l opercula contain several structures with roles in language, social behavior, and the kinds of motor planning you’d need in order to (for instance) make stone tools. Those structures include Broca’s area, a structure on the left side of the brain that’s strongly associated with the ability to produce speech.
Frontal opercula show up in endocasts from some early Neanderthal relatives from Sima de los Huesos in Spain and even in some Homo erectus (1.5 million years ago) endocasts. And we can say, at least, that no fronto-orbital sulcus—the structure found in Australopithecines—shows up on endocasts from earlier hominins like Homo rudolfensis (1.8 million years ago) and Homo habilis (2.5 to 1.5 million years ago), although researchers are still debating whether those casts show signs of frontal opercula.
“We think that another look at these specimens would be really useful, to see if the evolution of this brain region happened all in one step or whether there were different stages that these older fossils might represent,” University of Wisconsin paleoanthropologist John Hawks told Ars.
In the Homo naledi endocasts, Columbia University anthropologist Ralph Holloway and his colleagues found clear signs of frontal opercula. In casts from one skull, Brodmann’s area 47—a part of the frontal lobe associated with processing syntax and recognizing social emotions—is especially clearly visible.
Does that mean Homo naledi had a language?
“What exactly the span of the communicative abilities would be—there's no way of knowing just looking at an endocast,” Holloway told Ars. But since parts of Broca’s region are so clearly visible on the casts, “It really does suggest that their communicative abilities probably included some rudimentary language. Certainly that’s where my speculation would go.”
In fact, based on endocasts belonging to other hominin species from the 1.8 million-year-old Homo rudolfensis to the 400,000-600,000-year-old Homo heidelbergensis (this is including Homo erectus at about 1.5 million years old), the capacity for at least rudimentary language may stretch back around 1.8 million years in the human lineage.
But it’s still hard to say exactly how “smart” Homo naledi may have been.
Hawks told us:
The best way to answer this question is to build a better picture that draws in many kinds of evidence. We have debated how smart Neanderthals were for 150 years—and now that scientists are bringing together more evidence from archaeology, from pigments, from the brain and genetics, it is clear that they were not so different from us. We don’t have that breadth of evidence yet for Homo naledi, and that is our challenge, to find these other sources of evidence about behavior.
What’s in the back of your mind
The casts also show that Homo naledi’s occipital lobes were larger on one side than on the other—another humanlike trait. In humans, that asymmetry is probably associated with language-processing and producing centers of our left hemispheres being more developed. (That asymmetry might, as a side effect, be the reason most of us tend to have a dominant right hand.)
The Homo naledi casts suggest that asymmetry but aren't conclusive. Thanks to greater capacity for language, this may be a common trait shared by hominins but probably not our last common ancestor with the other great apes.
“We do know that apes, chimpanzees, [and] gorillas do have some handedness, but they don't show the same level or more consistent pattern that you find in hominins,” said Holloway.
Two of the skulls had larger left occipital lobes, but that doesn’t necessarily mean that those Homo naledi individuals were right-handed. Typically in humans, a larger left occipital lobe and right frontal lobe are associated with right-handedness, but none of the Homo naledi skulls preserves details of the right side of the frontal lobes, which limits what we can say about handedness.
“We can only speculate about handedness in Homo naledi, unfortunately,” said Hawks. “In some other hominins, like Neanderthals, scientists have some evidence that they were more oft