It is well-known that those who have charge of young infants, that it is difficult to feel sure when certain movements about their mouths are really expressive; that is when they really smile. Hence I carefully watched my own infants. One of them at the age of forty-five days, and being in a happy frame of mind, smiled... I observed the same thing on the following day: but on the third day the child was not quite well and there was no trace of a smile, and this renders it probable that the previous smiles were real.

Intelligence is based on how efficient a species became at doing the things they need to survive.

Delight itself, however, is a weak term to express the feelings of a naturalist.

But when on shore, & wandering in the sublime forests, surrounded by views more gorgeous than even Claude ever imagined, I enjoy a delight which none but those who have experienced it can understand.

I have been speculating last night what makes a man a discoverer of undiscovered things. As far as I can conjecture the art consists in habitually searching for the causes and meaning of everything which occurs.

What wretched doings come from the ardor of fame; the love of truth alone would never make one man attack another bitterly.

The formation of different languages and of distinct species and the proofs that both have been developed through a gradual process, are curiously parallel.