Latitude, digit ratios, and Allen's and Bergmann's rules: a comment on Loehlin, McFadden, Medland, and Martin (2006)

Abstract

Comments on an article by J. C. Loehlin, D. McFadden, S. E. Medland and N. G. Martin (see record 2007-07455-014). The authors investigated the relationship between latitude and digit ratio (2D:4D). Like digit ratio, height has been suggested to reflect physical masculinization. Height is also positively correlated with perceptual-verbal ability (in women) and mental rotation ability. Latitude effect may not be completely independent of the hypothesized organizational effects of testosterone. Sex ratios appear to be influenced by circulating hormone levels in the parents around the time of conception and sex ratios at birth appear to be male-biased towards the equator and relatively male-biased at high latitudes. Regardless, any link between organizational testosterone and stature on the one hand and digit ratio on the other, and inter-ethnic variation in all three physical traits, requires further investigation. We suggest that much of the variance in digit ratio attributable to latitude is actually due to an allometric relationship between body size and digit ratio across populations.