Charles Darwin —

“… any animal whatever, endowed with well-marked social instincts, would inevitably acquire a moral sense or conscience, as soon as its intellectual powers had become as well developed, or nearly as well developed, as in man.”  … 

“Notwithstanding many sources of doubt, man can generally and readily distinguish between the higher and lower moral rules. The higher are founded on the social instincts, and relate to the welfare of others..”….“As man advances in civilisation, and small tribes are united into larger communities, the simplest reason would tell each individual that he ought to extend his social instincts and sympathies to all the members of the same nation, though personally unknown to him. This point being once reached, there is only an artificial barrier to prevent his sympathies extending to the men of all nations and races.” …”Sympathy beyond the confines of man, that is humanity to the lower animals, seems to be one of the latest moral acquisitions.”… “This virtue, one of the noblest with which man is endowed, seems to arise incidentally from our sympathies becoming more tender and more widely diffused, until they are extended to all sentient beings.”

Mencius —

“Here is why I say that all human beings have a mind that commiserates with others. Now, if anyone were suddenly to see a child about to fall into a well, his mind would always be filled with alarm, distress, pity, and compassion. That he would react accordingly is not because he would use the opportunity to ingratiate himself with the child’s parents, nor because he would seek commendation from neighbors and friends, nor because he would hate the adverse reputation. From this it may be seen that one who lacks a mind that feels pity and compassion would not be human; one who lacks a mind that feels shame and aversion would not be human; one who lacks a mind that feels modesty and compliance would not be human; and one who lacks a mind that knows right and wrong would not be human.”