Second-to-Fourth Digit Ratio Has a Non-Monotonic Impact on Altruism

Abstract

Gene-culture co-evolution emphasizes the joint role of culture and genes for the emergence of altruistic and cooperative behaviors and behavioral genetics provides estimates of their relative importance. However, these approaches cannot assess which biological traits determine altruism or how. We analyze the association between altruism in adults and the exposure to prenatal sex hormones, using the second-to-fourth digit ratio. We find an inverted U-shaped relation for left and right hands, which is very consistent for men and less systematic for women. Subjects with both high and low digit ratios give less than individuals with intermediate digit ratios. We repeat the exercise with the same subjects seven months later and find a similar association, even though subjects' behavior differs the second time they play the game. We then construct proxies of the median digit ratio in the population (using more than 1000 different subjects), show that subjects' altruism decreases with the distance of their ratio to these proxies. These results provide direct evidence that prenatal events contribute to the variation of altruistic behavior and that the exposure to fetal hormones is one of the relevant biological factors. In addition, the findings suggest that there might be an optimal level of exposure to these hormones from social perspective.

Risk Preferences and Prenatal Exposure to Sex Hormones for Ladinos

“…This is consistent with the measure utilized in [22], [28]. Note that our analysis is robust to using alternative measures, such as the median.…”

Editorial: Prosocial and Antisocial Behavior in Economic Games

“…Galizzi and Nieboer replicate previous findings (Brañas-Garza et al, 2013) on the relationship between 2D:4D digit ratio (a biomarker of the relative prenatal exposure to testosterone vs. estrogens) and altruism in a Caucasian sample. In particular, individuals with an intermediate digit ratio give more money in a Dictator Game than individuals with either low or high digit ratios.…”

Cognitive (ir)reflection: New experimental evidence

“…This is supported by evidence that subjects with high CRT score are less inclined to behavioural biases than those with low CRT (Bergman et al, 2010;Hoppe and Kusterer, 2011;Oechssler et al, 2009) and by related evidence that subjects' altruism is correlated with their 2D:4D (Brañas-Garza et al, 2013).…”