Swiss researchers have found that it was extremely rare for humans to mate with Neanderthals, despite the fact that they coexisted for at least 10,000 years.

A recent Swiss study showed that two to three per cent of the human genome can be traced to the Neanderthals.

With that in mind, researchers wanted to figure out exactly where, when and how often Homo Sapiens interbred with Neanderthals.

Model calculations using simulated French and Chinese DNA samples showed that successful pairings – that is, intercourse resulting in a live birth – were truly rare.

The scientists estimate that the success rate was less than two per cent.

“Without these strong barriers to reproduction, we would have become Neanderthals,” said scientist Laurent Excoffier of the Swiss Institute of Bioinformatics and Bern University in a statement.

He was joined by research partner Mathias Currat of Geneva University.

The results of their study will be published in the specialist journal PNAS.

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