Association of height and weight with second to fourth digit ratio (2D:4D) and sex differences

Sex difference in 2D:46 digit ratio was studied in 386 right-handed students. The lengths of index (2D) and ring (4D) fingers were measured using a caliper. Height and weight of participants were recorded. Body height correlated negatively with right- and left-hand digit ratios in the total sample (N = 386); correlations were significant for the left-hand digit ratio of men and for the right-hand digit ratio of women (no significant correlations with weight). Males had a significantly lower 2D:4D ratio than females. After controlling for height, sex differences in right- and left-hand digit ratios completely disappeared. The results suggest that height of adults reflecting prenatal hormone status may play a role in differences between men and women in 2D:4D digit ratio for right-handers.     

Covariation of sex differences in mental rotation with body size

Sex difference in mental rotation ability was reconsidered. The Vandenberg-Kuse figures were administered to 120 male and 76 female students from the Medical School of BlackSea Technical University in Trabzon, Turkey to assess the mental rotation ability. Students' height and weight were measured. As expected, men outperformed women on this test and had greater height and weight. Number correct on mental rotation test significantly correlated with height and weight for the total sample and for men, but only with weight for women. Using weight as covariate, the sex difference was no longer significant. The mean mental rotation score was significantly higher for heavy women than for light men. There was a positive correlation between weight and mental rotation test scores for heavy women, but height and weight were negatively correlated with mental rotation test scores for light men. These results suggest that there is no sex difference in mental rotation ability as measured.     

Ratio of fourth to second fingertip extensions in relation to serum estradiol and testosterone levels in men and women

Sex differences in second (2D) and fourth (4D) fingertip extensions relative to the middle fingertip and 4D:2D fingertip extension ratios were studied in men and women. Body height positively correlated with index fingertip extensions, not with ring fingertip extensions, nor with their ratio. Mean 2D extension (both hands) was smaller in women than men; mean 4D extension (right hand) was smaller in men than women; 4D:2D fingertip extension ratios from both hands were larger in women than men. Serum estradiol concentration negatively correlated with 2D extensions for both hands (no significant correlation with 4D extensions), but positively correlated with 4D:2D extension ratios for both hands. Serum testosterone concentration positively correlated with 2D extensions of both hands (no significant correlation with 4D extension), but negatively correlated with 4D:2D extension ratios for both hands. These relations were also studied in men and women separately. It was concluded that the 4D:2D extension ratio was greater in women than in men; 2D and 4D extensions and 4D:2D extension ratios may be determined prenatally by sex hormones; fingertip extensions may be predictive of adult and prenatal sex hormone levels.     

The evil eye effect: vertical pupils are perceived as more threatening

Popular culture has many examples of evil characters having vertically pupilled eyes. Humans have a long evolutionary history of rivalry with snakes and their visual systems were evolved to rapidly detect snakes and snake-related cues. Considering such evolutionary background, we hypothesised that humans would perceive vertical pupils, which are characteristics of ambush predators including some of the snakes, as threatening. In seven studies (aggregate N?=?1458) conducted on samples from American and Turkish samples, we found that vertical pupils are perceived as more threatening on both explicit (Study 1) and implicit level (Studies 2–7) and they are associated with physical, rather than social, threat (Study 4). Findings provided partial support regarding our hypothesis about the relevance of snake detection processes: Snake phobia, and not spider phobia, was found to be related to perceiving vertical pupils as threatening (Study 5), however an experimental manipulation of saliency of snakes rendered no significant effect (Study 6) and a comparison of fears of snakes, alligators, and cats did not support our prediction (Study 7). We discuss the potential implications and limitations of these novel findings.