Reference

Jean-François Bonnefon, Wim De Neys, and Astrid Hopfensitz, Low second-to-fourth digit ratio predicts indiscriminate social suspicion, not improved trustworthiness detection, Biology Letters, vol. 9, n. 2, April 2013.

Abstract

Hormones can make us trust or distrust other people. Testosterone, in particular, appears to decrease feeling of trust. It had been assumed so far that testosterone made us less trusting because it made us better at spotting cheaters. This paper, however, suggests that testosterone makes us bluntly suspicious of everyone -- trustworthy and untrustworthy persons all the same. Prenatal exposition to testosterone (tracked by the relative lengths of index and ring fingers) predicted the way individuals trust 20 years after: Subjects with high prenatal exposure trusted less, but their ability to spot cheaters was the same as anybody else.