The more we learn about our evolutionary tree, the more complicated it has become,
for sure! and there's one recently discovered branch which raises a lot of questions. Not
only about the trajectory of human evolution but also about behavior that we pretty much consider
unique to us as a species. I'm of course talking about Homo Naledi so let's take a look at the
archaeological evidence and see what questions are raised by this distant cousin of ours.
One Friday night in 2013 two cavers were exploring a cave called rising
star within the Cradle of Humankind in South Africa, a region full of caves
containing hominin remains. The cavers squeezed through dark and narrow turns,
at times having to crawl on their stomachs just to fit through spaces only several centimetres wide.
Rather them, than me let me tell you.
They eventually arrived at a small enclosed space known as the Dinaledi chamber filled
with what appeared to be human bones. It ended up being a cache of over 1550 bones and teeth
belonging to at least 15 individuals. What was equally as shocking as finding over 15 hominid
individuals in the single cave chamber was what researchers didn't find. No evidence of fire,
even though the chamber was in the dark zone where light can't reach, no tools of any kind,
in fact other than the bones no archaeological traces of any kind, nothing, and no evidence of
any other animals except for six bones belonging to a single bird. Additionally most of the
individuals were articulated meaning that their bones hadn't separated from each other that much.
This suggests that they arrived in the Dinlaedi chamber alive or shortly after they died. Either
way, before they started to decompose. Plus they found individuals from every age group,
infants, elderly, males, females, this naturally raises a ton of questions.
Who were these people? When did they get in there?
How did they get in there? And what were they doing in there?
When the local University in Johannesburg got a look at these specimens the team knew right away
this was something they had never seen before. These individuals had primitive skeletons yet
at the same time had a unique combination of some modern features which were all highly consistent
across individuals, all the same. There was barely any anatomical variation between them. Their
skeletons were overwhelmingly archaic. In terms of body size, estimates for one individual range
from approximately 144 to 148 cm. With weights of eight individuals ranging from approximately
40 to 56 kilograms. This is about the same as the largest australopithecines and small
bodied Homo sapiens. Their brains also overlap in size with Australopithecus
and Paranthropus (which I also made a video on. Shout out to those STI riddled guys).
Their brains are about the third to half the size of our modern brains now. While
their brains were certainly smaller than more recent members of our family tree of Homo,
their skulls were similarly shaped. They were much rounder and taller compared to Australopithecus
and Paranthropus. What's really cool is that some of the homo Naledi skulls preserve an imprint of
the brain called an endocast. These endocasts show that their brains might have been organized
in a similar way to later species of Homo even though they were much smaller, and it makes you
wonder if they were shaped the same way, did they work the same way, did they think the same way?
They also had features that are thought to be adaptations to climbing which are seen in earlier
hominins. These include long arms and fingers and a flared rib cage and pelvis. On the other
hand they had very modern-looking wrists ankles hands feet and teeth which are much more similar
to Homo sapiens and other more recent hominins like Homo erectus and Neanderthals. All these
modern features are so important because animals use their teeth and hands and feet to directly
interact with their environments. This means that homo Naledi was probably eating, manipulating
objects, and walking upright in ways similar to us and was therefore perhaps also capable of similar
behaviors. Without any concrete evidence at the moment though we we still can't say for sure.
So where does homo Naledi fit on our evolutionary tree? Basically no one knows. Based on the sort of
archaic anatomy that they had it was hypothesized that they had evolved around two million years
ago, still definitely homo but at the base of our lineage. But that was really complicated by
a 2017 discovery. Anthropologists were able to obtain dates from one of the teeth of the homo
Naledi specimens and it turned out that they had lived around 300,000 years ago roughly.
That was quite the shock. Anthropologists still kind of feel that the anatomy of Homo Naledi is
just too archaic for them to have evolved around 300,000 years ago. So basically,
the current thinking is we're still looking at a relative of perhaps Homo erectus a species that
evolved 2 ish million years ago, but that homo Naledi somehow got geographically or
reproductively isolated and sort of just went on its own path basically. You could sort of
compare it perhaps to another small hominin on the other side of the world Homo floresiensis.
What's really interesting about that young date, that 300,000 ish year date, is that it
forces us to question the trajectory of human evolution. Before the discovery of homo Naledi
anthropologists had basically thought that once bigger framed, bigger brained hominins had evolved
that smaller more archaic species were basically out competed and would have disappeared from the
archaeological record. Homo Naledi basically shows that we were wrong about that or at least
it's more complicated. That in some areas, for whatever reason, smaller framed hominins
we're able to survive and perhaps thrive for hundreds of thousands of years.. so...uhh... yeah.
How and why they entered the Dinaledi chamber are still burning questions. One clue is that
according to the team's geologists the deposition of these individuals occurred
over an extended period of time. Vague but it can help us narrow things down and eliminate
situations that involved a single event. I know everyone always wants to say massacre
but doesn't look like it. There have been a number of hypotheses proposed. So far, one pretty obvious
one is that they lived in there. I mean, first of all the small chamber is incredibly hard to
access. Perhaps it had a different entry back then but it is a narrow chamber and like I said
earlier there's no archaeological evidence of anything at all especially not occupational
debris so this one's been eliminated for the time being. Another was that the cave had flooded,
carrying these individuals inside of the Dinlaedi chamber but there's no geological evidence that
the cave was ever majorly flooded nor that the bones themselves were ever submerged in water and
if the geologists are correct that the deposition occurred over an extended period of time this cave
would have had to have been continually flooded to keep bringing them in there. Could they have been
dragged in or chased by predators? Or could they have been the predators? If this was the case we'd
expect to see a few remains of these predators and prey or at least some bite marks on some of the
naledi bones as the predators consumed them, but we don't. There are no other animals found in the
chamber except for that partial bird skeleton and basically who knows how and when that got
in there. What if they just fell in? Well the geologists found that there wasn't a vertical
entrance to the chamber 300 thousand years ago and none of the individuals had injuries or
broken bones that had occurred when they died. The only hypothesis that the team thinks holds
any water is that the bodies were deliberately disposed of in the Dinaledi chamber. It's even
possible that the bodies were put there by other hominins, like modern humans perhaps.
As you can imagine this is highly debated, highly controversial. Remember these Homo Naledi hominins
had brains about the size of a chimps not much bigger. Is it possible that a hominin species with
such a small brain could be capable of these more advanced social and cognitive abilities? I mean,
I have made a video on how early hominins disposed of the dead. Chimpanzees do seem to
go through a process of mourning but two hundred thousand, three hundred thousand years ago,
structured deposition of individuals is still pretty highly debated even amongst hominins
with much larger brains. So it really makes us ponder. To make things even more complicated in
2017 a completely separate chamber within rising star called the lesedi chamber was found to also
have homo Naledi remains. They were found with other animals too including rodents
and mammals but again no archaeological traces of any kind no tools or anything.
So what can we say with some degree of certainty about homo Naledi? well they were certainly a
hominin, certainly a new species that we didn't know about before. They probably descended from
homo erectus or a similar style of hominin and that's about it really. As for what they were
doing in that cave we can only speculate at the moment but isn't it fascinating how
200-300 thousand years ago, how varied life was for our family tree on this earth. You had us,
Neanderthals, Denisovans, homo Naledi, homo erectus, Luzonensis, homo floresiensis, just
thinking about that and how, whether we could have communicated with them and what our interactions
were like with these different species, that were in some ways so similar to us and yet so
different. Thinking about that kind of stuff keeps me up all night, I don't know about you.
Anyway thanks for joining me on this walk through the woods, next time on the channel
we're going to be going even further back in time to talk about miocene hominins,
so thanks very much for my patrons for supporting me. Thanks to Amanda
Rosillo for helping me with script and research that's about it. See ya!