During the Japanese occupation of China in 1933, a man working on a bridge in the city of Harbin in the northeastern part of the country discovered a skull and immediately hid it from his Japanese overseers. In 2018, the elderly man revealed his secret to his grandchildren, who recovered the skull from the abandoned well where the man had concealed it 85 years earlier. They turned the skull over to scientists at the Geoscience Museum of Hebei GEO University. The researchers determined that the skull is at least 146,000 years old by using uranium series dating, which examines trace amounts of uranium and thorium in bone. Since uranium decays to thorium at a known rate, they were able to calculate the skull’s age from the ratio of the two elements. The skull has a unique mixture of traits associated with Homo erectus, such as a massive brow ridge and low forehead, and traits that appear only in more recent hominins, such as a relatively small face and large brain. The skull could possibly represent a previously unknown human lineage, says Chris Stringer of London’s Natural History Museum. Stringer’s colleagues have named the species Homo longi.

According to Stringer, it is also possible that the Harbin specimen may belong to the same species as the Denisovans, a lineage closely related to Neanderthals that is only known from a few small bones and a complete DNA sequence. In order to test this possibility, DNA would have to be recovered from the Harbin skull. Stringer points out that another fragmentary fossil skull, found at the site of Xuchang in central China, may represent yet another separate hominin lineage dating to about 100,000 years ago. If that it is the case, there may have been at least four different lineages of early humans in China at that time—Neanderthals, Homo sapiens, Homo longi, and the Xuchang hominin. “You’ve got all these different experiments in how to be human,” says Stringer, “and Harbin adds one more.”