'These findings offer rare insights into a culture that has, until now, been difficult to access directly,' one researcher said
What might be the world's first single-sex space has been uncovered in an ancient cave.
New research suggests the cave was used exclusively to bury the females of an evolutionary cousin to humans.
The species Homo naledi was only discovered in 2013 in South Africa's Rising Star Cave - but has intrigued scientists ever since.
Homo sapiens' evolutionary cousin has primitive traits, with features associated with modern humans.
Adults stood around four feet, 10 inches tall and had a brain volume of about 460 to 610 cubic centimetres, or a third of humans'.
But the species' feet resembled ours, indicating it walked upright.
It also had similar hands and wrists current humans, indicating it may have used tools.
Now researchers from the University of York, the University of Copenhagen and other institutions believe they have evidence which indicates all bodies in the cave are female - making it the first sex-specific burial site by an extinct human relative.
The study, published in Cell, extracted microscopic protein fragments known as peptides from 23 teeth representing 20 individuals.
The researchers tested the sample for Amelogenin-Y, a protein produced by a gene found on the Y chromosome - only found in males.
None of the protein was found, which suggests that no men were buried.
Marc Dickinson, from the University of York, said: "The lack of male markers with the group is truly fascinating.
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"It is incredibly exciting to gain a window not only into the biology of our ancestors, but also into how they lived.
"These findings offer rare insights into a culture that has, until now, been difficult to access directly.
"Advances in ancient protein analysis are opening the door to a far richer and more nuanced understanding of ancient hominins."
The age of the fossils - between 335,000 and 241,000 years old - means Home naledi overlapped in time with early Homo sapiens.
But there may be another explanation for the lack of the protein, the researchers have cautioned.
It is possible the protein had been mutated or disappeared out of the group - but the paleontologists view this to be a less likely explanation.
Palesa Madupe, who completed the work as part of her postdoctoral research at the University of Copenhagen, said: "Unlike those found in other remains like bone fragments, proteins in tooth enamel are preserved because dental enamel — the hardest tissue in the human body — shields proteins from environmental contamination even for millions of years.
"This makes them ideal carriers of genetic information from deep time. Our study helps in the long-standing mystery of why Homo naledi lacked significant variation; it’s probably because they could have all belonged to one sex."