Thorpe says the results “really surprised” him. That animals living side by side would diverge more than those separated by ocean challenges the traditional view of how species evolve, he says. “People need to rethink their assumptions.”
The paper contains “one of those unusual natural experiments that you don’t often see,” says evolutionary biologist Barry Sinervo of the University of California, Santa Cruz. He says the results show that allopatric speciation is important but can’t necessarily create new species by itself, even after millions of years. Rather, ecological separation might be needed to complete the process.