in, the mean 2D:4D for the control group in Milne et al. (Milne et al. 2006) is omitted from, and the percentage of the control participants in Milne et al. that was male is inaccurately reported in Hönekopp (2012).

  2. This study was not included in the meta-analysis of group comparisons because it did not include a control group.

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  1. Health, Hormones, and Behaviour Laboratory, Department of Psychology, Lakehead University, 995 Oliver Road, Thunder Bay, ON, P7B 5E1, Canada

    Missy L. Teatero

  2. Department of Psychology, Lakehead University, 995 Oliver Road, Thunder Bay, ON, P7B 5E1, Canada

    Charles Netley

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Teatero, M.L., Netley, C. A Critical Review of the Research on the Extreme Male Brain Theory and Digit Ratio (2D:4D). J Autism Dev Disord 43, 2664–2676 (2013). https://doi.org/10.1007/s10803-013-1819-6

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