Million-year-old skull may rewrite timeline of human evolution

A million-year-old human skull discovered in China may push back the origin of modern humans by at least half a million years, according to a new study published in Science.

The fossil, known as Yunxian 2, was unearthed in Hubei Province and initially classified as Homo erectus. But new analysis led by scientists from China's Fudan University and the UK's Natural History Museum suggests it may instead belong to Homo longi – a sister species of both Neanderthals and Homo sapiens.

If correct, researchers say the finding would mean early versions of our species and Neanderthals were already walking the Earth one million years ago, much earlier than previously thought.

Prof Xijun Ni of Fudan University, who co-led the study, said the team was initially shocked by the results. "From the very beginning, when we got the result, we thought it was unbelievable. How could that be so deep into the past? But after testing all the models and methods repeatedly, we are now confident," he said.

Prof Chris Stringer of the Natural History Museum, also a co-lead, said the analysis "dramatically shifts" the timeline of human evolution. "There are probably million-year-old fossils of Homo sapiens somewhere on Earth – we just haven't found them yet," he noted.

A challenge to established history

Until now, the earliest known evidence of Homo sapiens dates back 300,000 years in Africa. But the reclassification of Yunxian 2 suggests that three major human lineages – Homo sapiens, Neanderthals, and Homo longi – may have co-existed for nearly 800,000 years, potentially interacting and interbreeding.

The skulls, badly crushed when first excavated, were digitally reconstructed using 3D scanning and computer modelling techniques. The refined images allowed scientists to reassess their classification.

Prof Ni likened human evolution to a tree with several intertwined branches. "There were three major branches closely related, coexisting for almost one million years, with possible interbreeding. This is an unbelievable result," he said.

Skepticism remains

Some experts caution that the conclusions are far from settled. Dr Aylwyn Scally, an evolutionary geneticist at Cambridge University, said the methods used to estimate timing remain uncertain. "Even with the largest amount of genetic data, it is very difficult to place a time when these populations co-existed to within 100,000 years – or more," he said.

He described the study's conclusions as "plausible but not proven," noting that further fossil and genetic evidence is needed.

Still, if validated, the discovery could resolve what scientists call the "muddle in the middle" – fossil remains between 800,000 and 100,000 years ago that have been difficult to classify. Reframing them as part of the "big three" human species, or their ancestors such as Asian Homo erectus and Homo heidelbergensis, may help clear the confusion.

Prof Stringer said more work is required to integrate million-year-old fossils from Africa and Europe into the analysis before rewriting humanity's earliest chapters.