(dr) National Geographic
Here is the new Homo naledi, one of the oldest known ancestors of Man
A new analysis of proteins preserved in the teeth of Homo naledi found in the Rising Star Caves did not detect the AMELY variant, which is only present in men.
A groundbreaking genetic analysis of Homo naledi, one of modern humans’ most enigmatic relatives, has revealed a surprising possibility: all of the species’ known skeletons may have been women.
The findings, in the journal Cell, represent the first successful extraction and analysis of genetic information from Homo naledi, a species discovered deep within the Rising Star cave system in South Africa. The researchers examined proteins preserved in the teeth of 20 individuals around 300,000 years old and found no evidence of a genetic marker typically associated with biological males.
The study focused on ancient proteins found in tooth enamel using a technique known as proteomics. Scientists analyzed variants of the amelogenin gene, which can be used to determine biological sex. While one variant, AMELX, is present in both men and women, the AMELY variant is only found in men. The researchers detected an abundance of AMELX proteins, but found no trace of AMELY in any of the samples.
The results challenge long-held assumptions about Homo naledi. Some of the best-known specimens of the species, including DH1 — the individual originally chosen to represent the species — and the nearly complete skeleton known as Neo, were previously considered males based on their size and skeletal characteristics.
The discovery has reignited the debate about the nature of the Rising Star cave fossil assemblage. The researchers suggest that the absence of males could corroborate the controversial theory that Homo naledi intentionally discarded or buried their deadpossibly following sex-specific funeral practices. Such behavior would be notable given the species’ relatively small brain size, and would predate known burial practices associated with Neanderthals and modern humans.
However, scientists warn that alternative explanations are still possible. One hypothesis is that Homo naledi had a rare genetic deletion which affected the AMELY gene, making males genetically indistinguishable from females in protein analyses. The researchers consider this scenario unlikely for all 20 individuals, but acknowledge that it cannot yet be ruled out.
The study also revealed another intriguing clue about human evolution. Scientists discovered that Homo naledi shared a genetic variant linked to collagen production with Paranthropus robustus, a distant human relative that lived in southern Africa between one and two million years ago. The significance of this shared genetic trait remains unclear and will require further investigation.
“In short, this is a strange result for a hominid that was already strange. The crucial point to remember is that the absence of evidence for the AMELY gene does not mean that there were no males in the sample, it just means that none were detected,” Elizabeth Sawchuk, curator of human evolution at the Cleveland Museum of Natural History, who was not involved in the study, told .
Experts say the findings raise as many questions as they answer. Because Homo naledi is currently known from a single archaeological site, researchers emphasize the need for new fossil discoveries and more comprehensive protein databases to better understand the species’ position in the human family tree.
