All the Homo naledi skeletons in Rising Star Cave are female, and that probably didn’t happen by accident.
In 2013, a team of anthropologists led by Lee Berger unearthed the remains of more than 20 small-bodied hominins (ancient relatives of humans), all 335,000 to 236,000 years old, from the Rising Star Cave System in South Africa. Excavations at Rising Star have sparked debate about whether these little hominins had all ended up in the caves by tragic accident, or whether they’d been carefully placed there by other members of their enigmatic species, dubbed Homo naledi.
Now there’s a plot twist that may speak to how the remains got there: All of the hominins in Rising Star are female, at least according to the proteins in their dental enamel.
Little bits of teeth had a big surprise
Max Planck Institute for Evolutionary Anthropology molecular scientist Palesa Madupe and her colleagues recently analyzed the proteins in dental enamel from 23 Homo naledi teeth unearthed in four different cave chambers deep in the Rising Star system. Those 23 teeth came from at least 20 different individuals, ranging from babies with their first tiny teeth to older adults with teeth worn down from decades of chewing.
All of the samples contained a protein called amelogenin-X, or AMELX, which is encoded in the DNA of the X-chromosome. But not a single sample contained the male version, AMELY, which is encoded on the Y-chromosome.
In genetically male humans, dental enamel usually contains about a tenth as much AMELY as AMELX, and Madupe and her colleagues say that given the level of AMELX in their samples, they should have been able to detect AMELY if it was there. But it seemingly wasn’t. It appears that every single skeleton in the cave system, meaning every known Homo naledi (except the ones for whom the anthropologists found only bones, not teeth), is genetically female.
The odds of that being a coincidence are about the same as the odds of flipping a coin 20 times and landing on the same side every time: 0.0000954 percent, according to Madupe and her colleagues. In other words, the metaphorical coin must be weighted—in this case, by hominins doing things on purpose, like laying their dead to rest in the narrow, twisting darkness of Rising Star.
<small>Source: Ars Technica</small>
