"There can be no doubt that [during 'primeval' times] a tribe including many members who, from possessing in a high degree the spirit of patriotism, fidelity, obedience, courage, and sympathy, were always ready to give aid to each other and to sacrifice themselves for the common good, would be victorious over most other tribes; and this would be natural selection."
11 March 2016
He Said It: Darwin
From his 1871 The Descent of Man (pt. 1, chap. 5), Charles Darwin's explanation for why we seem to instinctively like the ideas of "giving back" and sacrifice for the common good: