Background: High relative androgen level (testosterone/estrogens) in utero plays an important role in the etiology of differential second digit (2D) and fourth digit (4D) lengths of hands, bilateral asymmetry, digit ratio (2D:4D), and handedness in males and females.

Methods: Present study was done in a sample of 20 to 50 year-old men (n= 56) and women (n= 53) from Merida, Mexico. Lengths of 2D and 4D were measured; 2D:4D and absolute fluctuating asymmetry were estimated; handedness was recorded.

Results: Mean value of age in men (35.46 years) and women (38.30 years) was not significantly different (p>0.05). Left-handedness was more frequent in men (16%) than women (9%). Mean of 2D length in men was lower than 4D that was reverse in women; men had mean of 2D:4D <1.0 (left 0.96, right 0.98) whereas the value was >1.0 in women (1.03 in both hands) with significant sex difference (p<0.05). Discriminant function analysis showed 2D:4D as the significant predictor for handedness in both sex.

Conclusion: Lower 2D length, 2D:4D in men, particularly in left-handed individuals, support the hypothesis of earlier studies suggesting these characteristics interact with relatively higher pre-natal testosterone exposure. Low bilateral asymmetry indicate canalization, similarities in environmental and developmental-genetic programs for digit lengths and ratio.