Research has indicated that mammalian sperm can survive being frozen for much longer than was previously thought, suggesting that it could potentially be recovered from species that have died out.

Several well-preserved mammoth carcasses have been found in the permafrost of Siberia, and scientists estimate that there could be millions more.

Last year a Canadian team demonstrated that it was possible to extract DNA from the specimens, and announced the sequencing of about 1 per cent of the genome of a mammoth that died about 27,000 years ago.

With access to the mammoth’s genetic code, and with frozen sperm recovered from testes, it may be possible to resurrect an animal that is very similar to a mammoth.

The mammoth is a close genetic cousin of the modern Asian elephant, and scientists think that the two may be capable of interbreeding.

The frozen mammoth sperm could be injected into elephant eggs, producing offspring that would be 50 per cent mammoth.

The suggestion that it may be possible to recreate an animal that is at least part-mammoth has emerged from a study of mice by Japanese, British and American scientists.

While many types of mammalian sperm, including that of humans, can be preserved by freezing, mouse sperm is vulnerable to damage that can limit its ability to fertilise eggs when it is thawed.

A team led by Narumi Ogonuki of the Institute of Physical and Chemical Research Bioresource Centre in Tsukuba, central Japan, has demonstrated that sperm better survives freezing if testes, or whole mouse bodies, are frozen.

Even sperm taken from mouse bodies that had been frozen 15 years ago was capable of fertilising mouse eggs and producing pups, the researchers found.

The work has technical implications for the breeding of laboratory mice for medical research, but it also shows in principle that mammalian sperm can survive in a body that has been frozen for several years.

This could mean that it is able to survive in similar fashion over much longer periods, as in mammoths frozen in permafrost.

“Restoration of extinct species could be possible if male individuals are found in permafrost,” Dr Ogonuki said.

“If sperm of extinct mammalian species, for example the woolly mammoth, can be retrieved from animal bodies that were kept frozen for millions of years in permanent frost, live animals might be restored by injecting them into oocytes [eggs] from females of closely related species.”

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