In however complex a manner this feeling may have originated, as it is one of high importance to all those animals which aid and defend one another, it will have been increased through natural selection; for those communities, which included the greatest number of the most sympathetic members, would flourish best, and rear the greatest number of offspring.

Any one whose disposition leads him to attach more weight to unexplained difficulties than to the explanation of facts will certainly reject my theory.

Blushing is the most peculiar and most human of all expressions.

...one doubts existence of free will [because] every action determined by heredity, constitution, example of others or teaching of others." "This view should teach one profound humility, one deserves no credit for anything...nor ought one to blame others.

So great is the economy of nature, that most flowers which are fertilised by crepuscular or nocturnal insects emit their odour chiefly or exclusively in the evening.

The instruction at Edinburgh was altogether by lectures, and these were intolerably dull, with the exception of those on chemistry.

Nature will tell you a direct lie if she can.