Human biology used to be simple: Babies were the sum total of sperm plus egg, give or take nine months. But now the simple arithmetic of baby-making is being challenged by a team of scientists at the University of Bath, who have figured out how to create embryos without the egg.

Wait, what?

The bizarre, though groundbreaking, study published today in the journal Nature Communications banks on previous research that showed that unfertilized — that is, sperm-free — eggs could be tricked into becoming “embryos.” These balls of cells, known as parthogenotes (or, more descriptively, “maternal uniparental embryos”), normally don’t survive very long because they’re missing all of the crucial baby-programming information that sperm normally carry.

What the scientists at the University of Bath figured out was how to take a parthogenote and inject it with sperm so that it eventually develops into a healthy adult. Carrying out their studies in mice, they created babies from parthogenotes — a feat long thought impossible — with a success rate of 24 percent.

Until now, the most successful process for creating healthy babies by manipulating eggs was nuclear transfer cloning, where DNA from one cell is moved into an empty egg. This technique is successful just two percent of the time.

Biologists used to believe that only egg cells were capable of coaxing a sperm cell into expressing the genes necessary for embryo development. After this study, they’ll need to rethink those assumptions.

“Our work challenges the dogma, held since early embryologists first observed mammalian eggs around 1827 and observed fertilisation 50 years later, that only an egg cell fertilised with a sperm cell can result in a live mammalian birth,” biologist Tony Perry, Ph.D., the senior author on the study, said in a release.

This is science flexing its philosophical muscles: At the heart of this research, as Perry outlines on his homepage, is the question of where life begins. “If this problem” — he’s talking about the conundrum of how life arises from sperm and egg — “may be likened to a 2000-piece jigsaw puzzle, science has so far only completed some of the edges; there’s a big hole in the middle.”

The new findings open up a whole world of ethical quandaries. Scientists used to think that using human parthogenotes as sources of stem cells would be totally kosher, at least in theory (nobody has attempted to make them yet), because there was no chance they would be viable. After this discovery, the moral implications aren’t so clear. The implications are less murky when it comes to non-human species, however: Developing this technique further could make it easier to breed endangered animals, though the researchers note that this future is still pretty far off.

Yasmin is a writer and former biologist living in New York. A Toronto girl at heart, her writing also appears in The Last Magazine and SciArt in America. You might recognize her as a past host of Scientific American's YouTube series.