Interpreting the universal phylogenetic tree

TLDR

The universal phylogenetic tree spans all extant life, with its root and earliest branchings marking pre‑modern cell stages, and primitive cellular entities were simpler and more modular than modern cells. The evolution of the cell is an interplay between vertically derived and horizontally acquired variation. Horizontal gene transfer was pervasive early on, dominating evolution, and the tree’s root marks the first stage when the cell became integrated and stable enough for true organismal lineages to emerge.

Abstract

The universal phylogenetic tree not only spans all extant life, but its root and earliest branchings represent stages in the evolutionary process before modern cell types had come into being. The evolution of the cell is an interplay between vertically derived and horizontally acquired variation. Primitive cellular entities were necessarily simpler and more modular in design than are modern cells. Consequently, horizontal gene transfer early on was pervasive, dominating the evolutionary dynamic. The root of the universal phylogenetic tree represents the first stage in cellular evolution when the evolving cell became sufficiently integrated and stable to the erosive effects of horizontal gene transfer that true organismal lineages could exist.