Inclusive fitness in humans is the application of inclusive fitness theory to human social behaviour, relationships and cooperation.

Inclusive fitness theory (and the related kin selection theory) are general theories in evolutionary biology that propose a method to understand the evolution of social behaviours in organisms. While various ideas related to these theories have been influential in the study of the social behaviour of non-human organisms, their application to human behaviour has been debated.

Inclusive fitness theory is broadly understood to describe a statistical criterion by which social traits can evolve to become widespread in a population of organisms. However, beyond this some scientists have interpreted the theory to make predictions about how the expression of social behavior is mediated in both humans and other animals – typically that genetic relatedness determines the expression of social behaviour. Other biologists and anthropologists maintain that beyond its statistical evolutionary relevance the theory does not necessarily imply that genetic relatedness per se determines the expression of social behavior in organisms. Instead, the expression of social behavior may be mediated by correlated conditions, such as shared location, shared rearing environment, familiarity or other contextual cues which correlate with shared genetic relatedness, thus meeting the statistical evolutionary criteria without being deterministic. While the former position still attracts controversy, the latter position has a better empirical fit with anthropological data about human kinship practices, and is accepted by cultural anthropologists.

Applying evolutionary biology perspectives to humans and human society has often resulted in periods of controversy and debate, due to their apparent incompatibility with alternative perspectives about humanity. Examples of early controversies include the reactions to On the Origin of Species, and the Scopes Monkey Trial. Examples of later controversies more directly connected with inclusive fitness theory and its use in sociobiology include physical confrontations at meetings of the Sociobiology Study Group and more often intellectual arguments such as Sahlins' 1976 book The use and abuse of biology, Lewontin et al.'s 1984 Not in Our Genes, and Kitcher's 1985 Vaulting Ambition:Sociobiology and the Quest for Human Nature. Some of these later arguments were produced by other scientists, including biologists and anthropologists, against Wilson's 1975 book Sociobiology: The New Synthesis, which was influenced by (though not necessarily endorsed by) Hamilton's work on inclusive fitness theory.

A key debate in applying inclusive fitness theory to humans has been between biologists and anthropologists around the extent to which human kinship relationships (considered to be a large component of human solidarity and altruistic activity and practice) are necessarily based on or influenced by genetic relationships or blood-ties ('consanguinity'). The position of most social anthropologists is summarized by Sahlins (1976), that for humans "the categories of 'near' and 'distant' [kin] vary independently of consanguinal distance and that these categories organize actual social practice" (p. 112). Biologists wishing to apply the theory to humans directly disagree, arguing that "the categories of 'near' and 'distant' do not 'vary independently of consanguinal distance', not in any society on earth." (Daly et al. 1997, p282).

This disagreement is central because of the way the association between blood ties/genetic relationships and altruism are conceptualized by many biologists. It is frequently understood by biologists that inclusive fitness theory makes predictions about how behaviour is mediated in both humans and other animals. For example, a recent experiment conducted on humans by the evolutionary psychologist Robin Dunbar and colleagues was, as they understood it, designed "to test the prediction that altruistic behaviour is mediated by Hamilton's rule" (inclusive fitness theory) and more specifically that "If participants follow Hamilton's rule, investment (time for which the [altruistic] position was held) should increase with the recipient's relatedness to the participant. In effect, we tested whether investment flows differentially down channels of relatedness." From their results, they concluded that "human altruistic behaviour is mediated by Hamilton's rule ... humans behave in such a way as to maximize inclusive fitness: they are more willing to benefit closer relatives than more distantly related individuals." (Madsen et al. 2007). This position continues to be rejected by social anthropologists as being incompatible with the large amount of ethnographic data on kinship and altruism that their discipline has collected over many decades, that demonstrates that in many human cultures, kinship relationships (accompanied by altruism) do not necessarily map closely onto genetic relationships.

Whilst the above understanding of inclusive fitness theory as necessarily making predictions about how human kinship and altruism is mediated is common amongst evolutionary psychologists, other biologists and anthropologists have argued that it is at best a limited (and at worst a mistaken) understanding of inclusive fitness theory. These scientists argue that the theory is better understood as simply describing an evolutionary criterion for the emergence of altruistic behaviour, which is explicitly statistical in character, not as predictive of proximate or mediating mechanisms of altruistic behaviour, which may not necessarily be determined by genetic relatedness (or blood ties) per se. These alternative non-deterministic and non-reductionist understandings of inclusive fitness theory and human behavior have been argued to be compatible with anthropologists' decades of data on human kinship, and compatible with anthropologists' perspectives on human kinship. This position (e.g. nurture kinship) has been largely accepted by social anthropologists, whilst the former position (still held by evolutionary psychologists, see above) remains rejected by social anthropologists.

Inclusive fitness theory, first proposed by Bill Hamilton in the early 1960s, proposes a selective criterion for the potential evolution of social traits in organisms, where social behavior that is costly to an individual organism's survival and reproduction could nevertheless emerge under certain conditions. The key condition relates to the statistical likelihood that significant benefits of a social trait or behavior accrue to (the survival and reproduction of) other organisms who also carry the social trait. Inclusive fitness theory is a general treatment of the statistical probabilities of social traits accruing to any other organisms likely to propagate a copy of the same social trait. Kin selection theory treats the narrower but more straightforward case of the benefits accruing to close genetic relatives (or what biologists call 'kin') who may also carry and propagate the trait. Under conditions where the social trait sufficiently correlates (or more properly, regresses) with other likely bearers, a net overall increase in reproduction of the social trait in future generations can result.