Digit ratio (2D:4D) and month of birth: A link to the solstitial-melatonin-testosterone effect

Digit ratio (2D:4D) is a sexually dimorphic trait and its determination in utero is influenced by testosterone. The solstitial-melatonin-testosterone hypothesis posits that melatonin inhibits the production of foetal testosterone and melatonin levels are at their lowest in months when light levels are high.
Source: Early Human Development - Category: Perinatology & Neonatology Authors: Source Type: research