Kin recognition: an overview of conceptual issues, mechanisms and evolutionary theory

Kin recognition (KR) is the ability to identify or distinguish kin from nonkin, and it is thought to be an important driving force in the evolution of social and sexual behaviour. Here, we provide an introduction to KR, including an overview of the main debates, the underlying mechanisms and evolutionary analyses. First, we examine the many evolving definitions for KR, as these have caused some confusion and debate. We explain why retaining both broad and narrow definitions can be instructive for thinking about the problem. Second, we provide examples of the different types of KR from empirical studies, ranging from the use of spatial cues to for selfinspection and green-beard genes. We also suggest a classification scheme of the different mechanisms based on whether they are considered to be KR in the broad or in the narrow sense. Third, we consider the key components necessary for most or all KR mechanisms, and explain why the central problem for any recognition mechanism is to balance the risk of acceptance versus rejection errors. Fourth, we summarise theoretical analyses addressing the evolution of nepotism through kin recognition, and the maintenance of genetic polymorphisms controlling KR. Fifth, we examine evolutionary analyses of apparent KR failures, errors, and mistakes. Finally, we suggest some of the main problems that need to be addressed in future KR research.