Edward Westermarck's memoirs reveal that he had decided to write a work addressing the 'origin and development of the moral consciousness' already before his first magnum opus The History of Human Marriage was completed. The development of Westermarck's theory of moral emotions remains one of the many under-explored parts of his work. This chapter explores Westermarck's ethics by tracing and analysing the phases of its development, both its continuities and discontinuities. It discusses Darwin's account of the evolution of morality which marks the beginning of Westermarck's interest in the subject. Darwin proposed a four-part explanation for the evolution of conscience of which Westermarck highlights the first two, the social instincts and the increased cognitive capacities, which are associated with the ability to remember one's past actions and to reflect on them afterwards by comparing selfish actions with other-regarding alternatives.