Adaptation and Inclusive Fitness

Inclusive fitness theory captures how individuals can influence the transmission of their genes to future generations by influencing either their own reproductive success or that of related individuals. This framework is frequently used for studying the way in which natural selection leads to organisms being adapted to their environments. A number of recent papers have criticised this approach, suggesting that inclusive fitness is just one of many possible mathematical methods for modelling when traits will be favoured by natural selection, and that it leads to errors, such as overemphasising the role of common ancestry relative to other mechanisms that could lead to individuals being genetically related. Here, we argue that these suggested problems arise from a misunderstanding of two fundamental points: first, inclusive fitness is more than just a mathematical 'accounting method' - it is the answer to the question of what organisms should appear designed to maximise; second, there is something special about relatedness caused by common ancestry, in contrast with the other mechanisms that may lead to individuals being genetically related, because it unites the interests of genes across the genome, allowing complex, multigenic adaptations to evolve. The critiques of inclusive fitness theory have provided neither an equally valid answer to the question of what organisms should appear designed to maximise, nor an alternative process to unite the interest of genes. Consequently, inclusive fitness remains the most general theory for explaining adaptation.