According to Confucianism, the motivation of human moral behavior is influenced by the intimacy between blood relatives. The closer the blood relationship is, the stronger altruistic motivation is. This is different from Mohism which insisted on universal love(兼愛) and Taoism which insisted on ethical relativism. Hamilton's inclusive fitness theory argues that the closer to blood relations are, the stronger the motivation of altruistic behavior is, as in the Confucian ethics of kinship. According to Hamilton's rule, a person takes an altruistic action when the value of beneficiary’s benefit multiplied by genetic relatedness is greater than the cost paid by the person. Genetic relatedness is defined as the probability of sharing a particular focal gene with another individual over and above the average population frequency of the gene. Hamilton's rules apply not only to humans but also to animals. Confucianism also argues that animals, like humans, do altruistic acts in partly blood relations. Degree of kinship(寸數) formed on Confucian culture has the same context as the genetic relatedness. The degree of kinship refers to the number of births associated between two individuals. The smaller the number of degree of kinship, that is, the fewer the number of births connected between the two individuals, the stronger the altruistic motivation is. The relationship between genetic relatedness and degree of kinship is summarized by a simple formula. The concept of degree of kinship is not just an analogy that emphasizes the importance of blood relations. The degree of kinship is unconsciously expressed the intention of Confucian ethics to quantify the importance of blood relations. Hamilton's inclusive fitness theory supports Confucian ethics, which regards blood relations as a powerful motive for altruistic behavior. Accordingly, the Confucian ethics of kinship should be reevaluated.