title: Digit ratio (2D:4D), salivary testosterone, and handedness.
abstract: The length of the index finger relative to that of the ring finger, the 2D:4D ratio, has been taken to be a marker of the amount of testosterone (T) that was present in the foetal environment (Manning, Scutt, Wilson, & Lewis-Jones, 1998). It has also been suggested (Geschwind & Galaburda, 1987) that elevated levels of foetal T are associated with left-handedness and that adult levels of circulating T might relate to foetal levels (Jamison, Meier, & Campbell, 1993). We used multiple regression analyses to investigate whether there is any relationship between either left or right hand 2D:4D ratio and handedness. We also examined whether adult levels of salivary T (or cortisol, used as a control hormone) predict digit ratio and/or handedness. Although the 2D:4D ratio of neither the left nor the right hand was related to handedness, the difference between the digit ratios of the right and left hands, D(R-L), was a significant predictor of handedness and of the performance difference between the hands on a peg-moving task, supporting previous findings (Manning & Peters, 2009; Manning et al., 1998; Manning, Trivers, Thornhill, & Singh, 2000; Stoyanov, Marinov, & Pashalieva, 2009). Adult circulating T levels did not predict the digit ratio of the left or right hand; nor was there a significant relationship between concentrations of salivary T (or cortisol) and either hand preference or asymmetry in manual skill. We suggest that the association between D(R-L) and hand preference arises because D(R-L) is a correlate of sensitivity to T in the developing foetus.
authors.affiliation: Department of Psychology, University of Swansea, Wales, UK. a.a.beaton@swansea.ac.uk
authors.forename: Alan A
authors.initials: AA
authors.lastname: Beaton
authors.forename: Nick
authors.initials: N
authors.lastname: Rudling
authors.forename: Christian
authors.initials: C
authors.lastname: Kissling
authors.forename: Regine
authors.initials: R
authors.lastname: Taurines
authors.forename: Johannes
authors.initials: J
authors.lastname: Thome
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D019521:Body Patterning / Q000502:physiology*; D005260:Female; D005385:Fingers / Q000196:embryology* / Q000254:growth & development; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012463:Saliva / Q000378:metabolism*; D012727:Sex Characteristics; D013739:Testosterone / Q000378:metabolism*; D055815:Young Adult
chemical_list: D013739:Testosterone