The first observable evidence that this happens has come from an experiment in which Anolis lizards were introduced to a group of Bahamian islands. Returning to the islands 14 years later, the scientists, led by Dr Jonathan Losos from Washington University, Missouri, found that the island lizards had changed to suit the vegetation of their new environment.
They had developed much shorter hind limbs and become lighter to help them perch on the thinner branches and twigs found on the islands. They also had wider toe-pads than lizards living in their natural home on the island of Staniel Cay.
Science journal Nature, which published the results today, said: "This may be among the most important work in evolutionary studies since Darwin studied the diversity of finches on the Galapagos Islands during the voyage of the Beagle."