The Spectrum of Sex and Gender.

I thank M.H. and S.H. for their helpful input on an earlier draft of this manuscript. Author Contributions Linda Arrighi has contributed to the conceptu- alization, writing—original draft, and writing—review and editing. Funding No funding was received to assist with the preparation of this manuscript. Declarations Conflicts of interest None. Ethics Approval Not applicable. Open Access This article is licensed under a Creative Commons Attri- bution 4.0 International License, which permits use, sharing, adapta- tion, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

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