Why is Conscientiousness negatively correlated with intelligence?

The aim of the present study was to investigate the nature of the negative relationship which has been observed between the trait of Conscientiousness and intelligence, using different measures of both variables (Furnham, Chamorro-Premuzic, & Moutafi, under review; Moutafi, Furnham, & Crump, 2003; Moutafi, Furnham, & Paltiel, under review). A total of 201 participants completed the Fifteen Factor Questionnaire (15FQ) and the General Reasoning Test Battery (GRT1), which included both measures of fluid and crystallized intelligence. Conscientiousness (Control) was significantly negatively correlated with abstract reasoning (fluid intelligence), but not with verbal reasoning (crystallized intelligence). This was interpreted as indicating that the negative relationship between intelligence and Conscientiousness is due to fluid intelligence affecting the development of Conscientiousness, in an educated and need-achieving population.