New discoveries of fossilised hominin remains have to varying degrees helped to shape our ever-morphing interpretation of hominin evolution. Homo naledi is a case in point.
Though many worker in the field of palaeoanthropology were disappointed with the confirmed Middle Pleistocene age of the Dinaledi remains, this news nevertheless fills a void in our understanding of Middle Pleistocene evolution.
H. naledi confirms what we have known since the astonishing discovery of Homo floresiensis, namely that small brained hominins continued to thrive in some part of the planet right up to recent times. H. naledi can now join Homo floresiensis in the small brain Middle to Late Pleistocene club.
Palaeoanthropologist can now exercise a high level of skepticism on dating hominin fossilised remains using morphological stucture and statistics. In 2015, palaeoanthropologist John Francis Thackeray concluded Homo naledi to be over 1.5 Ma, while Mana Dembo and her colleagues concluded an age of 930,000 years of age for the Rising Star remains. Though Dembo et al were closer to actual age of the remains, they were still nearly 600,000 years off.
Finally, H. naledi continues to confirm what we have known since the announcement of Australopithecus sediba that hominin evolution features an ever changing mosasicism. With Australopithecine-like shoulders and cranium, while the lower limbs and foot appears more derived.
John Hawks discusses the latest news on the Rising Star Project:
Africa’s richest fossil hominin site has revealed more of its treasure. It’s been a year and a half since scientists announced that a new hominin species, which they called Homo naledi, had been discovered in the Rising Star Cave outside Johannesburg.
Now they say they have established and published the age of the original naledi fossils that garnered global headlines in 2015. Homo naledi lived sometime between 335 and 236 thousand years ago, making it relatively young.
They’ve also announced the discovery of a second chamber in the Rising Star cave system, which contained additional Homo naledi specimens. These include a child and the partial skeleton of an adult male with a well-preserved skull. They have named the skeleton “Neo” – a Sesotho word meaning “a gift”.
The Conversation Africa’s Science Editor Natasha Joseph asked Professor John Hawks, a member of the team, to explain the story behind these finds.
To an ordinary person, 236 000 years is a very long time ago. Why does the team suggest that in fact, Homo naledi is a “young” species?
The course of human evolution has taken the last seven million years since our ancestors diverged from those of chimpanzees and bonobos. The first two-thirds of that long history, called australopiths, were apelike creatures who developed the trick of walking upright on two legs.
Around two million years ago some varieties of hominins took the first real steps in a human direction. They’re the earliest clear members of our genus, Homo, and belong to species like Homo habilis, Homo erectus and Homo rudolfensis.
Homo naledi looks in many ways like these first members of Homo. It’s even more primitive than these species in many ways, and has a smaller brain than any of them. People outside our team who have studied the fossils mostly thought they should be around the same age. A few had the radical idea that H. naledi might have lived more recently, maybe around 900,000 years ago.
Nobody thought that these fossils could actually have come from the same recent time interval when modern humans were evolving, a mere 236 to 335 thousand years ago.
How do you figure out a fossil’s age?
We applied six different methods. The most valuable of these were electron spin resonance (ESR) dating, and uranium-thorium (U-Th) dating. ESR relies on the fact that teeth contain tiny crystals, and the electron energy in these crystals is affected by natural radiation in the ground over long periods of time after fossils are buried.
U-Th relies on the fact that water drips into caves and forms layers of calcite, which contain traces of uranium. The radioactive fraction of uranium decays into thorium slowly over time. So the proportion of thorium compared to uranium gives an estimate of the time since the calcite layers formed. One of these calcite deposits, called a flowstone, formed above the H. naledi fossils in the Dinaledi Chamber. That flowstone helps to establish the minimum age: the fossils must be older than the flowstone above them.
For these two methods, our team engaged two separate labs and asked them to process and analyse samples without talking to each other. Their processes produced the same results. This gives us great confidence that the results are reliable.
What does the discovery of Homo naledi’s age mean for our understanding of human history and evolution?
For at least the past 100 years, anthropologists have assumed that most of the evolution of Homo was a story of progress: brains got bigger over time, technology became more sophisticated and teeth got smaller as people relied more upon cleverness to get better food and prepare it by cooking.
We thought that once culture really got started, our evolution was driven by a feedback loop – better food allowed bigger brains, more clever adaptations, more sophisticated communication. That enabled better technology, which yielded more food, and so on like a snowball rolling downhill.
No other hominin species could compete with this human juggernaut. You would never see more than one form of human in a single part of the world, because the competition would be too intense. Other forms, like Neanderthals, existed within regions of the world apart from the mainstream leading to modern humans in Africa. But even they were basically human with large brains.
That thinking was wrong.
Africa south of the equator is the core of human evolutionary history. That’s where today’s human populations were most genetically diverse, and that diversity is just a small part of what once existed there. Different lineages of archaic humans once lived in this region. Anthropologists have found a few fossil remnants of these archaic populations. They’ve tried to connect those remnants in a straight line. But the genetic evidence suggests that they were much more complex, with deep divisions that occasionally intertwined.
H. naledi shows a lineage that existed for probably more than a million years, maybe two million years, from the time it branched from our family tree up to the last 300,000 years. During all this time, it lived in Africa with archaic lineages of humans, with the ancestors of modern humans, maybe with early modern humans themselves. It’s strikingly different from any of these other human forms, so primitive in many aspects. It represents a lost hominin community within which our species evolved.
I think we have to reexamine much of what we thought we knew about our shared evolutionary past in Africa. We know a lot of information from a few very tiny geographic areas. But the largest parts of the continent are unknown – they have no fossil record at all.
We’re working to change that, and as our team and others make new discoveries, I’m pretty sure we are going to find more lineages that have been hidden to us. H. naledi will not be the last.
The first Homo naledi discoveries were made in the Dinaledi Chamber. What led researchers to the second chamber? And what did you find there?
The Dinaledi Chamber is one of the most significant fossil finds in history. After excavating only a very tiny part of this chamber, the sample of hominin specimens is already larger than any other single assemblage in Africa.
The explorers who first found these bones, Rick Hunter and Steven Tucker, saw what the team was doing when they were excavating in the chamber. The pair realised that they might have seen a similar occurrence in another part of the cave system. The Rising Star system has more than two kilometres of mapped passages underground. In another deep chamber, accessed again through very tight underground squeezes, there were hominin bones exposed on the surface.
Our team first began systematic survey of this chamber, which we named the Lesedi Chamber, in 2014. For two years Marina Elliott led excavations, joined at times by most of the team’s other experienced underground excavators. They were working in a situation where bones are jammed into a tight blind tunnel. Only one excavator can fit at a time, belly-down, feet sticking out. It is an incredibly challenging excavation circumstance.
The most significant discovery is a partial skeleton of H. naledi, with parts of the arms, legs, a lot of the spine and many other pieces, as well as a beautifully complete skull and jaw. We named this skeleton “Neo”. We also recovered fragments of at least one other adult individual, and one child, although we suspect these bones may come from one or two more individuals.
Is there a way for people to view these discoveries in person?
On May 25 – Africa Day – Maropeng at the Cradle of Humankind World Heritage Site outside Johannesburg will open a new exhibit with the discoveries from the Lesedi Chamber and the Dinaledi Chamber together for the first time.
For people outside South Africa, the data from our three-dimensional scans of the new Lesedi fossils are available online.
Anyone can download the 3D models, and people with access to a 3D printer can print their own physical copies of the new fossils, as well as the fossils from the Dinaledi Chamber. It’s a great way for people to see the evidence for themselves.
The ‘Black Hole’ of Palaeoanthropology is not a term you hear very often, but then again what is there to say about the biogeographic history of a 1.77 million square kilometer region (Turkey, Saudi Arabia, and Iran) with virtually no faunal, human or archaeological sites. At this point it would seem easy to resign yourself to the words of Timothy D. White at the dawn of the 21st century, that we are not going to find many more fossil hominins. The mark of a great palaeoanthropologist is to never give up that curiosity for the unknown. Since White’s depressing prediction, he has been roundhouse kicked to Wrongville, with the spectacular finds of Ethiopia, South Africa, Myanmar, China, Flores and much much more. We have learned so much thus far, don’t lets forget this. Sounds great but these inevitably throw up more questions than answers. And the ‘Black hole’ is a particularly hard nut to crack.
What does archaeology have to offer? Ethiopia features the earliest concrete evidence for hominin stone tool manufacture. At 2.6 million years of age it predates the earliest known human – Homo habilis – by less than 300,000 years years (Fossil Code: A.L. 666). Saudi Arabia has a rather rich representation of Mode 1 (Oldowan) stone tool clusters. If you don’t know to millimeter accuracy where the stone tool was found, or if it is a surface find then it is worthless to science. The Saudi sites were also used during the Holocene (11,700 years ago to present), begging the question how can you separate Early Pleistocene (2.5 million years ago to 700,000 years ago) from Holocene activity? At least we can tell that hominins took one route out of Africa. Stone tools similar to the Oldowan found at Perim Island supports the hypothesis that early hominins crossed the Bab al Mandab Strait (20 miles wide). Iran has probably the most depressing lack of archaeological evidence of the region. Isolated finds dominate, both the Oldowan and Acheulean records of Iran and few excavations have taken place. South of the Caspian Sea is the site of Ganj Par, which yielded 100 limestone tools within half a hectare. This assemblage shares similarities with those of Ubediya, Israel and the Oldupai Gorge (also known as the Olduvai Gorge), Tanzania. Turkey repeats much the same story. Of the 200 Palaeolithic sites, less than 25 have been even partially excavated. The majority are restricted to the fringes of the Anatolian plateau. None are any older than 1.3 million years of age, further supported by Argon-Argon dating of Kula, western Turkey to 1.24 million years of age. The site was the location of a palaeomeander which contained a solitary Quartz flake, 5 x 4 cm. Volcanic activity interfered with the palaeomeander and it was that lava flow that allowed the date to be so accurate. The take-home-message from Turkey is the earliest securely dated archaeological remains support the 1.1 million years calculated for the Kocabas skullcap, which shares affinities with OH 9 and KNM ER 3733, attributed to H. erectus. Debate continues as to its taxonomic status, but it does reflect a great deal of H. erectus characteristics. The Archaeology tells us that hominins with the ability to make stone tools were already out of Africa 1.8 million years ago, at the site of Dmanisi, Georgia.
It is the richest fossil hominin location at the ‘black hole’ fringe. The Fall of 2013 was just another milestone in sites long history of archaeological investigation. The discovered cranium (D4500) was reunited with its jaw (D2600) and the team of palaeoanthropologists led by David Lordkipandize concluded that the five individuals represented members of the same species, but retracted the classification of D2600 (Homo georgicus) for Homo erectus ergaster georgicus. This raised some eyebrows in the palaeoanthropological community, particularly Fred Spoor, palaeoanthropologist and lecturer at the UCL Department of Anthropology, who pointed out that such an action is not outlined in the code of zoological nomenclature. This is a minor debate in the palaeoanthropology, but most agree that Homo erectus exhibited a variation comparable to that seen in modern Homo sapiens today. Dmanisi is proof that hominins were already out of the African continent by 1.8 million years. Additionally, although the dating of the hominins of Java are in the doldrums, these specimens could be as much as 1.8 million years of age. Prior to that time some hominin species made it’s way north, but which one?
On the 23rd of January 1995, a French-Chadian team of palaeontologists discovered a fragment of fossil jaw (Fossil Code: KT 12/H1) lying on the gravel desert of northern Chad. The fossil (nicknamed “Abel”) could not be accurately dated, nevertheless stratigraphic layers nearby suggested it could as much as 3.5 million years of age. Back then, the river Bahr El Ghazal flowed into a 3 million square kilometer lake called Megachad. This hominin foraged on grasses that dominated the Koro Toro region. The palaeontologists gave “Abel” a new species name – Australopithecus bahrelghazali distinguishing it from another australopithecean – Australopithecus afarensis. That species lived in the eastern region of the continent, over 2,500 km from the Bahr El Ghazal site. The animal remains found in the stratigraphic layers of both regions were pretty much identical, which means the ecosystems were the same. Therefore, you can see why some palaeoanthropologists consider it plausible that “Abel” is just another Au. afarensis. This goes back to the argument that, what we are looking at here is just another variation of the same species. Either way, here we have australopitheceans in eastern and north central Africa. Theoretically, it is plausible for australopitheceans to have made their way into Arabia.
Every organism has a landscape format that they thrive within. Lions are quite at home in the savannah, Tigers frolick in the dense jungles of the Indian subcontinent and hominins, particularly australopitheceans, were quite at home in savannahs. If we are to prove that they made their way into Arabia, there should be an extension of savannah into the Eurasia 3-4 million years ago. Sadly we are not seeing this, but what do we see. The faunal record of Saudi Arabia is particularly fragmented and sparse. Western Turkey (Calta) 2.3 million years ago, saw Raccoons, Giraffes, Hippos and the extinct “Running” Hyena. Many associate Bethlehem with the Christian story, but few know that at about the same time, this region featured Raccoons, Sabre-Toothed Cats, Rhino, an ancestor to the Mammoth and ancestor to the modern boar. While 110 kilometers north of Bethlehem and 700,000 years later, Baboons lived south of the Lake of Tiberias, around Ubeidiya. Lakes were magnets for faunal activity and therefore hominin activity.
The An Nedfud desert of northern Saudi Arabia is classic wilderness today, 2 million years ago it was the hub of a diverse ecosystem with a lake as the centrepiece. The faunal remains were recovered from three localities and share similarities with the kind of fauna you would expect at Ubeidiya and the Oldupai Gorge. Hippos were found at these sites and since modern day counterparts prefer standing water to a depth of 5 meters, it gives an initial sense of the size of ‘Lake An Nedfud’. A lake capable of supporting fish life, but this is not the only lake to have supported faunal biodiversity in the ‘Black Hole’. ‘Lake Negev’ developed around 1.8 and disappeared around 1.5 million years ago under ever increasingly arid conditions. It supported fish populations and laid down 15 m thick sediments over 18 sq km². Besides these lakes, there were smaller lakes, Oases and springs that would have allowed hominins to hop, skip and jump out of Isis territory and into the more accommodating environments of Europe and eastern Asia. Looking at the faunal remains you can get a sense of the climate that prevailed at whatever time period you are interested in. The climatic mapping of the Pliocene and Early Pleistocene of the ‘Black Hole’ are, you’ve guessed it understudied. We do know that two and a half million years ago, the forests of Azerbaijan gave way to Savannah and the Arabian peninsula experienced 2 million years of humid conditions, capable of keeping many large (now extinct) rivers topped up.
There you have it. We know alot, but we know so very little about this massive region of the world. We lack fossil hominins in this region and I don’t think Isis would be willing in finding their early ape ancestry any time soon. It would definitely be a useful distraction from Wahhabism. Do something useful for a change, Isis! Get out there and find us those damn fossils! You ignorant misogynistic apes!
On the 23rd of January 1995, a team of palaeontologists discovered a fragment of fossil jaw lying on the gravel desert of northern Chad. The fossil could not be accurately dated, nevertheless stratigraphic layers nearby suggested it could be around 3.5 million years of age. Back then, the site of Koro Toro was on the edge of a 3 million square kilometre Lake called Megachad. The fossil, now codenamed KT 12/H1 consisted of the front portion of the jaw with a number of teeth still in place. By using Isotopic analysis the diet of the hominin shortly before it died, can be determined. The fossil showed a preference for C4 plants, including sedges and grasses, suggesting that the area around Koro Toro was predominantly grassland. Comparing the fossil to other hominins, the features were considered very different compared to Australopithecus afarensis, 2,500 km away in Ethiopia and Kenya. The French team, led by Michel Brunet, concluded the fossil was part of a new species of Australopithecus – Australopithecus bahrelghazali. This caused a bit of a stir in the palaeoanthropological community, but progressively began to die down. The lack of fossil finds in Chad thereafter contributed to the rate at which the palaeoanthropological community forgot about the fossil, that was, until 2001. Given the same variety of animals can be found in both Ethiopia and Chad, it is not a stretch to imagine australopithecines travelling between the two regions three million years ago and many palaeoanthropologists now consider the fossil, a variant of Australopithecus afarensis.
How did the fossil make palaeoanthropologists rethink their understanding human evolution? “Abel” as the fossil became to be known reminded palaeoanthropologists that human evolution could have been more complex than previously accepted. Though once you considered the features of an Australopithecus afarensis jaw and compare that to “Abel”, it is acceptable to attach it to the Ethiopian hominin. The differences are subtle. It is worth reminding here however that the use of species names don’t tell us much about the hominins palaeobiology, are primarily to put, order to our understanding of evolution and are a useful means of scientific communication. Palaeoanthropology has had a long history of naming new species, when later we realize we were too optimistic. In the sense, that we forget how useless this venture is. More is learned from the fossils, about a hominins diet, locomotion patterns and physical characteristics than what species it belongs too. Thankfully, science is less focused on this and we are now learning much more about the hominin and the ecosystem it was once a part of. The second way in which “Abel” got us thinking, was via the surprise geographic location. Up until that time, any fossil finds made on the continent of Africa were made exclusively in eastern and southern Africa. “Abel”, reminded us that hominins were not just restricted to those regions and likely could be found all over Africa. Exciting though this prospect was, it could not solve the problem of preservation in areas where fossils cannot survive, in the hostile environments of the Sahel.
This evening on the 11th of January 1964, fossil hunter Kamoya Kimeu (1940-Present) was crossing what had been an Early Pleistocene delta to the western side of Lake Natron, Arusha, Tanzania. He was there with a team led by Richard Leakey in search of our earliest ancestors. Barely a few days into the expedition, Kimeu found a hominin mandible, not one of our ancestors, but just an intriguing. It is 1964 and by this time, OH 5, representative of Paranthropus boisei was already gracing the covers of magazines throughout the world. Thought to be the first human that used stone tools for the first time, the Nutcracker Man was not all he was cracked up to be. As more hominin fossils from the Late Pliocene and early Pleistocene began to show, it became more and more clear, that while P. boisei may have been found on an archaeological layer, this is not enough evidence to support a “he’s the first human” hypothesis.
Ol Doinyo Lengai: A View from Lake Natron
Kimeu had found another representative of P. boisei at Peninj and it was a remarkably complete hominin mandible. The right condyle was missing and so too were the left and right coronoid processes, despite that the fossil had its complete set of teeth and that was particularly key. The teeth showed a great deal of wear to the point that you could see the dentine beneath the enamel. This individual must have eaten alot of sedges and grasses throughout its life to give that sort of result. Grasses and sedges that you could find around deltas like that one that would have entered Lake Natron, when it wasn’t quite as salty. But when exactly did our hominin friend give up its spirit along the shores of the Lake. The stratigraphic layers in the region are like the pages of a picture book, no words, but pictures that can tell better narratives that Twilight could ever even dream of. The mandible was uncovered in a sedimentary layers, comprising the deltas alluvial deposits, sandwiched between two volcanic layers. The volcanic Tuff atop the layer that contained the fossil was previously dated to between 1.6 and 1.4 million years of age, while the basalt below was dated to 1.7 million years of age. You may think that the fossil is probably going to be between 1.7 and 1.4 million years of age, but the team of geologists at the site conducted further analysis at the site to help get a more accurate result. They settled on an age for the mandible of between 1.5 and 1.3 million years of age. Enough time for the ph of a lake to reach beyond 12.
View of Lake Natron and a superimposed graphic of the hypothetical organisation of the layers around the fossil.
Since the discovery of the Peninj 1 mandible in 1964, another hominin with similar characteristics to P. boisei was found. Paranthropus aethiopicus now joined a trio of hominin species that became the Paranthropines, comprising boisei, robustus (South African hominin) and aethiopicus. Most of what we have collected of these creatures are crania and mandibles, though some postcranial remains have been found. Thankfully the teeth survive well and can tell us a great deal about their diet and the subtle, yet important questions of how they chew their greenery. There was a long drawn out debate over whether these three hominins deserved to live in a separate group – the Paranthropines. Originally, these hominins were classified as robust australopithecines and the palaeoanthropological community decided that a change was needed. The complete anatomy of the Peninj Hominin was never recovered and given that the mandible survived so well, this individual may have fallen to a carnivore in the delta. Below is a summary of the discovery that was made on the 11th of January 1964.