Interpreting the universal phylogenetic tree

摘要

The universal phylogenetic tree not only spans all extant life. but its root and earliest branchings represent stages in the evolution- ary 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. horizontaI gene transfer early on was perva- sive. dominating the evolutionary dynamic. The root of the uni- versal phylogenetic tree represents the first stage in cellular evoIution when the evolving cell became sufficiently integrated and stable to the erosive effects of horizontal gene transfer that true organismal lineages could exist.