Digit ratio (2D:4D) and its relationship to foetal and maternal sex steroids: A mini-review

The challenges of terrestrial existence may mean that the early development of tetrapod limb traits is linked to the development of the urogenital system and sex steroids. One such limb trait is the sex-dependent ratio of the lengths of the 2nd and 4th digits (2D:4D). Direct evidence for the associa...

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Bibliographic Details
Published in:Early human development 2023-08, Vol.183, p.105799-105799, Article 105799
Main Authors: Manning, J.T., Fink, B.
Format: Article
Language:English
Subjects:
2D:4D
Animals
Development
Digit ratio
Digit Ratios
Female
Fingers - anatomy & histology
Gonadal Steroid Hormones
Humans
Male
Pregnancy
Prenatal
Sex Characteristics
Sex Factors
Sex-steroids
Steroids
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Summary:The challenges of terrestrial existence may mean that the early development of tetrapod limb traits is linked to the development of the urogenital system and sex steroids. One such limb trait is the sex-dependent ratio of the lengths of the 2nd and 4th digits (2D:4D). Direct evidence for the association between early sex steroids and offspring 2D:4D can be obtained by manipulating foetal sex hormones. However, this is not ethically permissible in humans. It is widely accepted that 2D:4D is a biomarker for early foetal sex hormones in tetrapods but the link in humans remains controversial. Here we review the evidence that (i) manipulation of sex steroids in early development leads to sex-dependent changes in 2D:4D throughout the tetrapods, and (ii) maternal sex steroids cross the placenta and thus are associated with offspring 2D:4D in both non-human and human animals. We suggest a research focus on associations between human maternal sex steroids and offspring 2D:4D to clarify the link between 2D:4D and early sex steroids. A protocol is proposed to examine the correlation between 1st-trimester maternal sex steroids and offspring 2D:4D. Such an association may explain the existence and medium effect size of the human sex difference in 2D:4D. •Digit Ratio (2D:4D) may be a biomarker for early foetal sex hormones•Evidence for this link in humans remains controversial•Research on the manipulation of sex steroids in non-human animals is reviewed•Timing of 2D:4D development in humans is discussed in relation to the magnitude of the sex difference in 2D:4D•A protocol is suggested to examine the maternal sex steroids associations with offspring 2D:4D in the 1st trimester
ISSN:0378-3782
1872-6232
DOI:10.1016/j.earlhumdev.2023.105799