Ancient Proteins Uncover Potential Female Burial Site in Homo naledi Population

Scientists have extracted and analyzed the first-ever ancient proteins from the fossils of Homo naledi, revealing a potential all female burial site.

The study, published in the journal Cell, raises the possibility that South Africa's famous Rising Star Cave system could represent the first known example of a sex-specific burial site by a non-Homo sapiens.

Homo naledi, an extinct cousin of modern humans that lived between 335,000 and 241,000 years ago, has puzzled researchers since its initial discovery in 2013. The species possessed an unusual mixture of primitive, ape-like traits alongside human-like features.

But for over a decade, scientists have wondered why the adult fossils recovered from the cave's Dinaledi Chamber looked so remarkably identical. The remains showed almost none of the physical variations that would be expected between males and females.

To solve this puzzle, researchers from the University of York, the University of Copenhagen, and more than 10 other international institutions, investigated proteins from the skeletal remains. 

Using a minimally destructive acid etching technique, the team extracted microscopic protein fragments, called peptides, from 23 teeth representing at least 20 different individuals.

Researchers analyzed the tooth enamel for Amelogenin-Y, a protein uniquely coded by the male Y chromosome. 

The results revealed that the male marker was absent. To ensure the validity of the results, a team at the University of York's specialized chemistry facility analyzed the amino acids to prove the proteins were genuinely ancient and not the result of modern contamination.

Dr Marc Dickinson, from the University of York's Department of Chemistry, said: "The lack of male markers with the group is truly fascinating. 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 findings open up new questions about the culture and social structure of these ancient hominins. If the chamber was reserved exclusively for females, it may imply a level of complex, symbolic mortuary practice previously thought unique to Homo sapiens - modern humans.

The team noted, however, that there could be a biological explanation as well as a cultural one. It is possible that the Homo naledi population was highly isolated, causing the male-specific Amelogenin-Y gene to mutate or be deleted. 

This would mean males were present, but their teeth simply lacked the typical genetic signature.

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."

Palesa Madupe, University of Copenhagen  

"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."

As the largest extinct hominin population ever to undergo protein analysis, these ancient females - or genetically unique males - have prompted a rewrite of what scientists thought they knew about the dawn of human society.