A fossilised skull found in China could rewrite human evolution by suggesting Homo sapiens emerged at least half a million years earlier than previously believed.

The specimen, named Yunxian 2, was discovered in Hubei Province and dated to around one million years ago. It was long thought to be Homo erectus, but new analysis published in Science suggests it is closer to Homo longi, a sister species of Neanderthals and modern humans.

“From the very beginning, when we got the result, we thought it was unbelievable. How could that be so deep into the past?” said Prof Xijun Ni of Fudan University, who co-led the analysis. “But we tested it again and again to test all the models, use all the methods, and we are now confident about the result, and we're actually very excited.”

Prof Chris Stringer of the Natural History Museum in London, who co-led the research, said the findings shift the timeline of large-brained humans back by at least half a million years.

Some experts remain cautious. Dr Aylwyn Scally of Cambridge University said: “One has to be particularly tentative about the timing estimates, because those are very difficult to do, regardless of what evidence you're looking at, be that genetic or fossil evidence.” He added: “Even with the largest amount of genetic data, it is very difficult to place a time when these populations may have co-existed to within 100 000 years, or even more.”

The discovery raises the possibility that Homo sapiens, Neanderthals, and Homo longi co-existed for around 800 000 years, reshaping what scientists have long called the “muddle in the middle” of human evolution.