Shortest recorded vertebrate lifespan found in a coral reef fish

helping to overcome this gap. The ‘bottom up’ or genetic approach to studying speciation has hunted down genes responsible for premating and postmating isolation, and then shown that the gene sequences exhibit signatures of recent selection. But this approach has told us little about the nature of that selection. Is selection divergent or has divergence occurred under uniform selection? Was selection in response to environmental differences? Was it natural or sexual selection? Finally, we still know little about how mate preferences evolve within and between populations during the process of speciation. Sexual selection by mate choice might be a near-universal process in speciation, but what drives the divergence of mate preferences to begin with? Speciation study is in the midst of a surge of research effort, and part of the reason is that answers to many of these questions appear at last to be within reach. We expect that a combination of phenotypic and genetic approaches will soon close the gap between the genes and the mechanisms of selection, and yield a fuller account of how most species in nature have formed.