If evolution started all over again, would it repeat itself? In today's issue of Science, a real-life version of this thought experiment suggests that the answer may be yes--at least for island lizards.
Evolutionary ecologist Jonathan Losos of Washington University in St. Louis and his colleagues report that anole lizards on the four islands of the Greater Antilles--Hispaniola, Cuba, Jamaica, and Puerto Rico--independently evolved the same set of habitat-specialized traits. Although examples of convergent evolution, such as wings on bats and birds, are well known, "what's remarkable here is the degree of similarity that has evolved on all four of the islands," says Douglas Futuyma of the State University of New York, Stony Brook.
Losos and his team measured six characteristics that are linked to habitat, including mass, size of toepads, and length of body, tail, and legs, in about a dozen lizards from each of 46 species. They found that each species was, on average, most like those living in the same habitat on other islands--even if the species were only distantly related. The researchers conclude that the original lizard immigrants--likely a different species for each island--were subjected to similar evolutionary pressures and independently evolved into similar forms. "In this case, the power of natural selection is so strong that it overwhelms any differences between the islands and what has gone on there before," Losos says.
But not everyone is convinced. Futuyma points out that nature's experiment didn't produce exactly the same results on every island: Two kinds of lizards are missing from Jamaica and one from Puerto Rico. Still, says evolutionary ecologist Dolph Schluter of the University of British Columbia, it seems that at least in some cases, "history can repeat itself over and over."