Extensive fitness and human cooperation

TL;DR

This paper introduces the concept of extensive fitness in humans, which extends inclusive fitness by incorporating phenotypic similarity, and demonstrates through a model that populations utilizing extensive fitness outcompete those with only inclusive fitness.

Contribution

It proposes and models extensive fitness, a new evolutionary mechanism based on phenotypic similarity, and shows its advantage over traditional inclusive fitness in population competition.

Findings

Populations with extensive fitness outcompete those with only inclusive fitness.

Extensive fitness involves both competitive and cooperative components based on phenotypic similarity.

Larger groups with similar phenotypes lead to higher fitness gains.

Abstract

Evolution depends on the fitness of organisms, the expected rate of reproducing. Directly getting offspring is the most basic form of fitness, but fitness can also be increased indirectly by helping genetically related individuals (such as kin) to increase their fitness. The combined effect is known as inclusive fitness. Here it is argued that a further elaboration of fitness has evolved, particularly in humans. It is called extensive fitness and it incorporates producing organisms that are merely similar in phenotype. The evolvability of this mechanism is illustrated by computations on a simple model combining heredity and behaviour. Phenotypes are driven into the direction of high fitness through a mechanism that involves an internal estimate of fitness, implicitly made within the organism itself. This mechanism has recently been conjectured to be responsible for producing agency and goals. In the model, inclusive and extensive fitness are both implemented by letting fitness increase nonlinearly with the size of subpopulations of similar heredity (for the indirect part of inclusive fitness) and of similar phenotype (for the phenotypic part of extensive fitness). Populations implementing extensive fitness outcompete populations implementing mere inclusive fitness. This occurs because groups with similar phenotype tend to be larger than groups with similar heredity, and fitness increases more when groups are larger. Extensive fitness has two components, a direct component where individuals compete in inducing others to become like them and an indirect component where individuals cooperate and help others who are already similar to them.