title: Second to fourth digit ratio: ethnic differences and family size in English, Indian and South African populations.
abstract: BACKGROUND
  The second to fourth digit ratio (2D:4D) is lower in men than in women. 2D:4D may be established in utero and is negatively correlated with sperm counts and testosterone in men and positively correlated with oestrogen in men and women. Negative associations between male 2D:4D and family size and positive associations between female 2D:4D and family size have been found in some European populations.
  
  
  OBJECTIVE
  The study seeks to investigate the relationship between 2D:4D and family size in samples from Europe, Asia and Africa.
  
  
  METHODS
  Measurements of right hand 2D:4D were made in English (Merseyside, n = 403), Indian (Sugali and Yanadi, n= 160) and South African (Zulu,n = 258) populations.
  
  
  RESULTS
  2D:4D was weakly sexually dimorphic and showed strong ethnic differences. There were significant associations between 2D:4D and family size. For males these included negative associations in English and South African samples, and in the total sample. In females there was a positive association in the English sample, a negative association in the South African sample, and the total female sample showed a positive relationship between 2D:4D and family size.
  
  
  CONCLUSIONS
  2D:4D showed weak sex and strong ethnic differences. Low values of 2D:4D were associated with large family size in men. The situation was less clear in women but on balance there was evidence to support a relationship between high values of 2D:4D and large family size.
authors.affiliation: School of Biological Sciences, The University of Liverpool, Liverpool, UK. jtmanning@uclan.ac.uk
authors.forename: J T
authors.initials: JT
authors.lastname: Manning
authors.forename: P
authors.initials: P
authors.lastname: Henzi
authors.forename: P
authors.initials: P
authors.lastname: Venkatramana
authors.forename: S
authors.initials: S
authors.lastname: Martin
authors.forename: D
authors.initials: D
authors.lastname: Singh
mesh_terms: D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D004739:England / Q000453:epidemiology; D005191:Family Characteristics / Q000208:ethnology*; D005260:Female; D005298:Fertility; D005385:Fingers / Q000033:anatomy & histology*; D006801:Humans; D007194:India / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D012727:Sex Characteristics; D013019:South Africa / Q000453:epidemiology