=Sentiment of Duty.=--Another derivative of the sentiment of sympathy is that of _duty_, that is the moral sense. All sentiment of love or sympathy urges the one who loves to certain acts destined to increase the welfare of the object loved. This is why the mother nourishes her young and plucks feathers and hairs to make them a soft bed; and why the father brings food to his wife and young, and defends them against their enemies. All these acts, which are not to the advantage of the individual but to the object or objects of his sympathy, exact more or less laborious efforts, courage in the face of danger, etc. They thus provoke an internal struggle between the sentiment of sympathy and egoism, or the unpleasantness of undertaking things which are troublesome and disagreeable for the individual himself. From this struggle between two opposed series of sentiments is derived a third group of complex or mixed sentiments, that of duty, or _moral conscience_. When the sentiment of sympathy prevails, when the animal does his duty toward his young and his conjoint, he feels a sentiment of pleasure, of duty accomplished. If, on the contrary, he has been negligent, the egoistic instincts having for the moment prevailed, the remorse of conscience results, that is the painful uneasiness which follows all disobedience to the instinctive sentiments of sympathy. This uneasiness accumulates in the brain in the form of self-discontent, and may lead to an accentuated sentiment of _repentance_. These phenomena exist both in the male and in the female, and if it was not so, the accomplishment of duty would be impossible; the cat would run away instead of defending her young; would eat her prey instead of giving it to them, etc. We thus see the elements of human social sentiment already very marked in many animals. Remorse and repentance can only be formed on the basis of preëxisting sentiments of sympathy. =Sentiment of Kinship.=--A higher degree of the sentiments of sympathy is developed when these do not remain limited to a temporary union, but when the union of the sexes is transformed into durable or even life-long marriage, as we see in monkeys and in most birds. In another manner the sentiments of sympathy are developed by extension of the family community to a greater number of individuals, who are grouped together for the common defense, as we see in swallows, crows, and to a higher degree, in the large organized communities of social animals, as the beavers, bees, ants, etc. In the latter, the sentiment of sympathy and duty nearly always affects all the individuals of the community, while anger and jealousy are extended toward every being which does not form part of it.