Horizontal Gene Transfer in Evolution

Abstract The concept of horizontal or lateral gene transfer (the non‐genealogical transmission of genetic material between organisms) was introduced in 1990s to explain the observed incongruence in phylogenetic reconstructions using different genes. Today, horizontal gene transfer is accepted as an important force modulating evolution of Bacteria, Archaea and unicellular eukaryotes, and evidence is rising for their role in the evolution of pluricellular eukaryotes (fungi, plants and animals). The realisation that horizontal gene transfer plays an important role in evolution of both, prokaryotes and eukaryotes, 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 non‐genealogical transmission of genetic material between different organisms. Horizontal gene transfer has become a part of evolutionary thinking over the past 25 years. Horizontal gene transfer plays an important role in prokaryotic evolution. Horizontal gene transfer also modulates evolution of unicellular eukaryotes. Increasing evidence support the role of horizontal gene transfer in evolution of pluricellular eukaryotes. 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.