Small-brained hominid species challenges human exceptionalism, says paleoanthropologist

Quirks and Quarks18:53Unearthing a small-brained hominid species that challenges human exceptionalism

The 2013 discovery of the largest collection of hominid fossils ever found is rewriting the origin of complex behaviours we thought were uniquely human, says a renowned paleoanthropologist.

The fossilized bones belonged to an entirely new species of ancient human relatives called, Homo naledi, which lived in South Africa several hundred thousand years ago when the first Homo sapiens arrived on the scene. 

Paleoanthropologist and National Geographic explorer-in-residence Lee Berger spoke with Quirks & Quarks host Bob McDonald about this incredible find that he detailed in his latest book, Cave of Bones: A true story of discovery, adventure and human origins. Here is part of their conversation. 

Describe the Rising Star cave system where you found these bones. What's it like? 

It's not your typical cave. These are networks of incredibly tiny and tight passages, almost labyrinth-like, that extend from the surface down to 40 or 50 metres before they hit the water table. It's four-and-a-half kilometres of cave system and it's interrupted periodically by small to medium-sized chambers. And it's in these chambers, often hundreds of metres back from where we can access these caves, that we're finding these remains of Homo naledi. 

These are non-human, small-brained, ancient human relatives that appear to be burying their dead very deliberately in a ritual-like fashion back in these deep chambers throughout the system.

How did you find the fossils?

So the fossils were found by accident, deliberately, and that's not an oxymoron. I had sent out amateur cavers to use a map I had created almost a decade before in my search for ancient hominids that led to discovery of another species called Australopithecus sediba. And they went into this cave system as part of that exploration exercise, but on a night in September of 2013, they went off the map. 

They found a thing we now call "the chute labyrinth," an incredibly narrow — down to 17-and-a-half centimetres — 12-metre vertical passage that enters this remote cave system. There they saw bones, didn't know what they were, brought me these images, and I immediately recognized they had found something extraordinary. No scientist had ever seen images like this before. 

Well, what stood out to you when you first saw these bones? 

Oh, I instantly knew they were primitive. That is, the dentition was not shaped like a human. It had larger premolars and the molar proportions were different than ours. This looked like something truly ancient, but they were just lying on the floor of this really remote chamber. 

That led to the discovery of the largest assemblage of ancient human relatives ever discovered in history that we controversially said, when we announced in 2015, were deliberately disposing of the dead. And why that was controversial is they're not humans. They have the brain the size of a chimpanzee.

The remains were in holes in the ground that were dug; they'd been placed there and then buried with the dirt from those holes. 

You might obviously call that "a grave." We didn't recognize it because we kind of talked ourselves out of that being possible with something that wasn't human: that's the burial of the dead. 

So where then do H. naledi fit into the human evolutionary tree?

We have no idea. I know that's a terrible answer from a scientist, but H. naledi looks like it should belong with species like Homo habilis, some of the very earliest members of our genus, a very primitive Homo erectus. And that would have typically placed them at about two, two-and-a-half-million years. 

What was immensely surprising about H. naledi is that when we eventually got good dates, both directly on the fossils and on the site, they turned out to be from around 230 to 330,000 years ago. That's within the range of time that we thought only modern humans existed in Africa. 

So until that moment, we thought we were alone. And now we've dropped another species, very not like us, in many ways, right into the middle of that critical time period. 

Wow. So they were around at the same time as early Homo sapiens, our species? 

That's right. And I think that was the first thing that was most surprising to everyone. And then of course as we continued the research, and continued to study both the fossils themselves, but more importantly, the situation they were in. 

These discoveries began challenging our ideas of when critical events like burial of the dead, ritualized behaviours and the creation of things like perhaps meaning-making symbols that some people might call "art" occurred. Although we're very careful not to say that. They challenge the [human] origin stories that we thought we had all figured out.

Well, tell me more about the evidence that you found in the cave that you think they deliberately buried their dead.

So back in 2015 when we announced this new species, we had to explain why only the remains of Homo naledi were in these deep, deep underground systems. And so very controversially, we said at that time we believed that they were ritually disposing of the dead.

We were very careful not to use the word "burial." Burial implies a much, much more critical sort of advanced behaviour that most archaeologists would tie only to large-brain modern humans.

Then in 2018, we found these holes dug into the ground with bodies flexed in them in a fetal position deep in these systems. And we began to realize that these were what you would call "human graves." That was astounding. 

That led to a lot of research around describing these various graves as we found them in different locations throughout the system. Then July of 2022, that's when I actually entered the system and recognized that there were engravings and meaning-making symbols carved into the walls above these graves. 

The [engravings] have been done multiple times over, perhaps hundreds, if not, thousands of years, in a place where there's no evidence that humans have ever been. 

Now that was staggering because that begins to get into an idea that this non-human species is behaving like humans. I think what's really incredible, Bob, is that humans aren't doing that sophisticated behaviour at the same time. 

Wow.

They won't do it for another 100 to 150,000 years. 

Wow! 

This predates us, but likely has nothing to do with those behaviours in us that we use today to identify ourselves. 

So what does it say, then, about H. naledi's mental capacities if they were intentionally burying their dead, they were creating what looks like art, or they were scratching on the walls anyway, and yet they had brains the size of chimpanzees?

I think it says, at first, that we humans have created a kind of mythology around ourselves. Almost every religious text begins with an origin story that tries to explain why we are different and often superior to animals.

What I think we're learning with H. naledi is that that's not a true story; that H. naledi was capable of behaving in a way very nearly, if not as complex as we do today, doing it with a very small brain. 

This Q&A has been edited for length and clarity.