Lessons of Homo naledi

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.

Middle Pleistocene Homo naledi

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.

Explorers Mathabela Tsikoane, Maropeng Ramalepa, Dirk van Rooyen, Steven Tucker (seated), and Rick Hunter (seated) inside the Rising Star cave system. Wits University/Marina Elliott

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.

Geologist Dr Hannah Hilbert-Wolf studying difficult to reach flowstones in a small side passage in the Dinaledi Chamber. Wits University

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 DayMaropeng 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.

Reprint from The Conversation

Doctoral student addresses critics of the Cerutti Mastodon Controversary

An anonymous doctoral student associated with the Cerutti Mastodon research addresses critics on Reddit as follows:

First off, my qualifications: My current advisor is the third author on this paper and I worked under (and collaborated with) the second author when I worked at the San Diego Natural History Museum (in fact, I re-prepared some of the material in this paper about 6 years ago). Furthermore, I am a doctoral student in the final months (hopefully) of my PhD. My dissertation work has been on proboscideans (elephants and their relatives), but I have also done a fair amount of work on cetaceans (whales) and other vertebrates.

As far as the dating methods go, this site was dated using multiple types of absolute dating methods, which all resulted in a very similar age. However, the Uranium-series dating (not to be confused with radiocarbon dating, which could not give you an accurate age this old) that was used here got results with a very high confidence. In fact there is essentially no evidence of alteration that might lead to an older date (which really would not be common anyways). The dates recovered are almost unimpeachable (and I don’t say that lightly). I would be very surprised if a geochronologist or any other expert had a major problems with the dates themselves (in fact a geochronologist was a reviewer for this paper for just this reason). Also, to the people that are saying that it is perhaps time to reassess our methods of isotopic dating in general, I strongly suggest you spend more time researching and trying to understand these methods before you make a claim like this…

One other misconception that I keep seeing here are peoples’ interpretation of what is meant by “human” in this paper. “Human” is meant here in the sense of a species of the genus Homo, not necessarily Homo sapiens specifically. In fact, because of the old age it seems fairly unlikely that this would be the modern species of human rather than some other [unknown] species.

I’m sure there will be other questions or comments here throughout the next day or so, and I will try to check in from time to time and update this post. I’m also happy to answer any questions that I can (to the best of my knowledge).

Edit 1: To the folks wondering if this site could have been scavenged by humans (as opposed to hunted), I would say that, that is absolutely possible. In fact there is really no evidence one way or another to argue for hunting over scavenging at this site, and I don’t believe that this paper takes a stance on this either. In fact, I would say that the argument of hunting vs scavenging in association with this mastodon is somewhat irrelevant. What is important is that this extremely old site (relatively speaking, anyways) has fairly clear association with ancient human activity.

Edit 2: Several people have pointed out that the article discusses a lack of evidence of meat stripping on the specimen. This does suggest scavenging, as it likely means the soft tissue was at least somewhat rotted and not usable.

Edit 3: Many people are suggesting that this animal could have been scavenged or had its bones modified many thousands of years after its death (i.e., implying the tools are much younger than the mastodon). To that point 1) the type of breakage seen on these bones is indicative of damage while the bone was still fresh. Fresh bone (sometimes called “green bone”) breaks in a very different “spiral pattern” than older dried out bone; and 2) you have to remember that the sediments that the tools and mastodon are found in represent the context in which they were buried. Therefore since these materials were all found within the same layer they must have been buried at the same time. It is possible that ancient humans exhumed old bones (though I know of no actual evidence of this), but we would see telltale signs of disturbance to the sediment (which was not observed here).
In other words, I don’t think that arguments about this site will come down to whether the material is associated and coeval, but whether folks think that these artifacts are indeed stone tools. Those people who do not agree with this identification will then have to reconcile the crazy taphonomy at this site and attribute it to some other natural process (which will be no small feat, IMHO).

Edit 4: For the people asking why we don’t have any evidence of humans (or human remains) in North America in the time between the age of this site and more generally accepted dates:

First off, I would just like to note that we are almost certainly not talking about a direct lineage of humans between the time of this site and those of Clovis times (in fact, as I’ve stated above, we are likely not even talking about the same species). This was likely a very small population of humans that made it to North America that probably died out long before the modern species of human ever made it over. In that sense, there isn’t necessarily a gap of time to “bridge”.

As for why potential sites might not be preserved: There are a couple of reasons that you might not have evidence of humans found from this time. First off, you may not have rocks of the right age readily exposed in the region where the individuals were living (which is somewhat the case on the west coast, as far as I am aware). Second, the individuals could be living in an environment that is not conducive to preserving fossils (e.g., organisms that live in montane environments tend to not preserve in the fossil record because sediments are not being deposited in those regions). Third, getting preserved in the fossil record (in general) is very rare, and if your study organism has a very small population size or is short lived (as we would expect in the case here) then you have a very very low probability of being preserved (let alone found and collected). Finally, even if these scenarios aren’t the case, there is the possibility that scientists have just been looking in the wrong strata, region, or age.

Three reasons the Cerutti Mastodon was not manipulated by hominins

A team of scientists recently announced an extraordinary claim that the 130,000 Cerutti Mastodon was manipulated by hominins.

“I have read that paper and I was astonished by it,” archaeologist Donald Grayson of the University of Washington. “I was astonished not because it is so good, but because it is so bad. Cracked bones and chipped stones at a fossil site might mean anything”, said Grayson. “It is quite another thing to show that people, and people alone, could have produced those modifications. The study doesn’t take that step, he said, “making this a very easy claim to dismiss.”

Gary Haynes of the University of Nevada Reno had this to say, “The paper states that the bones were being exposed by a backhoe. These pieces of heavy equipment weigh seven to fifteen tons or more, and their weight on the sediments would have crushed bones and rocks against each other.” When asked, Holen, the study leader, said that it “was very easy to tell the difference” between fractures made by stone hammers and those seen in bones crushed by bulldozers. He did not elaborate on how the differences manifest. “He’s pretty much dead wrong — there’s no definable difference,” Haynes said. A similar fossil dispute broke out in 2015 over a 24,000 year old mammoth in Maryland, he noted, shown to be fractured by heavy equipment. Also troubling, the “hammer” and “anvil” stones described in the paper don’t unequivocally look like tools, said Michael Waters of Texas A&M’s Center for the Study of the First Americans.

Michael Waters of Texas A&M’s Center for the Study of the First Americans noted that the “hammer” and “anvil” stones described in the paper don’t unequivocally look like tools. The study also runs afoul of the mounting genetic evidence, which indicates that the first people to reach the Americas and eventually give rise to modern Native Americans arrived no earlier than 25,000 years ago.”

1.6 Million Year Old Woman of Eastern Africa (2017 Review)

When fossil hunter Bernard Ngeneo came across the remains of this fossil, only the upper portion of the orbits were protruding from the ground. Excavation revealed one of the best preserved skulls of this time period, and one of the most striking early human fossils of any age.

KNM-ER 3733 represents a mature female of the early human species Homo erectus. The sex identification comes from a comparison of the anatomical features of her face with several other crania from Koobi Fora: KNM-ER 3883 (male), and KNM-WT 15000 (also male), found on the opposite side of Lake Turkana. The features of KNM-ER 3733 are markedly less robust. It’s known to be an adult on the basis of the cranial sutures (which were fully closed), the extent of the wear on the teeth, and the eruption of the third molars before the individual’s death.

Origin of the higher primates – 1923 Expedition.

By Russell Ciochon

“On the road to Mandalay,/ Where the flyin’ fishes play,/ An’ the dawn comes up like thunder outer China ‘crost the Bay!” So wrote Kipling at the turn of the century of the wonders and enchantment of Burma and its city of Mandalay. Today, as enchanting as ever, the road to Mandalay beckons to paleontologists because Burma is the only place in the world that has yielded fossil evidence of an important link in the primate order. There are two groups of primates on the earth today. The higher primates – monkeys, apes, and humans – are the most familiar. They are sometimes called the Anthropoidea, or humanlike primates. The lower primates – the lemurs, lorises and tarsiers – make up the second group. These primitive primates, often called Prosimii, or pre- apes, were the first to evolve and were the forerunners of all later forms. However, fossils showing the beginning of the evolutionary branch leading from prosimians to anthropoids have been hard to come by.

An early discoverer of the “Burmese link” that demonstrates this transition was the legendary fossil collector Barnum Brown, a paleontologist at the American Museum of Natural History. In the spring of 1923, Brown and his wife, Lilian, arrived in Rangoon, the capital of Burma. They journeyed by river steamer up the broad , muddy Irrawaddy to the port of Pakokku. From there they mounted a mini expedition to the little-explored Ponnyadaung (or Pondaung, as Brown spelled it) Hills, located deep in the teak-bamboo forest of Upper Burma. Outfitted with four bullocks, two small, mat-covered carts, and a pair of sway-backed saddle horses, they rode in search of the varicolored sandstones of the Pondaung Formation, rock deposits that had been discovered earlier in the century by British economic geologists. In the words of Lilian Brown, they were “rainbow-chasing” – following the sedimentary rocks shaded yellow, gray, red, purple, and green, seeking a prehistoric pot of gold. When Brown arrived in Burma, virtually nothing was known about the early prehistoric life of southern Asia. The prevailing scientific opinion was that Asia was the mother of all continents, the center of origin for much of the earth’s life. Brown had been sent by the American Museum to collect late Eocene (40- to 45-million-year-old) fossils in support of this “Garden of Eden” theory. He specifically sought to collect large skulls and skeletons of extinct animals that could be exhibited at the American Museum.

B. Brown In 1923, Barnum Brown (mounted) collected fossils in Burma’s Ponnyadaung Hills. This photograph (here tinted) was printed in Natural History in 1925, with a caption noting that the servant Mari (in the cart) died of malaria contracted on the journey. For two months, Brown’s small bullock-cart caravan creaked along the dirt tracks, the only roads in this remote part of Burma. Because the resident commissioner of Burma had provided a letter of introduction to all village headmen along the route, Brown was able to camp in villages that were nearest to exposures of the fossil-bearing Pondaung sandstones. One such stop brought him to the outskirts of Mogaung village, where he set up camp with Lilian and their two servants, Mari and Dos. Early each morning Brown would ride off in search of new fossil sites. One day, a short distance northwest of the village, he came upon a locality where he saw a number of small bones and teeth eroding out of the rock. Here he picked up part of a jaw with three teeth – a piece about the size of a fifty cent coin – that belonged to a medium size primate.

Barnum Brown probably did not realize that what he had discovered was an early higher primate. But Edwin Colbert, Brown’s colleague at the American Museum, did, and in 1937 he named the jaw Amphipithecus mogaungensis (near-ape of Mogaung). Amphipithecus joined the ranks of another Burmese fossil primate, discovered in 1913 by paleontologist G.D.P. Cotter. Cotter had explored the southern exposures of Burma’s Ponnyadaung Hills while working for Britain’s Geological Survey of India. A description of this specimen (a piece of upper jaw and two pieces of lower jaw) was published in 1927 by Guy Pilgrim, who named it Pondaungia cotteri. Pilgrim thought it could be an Eocene higher primate, but the fragments were too scrappy for precise identification. With Colbert’s more confident description of Amphipithecus in 1937, the late Eocene beds of the Ponnyadaung Hills became known as the source of earliest record of the Anthropoidea.

Anthropologists debated the evolutionary affinities of Amphipithecus and Pondaungia for the next four decades. Were they really the world’s earliest higher primates or were they prosimians with a few independently evolved anthropoid like features? Was Asia even the place to look for the origin of the higher primates? More fossil evidence was needed, but no one was able to work in the Ponnyadaung Hills during the years embracing the Japanese invasion, World War II, Burma’s achievement of independence, and the emergence of nationalistic policies that followed. I first visited Burma in 1975, to discuss the possibility of a joint U.S.-Burmese paleoanthropological research project. With U.S. involvement in the Vietnam War drawing to a close, my proposals fell on receptive ears. After discussing plans with geologists at the Mandalay Arts and Sciences University, I submitted a letter to the Ministry of Foreign Affairs. The reply stated that the Ministry had “no objection to a planned paleontological visit.” On my return to the United States I teamed up with Donald E. Savage, a seasoned paleontologist, and in March 1977, having obtained the necessary funding and entry visas, we set off on a two-month research tour of Burma.

Upon arrival in Rangoon, however, we were only given permission to prospect for fossils along the Irrawaddy River drainage, where the sediments date from the Pleistocene epoch (the last 2 million years of earth history). Ministry officials declared that the area around the more ancient Ponnyadaung Hills was so dangerous that we would need a police escort, which could not be provided at the time. Swallowing our disappointment, we flew north to Mandalay, where we were met by U Ba Maw and U Thaw Tint, our colleagues at Mandalay University, along with a geology student who was to be our field coordinator, Tin Maung Oo (who likes to be called “Tin”). For the next six weeks we explored a 300-mile section of the Irrawaddy River, collecting fossils along its banks and terraces. This fieldwork was rewarding, but we yearned to visit the Ponnyadaung Hills, a mere 200 miles to the west. To impress upon our Burmese colleagues how eager we were for information about the 40-million-year-old fossil beds, we left our copies of Barnum Brown’s field maps and publications with them. They promised to attempt a reconnaissance of the region in the late fall dry season.

Savage and I returned home and awaited further word on our research proposal to the Burmese government and on results from our Burmese collaborators’ visit to the Ponnyadaung Hills. We heard nothing for almost a year when suddenly a small package arrived from Mandalay. It contained plaster casts of jaws and teeth of several Eocene mammals, one of which was a nicely preserved jaw of Pondaungia. U Ba Maw and U Thaw Tint had not only found Brown’s localities; they had also succeeded in recovering a new fossil primate. An accompanying letter stated that they had found many more fossil mammal specimens, several of which they thought could also be primates. They encouraged us to return to Burma as soon as possible to visit the localities and to work with them on publication of the finds. In December 1978, arrangements were made, and we departed once again for Burma. On our approach into Mingaladon Airport in Rangoon we were asked to set our watches back in accordance with Burma Standard Time. The British businessman sitting next to me intoned, “Set your watch back thirty minutes and turn time back thirty years.” Indeed, little has changed in Burma since its independence in 1948. But our minds were set on a much longer time frame, for we were hoping to turn time back 40 million years!

Our knowledge of Amphipithecus comes from fragments of two separate jaws. One portion was found in 1923, another (shown overlapping) in 1977. This drawing of Amphipithecus is based on fossil evidence and an interpretation of the order of evolution of anatomical features found in living higher primates. After several days of preliminaries, we made the short hop by air to Mandalay and prepared for our journey to the Ponnyadaung Hills. U Ba Maw and U Thaw Tint could not accompany us on this trip since they were in the middle of university exams, but they sent some of their students with us. Before dawn on December 20, our small caravan – two World War II-vintage jeeps loaded with camping and excavation equipment, four geology students, a cook, a mechanic, two drivers, Tin, Savage, and myself – left for the field. To reach the Ponnyadaung Hills we had to cross the two great rivers of Burma. Crossing the Irrawaddy was a simple matter of driving over a steel-girder bridge, but at the Chindwin River our two jeeps had to be loaded onto a flatbed barge, along with chickens, goats, bicycles, and a large number of other passengers. A small tug then towed us across the mile-wide river. After several more hours of driving we reached the Pale Township People’s Council, where we checked in and picked up an escort of several armed policemen. Our Burmese colleagues had assured us that the only danger in the Ponnyadaung Hills was an unlikely encounter with a Bengal tiger, but for the sake of appearances, we decided to accept the offer of an escort.

On our five-hour climb from Pale into the Ponnyadaung Hills, the road deteriorated rapidly from a graded gravel track into a series of potholes and dust bowls interspersed by a washboard. The open scrub-brush and farmland near the Chindwin River quickly gave way to gently rolling forested hills. As we climbed still farther, the road became very steep, and the teak and bamboo forest surrounding us came alive with azure butterflies, screeching parakeets, and scampering red- orange jungle fowl. We encountered young Burmese men driving oxcarts loaded down with teak logs, but not a single motorized vehicle. At the fifty-five- mile post the road became impassable for even a four-wheel-drive jeep. We transferred our supplies onto two oxcarts, each pulled by two grunting oxen, and began the eight-mile hike down an old cart road into Mogaung village. The oxcart wheels creaked and squeaked – but not as a result of neglect, I was told; rather, the local villagers never grease the wheels because they feel the noise keeps away evil spirits.
Late in the evening of our daylong trek we reached our destination – Mogaung, a village of some nine hundred people. Surrounding the village, which consists of small teak huts raised off the ground on poles, is a bamboo fence. Inside, banana, coconut, and toddy palm trees grow in abundance, and pigs and chickens roam freely. We were lead to the hut of U Gyo, the village headman, where we were fed a traditional snack of bananas and green leaf tea. With Tin acting as translator, U Gyo greeted us graciously and suggested we use the new village schoolhouse as a base camp. It was rice-planting time, and school was not in session. We were exhausted, and after a quick meal of chicken curry, everyone bedded down. Early the next morning, with Barnum Brown’s field map in hand, we proceeded on foot northwest from Mogaung, through flooded paddy fields, across small streams, and along well-worn paths in the forest. After we had walked about one mile through the lush forest cover, the rainbow- banded sediments of the Pondaung Formation suddenly appeared. The local villagers called these areas kyit chaung, “placed without vegetation.” Owing to the chemical properties of the sediments, vegetation, especially fragile young rice plants, is not able to grow in them. In this case the villager’s loss is the paleontologist’s gain.

A family tree of the primates lists living groups at the top. The major fossil species, some of which left no descendants, are represented vertically by the branching tree. The Anthropoidea, or higher primates, are shown in orange; the Prosimii, or lower primates, which comprise all other primates, form a less unified group (yellow). Some early prosimians, perhaps a group related to lemurs and lorises, gave rise to the Anthropoidea. Amphipithecus and Pondaungia are transitional forms that possess a number of anthropoid features but also retain a few prosimian characteristics. Since Barnum Brown had left very precise field notes, we had no trouble finding his localities, and we soon began to accumulate a treasure trove of fossils. The Burmese geology students also showed us the spot where the new primate jaw had been found. Over the next couple of days, Savage and I collected the remains of many extinct animals, including hippo- and piglike anthracotheres, rhinolike brontotheres, small deerlike artiodactyls, rodents, lizards, turtles, fishes, and crocodiles. From studies of this fauna and some associated plant remains, together with an understanding of the type of rocks in which they occur, we can reconstruct the paleoenvironment of this part of Burma in the late Eocene. The sediments were deposited by a medium-size river that drained seaward toward the Burmese Gulf, which in the past was located much farther north. Along the banks of this river, which was partially covered by a forest canopy, anthrocotheres, brontotheres, and small artiodactyls came to drink. Turtles, crocodiles, and fish swam in the river. In the trees above, the ancestors of the higher primates romped.  On our second night in Mogaung village, the headman, U Gyo, honored us with a visit to “get better acquainted.” As spiritual leader and chief administrator of Mogaung, U Gyo had considerable power, but being sixty-five years of age, he had learned to use his position wisely. He spoke of how Mogaung village had changed over the past half century (“actually, very little”). I then asked him when Mogaung had last been visited by Westerners, “people like ourselves”. U Gyo thought a while and then began to recount the following story:

When I was a young boy of ten, I remember a white man and woman coming on horseback with several oxcarts of supplies. With the help of Mogaung villagers, they set up camp only a few hundred yards from where we are sitting. The man would ride off each morning and return late in the evening with his horse packed with odd-shaped rocks. The woman, who wore pants but was strikingly beautiful, would stay in camp and play with a small dog, whose hair she was constantly combing. We immediately realized that U Gyo was describing Barnum and Lilian Brown. I later showed him a photograph of Brown taken in Burma in 1923, and he confirmed the identification.

Outcrops of the 40-million-year-old Pondaung Formation are bare of vegetation.
After several more days of fossil hunting around the Mogaung village, we decided to hike to a locality Brown had discovered some six miles to the northeast, near the village of Gyat. We found some excellent exposures near a large lotus pond, which we could recognize from a photograph by Brown published in Natural History in 1925. Unfortunately, we were not able to find any fossils. In the late afternoon we trekked back to Mogaung, where our cook was preparing a special holiday meal of roast chicken and potatoes. It was Christmas Eve. Savage and I rested and sipped a clear, sweet alcoholic drink distilled from the fruit of the toddy palm tree. As the sun sank behind the mountains, the air became chilled, bringing out the smell of the teakwood smoke and frying oil.

As darkness fell we heard a commotion in the distance. One of our police guards, who had not returned with the field party, burst into camp brandishing his weapon proudly. He led a procession of villagers, two of whom shouldered a rough-hewn pole carrying a small deer. The deer was immediately butchered and some parts roasted that night. The following day we proceeded to our next camp, at nearby Legan village. There, the deer meat provided a magnificent Christmas Day feast for our entire field party and all the village elders. After another week of fossil hunting, we journeyed back to Mandalay, where more excitement was in store for us. At the Mandalay Arts and Sciences University we met with U Ba Maw and U Thaw Tint, who produced a box of small fossil jaws they had collected in the Ponnyadaung Hills. They weren’t sure what the six pieces were, but they had an idea they might be primates. Savage and I were almost breathless as each jaw was removed from the box. The first was a primate, the original of the cast they had previously sent us. Three of the others also proved to be early anthropoids. U Ba Maw and U Thaw Tint had tripled the early anthropoid sample of Burma. Of the four primate jaws they had discovered, two were Pondaungia and one was Amphipithecus. The fourth may represent a type of primate previously unknown to science. Our Burmese colleagues asked us to help them publish these finds in Western journals.

After returning to the United States, Savage and I began to study the casts and photographs of the new Ponnyadaung fossils, making comparisons with Brown’s Amphipithecus jaw and Cotter’s Pondaungia specimens. Since several of the new specimens are more complete than the older fossils, the characteristics of the two species are becoming clearer. Both fossil forms exhibit a combination of lower and higher primate features, with the latter considerably more predominant, indicating that they were at or across the evolutionary transition from prosimian to anthropoid.  Some of the lines of evidence that point to this conclusion can be illustrated by a look at Amphipithecus, the better known of the two species. For one thing, this gibbon-size animal, probably weighing about twenty pounds, was relatively large in comparison to most lower primates alive in the Eocene or even today. The lower jaw is deep (top to bottom), both absolutely and in relation to the height of the teeth, and this depth extends the full length of the jaw. In the lower primates, the jaw is not as deep and lessens in height toward the front. The Amphipithecus jaw is also very robust (thick). These jaw characteristics relate to the fact that the right and left halves of the lower jaw were fused, unlike those of nearly all extinct and living prosimians, whose jaws move independently as they chew. The fused jaws of anthropoids, which evolved for chewing tougher foods, are strengthened and reinforced to withstand the extra stresses that are placed on them during mastication. As in all anthropoids, the jaws of Amphipithecus are buttressed where they join by two horizontal, shelf-like thickenings of bone, called tori. (In contrast, the minority of Eocene lower primates that have fused jaws exhibit only one torus, suggesting they are unrelated to Amphipithecus.)

The cusps, or elevations, on the chewing surfaces of the teeth are relatively flat, a trend found in fruit eaters. Most prosimian teeth, instead, have a very crested cutting surface, useful for a diet of insects or leaves. In this respect, Amphipithecus resembles 30- to 35-million-year-old anthropoids found in Egypt’s Fayum province (see “Dawn Ape of the Fayum,” by Elwyn L. Simons, Natural History, May 1984.) Another important consideration is the number of teeth in the jaw. Among primates in general, there is a long evolutionary trend toward reduction in the number of teeth. Amphipithecus has three premolars, a relatively primitive feature it shares with some prosimians and New World monkeys. Old World monkeys (as well as apes and humans) have two premolars. In this respect, Amphipithecus (or some closely allied species) is a suitable candidate as a forerunner of both the New World and Old World anthropoids – in other words, of all higher primates.

The original specimen of the Amphipithecus lower jaw contained the root of the canine tooth, the root of the first premolar, the second and third premolars, and the first molar. Luckily, the new specimen has helped complete the picture, since it contains the first and second molars and part of the third. The square shape of the second molar (viewed from above) is significant, because this is characteristic of anthropoids. In contrast, among the lower primates there is a narrowing toward the front of this tooth. The newly discovered first molar has resolved a rather arcane controversy over the possible position of a rearward cusp known as the hypoconulid. A nick in the original specimen, where some believed this cusp has broken off, was not in the position characteristic of higher primates. As it turns out, the new specimen shows there is no hypoconulid cusp at all on the first and second molars. In this feature, Amphipithecus differs from all Old World anthropoids but resembles many New World monkeys.

Migration of the Early Anthropoids: The relative positions of continents, oceans, and shallow seas 40 million years ago are reconstructed in a map of the earth’s surface. Before higher primates (anthropoids) evolved, lower primates were present in Europe, Asia, North America, and probably Africa. The Burma fossil finds suggest that the higher primates arose from lower primates in Asia. Early forms probably then spread to Africa and, by way of volcanic islands, to South America (red arrows). Those in Africa subsequently gave rise to all the Old World monkeys, apes, and humans, while the New World monkeys evolved on their own in South America.  Another possibility (indicated by the blue band) is that a population of early higher primates came to occupy parts of both Asia and North America, which were connected by a land bridge. When this connection was severed, the New World and Old World groups began to evolve independently, the New World group eventually migrating to South America. No one has discovered fossils of higher primates in North America to support this second hypothesis.
The fossil finds from Burma suggest that the first higher primates evolved in Asia some 40 to 45 million years ago and spread from there to the other parts of the world. This geographic spread could have occurred by way of a number of routes, but I believe that the most likely sequence was the following one. At the end of the Eocene, early anthropoids, the Ponnyadaung primates or their close relatives, migrated across Asia into Africa by crossing the narrow, swamplike Tethys Sea, which then separated the two continents. Once in Africa, these early higher primates continued to evolve, with some populations becoming ancestors of the 30- to 35-million-year-old Fayum primates of Egypt (and ultimately of all Old World monkeys, apes, and humans). Other populations crossed the then-narrow equatorial Atlantic Ocean by island hopping along a series of volcanic islands. In this way they reached South America and became the ancestors of the New World monkeys.

The increasing clarity with which Western paleontologists are now able to view these events in primate evolution is owed in large part to the discoveries made by our Burmese colleagues, who continue to search for more fossil evidence. Although I have returned to Burma several times since my memorable visit to Mogaung village, I have not been granted further opportunity to visit the Ponnyadaung Hills. While a field trip to southern China was arranged in 1983, and one to Vietnam is planned for next year (both countries have related geological deposits), the road to Mandalay still beckon.

Reprint from Meta Religion

Favourite Quotes from Charles Darwin’s “The Descent of Man” (1871)

Charles Darwin

“It is impossible not to regret bitterly, but whether wisely is another question, the rate at which man tends to increase, for this leads in barbarous tribes to infanticide and many other evils, and in civilised nations to abject poverty, celibacy, and to the late marriages of the prudent”

 p. 168 – Chapter 5 – Civilised Nations

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“But we must not fall into the error of supposing that the early progenitors of the whole simian stock, including man, was identical with, or even closely resembled, any existing ape or monkey”

p. 182 – Chapter 6 – On the affinities and genealogy of Man

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” At the same time the anthropomorphous apes, as Professor Schaaffhausen has remarked will not doubt be exterminated”

p. 183 – Chapter 6 – On the affinities and genealogy of Man

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“At a still earlier period the progenitors of man must have been aquatic in their habitats for the morphology plainly tells us that our lungs consist of a modified swim bladder which once served as a float”

p.188 – Chapter 6 – On the affinities and genealogy of Man

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“The world, it has often been remarked, appears as if it had long been preparing for the advent of Man, and this, in one sense is strictly true, for he owes his birth to a long line of progenitors. If any single link in this chain had never existed, man would not have been exactly what he now is. Unless we willfully close our eyes, we may with our present knowledge approximately recognise our parentage, nor need we feel ashamed of it”

p.193 – Chapter 6 – On the affinities and genealogy of Man

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“Those who do not admit the principle of evolution, must look at species as separate creations, or as in some manner as distinct entities; and they must decide what forms of man they will consider as species by the analogy of the method commonly pursued in ranking other organic beings as species. But it is a hopeless endevour to decide this point until some definition of the term ‘species’ is generally accepted; and the definition must not include an indeterminate element such as an act of creation”

p. 205 – Chapter 7 – The Races of Man