On Jun. 14, 1996, an analysis 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.

It is well known that only a few weeks are required for the rapid spread of duplicates in bacterial populations under the stress conditions of directed evolution experiments. There appear to be no experimental measurements of the rate of formation and fixation of new enzyme activities resulting from gene duplication. However, recent results on the organophosphate and phosphonate hydrolyzing phosphotriesterase from Pseudomonas diminuta and other soil eubacteria suggest that this new enzyme diverged by duplication from the α/β barrel family and reached the diffusion limit in only 40 years (Scanlan and Reid 1995). Thus, the rate of duplication and fixation of new genes can be surprisingly fast on the geological timescale.

There are a number of additional mechanisms that could have increased the rate of metabolic evolution, including the modular assembly of new proteins, gene fusion events, and horizontal gene transfer as seen in extensive antibiotic resistance in bacteria. Directed evolution experiments have shown that new substrate specificities appear in a few weeks from existing enzymes by recombination events within a gene (Hall and Zuzel 1980). This suggests that mosaic proteins may have enhanced the catalytic repertoire of ancient organisms.

It is likely that the widespread belief that the origin and early evolution of life were slow processes requiring billions and billions of years stems from the classical Darwinian approach that major changes are slow and proceed in a stepwise manner over extended periods of time. All the evidence reviewed here suggests that stability of monomers and polymers essential for the origin of life strongly limited the possibility of a slow emergence of life. 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. At a macroevolutionary level, this represents a case of conservatism that is even more striking than the maintenance of the major animal body plans that appeared at the base of the Cambrian, and which have remained basically unchanged for 600 million years.