There is no fundamental difference between man and the higher mammals in their mental faculties...The difference in mind between man and the higher animals, great as it is, certainly is one of degree and not of kind.

I suppose you are two fathoms deep in mathematics, and if you are, then God help you. For so am I, only with this difference: I stick fast in the mud at the bottom, and there I shall remain.

As for a future life, every man must judge for himself between conflicting vague probabilities.

I long to set foot where no man has trod before.

Multiply, vary, let the strongest live and the weakest die.

Jealousy was plainly exhibited when I fondled a large doll, and when I weighed his infant sister, he being then 15? months old. Seeing how strong a feeling of jealousy is in dogs, it would probably be exhibited by infants at any earlier age than just specified if they were tried in a fitting manner

One day, on tearing off some old bark, I saw two rare beetles, and seized one in each hand. Then I saw a third and new kind, which I could not bear to lose, so I popped the one which I held in my right hand into my mouth. Alas! it ejected some intensely acrid fluid, which burnt my tongue so that I was forced to spit the beetle out, which was lost, as was the third one.