From the First Cell to the Last Universal Ancestor (LUA)

Abstract

This chapter considers what must have happened to create the First Cell and what must have developed between the time when the First Cell arose and the time when the Last Universal Ancestor gave rise to multiple lines of descent. The First Cell was the first entity that could improve itself and its lot by Darwinian evolution. The Last Universal Ancestor is defined operationally as the latest organism that had various descendants that evolved into eubacteria, archaebacteria (archaea), eukaryotes, and organelles of eukaryotes. The parent of subcellular genetic elements, such as viruses, insertion sequences, and plasmids, has been little considered, but arguments can be made that its development was fairly late. The Last Universal Ancestor probably had many of the characteristics that we now find retained in bacteria and, of course, many of the features of most living organisms. During the intervening “monophyletic” epoch between the First Cell and the Last Universal Ancestor, the processes shown in the central part of Fig. 1.1 were being perfected, but had not reached the state in which we now find them in various organisms today. In this diagram, no phylogeny is implied except that within the epoch many mutations and changes occurred, but each improved organism totally displaced its predecessors and the side shoots, and that multiple branching occurred after the Last Universal Ancestor to produce a diversity of types of biological descendants.