What causes personality maturation in early adulthood? Some researchers say maturation is determined by genetic factors (five-factor theory); others say it is related to culture-specific expectations for behavior at a certain age (social-investment theory). In the research reported here, Bleidorn et al. (2013) examined Big Five personality data, collected as part of the Gosling-Potter Internet Personality Project from participants in 62 countries, and indices of the timing of a variety of socially normative behaviors — such as marriage, parenthood, and entry into the workforce — for those countries. Although personality did mature as people aged, the faster maturation found in countries with earlier transition to adult roles supports social-investment theory.