Lecture, three hours; discussion, one hour (when scheduled). Recommended requisite: course 1 or Life Sciences 1 or 7B or Psychology 10. Evolutionary hypotheses for existence of stable differences among individuals in patterns of thought, emotion, and behavior. Descriptive accounts of personality structure (e.g. Big Five). Comparison of explanatory models including balancing selection, facultative calibration, and mutation-selection balance. P/NP or letter grading.