If a planet like earth exists elsewhere it would probably have the same species on it, the British Association heard.

Evolutionary biologist Paul Harvey, of Oxford University, said that DNA testing has provided evidence that remarkably similar species have evolved independently.

This undermines the idea that evolution is so full of chances that the same pathway could never be followed twice - an idea put forward by Steven Jay Gould among others.

Scientists have been using DNA techniques to work out how much different species have in common and whether and when they evolved from a common ancestor.

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He has looked at lizards living on the two Caribbean islands of Jamaica and Puerto Rico. On Jamaica there are five lizard species, specialised to live on different parts of the tree or on the surrounding grass.

DNA testing has shown that they all evolved from a common ancestor - a "generalist" lizard. Paul; Harvey has established the order in which the species evolved from this generalist.

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In Puerto Rico there are also five species of lizard, which are "remarkably similar" and have adapted to live in the same five ecological niches.

Yet DNA testing has shown that they are not related to the Jamaican lizards despite the fact that they evolved in the same order as their Jamaican counterparts.

"We found these five species on both islands but they have got a different common ancestor - they evolved independently and in exactly the same sequence," he told the meeting.

"This means that, to some extent, evolution is predetermined. This is one way in which we can demonstrate that evolution is repeatable."

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