inclusive fitness: a standalone construct

W. D. Hamilton coined the term in The genetical evolution of social behaviour (1964) to solve a puzzle in Darwinian theory: why an animal would ever help others at a cost to its own breeding. His answer was to widen the accounting. Inclusive fitness is the sum of an individual's own reproductive success plus the extra reproduction it causes in relatives, with each relative's contribution weighted by relatedness, the probability that the two share a given gene through common descent, so a full sibling counts about half as much as an offspring and a cousin about an eighth. Because a gene that prompts helping relatives can still spread when the benefit to those relatives, discounted by relatedness, exceeds the cost to the helper, a rule later written as rb greater than c and known as Hamilton's rule, the construct explains cooperation and self-sacrifice, including the sterile worker castes of ants and bees, without appeal to the good of the group. Later work, such as Gardner, West, and Wild (2011), placed inclusive fitness on a formal population-genetic footing and clarified its assumptions and limits. Its distinctive scope is that it measures selection from the point of view of the gene rather than the single organism, making the reproduction of kin part of an actor's own evolutionary success.[1][2][3]

Unit

A fitness quantity in offspring-equivalents, formed by summing own reproduction and relatedness-weighted effects on the reproduction of others

Recovery means

Not applicable

Measured by

Estimated in field and model systems by combining coefficients of relatedness (from pedigree or genetic markers) with the reproductive costs and benefits of a social act, then evaluated against Hamilton's rule