Finger-length ratios show evidence of prenatal hormone-transfer between opposite-sex twins

Horm Behav. 2006 Mar;49(3):315-9. doi: 10.1016/j.yhbeh.2005.08.003. Epub 2005 Sep 6.


Finger-length ratio (second to fourth finger; 2D:4D) has been associated with various measures thought to be related to prenatal androgens. In addition, hormone-transfer theory posits that hormones can transfer between twins. We examined 2D:4D in same-sex (SS) and opposite-sex (OS) dizygotic twins to test both propositions. Results show that 2D:4D is masculinized in OS females compared to SS females. This provides strong evidence that 2D:4D is laid down prenatally, and that hormones (likely androgens) can transfer from male to female fetuses. Implications for developmental timeframes for both hormone-transfer and 2D:4D are discussed.

Publication types

  • Clinical Trial
  • Comparative Study
  • Twin Study

MeSH terms

  • Adolescent
  • Anthropometry
  • Child
  • Child, Preschool
  • Female
  • Fingers / anatomy & histology*
  • Gonadal Steroid Hormones / physiology*
  • Humans
  • Male
  • Organ Size
  • Pregnancy
  • Prenatal Exposure Delayed Effects*
  • Sex Characteristics*
  • Twins, Dizygotic / physiology*


  • Gonadal Steroid Hormones