But scientists do not know why the geckos, which live just 100m away from each other, stopped mating.

Mitzy Pepper, a postgraduate student at the Australian National University School of Botany and Zoology, analysed DNA from several populations of the gecko Diplodactylus stenodactylus to piece together the lizard's family tree.

She used a known rate of mutation in a lizard gene to calculate when the geckos last shared a common ancestor and split into two distinct groups.

One group lives within the Pilbara region while the other lives on its border.

Ms Pepper said there were a few theories describing why the geckos might spurn their neighbours.

''An idea is that in the past there was some kind of barrier that separated them, so that they evolved separately and by the time they came back in contact with one another, they were too different,'' she said.

''But the thing is, there are no barriers there.''

The Pilbara is an ancient land, containing some of the oldest rocks in the world, some more than three billion years old.

It has been stable for 160 million years, while places on Australia's east coast were still active 60 million years ago.

It is a known biodiversity ''hot spot'', but it is also a major iron ore mining site.

''There's hardly anything known about the biodiversity there at the moment, which is a bit of problem if there's a lot of mining going on,'' Ms Pepper said.

''This [research] is like a first step trying to get a grasp on the reptile diversity.''

Lizards can provide insights into evolutionary processes because, unlike animals such as birds or kangaroos, many generations stay in one place for millions of years.

Ms Pepper's research on the 12cm ''large eyed and velvety skinned'' geckos is the first of its kind in the Pilbara.

It suggests the different clans of geckos, although they may look the same, could be different species.

Ms Pepper said knowledge of genetic differences was vital in conserving species.

''With genetic and molecular techniques that we have these days, we're realising that with a lot of things that were previously thought to be one species, because they all look the same, are genetically all very, very different,'' she said.

''We need to know how genetically different ... populations are in order to conserve all of that diversity. Because you don't want to lose diversity just by not knowing its there.''

Ms Pepper hopes to finish her PhD research in about two years.