There is no fundamental difference between man and animals in their ability to feel pleasure and pain, happiness, and misery.

For no amount of exercise, or habit, or volition, in the utterly sterile members of a community could possibly affect the structure or instincts of the fertile members, which alone leave descendants. I am surprised that no one has advanced this demonstrative case of neuter insects, against the well-known doctrine of Lamarck.

Natural selection, also, leads to divergence of character; for more living beings can be supported on the same area the more they diverge in structure, habits, and constitution.

Man in his arrogance thinks himself a great work.

I believe man . . . in the same predicament with other animals.

Embryology will reveal to us the structure, in some degree obscured, of the prototypes of each great class.