A widely cited 2015 study claimed a man’s finger ratios could predict how agreeably he treated women. However, subsequent replication failures, broader economic experiments, and a 2024 meta-analysis show no robust link between digit ratios and prenatal testosterone or actual social behavior.
For years, a distinct physical measurement caught the attention of researchers and headline writers alike. Known as the second-to-fourth digit ratio, or 2D:4D, the calculation involves comparing the length of a person’s index finger to their ring finger. Men generally have slightly lower ratios than women, and scientists previously investigated the metric as an indirect marker of exposure to sex hormones like testosterone before birth.
What the 2015 Study Claimed About Digit Ratios and Behavior
In 2015, researchers published a study involving 155 participants who logged daily social interactions lasting more than five minutes. Men with small digit ratios reported roughly a third more agreeable behaviors and about a third fewer quarrelsome behaviors than men with large digit ratios, according to the findings.
When with women, men with smaller ratios were more likely to listen attentively, smile and laugh, compromise or compliment the other person.
Debbie Moskowitz, Professor of Psychology at McGill and lead author
The original authors also suggested this dynamic might help explain why men with shorter index fingers relative to ring fingers tended to have more children, as these behaviors assist in forming and maintaining relationships with women. However, researchers noted at the time that the association was purely observational and could not establish causation.
Replication Failures and Broader Tests Challenge the Link
Subsequent investigations failed to sustain the original conclusions. In 2021, Michelle Spix and Marije aan het Rot attempted to replicate the earlier work using everyday social interactions among 81 participants. While male participants generally behaved more agreeably toward women than toward men, this behavioral difference did not depend significantly on their 2D:4D ratios, though the authors acknowledged their smaller sample size as a limiting factor.
Additional skepticism arrived in 2019, when a study examined 560 people participating in economic games involving real money. Those experiments found no clear relationship between 2D:4D and generosity, bargaining, trust, reciprocity, or punishment.
Current Scientific Standing of 2D:4D Ratios
Discussions regarding what finger ratios actually reveal remain active among specialists. A 2025 commentary published in Hormones and Behavior defended the right-hand digit ratio as a useful retrospective indicator of prenatal androgen exposure. Conversely, a 2024 meta-analysis found no overall relationship between digit ratios and prenatal testosterone across the evaluated studies.
Current scientific assessments indicate that while biological markers may still exist within finger lengths, they do not provide a reliable method for determining individual prenatal hormone levels or predicting whether a specific man will act kindly or argumentatively toward women.
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