Inclusive fitness encompasses conventional Darwinian fitness (=evolutionary fitness) with the addition of behaviors that contribute to an organism’s individual fitness through altruism.
Further explanation: An organism’s success, from the gene's point of view, ultimately depends on leaving behind the maximum number of replicas of its genes present within a population. Until 1964 it was generally believed this was done only by leaving the maximum number of viable offspring possible. However, in 1964 W. D. Hamilton showed that since relatives of an organism are likely to share more genes in common, an organism also may increase its own fitness by keeping its collateral relatives viable so they can pass those genes on to the next generation.