The data on a group of 22 rats, each measured for their speed of reasoning, accuracy of reasoning, response flexibility, and attention for novelty, were subjected to two different methods of factor analysis. By both methods, the correlation matrix of their performance was consistent with a single-factor model. In a second cohort of rats, where brain size was known, the score for this ‘general factor’ was computed. The regression for brain weight and the general factor was significant.