By DAVID DERBYSHIRE

Last updated at 21:12 07 February 2008

Imprisoned in a tank hundreds of miles from a mate, Ibolya the female shark resorted to desperate measures. To the astonishment of her keepers, she spontaneously produced a perfectly healthy pup.

The virgin birth is making biologists think again about one of the oldest and - in evolutionary terms - most successful creatures.

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"When I saw the baby shark lying on the bottom of the tank I thought it was a joke," said Attilia Varga, the director of the Nyiregyahaza Centre in Hungary. "I was amazed when I realised it was a real shark."

Ibolya, a white-tipped reef shark, has been with the aquarium for seven years. In that time, she has never shared water with a male.

The pup has been a hit with visitors - but has left keepers looking for a bigger tank. They also plan to find a male so Ibolya can breed conventionally next time.

Virgin birth - parthenogenesis - happens when an egg begins to divide without being fertilised. Common in insects, it is rare in vertebrates such as fish, birds and reptiles.

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Scientists believe that sharks use it as an emergency survival mechanism. Normally animals rely on genetic diversity - the interplay of genes from two parents - to evolve. However, reproduction without sex is a useful stopgap.

Sharks are one of Nature's great survivors, appearing in the oceans 400million years ago - before the dinosaurs. Normally their eggs are fertilised inside the female.

In the white tip and most other species, the female gives birth to live young.