Ancient rock carvings created thousands of years ago depict scenes of bisexual and transgender activity, according to a report.
If true, the images, dubbed the Kangjiashimenji Petroglyphs, would be the oldest depictions of homosexual activity known to humanity.
The explicit carvings, which could date back to 2000BC, show 100 figures and cover a 30 sq ft area of rock in remote Xinjiang region in northwest China.
They were discovered in the late 1980s by archaeologist Wang Binghua - but now a fresh light has been thrown on them by author Mary Mycio.
Mycio claimed that bisexual participants can be identified as hermaphroditic figures that combine male and female features.
The rock carvings depict females with masculine triangular torsos, hips and legs, adorned with feminine headdresses and jewellery. Males are smaller, have thin legs, and wear no decorations.
Mycio identified a third group bearing male phalluses but wearing female headdresses.
One tableau depicts an aroused male with his arm around another man in the same state. The pair are watching nine women and two men dancing in a circle. At the foot of the scene a lone male masturbates.
In another scene, a group of men and women dance around a large bisexual figure in a state of arousal who is preparing to couple with a woman.
"The tableau is a spectacular demonstration of sex as one of the driving forces behind the creation of art," said Mycio.
Viktor Mair, a professor of Chinese language and literature at the University of Pennsylvania, said the carvings were "a forest of phalluses and vulvas blanketed in sexual symbolism".
"Such overt, pervasive attention to sexual reproduction is extremely rare for a burial ground," he said.
An alternative reading of the "bisexual" figures is that they might be shamans. Another theory is that the male/female composites are "twin-spirited" people.