Reticulate evolution

Reticulate evolution, also network evolution, describes the origination of a lineage through the partial merging of two ancestor lineages, leading to relationships better described by a phylogenetic network than a bifurcating tree.

Crossing of distinct lineages can happen through recombination, horizontal gene transfer, or hybrid speciation, and a lineage of such origin thus has two most recent common ancestors. Reticulate evolution can involve species, but also genes, chromosomes, or genomes.

Reticulate evolution can happen between lineages separated only for a short time, for example through hybrid speciation in a species complex. Nevertheless, it also takes place over larger evolutionary distances, as exemplified by the presence of organelles of bacterial origin in eukaryotic cells. Although it is accepted that reticulate evolution occurred repeatedly in the tree of life, there is strong evidence for only one common ancestor of all life on earth.

Reconstructing phylogenetic relationships under reticulate evolution requires adapted analytical methods.

The study of reticulate evolution is said to have been largely excluded from the modern synthesis. Nathalie Gontier has stated that "reticulate evolution today is a vernacular concept for evolutionary change induced by mechanisms and processes of symbiosis, symbiogenesis, lateral gene transfer, hybridization, or divergence with gene flow, and infectious heredity." She calls for an extended evolutionary synthesis that integrates these mechanisms and processes of evolution.