Arquivo da tag: Fósseis humanos

Out of Savannastan by Tim Flannery (New York Review of Books)

New York Review of Books, November 4, 2021

By Tim Flannery

Ancient Bones: Unearthing the Astonishing New Story of How We Became Human by Madelaine Böhme, Rüdiger Braun, and Florian Breier, translated from the German by Jane Billinghurst and with a foreword by David R. Begun. Greystone, 337 pp., $34.95

In 1863 the biologist T.H. Huxley proposed an African origin for humanity. Known as “Darwin’s bulldog” for his ferocious defense of Darwin’s evolutionary theory, he had been struck by the distribution in Africa of our nearest living relatives, the common chimpanzee and the gorilla. (The latter had first been described by Europeans just sixteen years earlier, in 1847.) Darwin himself, however, demurred. Aware of the discovery of fossils of apes in Europe dating to the Miocene Epoch (around 23 to 5 million years ago), he opined that “since so remote a period the Earth has certainly undergone many great revolutions, and there has been ample time for migration on the largest scale.”

It was the pioneering and indefatigable Leakey family who found evidence for Huxley’s narrowly supported hypothesis. Louis and Mary Leakey began their search for fossils of human ancestors in Olduvai Gorge, in what is now Tanzania, in the 1930s. Amid the dust, sweat, and inconvenience of remote field camps, they simultaneously dug for fossils and raised three boys, often finding nothing of significance for years at a time. Then, in 1959, Mary discovered a fossilized skull that made headlines around the world. Paranthropus boisei, as it became known, belonged to a male upright ape who had stood around five feet high, weighed 110 pounds, and lived 1.8 million years ago. With powerful teeth and a prominent crest atop his braincase to anchor prodigious chewing muscles, he was an archetypal “ape man.” I recall as a child staring awestruck at a painting of Paranthropus that combined the features of gorillas, chimps, and humans, and that powerfully cemented in my mind the idea that Africa had been humanity’s cradle.

A few months after this discovery, the Leakeys made a second, even more significant find—a jaw attributable to an early member of our own genus. Homo habilis, or “Handy Man,” was a toolmaker hailed as the oldest “true” human ever discovered. After that, the discoveries just kept coming. In 1974 an international team in Ethiopia led by the paleoanthropologist Donald Johanson unearthed the skeleton of the three-foot-tall bipedal ape Australopithecus afarensis, who became popularly known as Lucy. With a catchy name and providing powerful, easy-to-understand support for an African origin, Lucy soon became a household name. Four years later Mary Leakey found 3.6-million-year-old hominin footprints at Laetoli, Tanzania, providing the earliest evidence of bipedalism.

In 1984 a team led by Louis and Mary Leakey’s son Richard unearthed a skeleton of Homo erectus at Lake Turkana in northern Kenya that was 90 percent complete. It seemed as if these astonishing African fossils illustrated most of the important steps in the human evolutionary story. When, beginning in the 1980s, genetic evidence suggested that our species (Homo sapiens) originated in Africa, the case seemed settled: Huxley, rather than Darwin, had been right about our origins. Some researchers began elaborating an all-encompassing Out of Africa theory, which had three components: (1) our hominin lineage (which split from chimpanzees between 13 and 7 million years ago) arose in Africa; (2) our genus, Homo, arose in Africa about 2.3 million years ago, and (3) our species originated in Africa about 300,000 years ago.

But there were always a few dissenters who, like Darwin, felt that the significance of fossilized fragments from Europe and Asia had been overlooked. They pointed to a suspicious gap in the African fossil record between 12 and 6 million years ago, just when the human and chimpanzee lineages were diverging. And some worried that the Leakeys and others had found fossils only where they looked for them—in Africa. If equivalent effort was put in elsewhere, skeptics argued, important finds might be made.

These objections had long been ignored, but now, in her splendid and important new book Ancient Bones, Madelaine Böhme and her collaborators Rüdiger Braun and Florian Breier have taken them up. Scientifically rigorous and written with a clarity and candor that create a gripping tale, it presents a powerful challenge to proponents of the Out of Africa hypothesis. The book begins with a foreword by one of the earliest and most prominent objectors to the hypothesis, the University of Toronto professor David R. Begun. Begun believes that apes became extinct in Africa around 12 million years ago and that our earliest direct ancestors evolved in Europe, which is rich in ape fossils from 12 to 6 million years old. Böhme, a terrestrial paleoclimatologist and paleoanthropologist at the University of Tübingen, has excavated and researched many specimens of European apes herself, and her account of the history of Europe’s lost apes is imbued with the sweat, grime, and triumph that is the lot of the fieldworker, and carries great authority.

As Böhme illustrates, the evolution of the human lineage is complex. A crucial event occurred around 25 million years ago, when the apes and Old World monkeys originated from a common ancestor in East Africa. The monkeys flourished in Africa, but as time went on the apes dwindled, until around 16 million years ago some reached Europe, where they thrived. Climatic changes in Europe, including increased seasonality, seem to have favored their diversification, and twelve genera are now known from the European Miocene, varying from gibbon-like creatures that swung through the forest canopy to gorilla-sized, presumably terrestrial ramblers.

As oak and beech trees started to crowd out the tropical vegetation that had dominated Europe till then, the apes were forced to alter their diet. Depending on which part of Europe they lived in, they had to go for between two and four months without fresh leaves, fruits, or nuts. Around 15 million years ago, a genetic mutation occurred that resulted in their inability to produce uricase, the enzyme used by mammals to break down uric acid so that it can be excreted in urine. This mutation led to high levels of uric acid in the apes’ blood, allowing them to rapidly convert fructose into fat. And fat, stored in the liver and other tissues, is an energy reserve that made it possible for the apes to survive lean seasons.

I often curse this adaptation, for I’m a victim of that singularly painful condition, gout, which is caused by a buildup of uric acid in the blood. Were it not for the availability of uricase in pill form (thank God for modern medicine!), I’d be a bedridden old grouch by now. But gout is just one of the many “diseases of civilization” inflicted on us by this adaptation in our ape ancestors. Diabetes, obesity, high blood pressure, and heart disease are all related to some degree to the loss, in some long-extinct European ape, of the ability to remove uric acid from the blood.

One of Böhme’s most important fossil finds was made near Kaufbeuren, in southern Germany. There, while visiting a lignite pit, she examined small black lumps of what was supposedly coal, only to discover that they were ancient bones. The deposit was about to be mined and destroyed, and, with no alternative, Böhme asked that twenty-five tons of fossil-rich sediment be scooped up and dumped where paleontologists could sort through it without interrupting the quarrying. After two field seasons of arduous work, she recovered 15 percent of the skeleton of a single great ape, along with fragments from three others. Named Danuvius guggenmosi, the creature had lived 11.62 million years ago, in a subtropical environment. At just three feet tall and weighing around sixty-five pounds, Danuvius had big, powerful thumbs and toes and an elongated lower back that permitted an upright stance. Böhme quips that “from the waist up he looked like an ape and from the waist down he looked like an early hominin.” Danuvius is in fact one of the candidates for the last common ancestor of chimps and humans.

As the climate cooled later in the Miocene, savanna replaced forest in some parts of Europe, and this had a big impact on the continent’s apes. According to Böhme, a crucial piece of evidence indicating what happened was unearthed in June 1944, when besieged German soldiers dug a bunker near Athens. Bruno von Freyberg, a geology professor from Erlangen who was then serving in the German army, asked his workers to alert him to any fossils they encountered. Despite having lost an arm in World War I, Freyberg personally unearthed the finds, including the jaw of an ape, then sent his fossils to the Natural History Museum in Berlin for safekeeping. But the museum was bombed on February 3, 1945, and the priceless jawbone was severely damaged, losing most of its teeth.

In 1969 the great paleoanthropologist Gustav Heinrich Ralph von Koenigswald examined the damaged bone and named it Graecopithecus freybergi—Freyberg’s Greek ape. But it was so extensively mangled that other researchers concluded it was not identifiable, and so sought to suppress Koenigswald’s name. The jawbone might have been forgotten altogether but for Böhme, who tracked it down to a long-forgotten safe in a university department. When she had the jaw x-rayed, she saw that the roots of the teeth shared unique features with those of the subfamily Homininae, to which humans belong. She also redated the find, establishing that it was 7.175 million years old.

Her conclusion that the oldest human ancestor had lived in Greece around six to seven million years ago was so inconsistent with the dominant Out of Africa hypothesis that the paleoanthropological community largely reacted with stunned silence. But then, within months of Böhme’s analysis of Graecopithecus being published in 2017, a second, even more stunning and unexpected discovery was announced.

In 2002 the Polish paleontologist Gerard Gierliński had been vacationing with his girlfriend near Trachilos, Crete. On a slab of rock by the water he saw oblong marks that he recognized as fossilized footprints. But he didn’t follow up until 2010, when he mentioned them to a colleague; the two scientists hypothesized that the footprints might have been made by a bipedal ape. Analysis revealed that the feet that had left the tracks were small (between 4 and 8.5 inches long) and had five toes, a pronounced ball of the foot, and a big toe aligned with the other toes. The feet that left the prints undeniably resembled humans’ feet but lacked some features, such as an arch. Astonishingly, dating revealed that the prints were made more than six million years ago, when Crete was a long, southward-projecting peninsula of Europe.

I recall my own skepticism upon reading of this find: the discovery of six-million-year-old humanlike footprints on a Greek island seemed too outlandish. And evidently the paleoanthropological community felt similarly, for Gierliński and his colleagues had tried in vain for six and a half years to get their results published. According to Böhme, the manuscript was repeatedly rejected by anonymous reviewers whose reasoning was often difficult to decipher. But following the publication of Böhme’s reanalysis of Graecopithecus, Gierliński’s paper on the Trachilos footprints finally made it to press.

Böhme thinks that the tracks could have been left by Graecopithecus around the time upright apes migrated from Europe back to Africa, allowing them to repopulate a continent that they had been absent from for six million years. Whatever the case, there is no doubt that Graecopithecus and the Trachilos footprints present a strong challenge to the first part of the Out of Africa theory.

To most proponents of the Out of Africa theory, many of whom have invested lifetimes excavating sites in Africa, claims about human origins in Europe are heretical. A sense of just how high the stakes are can be gained from the controversy surrounding the discovery at the turn of the twenty-first century of the skull of Sahelanthropus tchadensis, a hominid species. The skull—which was found in the desert in Chad and studied by Professor Michel Brunet, then at the University of Poitiers—is thought to be six million years old and has been used to support the theory that the oldest human ancestor lived in North Africa six to seven million years ago. This finding has been widely accepted and celebrated: there is a street on the campus in Poitiers named for Brunet, and a parking garage named for Toumaï, as the skull is popularly known.

The skull is horribly fractured, and the area where it articulated with the spinal column is heavily damaged. The reconstruction by Brunet’s team made it appear that the skull sat atop the vertebral column, as it does in bipedal apes. But others disagreed, saying that the articulation was farther back, as in gorillas. Indeed, critics say, the skull has a number of gorilla-like features and may belong to an ancestral gorilla.

There matters might have remained, if not for the publication of a photograph of the skull as it was upon discovery. It lay in sand, surrounded by a scatter of other bones including a thighbone that was possibly part of the same individual as the Sahelanthropus skull. While Brunet was doing fieldwork, Aude Bergeret, a Ph.D. student who was studying the bones in her lab, concluded that the thighbone belonged to a great ape and that Sahelanthropus was not bipedal. According to Böhme, when Bergeret’s assertion became known, “the thighbone disappeared without a trace and the doctoral student lost her position at the university.”

In 2018 Bergeret and a colleague offered to give a presentation on the thighbone at the annual meeting of the Société d’Anthropologie de Paris, but they were refused. “Could it be,” Böhme asks, “that Michel Brunet, one of the icons of French science, Knight of the Légion d’honneur, recipient of the Ordre national du Mérite, did not want to be challenged?”

Questions about Sahelanthropus continue to pile up. Because the bones were found not in the sediments that preserved them but in sand drifts, it is unclear how old they are. And is Sahelanthropus an early gorilla or a member of the human lineage? The fossil record of gorillas is almost entirely unknown, so the discovery of an ancestral gorilla would be of huge significance. But it’s hard to imagine a street in a university being named for the discoverer of such a fossil.

The second part of the Out of Africa hypothesis states that the genus Homo evolved in Africa. Böhme strongly challenges this, arguing instead that our genus evolved in a great, now fragmented grassy woodland known as Savannastan, which covered parts of Europe, Asia, and Africa 2.6 million years ago. In support of the idea, she cites 1.8-million-year-old Homo skeletons from Georgia and, more intriguingly, a jaw and a few isolated teeth found in cave sediments in Longgupo Cave, in Wushan County in China’s Sichuan Province. The Chinese fossils were named as a new species, Homo wushanensis, by researchers in 1991, and according to Böhme the remains are between 2.6 and 2.48 million years old. As the oldest Homo habilis remains from Africa are only 2.3 million years old, the dating of the Chinese finds, if verified, would pose a direct challenge to part two of the Out of Africa hypothesis.

But interpretation of the fragmented remains of Homo wushanensis is complicated. In 2009 Russell Ciochon, an American researcher who described Homo wushanensis, declared that he had made a mistake. The jaw and some of the teeth did not belong to an early human, he said, but to one or more “mystery apes.”

 His retraction was acclaimed by some as a welcome act of intellectual honesty in a field characterized by fierce rivalry. Yet it has hardly settled matters. Böhme, for example, notes that stone tools were also found in Longgupo Cave, suggesting the presence of early humans. Others have speculated that the tools (along with some of the teeth) may have found their way into the deposit from more recent sediments, but Böhme is not satisfied by this explanation. Instead, she asks of Ciochon’s retraction, “Why the spectacular retreat? Was it to avoid jeopardizing the Out of Africa…hypothesis?”

Böhme, it seems, is just as determined to defend her hypothesis as the Out of Africanistas are to defend theirs.

Ancient Bones makes clear that Graecopithecus and the Trachilos footprints provide convincing evidence that our earliest direct ancestors evolved in Europe, and that they were walking upright as early as six million years ago. But the book, I think, is overly confident in its challenge to the idea that the genus Homo arose in Africa. That’s because, while there are intriguing clues that Homo may have been present in Europe or Asia before the oldest African finds (which date to around 2.3 million years ago), the evidence is far from conclusive. And of course the third part of the Out of Africa hypothesis, that Homo sapiens evolved in Africa, remains unchallenged—though the recent discovery that all living people carry genes from other hominin lineages, such as Neanderthals and Denisovans, which appear to have evolved in Europe and Asia, respectively, adds an intriguing twist to the tale.

What Ancient Bones does make clear, however, is that we place far too much emphasis on rewarding the discovery of our ancestors. In science, a discovery that leads in an unexpected direction, or even to a dead end, is often as productive as a lucky find. If we could only get past the great egos that swell in the field of paleoanthropology and reward the search as much as we do the discovery! But that, perhaps, would require an objectivity and generosity that aren’t entirely human.

Fossil analysis pushes back human split from other primates by 2 million years (Los Alamos National Laboratory)


Nature paper places human evolution in Africa, not Eurasia

DOE/Los Alamos National Laboratory


LOS ALAMOS, N.M., February 16, 2015–A paper in the latest issue of the journal Nature suggests a common ancestor of apes and humans, Chororapithecus abyssinicus, evolved in Africa, not Eurasia, two million years earlier than previously thought.

“Our new research supports early divergence: 10 million years ago for the human-gorilla split and 8 million years ago for our split from chimpanzees,” said Los Alamos National Laboratory geologist and senior team member Giday WoldeGabriel. “That’s at least 2 million years earlier than previous estimates, which were based on genetic science that lacked fossil evidence.”

“Our analysis of C. abyssinicus fossils reveals the ape to be only 8 million years old, younger than previously thought. This is the time period when human and African ape lines were thought to have split, but no fossils from this period had been found until now,” WoldeGabriel said.

Chimpanzees, gorillas, orangutans and humans compose the biological family Hominidae. Our knowledge of hominid evolution–that is, when and how humans evolved away from the great ape family tree–has significantly increased in recent years, aided by unearthed fossils from Ethiopia, including the C. abyssinicus, a species of great ape.

The renowned international team that discovered the extinct gorilla-like species C. abyssinicus(reported in the journal Nature in 2007) reports new field observations and geological techniques that the authors say revise the age-constraint of the human split from their brethren.

The authors’ new paper, “New geological and palaeontological age constraint for the gorilla-human lineage split,” was published this week in Nature. WoldeGabriel coauthored the paper and his role was to characterize the volcanic ash and provide chemistry for local and regional correlation of the ashes sandwiching the fossils from Ethiopia’s Chorora area, a region where copious volcanic eruptions and earthquakes entombed fossils recently uplifted via ground motion and erosion.

Filling Gaps in the Fossil Record

Most of the senior members of the Chorora research team also belong to the Middle Awash project team that has recovered the fossil remains of at least eight hominid species, including some of the earliest hominids, spanning nearly 6 million years.

In the 1990s, before this team excavated the gorilla-like C. abyssinicus, they discovered the nearly intact skeleton of the 4.4-million-year-old species Ardipithecus ramidus (nicknamed “Ardi”) and its relative, the million-year-older species Ardipithecus kadabba. These Ardipithecusfossils were the earliest ancestor of humans after they diverged from the main ape lineage of the primate family tree, neither ape-like nor chimp-like, yet not human either. Notably, both were bipedal–they walked upright.

While the team was still investigating Ardi and Kadabba, they published their results about C. abyssinicus. From the collection of nine fossilized teeth from multiple C. abyssinicus individuals, the team surmised that these teeth were gorilla-like, adapted for a fibrous diet. Based on their research from the Chorora, Kadabba and Ardi finds, the team says the common ancestor of chimps and humans lived earlier than had been evidenced by genetic and molecular studies, which placed the split about 5 million years ago.

According to the paper, C. abyssinicus revealed answers about gorilla lineage but also provided fossil evidence that our common ancestor migrated from Africa, not Eurasia, where fossils were more prolific prior to this discovery of multiple skeletons. While some skeptics say that more fossil evidence is needed before they accept this team’s conclusions, many agree that the discovery of a fossil ape from this time period is important since only one other had been found.

Extensive Analysis Provides New Evidence

WoldeGabriel and the research team used a variety of methods to determine the age of teeth they found at the Chorora Formation. They estimated the age of the volcanic rocks and sediments that encased the fossils with argon-dating and paleomagnetic methods. The team investigated patterns of magnetic reversals–another method to determine age based on knowledge about an era’s magnetic orientation–and calibrated the sediments containing the fossils using Geomagnetic Polarity Time Scale (GPTS).

Through fieldwork, volcanic ash chemistry and geochronology, WoldeGabriel helped nail down the age of the fossils to approximately 8 million years old. Based on this new fossil evidence and analysis, the team suggests that the human branch of the tree (shared with chimpanzees) split away from gorillas about 10 million years ago–at least 2 million years earlier than previously claimed.