Two studies compared the development of beliefs about the stability and origins of physical and psychological traits in Japan and the United States in three age groups: 5-6-year-olds, 8-10-year-olds, and college students. The youngest children in both cultures were the most optimistic about negative traits changing in a positive direction over development and being maintained over the aging period. The belief that individual differences in traits are inborn increased with age, and in all age groups, this belief was related to predictions of greater trait stability. In both cultures, all ages believed positive traits would be maintained over development. In addition to developmental similarities across cultures, cultural variations, consistent with the hypothesis that interdependent cultures have a more incremental view of traits, were present. Japanese participants were more optimistic than American participants about negative traits changing towards the positive and were more likely to attribute differences in trait expression to effort. (C) 2007 Elsevier Inc. All rights reserved.