Digit ratio (2D:4D) and hand preference for writing in the BBC Internet Study

Area of Science:

• Human biology
• Behavioral neuroscience
• Endocrinology

Background:

• The second to fourth digit ratio (2D:4D) is a proposed marker for prenatal androgen exposure.
• Hand preference, a complex trait, has been theoretically linked to prenatal hormone levels and 2D:4D.
• Previous research suggests a connection between 2D:4D and handedness, but large-scale data is needed.

Purpose of the Study:

• To investigate the association between 2D:4D and writing hand preference in a large sample.
• To replicate existing findings on the relationship between right 2D:4D and handedness.
• To explore novel correlations between left 2D:4D, the difference in 2D:4D (Dr-l), and writing hand preference.

Main Methods:

• Analysis of self-reported finger length data (2D:4D) and writing hand preference from over 170,000 participants.
• Statistical examination of correlations between right 2D:4D, left 2D:4D, Dr-l, and writing hand preference.
• Comparison of 2D:4D values between left- and right-handed individuals, stratified by sex.

Main Results:

• A significant association was confirmed between right 2D:4D and writing hand preference (lower right 2D:4D linked to left-handedness).
• A significant correlation was found between Dr-l and writing hand preference (lower Dr-l linked to left-handedness).
• A novel significant correlation emerged between left 2D:4D and writing hand preference (higher left 2D:4D linked to left-handedness).
• Significant interactions showed left 2D:4D > right 2D:4D in left-handers, and right 2D:4D > left 2D:4D in right-handers, irrespective of sex.

Conclusions:

• Digit ratio (2D:4D) is robustly associated with writing hand preference.
• The findings support the hypothesis that prenatal hormone exposure influences both 2D:4D and hand preference.
• Asymmetry in 2D:4D between hands is consistently related to handedness, with distinct patterns for left- and right-handers.