I believe there exists, & I feel within me, an instinct for the truth, or knowledge or discovery, of something of the same nature as the instinct of virtue, & that our having such an instinct is reason enough for scientific researches without any practical results ever ensuing from them.
Darwin and Henslow: The Growth of an Idea; Letters, 1831-1860 (ed. Univ of California Press, 1967)