THERE’S nothing like the threat of being eaten to make an animal evolve in double-quick time, a study of lizards has shown.

Twice within a year the brown arole lizard has evolved changes in its body and behaviour to outwit a predator — confirming Charles Darwin’s theory on natural selection.

Changes in limb length were observed by biologists after they introduced a predator, the northern curly-tailed lizard, to islands off the Bahamas where the brown arole is found.

In the first six months the brown arole, Anolis sagrie, developed longer legs so that it could outrun its predator, Leiocephalus carinatus.

Over the second six-month period the arole changed its behaviour so that it spent far less time on the ground and longer on branches and plant stems.

After a year the surviving aroles had much shorter, stumpier legs that were more suited to clinging on to thin branches. “We showed that selection dramatically changed direction over a short time, within a single generation,” the researchers reported in the journal Science.

They said that the findings counter the “widespread view of evolution as a process played out over the course of eons”. The evolutionary changes had been predicted by scientists after observing lizards on other small Bahamian islands, known as cays.

The researchers introduced the predator lizard on to six islands in the hope of observing changes and establishing how quickly they occurred.

Six more islands were kept free of the predator as a control for the experiment.

Aroles were already present on the islands selected for the experiment. The predator was a species present on nearby islands and known to colonise cays naturally.

Jonathan Losos, of Harvard University, said: “Long-legged lizards fared best at first, because they could run faster. As they began climbing trees to escape, however, short-legged individuals proved more nimble on the branches and more likely to survive.

“These changes occurred within a single generation, showing how the effects of natural selection can play out very quickly.”

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