The more we devote ourselves to observing animals and their behaviour, the more we love them, on seeing how greatly they care for their young; in such a context, we cannot even contemplate cruelty to a wolf. Leibniz put the grub he had been observing back on the tree with its leaf, lest he should be guilty of doing any harm to it. It upsets a man to destroy such a creature for no reason, and this tenderness is subsequently transferred to man.
— IMMANUEL KANT