a metric denoting the proportion of shared genetic material between any two individuals relative to average degrees of genetic variance in the population under study. This coefficient of relationship is an important component of the theory of inclusive fitness, a treatment of the evolutionary selective pressures on the emergence of certain forms of social behavior. Confusingly, inclusive fitness theory is more popularly known through its narrower form, kin selection theory, whose name clearly resonates with former conceptions of "kinship" in anthropology. Whilst inclusive fitness theory thus describes one of the necessary conditions for the evolutionary emergence of social behaviors, the details of the proximate conditions mediating the expression of social bonding and cooperation have been less investigated in sociobiology. In particular, the question of whether genetic relatedness (or "blood ties") must necessarily be present for social bonding and cooperation to be expressed has been the source of much confusion, partly due to thought experiments in W. D. Hamilton's early theoretical treatments. In addition to setting out the details of the evolutionary selection pressure, Hamilton roughly outlined two possible mechanisms by which the expression of social behaviors might be mediated: Traditional sociobiology did not consider the divergent consequences between these basic possibilities for the expression of social behavior, and instead assumed that the expression operates in the "recognition" manner, whereby individuals are behaviorally primed to discriminate which others are their true genetic relatives, and engage in cooperative behavior with them. But when expression has evolved to be primarily location-based or context-based—depending on a society's particular demographics and history—social ties and cooperation may or may not coincide with blood ties. Reviews of the mammal, primate, and human evidence demonstrate that expression of social behaviors in these species are primarily location-based and context-based (see nurture kinship), and examples of what used to be labeled as "fictive kinship" are readily understood in this perspective. Social cooperation, however, does not mean people see each other as family or family-like, nor that people will value those known not to be related with them more than the ones who are or simply neglect relatedness. See also Adelphopoiesis Blood brother Body of Christ Brother-in-arms Charge nurse Compadre Filiation Fraternity Godparent Inclusive fitness Kin recognition Kin selection Kinship terminology Law of adoption (Mormonism) Milk kinship Nurture kinship Social Bonding and Nurture Kinship References Bibliography External links Social Structure and Kinship in Rural Mexico - The Tlaxcala Project Fictive Kinship: