The mysterious ancient man

An amazing cache of fossils is causing great excitement in the scientific community and the media, raising questions about human origins / Kate Wong

 

The article was published with the approval of Scientific American Israel and the Ort Israel network

 

in brief

• In 2013, speleologists discovered a cache of mysterious fossils in an underground cave system known as the "Rising Star", near Johannesburg in South Africa.
• During two research trips to the area, scientists at the site collected more than 1,550 items that could be attributed to at least 15 items of an ancient man.
• In September 2015, the scientists published the discovery with great fanfare, and announced that the bones that were uncovered indicate the existence of a species that was not known until now, Homo naledi, which casts doubt on the accepted opinion regarding the origin of man and his evolution.
• Criticism of the discovery raises questions about how the fossils were extracted and the analysis of the findings.

In the new fossil hall at the University of the Witwatersrand in Johannesburg, South Africa, there is almost no room left on the shelves. The cabinets with glass doors that decorate the walls of the hall are filled to the brim with the bones of our ancestors that were discovered over the past 92 years in the many caves scattered in the area known as the "Cradle of the Human Race" located only 40 kilometers northwest of Johannesburg. The fossil record of extinct species of early man found in this area is one of the most extensive of its kind in the world. However, recently the volume of the collection was doubled with the discovery of hundreds of items in a cave system known as the Rising Star". According to the paleoanthropologist Lee Berger and his colleagues, who uncovered and analyzed the remains of the ancient skeletons, these fossils represent a human species that was not known until now: Homo naledi, named after the word "star" in the Sutu language of the local people. These fossil remains call into question some of the views deeply rooted in our consciousness regarding the origin and evolution of the biological species (genus) to which we belong, Homo.

 

Berger, elegantly dressed in a brown leather blazer, was prepared and ready to speak before the dozen or so journalists, including myself, who had gathered in the Fossil Hall at the end of 2015. As we surrounded him, he directed our attention to six carrying cases, originally intended for carrying assault rifles, which were arranged on tables around the hall. Each of them contained a dizzying selection of fossils placed on a foam bed. In the cabinets along the back wall we saw additional remains of fossilized bones, displayed in dozens of transparent plastic containers bearing labels such as "skull fragments", "femoral pelvis", "radius bone". Berger reached for box number 2, where the crown jewels of the "Rising Star" collection are kept: the group of bones that was used to define the new species. He pulled out an upper jaw bone and a lower jaw bone from the box and held them carefully, one above the other, and as someone skilled in this, put them on display in such a way that the matching pair of jaws was clearly visible to all. The audience murmured in appreciation, scribbled with pens and flashed cameras. Berger continued to step from delicacy to the next exhibit as he answered the journalists' questions, cooperated with the photographers, and encouraged the guests to immortalize themselves in selfies with the new celebrities of the Hall of Fossils.

Until only a few decades ago, it was possible to store all the fossil remains of our ancient ancestors and extinct relatives, known as hominins, in one desk drawer. Those days of few finds are long gone. Since then, scientists have accumulated more and more evidence for the evolutionary history of the human family. In fact, the number of these fossils is much greater than the fossils of many other creatures, including those closest to us alive today, the great apes. From this evidence, scientists conclude, among other things, that humanity's roots go back at least seven million years, and that during that time, over extended periods, our ancestors shared the world with other hominins.

 

However, the hidden is still greater than the revealed. Some of the chapters in the story of the human race are still left in the abyss that the fossil finds in our hands do not disperse. Other chapters were written in general terms based on such scanty evidence that they are nothing more than conjectures. The database of fossils documenting the evolution of the human species is indeed considerably larger today than it was in the past, but it is not comprehensive enough, and often, new findings change the scientific perception of stages in the development of the human species, and in some cases, even significantly.

The discovery of the Rising Star fossils is the latest example of such an upheaval in the paleoanthropological community. Berger and his team claim that Homo Naledi can shed new light on the origin of the biological species Homo and redraw the evolutionary tree of the human family. Moreover, according to them, this creature, which had a small brain, the size of which did not exceed that of an orange, engaged in ritualistic behavior that was previously attributed only to much more intelligent hominins, a discovery that undermines the popular opinion regarding the connection between cognitive sophistication and brain size.

Some critical scientists reject these claims outright. Others received them with uncharacteristic silence. According to many, one of the main stumbling blocks on the way to confirming these claims is the fact that the age of the bones is unknown. They can be more than four million years old or less than 100,000 years old. But the problem of bone lengthening is not the only problem that bothers outside observers. The manner in which the fossils were uncovered, the method of their analysis and the way in which the public announcement of the discovery was conducted caused uneasiness among some of the leading researchers in the field. They claim that Berger and his colleagues accelerated the process and favored publication over scientific scrutiny. In this field, which is characterized by fierce rivalries, heated debates about new discoveries are commonplace. But what is at stake in the controversy over the rising star fossils is more than the egos of some of those involved in the issue. The scientists' response to this discovery in the longer term may pave a new path in the study of human origins and change not only the questions scientists ask, but also the way they try to answer them.

The mysterious ancient man_1
The Bone Room: Cave diggers discovered the fossils associated with a new human species, Homo naledi, in an underground cave system known as the "Rising Star", not far from Johannesburg in South Africa (see map). The bones were found in a hidden room in the cave system, 30 meters below the ground. In order to reach it, the excavation team had to make its way along a path that winds steeply up and down, and squeeze through narrow passages (in the diagram). Homo naledi apparently required no less efforts to reach the room. Scientists believe that he placed Matthew in the chamber on purpose (in the small lower diagram), and although geologists are still trying to find out exactly how the cave system was formed and what changes took place in it over time, they cannot prescribe a plausible alternative route through which Homo Naledi might have reached the chamber . (Source: “The Geological and Taphonomic Relationship of the New Hominin Species Homo Naldi from the Ninaldi Chamber, South Africa” by Paul H. J. M. Dierks and colleagues, Article #09561, eLife; September 10, 2015; Illustration: Jose Miguel Mayo)

Chamber of Secrets

The controversy flared up, in part, due to some grainy photos that were shown to Berger on October 2013, XNUMX. Berger wanted to go back and scan the "Cradle of the Human Race" area in an attempt to find new sites of hominin fossils, and for this purpose he hired the services of geologist Pedro Boschoff. Over the years, miners and fossil hunters have scoured the area time and time again. But Berger had good reason to believe that all was not yet revealed. Five years earlier, right in the heart of the cradle of the human race, our son, who was nine years old at the time, came across the fossilized bones of a member of a hitherto unknown species in the human family, Australopithecus sediva.

Boshoff conducted his scans along with local speleologists Rick Hunter and Steven Tucker. And here, in a room that was extremely difficult to access, at a depth of 30 meters in the condensing system of the Rising Star Caves, the three discovered what looked like ancient human bones scattered on the floor. It was only a few kilometers away from where Berger and his son discovered the remains of Australopithecus sediva. The researchers did not take any items from the area with them, and contented themselves with photographing the findings. The moment Berger saw the photos he realized that the findings were of great importance. The bones that were discovered had distinctly different characteristics from those of human species anatomically similar to modern humans, Homo sapiens. And the number of bones was very large, more than enough to assemble a skeleton from them.

Berger immediately began preparations to collect the findings. But he is faced with a problem. The path that led from the cave entrance to the room where the bones were discovered included several sections too narrow to allow passage for a broad-shouldered person like him or most of his team mates. Expanding the narrow passages could have undermined the structure of the cave and caused damage to the fossilized bones. Berger rejected this possibility outright. He therefore put out a call on Facebook for small-scale scientists, experienced in digging caves and uncovering ancient remains, who could come to Johannesburg on short notice and go on a research trip in exchange for little more than a plane ticket and a promise of adventure.
Five weeks after Boschoff presented Berger with the photographs that ignited his imagination, Berger selected a team of diggers - coincidentally, all women - for the difficult and dangerous task of collecting the bones from the underground chamber, as well as a support team to assist them in their mission. He formulated a procedure for collecting the findings and documenting the exact place in the room where each piece of bone was found. At the same time, Berger appointed a group of senior scientists to supervise the excavation operation via CCTV, and to record and store the findings when they were removed from the cave. He also outlined a plan to publicize the project: a large-scale media campaign, in collaboration with National Geographic and NOVA, which will include live Twitter updates, daily blogs, radio interviews, and videos straight from the field, as well as a television documentary to be broadcast at a later date, after the publication of the findings. On November 10, 2013, after the cameras were activated, the excavators began crawling, climbing and twisting their way through the undergrowth of the cave system on their way to the hidden chamber alta to begin the job of collecting the bones.

Marina Elliott was the first scientist to enter the room. "I didn't know what to expect, but I was all excited," said Marina when I accompanied her to the Rising Star website. It was lunchtime on a bright, hot summer day in the southern hemisphere, and outside the cave you could hear, carried by the wind, the whir of cars speeding by on the nearby highway. But the cave was dim, cool and still - the stillness of ancient ages. A ray of light that penetrated through a natural opening in the ceiling of the cave flooded its rocky walls with splendor, and served in it the atmosphere of a place of worship.

But the peace in this part of the cave does not imply the danger lurking in the continuation. Eliot illuminates one of the corridors with a flashlight and in the beam of light a perforated limestone partition is revealed to our eyes. Behind it lies the first obstacle on the way to the fossil room, Elliott explains - a narrow tunnel that was nicknamed "Superman's crawl", which the excavators had to crawl through on their stomachs, with one arm extended in front, like Superman's raised arm. The journey didn't get any easier from there. Further down the road rises the jagged "back of the dragon" and after it opens a narrow vertical shaft, less than 20 centimeters wide, leading along 12 steep meters to the opening of the bone room.

But at the end of the arduous route, the diggers won a generous reward for their efforts. The bones were scattered across the length and breadth of the room and their number far exceeded what was required to assemble the only skeleton Berger hoped to retrieve from the cave. Over the next 21 days, Elliott and her teammates collected and hauled more than 1,200 items. A second expedition, which worked for a shorter time in March 2014, yielded several hundred more items. In total, the excavation team extracted from the room, which was the size of a card table, more than 1,550 bones and bone fragments of at least 15 individuals, including babies, children, young and old. This is the Bloom Treasure, one of the largest collections of hominin fossils ever discovered. And these are only the bones collected on the surface. Many more bones, perhaps thousands of bones, remained buried in the chamber.

A Star Is Born
As more and more hominin fossils piled up in the cabinets, Berger and his colleagues found themselves faced with the daunting challenge of sorting through the finds and evaluating them. But even earlier, when the researchers began the process of scientific evaluation, already at the time of extracting the bones from the cave, a cloud of mystery began to surround the findings. First, the bones seemed to be characterized by a strange combination of primitive and modern features. Moreover, with the exception of the remains of a few birds and small rodents, no remains of other animals were found in the bone room. Fossils of larger animals, such as monkeys, antelopes and hyenas, were almost always found alongside hominin fossils that had been discovered up to that time, especially those discovered in underground caves. The absence of fossils of such species in the Rising Star Caves requires an explanation.

Berger therefore recruited a team of 35 researchers at the beginning of their professional career to help him characterize the findings, and during a month-long workshop held in Johannesburg in May 2014, the team members engaged in describing the fossils. For most of the participants, many of them doctoral students, it was a rare opportunity to investigate newly discovered fossils themselves, instead of learning from findings that had already been characterized by other, more experienced scientists. The work was done in groups that each dealt with different parts of the skeleton: skull, hand, teeth, spine, thigh, leg, foot, and so on.

When the scientists combined the results of their work, an amazing picture emerged: a hominin with upper limbs adapted for climbing and using tools, lower limbs adapted for upright walking, and a tiny brain. "It really is a very strange creature," Berger says.

One Friday afternoon in December 2015, John Hawkes of the University of Wisconsin-Madison, a senior researcher on Berger's team, takes me on a return visit to the fossil hall to demonstrate to me some of the salient features of the Rising Star bones. His teammates are still outside celebrating the Christmas break with a beer party and barbecue, but Hawkes prefers to go inside. Here, among the bones, he feels at his best. He runs around here and there, arranges the boxes of fossils on the tables, and chooses for comparison exact replicas of other hominin fossils from the rich collection of the paleoanthropology department.

The skull itself is a myriad of features that have so far been associated with different species of hominins. The skull contained a brain whose volume was, most likely, only 450 to 550 cubic centimeters. It's a brain as small as that of another ancient human species, known as Australopithecus afarensis, which gained wide publicity because of the 3.2-million-year-old skeleton of "Lucy" that decomposed in Ethiopia in 1974. However, the shape of the skull actually reminds of Homo erectus, which is closer to the modern human species. The teeth, however, resemble those of Homo habilis, one of the most primitive species of the biological genus Homo. They get bigger and bigger from the front of the jaw towards the back side. But unlike those of Homo habilis, they are relatively small, the molars having simple crowns and low tooth mounds and their number is smaller, features that characterize later species in the lineage of the genus Homo.

The same mosaic of characteristics is also evident in the bones below the head. The upper limbs as well as the shoulders and fingers are adapted for climbing, while the wrist and hand are adapted for holding stone tools, an activity previously attributed only to hominins in a more advanced stage of development, after they came down from the trees and developed a larger brain, and with it a more developed ingenuity. In the lower limbs, the hip joint is similar to Lucy's, while the foot is practically no different from ours. The working assumption in the scientific community was that the characteristics that distinguish the biological type Homo all evolved together: a palm adapted to making tools, a large brain and small teeth, for example. But "Australopithecus sediba and Homo naledi demonstrate that features we thought evolved together, side by side, did not necessarily evolve at the same time," says Hawkes.

This unprecedented combination of primitive and modern features is not the only distinctive feature of Homo naledi. The fossils found in the cave have features that have never been seen in any individual belonging to the human family. Hawkes pulls out a finger bone from the foam substrate, the first of the palm bones, the one below the thumb and displays it next to the corresponding bone of Homo sapiens: the difference is obvious. The bone of the first bone in Homo Spines is smooth, thick and wide throughout. That of Homo naledi, on the other hand, is narrow at the base and wide at the head, running along it like a sharp ridge, both sides of which are decorated with thin bony wings. The femur and other skeletal parts of Homo naledi also have unique characteristics.

Berger and his colleagues believe that this combination of characteristics of Australopithecus and Homo, which has not been seen before, and the other unique characteristics of Homo naledi justify the association of the rising star fossils with a new species of hominin. Although the researchers have not yet determined the age of the fossils, in the article in which they announced the discovery, published in September 2015 in the online and open scientific journal eLife, they hypothesize that based on the primitive characteristics of Homo naledi, compared to the characteristics of early species in the human lineage such as Homo habilis and Homo Arctus, his age is apparently more than two million years old and his roots lie in an ancient stage in the evolution of the biological species Homo - at the base of the human family tree. If this is indeed the case, the discovery is a real achievement. The origin of man is probably the greatest mystery in the evolution of the human race, and a solution has not yet been found to it, since there are transitional fossils, those that bridge between Australopithecus and their species, for their many characteristics similar to those of monkeys, and later species of Homo, characterized by a body structure similar to this of modern man, are extremely rare fossils and most of those that have been uncovered are no more than fragments. Scientists have been trying for years to find the answer to the question of which hominin species founded the branch of the genus Homo in the hominin family tree. They are eager to find new evidence to explain how the features that characterize the body structure of modern humans evolved.

But Berger and his team were not content with declaring that their discovery could be relevant to the question of man's origin. They argued that the unexpected combination of features found in Homo Naledi indicates that single and isolated bone fragments, from which it is impossible to assemble a complete skeleton, cannot serve as a basis for explaining the evolutionary relationships between hominin fossils, since it is impossible to learn from the parts about the whole. In doing so, they stood in contrast to other researchers who saw such single bones, which were uncovered here and there, as the earliest evidence of the genealogy of the biological species Homo.

And perhaps what arouses even more controversy than Berger and his team's claim regarding the meaning of Homo naledi when it comes to understanding the evolutionary connections between the different hominin species, is their interpretation of the behavior of Homo naledi. In an attempt to understand how the hominin fossils got to the bone room, the researchers considered several possible mechanisms that are accepted as an explanation for the presence of hominin fossil accumulations in other sites. Among other things, the possibility that the bones were swept into the cave system during a flood or that large predators dragged the hominins into the cave to eat their flesh. But the evidence found in the field is inconsistent with these explanations. Flood waters would certainly have swept the remains of other animals into the bone room with them, and carnivores would inevitably have left incriminating teeth marks on the bones. Because of this, Berger and his team came to the conclusion that the bodies were placed in the bone room on purpose by a Naledian homo.

The excavations in the Rising Star cave system yielded more than 1,550 items of Homo Naledi fossils that can be assigned to at least 15 items, in the entire age range, from infancy to old age. Almost every bone in the body is represented in the fossil record, and many of them, in more than one item. Based on these remains, scientists have reconstructed a creature that is characterized by an amazing mosaic of features: some of them are those associated with the ancient Australopithecus and others that characterize different species associated with the biological genus Homo, as well as features that have never been seen in any species of hominins.

To do this, the hominins had to invest great efforts. The geologists on Berger's team still do not know exactly how the Rising Star cave system was formed and what changes took place in it over time. So far they have found only one opening leading to the bone room, the one through which the excavators were pushed on their way to collect the fossils. And if this was indeed the only opening, then the person who placed the bodies of the dead in the room was required, at the very least, to make his way along the path that winds up and down along the 20 meters of the "dragon's back" in order to reach the top of the vertical shaft leading to the opening of the room. From there it was possible to reach the room by crawling along the shaft, while dragging the bodies, or simply throw them in, so that they slide down the shaft to the room at the bottom. And if indeed the path leading to the hidden room was always shrouded in total darkness, as the research team speculates, it is likely that the hominins used an artificial light source to find their way to it in the thicket of the cave system. If so, the claim is that Homo Naledi with the tiny brain not only performed funeral rites, but also knew how to use fire.

Berger, sprawled in a leather armchair in the reception area of ​​his office, with a cup of coffee in his hand, tries to explain what the findings of the rising star say about the evolution of the human race. It is 7:30 in the morning, but the blinds are still closed and the room is half dark. Leather carpets are spread on the floor and jazz sounds emanate from a vintage-designed turntable. The feeling is as if we are in an English gentleman's hunting lodge and not in a study. "Whatever the age [of the findings], they will be controversial," Berger says. If they are ancient, then this may indicate that important physical characteristics and behavioral traits first appeared already at the roots of our biological species, Homo, or even earlier, and not in the later species, as previously thought. According to Berger, if Homo naledi is an even more ancient species, it may displace the Australopithecus species from their place in the genealogy leading to modern man. If, on the other hand, the fossils uncovered are relatively young, researchers will have to reconsider who the species are that left behind the traces of human culture at key archaeological sites across Africa.

Homo naledi may have appeared for the first time millions of years ago, and managed to survive without change over the generations, and sometimes even alongside other species belonging to the human family, including Homo sapiens, similar to the coelacanth fish [an ancient series of fish known in fossils, which was considered extinct, until two of its representatives were discovered in the 20th century]. It is also possible that Homo Naledi developed some of the cultural traditions that archaeologists attribute to our species in the human lineage, Berger says. And it is possible that Homo Naledi contributed DNA to the modern human gene pool through hybrid breeding with our ancestors, similar to Neanderthal man and Denisovan man.

under the criticism tribe

When Berger's team published the scientific paper announcing the discovery in September 2015 in eLife, Homo Naledi received an enthusiastic reception. The news made waves around the world and it seemed that no media channel missed the opportunity to report on the discovery. Even the satirical website The Onion jumped on the bandwagon and published a redacted photo of a tearful Berger next to an article titled: "Grieving archaeologists discover 100,000-year-late ancestor of deceased human." But the wave of public enthusiasm passed over some top members of the paleoanthropological community. Although, there is no disputing the importance of the findings: a cave full of fossils of our ancient ancestors is undoubtedly an extraordinary discovery. But the approach taken by the team regarding the extraction of the fossils and the characterization of the bones and the interpretation they gave to the findings raised quite a few question marks.

Berger is no stranger to looks of disdain and criticism from colleagues in academia. As someone who is gifted with eloquence and a "screen-passing" appearance, Berger was a member of National Geographic at the beginning of his scientific career. The collaboration resulted in funding for his research, the publication of his articles, and television appearances. But he uncovered very few fossils, and the articles he published, both scientific and popular, provoked criticism among some of the top paleoanthropologists, including Tim White of the University of California at Berkeley and Bernard Wood of George Washington University, who accused him of scientific negligence and chasing headlines.

The discovery of Australopithecus sediva in 2008 raised Berger's profile in the scientific community. Even his staunchest critics admitted that the discovery, which included two complete skeletons nearly 1.98 million years old, was nothing short of amazing. But many disagreed with his interpretation of the findings. All along the way Berger claimed that in the search for the origin of man, South Africa was neglected in favor of East Africa.

Australopithecus sediba consists of a mosaic of characteristics and features, a combination of Australopithecus and Homo. This may indicate that the origin of man is in southern Africa. The difficulty is that the earliest fossils associated with the biological genus Homo are items from periods that preceded Australopithecus sediva and were found in East Africa. Berger claimed even then, that single and isolated fossil fragments (that do not form a complete skeleton), such as those found in East Africa and considered the earliest remains of the genus Homo, cannot be attributed to one species or one type or another, since the skeletons he discovered, which were characterized by a surprising combination of features, prove that it is impossible to learn from them about the whole. Most of his colleagues rejected this claim.

The discovery of Homo Naledi strengthened Berger's position in the public and his controversial ideas about the origin of man and the meaning of scattered fossil fragments. But his opponents did not hesitate to criticize him. In an interview that White gave to "California", the journal of his university's alumni organization, he claimed that the fossils of the rising star probably belong to an ancient species of Homo erectus, and not to a new species. White is best known for discovering hominin fossils in Ethiopia, including 2.4 million year old Australopithecus garhi fossils. Based on the age of the fossils and the location where they were discovered, White and Berhana Aspao of the Rift Valley Research Institute and their colleagues argued that Australopithecus garhi was most likely an ancestor of the biological species Homo. In the interview, White pointed the finger of blame at the Rising Star team, which he said damaged the fossils during their discovery and prematurely published his findings. In a poignant article published some time later on the Guardian's blog site, White warned of the dangers inherent in mixing scientific work with showmanship. "We are witnessing the deterioration of certain fields of science becoming part of the entertainment industry," White wrote.

White is not the only scientist who has expressed doubts about the Rising Star findings. Carol Ward of the University of Missouri says that while the fossil record is impressive in scope, it is still unclear how significant it is. Ward emphasizes the importance of dating the bones: "Only when we know the age of the bones, we can determine what their significance is regarding the evolution of the human species."

Ward also has criticism of the article describing the fossils. According to her, it does not have enough comparative data to allow outside scientists to compare them with other relevant fossils to evaluate the claims of Berger and his team. The article also lacks a phylogenetic analysis - essentially, the study of the evolutionary relationships in a group of creatures based on a computerized comparison of their features - which would have taught where Homo Naledi is located in the evolutionary tree of the human family. "It seems that [the authors of the article] are eager to link Homo naledi to the roots of the human family tree," says Ward, but in the absence of detailed phylogenetic analysis or dating, we cannot know if such a connection actually exists.
Many researchers support the view that according to the evidence we have today, the biological type Homo first appeared in East Africa. In March 2015, a few months before the details of the Homo Naledi discovery became public, Brian Wilmore of the University of Nevada, Las Vegas, Kay Reed of Arizona State University and their colleagues announced their own discovery: a 2.8 million year old lower jaw bone found at the Ledi-Gararu site in northeastern Ethiopia. According to them, this fossil is the earliest representative found so far of the genus Homo. The jaw has clear hallmarks that distinguish the biological type Homo, the researchers claim. Along with these, it is possible to distinguish features that indicate a transition between Australopithecus and Homo. Until the age of the Homo Naledi fossils is determined, the jaw found in Ladi-Geraro cannot be dismissed as the earliest evidence of our family tree, Reed says. It also rejects Berger, Hawkes and their colleagues' claim that partial anatomical findings cannot be assigned with certainty to any taxonomic group. "I have a clear dating, 2.8 million years, and our find has characteristics of a homosexual," she insists.

The question of which fossils herald the dawn of humanity arouses controversy in the paleoanthropological community partly because they themselves disagree on the question of what defines the biological species Homo in the first place. Homo Naledi "turns the spotlight on the debate over the definition of the biological species Homo, whether based on only partial evidence or based on evidence that provides a more complete picture," says Susan Anton of New York University, an expert on the earliest species in the evolution of the human lineage. The distinction between Australopithecus and Homo "is not a simple task at all today. We all wonder how the distinction should be made, and different people have different views." Anton and her partners distinguish between these types of hominins based on the characteristics of the skull, jawbones and teeth. Other researchers argue that the distinction should be based on the structure of the skeletal bones below the skull, known as postcrania, as they reflect the most significant adaptive changes that the hominins underwent in the transition from forested environments to bare, vegetation-free areas. However, not much is known about the bones of the skeleton under the skull in the ancient species in the evolution of the human lineage. Rising star fossils are "rich people's trouble," says Anton. The mosaic of features that characterize them points in different directions and Berger's team did not explicitly state how and on what basis it defines the biological type gay. "The discussion on the subject is far from exhausted," says Anton.

But even if the remains found in the Rising Star Caves justify the association of the fossils with a Homo species, and even if it turns out that they are more than two million years old, it will not be enough to convince the skeptics that Homo Naledi was among the species that led directly to us or was even close to the branch in the family tree leading to man contemporary Bernard Wood of George Washington University believes the bones represent an extinct population that likely developed its peculiar traits in relative isolation. "South Africa is a dead end at the edge of the African continent," says Wood. "My hypothesis is that gene exchange at the edge of the continent was not as common as it was in East Africa, where the possibilities for gene exchange between populations originating from the south and center of the continent and the unification of their traits were considerably numerous." As another example of such an extinct and isolated population, Wood mentions another strange species of Homo, Homo floresiensis, which was characterized by a small brain and an extremely short stature and lived on the island of Flores in Indonesia for a long time after Homo sapiens had already first appeared in Africa.

The claim that the small-brained Homo Naledi performed burial rites for the dead also met with opposition. "This is a far-reaching claim," says archaeologist Alison Brooks of George Washington University. It is widely believed that this practice is unique to human species with much larger brains and a more modern anatomical structure. The first to demonstrate such intelligent ritual behavior seem to have been the Neanderthals. However, burial rites only became common about 100,000 years ago. "I wouldn't want to completely rule out the possibility that there is truth in their claim [of the rising star researchers]," says Brooks, "but in my opinion, its likelihood is so low that much more solid evidence is required to confirm it."

In fact, even the excavation team that recovered the fossils raised doubts about the idea that Homo Naledi had intentionally placed Matthew in that deep underground chamber, if only for logistical reasons. "It's really not easy to make your way there with a backpack on your back, and certainly not while dragging a body," says Elliott. "But for two years we tried to find another explanation for the mystery, without success."

However, even if Homo Naledi did indeed bring Matthew to be buried in that deep room, this behavior does not necessarily indicate cognitive sophistication. Travis Pickering of the University of Wisconsin-Madison, who has been researching the Cradle of Humankind area for the past 20 years, agrees that the most logical answer to the question of how the bones ended up in the remote chamber is that other hominins placed them there on purpose. Pickering believes that the question cannot be decided at the moment "whether this means that Homo Naledi was a culturally quite advanced species that developed ritualistic burial practices or simply a primitive species that was ordered by an innate primitive drive to stay away from rotting corpses."

In the race for the coveted prize

Berger rejects the claims of his opponents and says that they were all raised in popular science articles in the press and on social networks and not in the strict framework of a scientific journal. According to him, "Their evidence is based only on their words." He is of the opinion that his team took extreme care in extracting the fossils, and explained in a post he uploaded on Facebook that the damage to the bones was caused even before the Rising Star team first arrived at the scene. Berger assumes that unknown amateur cave diggers used the bones when they explored the scene in the past. Berger says his excavation team was able to work efficiently and quickly because "we didn't run into the problems that other teams run into." In other sites the fossils were usually preserved embedded in the rock. Extraction and cleaning of such fossils involves arduous and lengthy work. In contrast, at the Rising Star site the fossils were simply lying on moist soil that was easily removed. Moreover, unlike other teams, which are often small and conduct research trips to remote sites for six to eight weeks a year, Berger's team is large and based in Johannesburg, so he can work on site at any time or continue research in the fossil hall at the university. If you look at the work invested by the Rising Star team in terms of man-hours, as recorded in the time period between the discovery of the fossils and the publication of the findings, "the investment is no less than that of any other team," Berger firmly states.

As for White's claim that the rising star fossils probably belong to an ancient species of Homo erectus, and not to a new species, "he disputes every finding, with the exception of findings that he himself defined," says Berger pointedly. If we associate the remains of Homo naledi with Homo erectus, this would mean that Homo erectus was characterized by greater biological diversity than is evident in our species, and in Berger's opinion, this is unlikely. And as a matter of fact, Homo Naledi has unique features not found in any other hominin. "If the subject of the discussion is evolutionary biology, there is no more room for debate," declares Berger. "Frankly, I'm surprised that [people] haven't claimed that this is a new biological type," and not just a new species.

When asked about the dating of the rising star fossils, Berger says that the issue is under investigation by geologists, and that sooner or later the answer to that will be found as well. But according to him, the age of the findings, as will be determined, will not change the basic concept of his team regarding the connections between Homo naledi and other species belonging to the human family. Although Homo naledi has several key features that characterize the biological genus Homo, in some ways its overall mosaic of features is even more primitive than that of Homo habilis and, in fact, even that of the Maldi-Gerraro jawbone, the fossil considered to be the earliest representative of the human lineage. Whatever the age of the rising star fossils, their properties indicate that the Homo naledi branch of the human evolutionary tree predates these branches. And if the age of the fossils turns out to be younger, then they represent a late population of this [ancient] species.

If so, why didn't the team include a phylogenetic analysis in the paper announcing the fossils as representing a new species? To understand the evolutionary relationships between different creatures, evolutionary biology scientists use a method called cladistics, which classifies genera and species into groups based on new features they share with their most recent common ancestor, but not with more ancient ancestors. The problem is that the method is mainly effective when the characteristics are observed in all the creatures in question.

When it comes to fossils, this requirement is impractical, since they differ markedly from each other in the properties that have been preserved in them. Paleoanthropologists apply the method mainly when they analyze skull and teeth characteristics of the fossils. The skull is of particular importance in these analyses, as the shape of the skull varies considerably from one hominin to another, and therefore has always been considered highly significant for the definition of hominins by species. Whereas the teeth are the most common remains left behind by the hominins. Bones originating from other parts of the skeleton are not always exposed next to the skull or teeth and therefore it is difficult to assign them to any species defined based on the remains of the skull or teeth. Also, skeletal bones that characterize a certain species do not necessarily appear in other species.

As a matter of fact, some of the key elements in the Homo Naledi fossils - including the almost complete sets of bones of the hands and feet - are only partially represented, if at all, in the fossil record of other hominins that have been discovered so far, such as Homo erectus and Homo habilis. In the absence of parallel skeletal parts that could be compared, the researchers could not conduct cladistic analyzes of Homo naledi to learn about the variety of intriguing features that characterize the bones of the skeleton below the skull, and therefore conducted an analysis based on the characteristics of the skull and teeth. But some of the results of the analysis raised doubt in their hearts, since they ordered that Homo Naledi, with its many primitive characteristics, is closer to Homo Spines than to the much earlier Homo Arctus. Berger sees this as confirmation of his claim that genealogies based on partial anatomical data that focus on only one element of the skeleton, such as the head or teeth, are unreliable.

Berger still believes that in some way, Homo Naledi will bring about a revolution in the scientific perception of human evolution, but he does not ask his colleagues to take his words as they are. Contrary to what is customary in the paleoanthropological community, which is known for its secrecy when it comes to fossil finds and the limitations imposed on access to them, Berger instituted an explicit policy regarding the fossils of the rising star that allows any researcher interested in this to examine them closely. Moreover, simultaneously with the publication of the discovery in eLife, the team of researchers released XNUMXD scans of bones of considerable importance for publication in MorphoSource - a digital database of anatomical data, and visitors to the database are invited to print XNUMXD copies of the findings. Admittedly, at this stage the resolution of the scans is not high enough to allow independent research, but "it is good enough to allow anyone to examine our claims," ​​Berger says.

"The free access to the findings that people receive is a huge advantage; The complaints are just background noise," says David Strait of Washington University in St. Louis. Straight mentions a well-known editorial written by White in 2000, in which he argued that due to the enormous public interest in human origins, paleoanthropologists have a special duty to get the facts straight. "This is a fundamentally wrong approach," says Straight. "It goes without saying that we have to do our job faithfully, but science is supposed to work in a way of denying possibilities. We are narrowing down the range of possible truths to understand what happened in the past, but new data can always emerge that will change the prevailing perception." The free access to fossils that Berger gives other researchers, Strait says, allows scientists who disagree with him to put their claims to the test and test them against his own. "The field only advances when people can examine the findings."

Meanwhile, the Rising Star team continues its work at full speed, without waiting for the opposition's approval. The geologists are engaged in reconstructing the history of the cave system; The diggers extract more and more fossils from the bone room; The molecular biologists are trying to extract DNA from the bones. And as for the fossil hunters, they will look for new finds, in other places. "[Homo Naledi] heralds a new era of scientific research, the most wonderful we have ever known," Berger declares with characteristic enthusiasm. And if it's not Homo Naledi, it will be the team's next discovery: Berger reveals that his team of researchers is already making progress on this new research front, but refuses to provide further details. However, he adds with a mischievous smile that the team has already located "more than one new site" that ignites his imagination and spurs him on to race once more, just as the grainy images from the Rising Star Caves excited him when he first saw them and motivated him to go on an adventure. In this drama, the last word has not yet been said..