What leads personality to develop in adulthood? Values, guiding principles that apply across contexts, may capture motivation for growth and change. An essentialist trait perspective posits that personality changes only as a result of organic factors. But evidence suggests that psychosocial factors also influence personality change, especially during young adulthood. In the Life and Time study of sources of personality change in adulthood, we specifically explore ethically-relevant value priorities, those related to the relative prioritization of narrow self-interest over the concerns of a larger community. According to Rollo May (1967), “mature values”, including aspects of both self-transcendence and self-determination, should serve to diminish or prevent neurotic anxiety. This is consistent with research on materialism, which is associated with lower well-being. An index based on May’s proposal and several related constructs (materialism, unmitigated self-interest, collectivism and individualism) are tested longitudinally as possible antecedents of Big Five/Six personality trait change using bivariate LCMSR models in a national community sample (N = 864 at Time 1). Contrary to an essentialist trait perspective, these value priorities more often preceded change in personality traits than vice-versa. Somewhat consistent with May’s theory, higher “mature” values preceded higher openness (statistically significant at the p < .005 level). Higher vertical individualism significantly preceded lower compassion, intellect and openness. At the suggestive (p < .05) level, higher unmitigated self-interest preceded lower conscientiousness, higher vertical individualism preceded higher volatility, higher mature values preceded higher honesty/propriety and politeness, higher horizontal collectivism preceded higher orderliness, agreeableness, and assertiveness and lower intellect, and higher horizontal individualism preceded lower withdrawal. In two of three cases, suggestive personality-as-antecedent-of-values-change effects were reciprocal with the values-effects: higher conscientiousness scores reciprocally preceded lower unmitigated self-interest, and higher volatility higher vertical individualism. No significant or suggestive “stand-alone”, non-reciprocal personality on values effects were found.