Horizontal Gene Transfer in Evolution

Abstract Twenty years ago the concept of horizontal or lateral gene transfer (the nongenealogical transmission of genetic material between organisms) was introduced as an explanation to incongruence in phylogenetic reconstructions using different genes. Today, horizontal gene transfer is accepted as an important force modulating evolution of prokaryotes and unicellular eukaryotes, whereas the extent to which it impacts on the evolution of metazoan eukaryotes remains unknown. Evidence for the role of horizontal gene transfer in evolution put in question the metaphor of the tree of life and the traditional view of evolution as a slow process. A more pluralistic approach to evolution is emerging that encompasses different evolutionary mechanisms operating at different levels of complexity. Key Concepts: Horizontal gene transfer is the nongenealogical transmission of genetic material between different organisms. Horizontal gene transfer plays an important role in prokaryotic evolution. Horizontal gene transfer also modulates evolution of unicellular eukaryotes. The importance of horizontal gene transfer in metazoan evolution is uncertain. Horizontal gene transfer challenges the tree of life metaphor. Horizontal gene transfer challenges the traditional view of evolution as a slow process. A pluralistic approach to evolution is needed.