All animals but men know that the principle business of life is to enjoy it - and they do enjoy it as much as man and other circumstances will allow it.
If we hold genuine moral principles about animals, these will not differ in substance from those we hold about human beings . . . If humans have natural rights, then so do animals.
If we possessed a thorough knowledge of all the parts of the seed of any animal (e.g. man), we could from that alone, be reasons entirely mathematical and certain, deduce the whole conformation and figure of each of its members, and, conversely if we knew several peculiarities of this conformation, we would from those deduce the nature of its seed.