The question is not, Can they reason? nor Can they talk? but, Can they suffer?
— Jeremy Bentham
There is no fundamental difference between man and the higher animals in their mental faculties... The lower animals, like man, manifestly feel pleasure and pain, happiness, and misery
— Charles Darwin
If a man's aspiration towards a righteous life are serious, his first act of abstinence is from animal food, because it is plainly immoral as it requires an act contrary to moral feeling, ie., killing - and is called forth only by greed
— Leo Tolstoy
I have from an early age abjured the use of meat and a time will come when man such as I will look upon the murder of animals as they now look upon the murder of men
— Leonardo Da Vinci
True benevolence or compassion, extends itself through the whole of existence and sympathises with the distress of every creature capable of sensation