In each of us homo sapiens, Yin includes altruism and Yang includes selfishness. Both are needed in as close to a 50-50 balance as we can each manage. An amount of selfishness is needed because one can't give away what one doesn't have. Scientifically speaking, our group selection put altruism in almost all of us and the individual's evolution *within* the group put self-centeredness in almost all of us:

"If we assume that groups are approximately equal to one another in weaponry and other technology, which has been the case for most of the time among primitive societies over hundreds of thousands of years, we can expect that the outcome of between-group competition is determined largely by the details of social behavior within each group in turn. These traits are the size and tightness of the group, and the quality of communication and division of labor among its members. Such traits are heritable to some degree; in other words, variation in them is due in part to differences in genes among the members of the group, hence also among the groups themselves. The genetic fitness of each member, the number of reproducing descendants it leaves, is determined by the cost exacted and benefit gained from its membership in the group. These include the favor or disfavor it earns from other group members on the basis of its behavior. The currency of favor is paid by direct reciprocity and indirect reciprocity, the latter in the form of reputation and trust. How well a group performs depends on how well its members work together, regardless of the degree by which each is individually favored or disfavored within the group. The genetic fitness of a human being must therefore be a consequence of both individual selection and group selection." - Wilson, Edward O.. The Social Conquest of Earth (Kindle Locations 765-774). Liveright. Kindle Edition. (Some words bolded by me.)