CAPE TOWN, June 25 (Xinhua) -- Scientists in South Africa have found no biological male markers in fossils of an extinct archaic human species, a discovery that is raising new questions about possible sex-specific burial practices among a population that lived hundreds of thousands of years ago.
In a statement issued on Thursday, the University of the Witwatersrand said the findings were reported in an international study published in the journal Cell on Wednesday.
The fossils belong to Homo naledi, an extinct species of archaic human discovered in 2013 in South Africa's Rising Star Cave system in the Cradle of Humankind World Heritage Site.
Researchers analyzed 23 fossil teeth from at least 20 individuals using paleoproteomic techniques. They searched for Amelogenin-Y, a protein linked to the Y chromosome and biological males, but found no trace of it in any sample.
Scientists from the University of Copenhagen in Denmark and the National Geographic Society in the United States, together with collaborators from other institutions, said the results could indicate either a strongly sex-biased burial pattern or an unusual genetic feature within the population.
"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," said Palesa Madupe, South African-born lead author of the study.
"Our study helps resolve the long-standing mystery of why Homo naledi lacked significant variation; it's probably because they could have all belonged to one sex," she added.
National Geographic Explorer and co-author Lee Berger said the pattern may reflect behavior rather than biology. "It appears that the most likely explanation for the observed absence of an Amelogenin-Y marker in these individuals is that we are seeing a sex-bias in mortuary practice," he said.
He added that the probability of sampling 20 individuals of one sex is extremely unlikely.
Researchers also noted that the Y-linked marker gene may have been lost or mutated over time, although they said it is unlikely that such a scenario would affect an entire population.
The study adds to the ongoing debate about Homo naledi, a small-brained but behaviorally complex human relative that lived in southern Africa hundreds of thousands of years ago and may have engaged in unexpectedly advanced cultural practices. ■