PARIS • We all grow up accepting certain unassailable facts: Water is wet, the earth is round, and to produce a baby, you need an egg and sperm.

As it turns out, the last of these may not be true.

This week, scientists announced they had produced baby mice by fusing sperm and a type of cell that is not an egg, reported Agence France-Presse.

Writing in the Nature Communications journal, the scientists from Britain and Germany described how they took mouse eggs and used chemicals to trick them into developing as if they had been fertilised. These pseudo-embryos behave much like skin and other cells in the body.

The scientists next injected sperm into the "fake" embryos and found that rather than dying, they developed normally, and when transferred into female mice, led to apparently healthy mouse pups.

The researchers reasoned that if injecting sperm into mouse pseudo-embryos could produce healthy babies, then it might one day be possible to achieve a similar result in humans using cells that are not from eggs.

The findings in Nature Communications could, in the distant future, mean women can be removed from the baby-making process, said the researchers.

In the mouse experiments, the odds of achieving a successful pregnancy were one in four.

The report's senior author, Dr Tony Perry of the University of Bath, told the BBC News website: "This is the first time that anyone has been able to show that anything other than an egg can combine with a sperm in this way to give rise to offspring.

"It overturns nearly 200 years of thinking."

Although the researchers began with an egg cell for the experiment, they do not believe it is required to spark the same development, reported The Telegraph. In theory, the technique should work with any cell in the body as long as half the chromosomes are removed first to allow them to fuse with the sperm's chromosomes.

The so-called motherless technique raises the possibility that two men could have a child, with one donating an ordinary cell and the other, sperm, although a woman would still need to act as a surrogate. Or one man could have his own child using his own cells and sperm - with that child being more like a non-identical twin than a clone.

Dr Perry stressed that such scenarios were still "speculative and fanciful" at this stage, reported the BBC.

More realistically, the technique could potentially allow women whose fertility has been wiped out by cancer drugs or radiotherapy to have their own children, reported The Telegraph.

The researchers are planning to test out the theory using skin cells.