After stunning conservationists by mating for the first time in decades, a giant tortoise from the Galapagos islands called Lonesome George, who is the last of his kind, still may not become a dad.

George, a 90-year-old conservation marvel and one of the world's rarest creatures, mated this year with two females, but 80 per cent of the eggs they laid appear infertile.

The females belong to a different subspecies of giant tortoise.

A Pinta Island tortoise, George had showed little interest in sex during 36 years in captivity. His new-found libido has raised hopes he could save his subspecies from extinction

Ecuadorean scientists are studying the eggs and have not ruled out that George could be sterile.

"We are puzzled. We will leave the eggs in the incubators and try to find answers," said Washington Tapia, a park official in change of George's reproduction program. "It's too early to say if George is infertile, only genetic research could tell us that."

However, hope is not lost. Scientists said 20 per cent of the remaining eggs could still produce offspring.

George's keepers placed his eggs in incubators decorated with religious images in hopes of a miracle.

Scientists are also searching for distant relatives in a nearby island, hoping to find another male for mating.

Variations in tortoises from different islands were among the features of the Galapagos that helped Charles Darwin formulate his theory of evolution in the 19th century.

Since then, tortoises have been hunted by pirates and sailors for their meat and their habitat has been eaten away by goats introduced onto the islands. George was the last tortoise found on Pinta in 1971.

Ecuador has declared the islands at risk and the United Nations says efforts to protect them should continue. Some 20,000 giant tortoises still live on the islands.

After trying almost everything from artificial insemination to having George watch younger males mate, his keepers had nearly lost hope. At 90 years old George is in his sexual prime and his low libido even raised tabloid-like rumours the 198 pounds creature preferred other males.

With files by Reuters