Deep in the cave system where Homo naledi was discovered, skull fragments of a naledi child have been found. Combining the pieces tells us something about naledi anatomy at the age of six or so, but the site where they were located could be the most important part of the discovery.
The discovery of Homo naledi was one of the biggest science stories of the last decade. We have more of their fossils just from the Rising Star Cave System than most other hominins. Nevertheless, we still know very little about the behavior of this offshoot of the human family that co-existed with modern humans. The finding of the skull of the naledi child dubbed Leti, the first naledi child fossil discovered, may offer us an entry point.
With a brain size of 480-610 cubic centimeters (29-37 cubic inches), Leti had reached; “90% to 95% of its adult brain capacity,” Dr Debra Bolter, a co-author on the paper, said, despite teeth suggesting she was only age four to six. (Leti’s sex has not been determined, but anthropologists are using female pronouns for the moment).
“Homo naledi remains one of the most enigmatic ancient human relatives ever discovered,” team leader Professor Lee Berger said. “It is clearly a primitive species, existing at a time when previously we thought only modern humans were in Africa. Its very presence at that time and in this place complexifies our understanding of who did what first concerning the invention of complex stone tool cultures and even ritual practices."
When first announced in 2015, naledi's small brain size led to it being seen as very ancient, with one estimate putting the fossils’ age at two million years. However, subsequent research using electron spin resonance showed the teeth to be between 335 and 241 thousand years old, meaning Homo Sapiens, or our immediate predecessors, were living in Africa at the time, probably quite close by.
“The area where Leti was found is part of a spiderweb of cramped passages,” Maropeng Ramalepa, who helped bring items to the surface, said. Exploring these passages, sometimes just 15 centimeters (6 inches) wide, has proven challenging, with only small women able to reach many parts of the system, and then only with difficulty. Homo naledi were smaller than us but still must have found some of the cave passages a squeeze, something they presumably managed without light.
Leti’s skull was found so far from other naledi skeletons the name is a shortening of letimela, which means “the lost one” in Setswana. There are no signs of Leti’s other bones, and with the skull sitting on a shelf 80 centimeters (32 inches) above the cave floor it couldn’t have been washed there or dragged by predators.
The authors conclude other naledi must have placed the skull there. Why they did this is uncertain. Perhaps it was an act of honor from a grieving parent. If so it would indicate that while the naledi had brains much smaller than ours, they practiced the basics of funeral rites. Previous papers have argued the adult naledi fossils found in the Rising Star Cave System did not die there, but instead, the caves were a mausoleum for placing the dead, perhaps to protect bodies from predation. If so, the absence of signs of damage from carnivores or scavengers shows it was a success.