In Ethics and the Descent of Man, Charles Darwin attempts to explain how morals evolved naturalistically and why mankind has a sense of remorse when other, lower animals do not exhibit such a behavior. Darwin argues that man has a “well-marked social instinct” that aided in the development of a moral sense. He attempts to show how this instinct manifests itself in animals, and then applies it to human behavior. His theory lies mainly in the great weight of public opinion that people have for each other’s approval in this social instinct that he claims is strengthened by habit.
Read more at: Think Divinely – Did Morality Simply “Evolve”?