Genomic islands seemed here to stay. The concept, says Luke Harmon, an evolutionary biologist at the University of Idaho in Moscow, “was viewed by many people as perfect for understanding ecological speciation.” Part of the appeal was the beautiful metaphor: Water represented gene flow, and islands emerged, like volcanoes poking up from the ocean, where gene flow fails and divergent selection occurs. The islands would expand just as volcanic islands grow, until reproductive isolation locked in and a species had split into two. At first, the islands extend beyond the beneficial mutation because DNA right next to the advantageous DNA tends to be transmitted as a unit, due to reduced recombination in this region. Over time, other beneficial mutations in the vicinity would add to this recombination coldspot, expanding the island further. And over subsequent generations, more islands would pop up, as the effects of even small survival advantages accumulated.