On Jun. 14, 1996, Aanalysis of genes in living organisms suggested that the world’s first animals emerged a billion years ago, far earlier than previously believed. After the explosive metabolic evolution that took place soon after the beginning of life, the basic genetic processes and major molecular traits have persisted essentially unchanged for more than three-and-a-half billion years, perhaps owing to the linkages of the genes involved and the complex interactions between different metabolic routes.