Whatever did occur during that phase of Earth’s history, its most consequential result was a single lineage, some manner of creature, that became the universal ancestor of all three kingdoms of life. For this certitude, we do have evidence: the universality of the genetic code itself, a system that uses the same coding—these bases specify those amino acids—in bacteria, in archaea, and in eukaryotes. The genetic code is the ultimate shared character, uniting all forms of life within one ancestry. And that ancestry had its origin among progenotes.
