Ancient human relative study reveals an absence of male markers

A study has revealed a discovery about Homo Naledi, an extinct human relative that lived in South Africa between 335,000 and 241,000 years ago

Researchers analysing ancient proteins preserved in fossil teeth found no evidence of biological males among a group of at least 20 individuals, raising questions about the species’ biology and behaviour.

The research, published in the journal Cell, is the first time scientists have successfully extracted and analysed ancient proteins from the teeth of Homo Naledi. The fossils were recovered from the Rising Star cave system in South Africa’s Cradle of Humankind, one of the world’s most important archaeological sites.

Tooth enamel provides clues from deep time

The international team examined 23 teeth belonging to at least 20 individuals. By analysing proteins trapped within tooth enamel, researchers searched for a protein known as Amelogenin-Y, which is produced by a gene located on the male Y chromosome.

Tooth enamel is the hardest tissue in the human body and can preserve biological information for hundreds of thousands of years. This makes it an invaluable source of evidence when DNA is no longer available.

The researchers found that none of the teeth contained traces of Amelogenin-Y. The absence of this protein suggests that all of the individuals studied were biologically female.

The findings may help explain a puzzle that has perplexed scientists since Homo Naledi was first discovered in 2013. Fossils recovered from the Dinaledi Chamber showed little variation in size and shape among adults.

In many human and animal populations, males and females display noticeable physical differences, which is known as sexual dimorphism. The lack of variation among the Homo Naledi remains led researchers to wonder whether the group might represent individuals of the same sex.

The new protein analysis provides the strongest evidence yet that this could be the case.

Evidence of ancient burial practices?

One possible explanation is that the cave chamber was used in a sex-specific way, perhaps as part of a burial or mortuary practice. If correct, this would represent one of the earliest known examples of this behaviour in a human relative.

The odds of randomly sampling 20 individuals and finding only one sex are extremely low, leading researchers to consider the possibility that females were deliberately placed in the cave.

Previous studies have already suggested that Homo Naledi may have engaged in surprisingly complex behaviours. Research conducted by the Rising Star team has identified possible evidence of intentional burials, the use of fire, and the creation of symbolic engravings.

Alternative explanations remain

Scientists also suggest another possibility. The gene responsible for producing Amelogenin-Y may have been altered or even deleted in Homo Naledi. Similar genetic changes have been observed in a small number of modern humans and in at least one Neanderthal.

However, researchers believe it would be highly unusual for this deletion to occur across an entire population or among all 20 individuals examined.

Rethinking human evolution

The discovery is particularly unique because Homo Naledi had a brain only slightly larger than a chimpanzee’s. Despite this, growing evidence suggests the species may have displayed behaviours once thought unique to modern humans.

Whether the findings point to female-only burial practices or a previously unknown genetic trait, the study highlights how much remains to be learned about our ancient relatives.