Correlation between general factors for personality and cognitive skills in the National Merit twin sample

General factors of personality (based on the California Psychological Inventory) and cognitive skill (the National Merit Scholarship Qualifying Test selection score) were correlated .284 in a sample of 490 monozygotic and 317 dizygotic twin pairs. The correlation was partitioned into genetic, and shared and unshared environmental sources: approximately 39%, 50% and 11%, respectively. The results offered some support to a theory that such a correlation may reflect evolutionary trends, although questions remained about the role of nonadditive genetic variance and the nature of the selection involved.