Caribbean Island Lizards Reveal Evolution is Predictable

Evolution occurs as environments shift and change, selecting some traits over others. With this in mind, you may think that evolution is unpredictable, depending largely on conditions. Not so, say researchers. Apparently, evolution is extremely predictable--at least when it comes to Caribbean lizards.

The predictability of evolution over millions of years has long been debated by scientists. Some people believe that if you "rewound" time, completely different species would emerge. For example, small events like storms could potentially wipe out a particular pond which would, in turn, have a disproportionate effect on species in the area. Other researchers, in contrast, believe that evolution would follow the same lines as species in similar habitats evolved.

In order to test whether evolution was wild or predictable, scientists turned to the Anole lizards that live on four neighboring islands, including Cuba, Hispaniola, Jamaica and Puerto Rico. About 40 million years ago, these reptiles arrived on the islands and began to colonize them in the vastly similar climates. By studying these creatures, the scientists were able to catch a glimpse of evolution at work.

In all, the scientists studied 100 of the 119 Anole lizard species from the islands. They then combined the body-form data with a family tree of the Anoles in order to construct an "adaptive landscape" for the lizards. An adaptive landscape is a fundamental concept in evolutionary biology, but difficult to show in practice. Peaks on an adaptive landscape represent various combinations of features that will be favored by natural selection, whereas valleys are just the opposite.

After examining the lizards fully, the researchers found that there was a striking degree of convergence. On each island, evolution had produced a set of very similar-looking lizards occupying similar environmental niches. In other words, the reptiles evolved the same way in different locations.

"The adaptive radiations match on all four islands--with few exceptions, each species on an island has a match on the other islands," said Luke Mahler, a postdoctoral fellow at UC Davis, in a news release.

In other words, evolution was predictable. The same kinds of adaptations formed for lizards that lived in similar environments in different locations. Looking back at the lizards' evolutionary history, researchers could tell that the landscape drove the convergence that they saw.

The findings are published in the journal Science.