Charles Darwin defends a naturalist approach to morality. In The Descent of Man, he argues that moral behaviour has outgrown from animal tendency for empathy through evolution of morality. By comparing human and animal behavior through a naturalist approach, he concludes that moral sense is based on the species' sociability, notably altruism.
Morality from Sympathy
Darwin suggests sympathy is at the core of sociability and is an instinctive emotion found in most social animals. The ability to recognize and act upon others' distress or danger, is a suggestive evidence of instinctive sympathy; common mutual services found among many social animals, such as hunting and travelling in groups, warning others of danger and mutually defending one another, are some examples of instinctive sympathy Darwin offers. He insists it must be sympathy that compels an individual to risk his or her own life for another from his community.
Darwin suggests further that the role of acceptance of others acts as a guide for conduct; sympathy enables to obtain approval of others instead of rejection. Social animals, when separated from the herd, cannot endure solitude and oftentimes perish. Darwin argues social animals have a natural dislike for solitude, and states: "solitary confinement is one of the severest punishments which can be inflicted
As Darwin notes, the moral difference between mankind and animals, however, is "certainly one of degree and not of kind."Emotions such as remorse, regret or shame one may feel, stem from human's incessant reflection on past experiences and preoccupation with the judgement of others.