With me the horrid doubt always arises whether the convictions of man’s mind, which has been developed from the mind of lower animals, are of any value or at all trustworthy. Would any one trust in the convictions of a monkey’s mind, if there are any convictions in such a mind?
–Charles Darwin to W. Graham, July 3, 1881, in The Life and Letters of Charles Darwin, ed. Francis Darwin (1887; repr., Boston: Elibron), 1:285.
Reflections 