By comparing human and animal behavior through a naturalist approach, he concludes that moral sense is based on the species' sociability, notably altruism.
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.
[3] 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.
Darwin argues social animals have a natural dislike for solitude, and states: "solitary confinement is one of the severest punishments which can be inflicted.
"[8] 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.