Biologjia Online

Evolutionary biologists agree that gene duplication has played an important role in the history of life on Earth, providing a supply of novel genes that make it possible for organisms to adapt to new environments (1). The existence of diverse multigene families, particularly in eukaryotes, provides evidence that numerous events of gene duplication followed by functional diversification have shaped genomes as we know them. But it is less certain how this panoply of new functions actually arises, leaving room for ingenious speculation but not much rigor. Cases where we can reconstruct with any confidence the evolutionary steps involved in the functional diversification are relatively few. Thus the report in this issue of PNAS by Tocchini-Valentini and colleagues (2) on tRNA endonucleases of Archaea is particularly welcome as a concrete example of how new protein functions can arise.