A little over a decade ago in a cave in South Africa we discover to a distant relative of homo sapiens: the Homo naledione of the most enigmatic hominids in evolution. Its body had a curious shape from the point of view of paleontology: the head and shoulders were similar to Australopithecusbut hands, feet and face gave an air of the genre Homo. His brain was also about a third of ours.
Something that caught our attention from the beginning was how homogeneous the skeletons found in the Rising Star cave system were with each other. Perhaps, too much so. So they assumed the usual: that there were males and females and that the largest skeletons corresponded to the males. They were wrong.
The discovery. This assumption was never verified on a molecular scale, something that has now been done: for the first time a team has analyzed his teeth. More specifically, the enamel of 23 teeth from at least 20 specimens. What they were interested in was looking for the Amelogenin-Y protein, which only exists in males since it is encoded in the Y chromosome. They did not find it. What does that mean? That all the specimens analyzed were biologically female.
Why is it important. Because this analysis is the largest scale carried out on an extinct hominid population and suggests that Rising Star is the first exclusively female burial site created by a species that was not Homo sapiens. In other words, hundreds of thousands of years before we thought, funerary rituals already existed.
And it also solves one of the enigmas of the homo naledi: why they are so similar to each other on a morphological level. Well, because what seemed like a biological characteristic of the species is simply the result of all known individuals belonging to a single sex.
Context. He naledi has been a controversial species for paleontology from the beginning. When was discovered in 2015the researchers already pointed out that it was the ancient hominid species with the smallest difference in size between its adult individuals ever found. Now we know why.
Tooth enamel is the hardest tissue in the body, so much so that it protects proteins from environmental degradation for an eternity. For this reason, the technique has been used on remains that are up to two million years old: the fossils of H. naledi They are “only” between 241,000 and 335,000 years old, so they are within that analysable range.
In detail. To validate the results and rule out internal errors, the analysis was carried out in two laboratories independently and the team from the University of York also analyzed the amino acids to rule out that the proteins were a product of contamination. Lee Berger, one of the authors of the study, holds That if the adults lived separately by sex, we would expect to find at least male babies in the cave, but this was not the case. More than a coincidence, it suggests that this segregation was a mortuary practice.
The paper also explains that the Homo naledi has a unique amino acid never seen in other hominids and that shares a characteristic in a bone protein with the Paranthropus robustuswhich helps contextualize both species in the tree of evolution.
Yes, but. The study includes a possibility to take into account: that the absence of a male marker is due to a mutation or disappearance of the gene throughout evolution, which would make biological males indistinguishable from females with this technique. Elizabeth Sawchuk, curator of human evolution at the Cleveland Museum of Natural History and outside the study, sums it up: “it is a strange result in a species that was already strange.” The most spectacular interpretation, which H. naledi buried their dead separated by sex, is also the most difficult to prove.
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Cover | Rising Star Program (Hawks et al., eLife (2017))
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