New species might arise as a result of single rare events, rather than through the gradual accumulation of many small changes over time, according to a study of thousands of species and their evolutionary family trees. This contradicts a widely accepted theory of how speciation occurs: that species are continually changing to keep pace with their environment, and that new species emerge as these changes accrue. Known as the 'Red Queen' hypothesis, it is named after the character in Lewis Carroll's book Through the Looking-Glass, and What Alice Found There who tells a surprised Alice: “Here, you see, it takes all the running you can do, to keep in the same place.”
The Red Queen hypothesis rests on the idea that species must continuously evolve just to hang on to their ecological niche. That gradual evolution is driven by the constant genetic churn of sexual selection. A consequence of this is that all of the species in a particular family, or genus, gradually evolve to form new species at the same rate.
But Mark Pagel and his team at the University of Reading, UK, challenge this idea.