Biased gene transfer contributes to maintaining the tree of life

Abstract

Horizontal gene transfer (HGT) between closely and distantly related lineages is a recurrent event in the Tree of Life (ToL) and provides genetic novelty that the recipient can utilize. Often, HGT is considered as an impediment in the reconstruction of life's genealogy, and hence the concept of the ToL as a representation of evolutionary events is considered by some as erroneous. However, biased gene transfer, or the transfer between closely related lineages, can actually reinforce the familiar tree-like pattern by making organisms in close phylogenetic proximity appear even more closely related. The consequence of this bias is that the ToL remains tree-like when viewed from a distance, but looking closely, branches are fuzzy and boundaries between lineages may become indistinct as a result of recurrent HGT.