Abstract
Inversion polymorphisms provided critical case studies in the early development of population genetics. Recently, interest in their evolution has been re-invigorated by the discovery of inversion polymorphism in many animal and plant species using genomic approaches and by new theoretical developments. In parallel, genomic approaches are providing new insights into the origin, prevalence and consequences of inversions in human populations. In this article, I consider how observations on human inversions fit into the prevailing view of inversion polymorphism in the evolutionary biology community. Surveys in humans have revealed many small inversions that are missed in animal and plant studies. These surveys show a mix of origins via non-allelic homologous recombination and non-homologous end-joining processes. Importantly, homologous recombination can lead to recurrent origins with significant evolutionary consequences. Direct selection operates against inversion heterozygotes via both breakpoint and recombination effects. Both fields infer the maintenance of common polymorphisms by balancing selection, arising due to linkage disequilibrium between inversions and the loci they contain, but it remains difficult to identify the underlying causes. Research on non-human species tends to concentrate on large inversions and those maintained at high frequency. As a result, the evolutionary field has much to learn from work on humans about inversion origins and the pathological effects of rare variants. Medical research on inversions may benefit from considering the evolutionary processes underlying their behaviour in human populations.