Creationists stomp and pout that, despite forces of natural selection, science hasn’t ever observed the evolution of one species into different species. That critique depends upon the belief that a species is an eternal, Platonic form that has absolute literal reality. In scientific terms, that’s not how the concept of a species works. A species exists throughout time, rather than in an eternal moment of never-ending sameness. The theory of biological evolution through natural selection posits that, at the present moment, a species may seem absolutely separate, but go backwards in the dimension of time, and that same species is ultimately connected with all other species of living beings.
Just that sort of connection through time has been observed in 3 species of a reef fish known as the King demoiselle. The species are so close that they had been asserted to be a single species. More careful observation, however, noted that the 3 groups of King demoiselle, varying in color from each other, tended to gather together, rather than with members of the other groups. A genetic evaluation found that the groups had developed genetic distinctiveness from each other. What’s more, genes that are known to have higher rates of mutation had higher rates of divergence, showing that the evolutionary split between the 3 species of King demoiselle was fairly recent in time. We get a snapshot in time of the fish as separate, along with a genetic time machine showing how the species flowed from a single source.
