Arquivo da tag: Paleoantropologia

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.

The Death of the Bering Strait Theory (Indian Country Today)

indiancountrytoday.com

Alexander Ewen


Updated: Sep 13, 2018. Original: Aug 12, 2016

Two new studies have finally put an end to the theory that the Americas were populated by ancient peoples who walked across the Bering Strait.

Two new studies have now, finally, put an end to the long-held theory that the Americas were populated by ancient peoples who walked across the Bering Strait land-bridge from Asia approximately 15,000 years ago. Because much of Canada was then under a sheet of ice, it had long been hypothesised that an “ice-free corridor” might have allowed small groups through from Beringia, some of which was ice-free. One study published in the journal Nature, entitled “Postglacial Viability and Colonization in North America’s Ice-Free Corridor” found that the corridor was incapable of sustaining human life until about 12,600 years ago, or well after the continent had already been settled.

An international team of researchers “obtained radiocarbon dates, pollen, macrofossils and metagenomic DNA from lake sediment cores” from nine former lake beds in British Columbia, where the Laurentide and Cordellian ice sheets split apart. Using a technique called “shotgun sequencing,” the team had to sequence every bit of DNA in a clump of organic matter in order to distinguish between the jumbled strands of DNA. They then matched the results to a database of known genomes to differentiate the organisms. Using this data they reconstructed how and when different flora and fauna emerged from the once ice-covered landscape. According to Mikkel Pedersen, a Ph.D. student at the Center for Geogenetics, University of Copenhagen, in the deepest layers, from 13,000 years ago, “the land was completely naked and barren.”

“What nobody has looked at is when the corridor became biologically viable,” noted study co-author, Professor Eske Willerslev, an evolutionary geneticist at the Centre for GeoGenetics and also the Department of Zoology, the University of Cambridge. “The bottom line is that even though the physical corridor was open by 13,000 years ago, it was several hundred years before it was possible to use it.” In Willerslev’s view, “that means that the first people entering what is now the U.S., Central and South America must have taken a different route.”

A second study, “Bison Phylogeography Constrains Dispersal and Viability of the Ice Free Corridor in Western Canada,” published in the Proceedings of the National Academy of Sciences, examined ancient mitochondrial DNA from bison fossils to “determine the chronology for when the corridor was open and viable for biotic dispersals” and found that the corridor was potentially a viable route for bison to travel through about 13,000 years ago, or slightly earlier than the Nature study.

Geologists had long known that the towering icecaps were a formidable barrier to migration from Asia to the Americas between 26,000 to 10,000 years ago. Thus the discovery in 1932 of the Clovis spear points, believed at that time to be about 10,000 years old, presented a problem, given the overwhelming presumption of the day that the ancient Indians had walked over from Asia about that time. In 1933, the Canadian geologist William Alfred Johnston proposed that when the glaciers began melting, they broke into two massive sheets long before completely disappearing, and between these two ice sheets people might have been able to walk through, an idea dubbed the “ice-free corridor” by Swedish-American geologist Ernst Antevs two years later.

Archaeologists then seized on the idea of a passageway to uphold the tenuous notion that Indians had arrived to the continent relatively recently, until such belief became a matter of faith. Given the recent discoveries that place Indians in the Americas at least 14,000 years ago, both studies now finally lay to rest the ice-free corridor theory. As Willerslev points out, “The school book story that most of us are used to doesn’t seem to be supported.” The new school book story is that the Indians migrated in boats down along the Pacific coast around 15,000 years ago. How long that theory will hold up remains to be seen.

Por que somos a única espécie humana do planeta (El País)

brasil.elpais.com

Nuño Domínguez, 04 jul 2021 – 12:48 BRT

Três grandes descobertas feitas nos últimos dias nos obrigam a repensar as origens da humanidade


Três descobertas nos últimos dias acabam de mudar o que sabíamos sobre a origem da raça humana e da nossa própria espécie, Homo sapiens. Talvez − dizem alguns especialistas − precisemos abandonar esse conceito para nos referir a nós mesmos, pois as novas descobertas sugerem que somos uma criatura de Frankenstein com partes de outras espécies humanas com as quais, não muito tempo atrás, compartilhamos planeta, sexo e filhos.

As descobertas da última semana indicam que cerca de 200.000 anos atrás havia até oito espécies ou grupos humanos diferentes. Todos faziam parte do gênero Homo, que nos engloba. Os recém-chegados apresentam uma interessante mistura de traços primitivos − arcos enormes acima das sobrancelhas, cabeça achatada − e modernos. O “homem dragão” da China tinha uma capacidade craniana tão grande quanto a dos humanos atuais, ou até superior. O Homo de Nesher Ramla, encontrado em Israel, pode ter sido o que deu origem aos neandertais e aos denisovanos que ocuparam, respectivamente, a Europa e a Ásia e com quem nossa espécie teve repetidos encontros sexuais, dos quais nasceram filhos mestiços que foram aceitos em suas respectivas tribos como mais um.

Agora sabemos que devido àqueles cruzamentos todas as pessoas de fora da África têm 3% de DNA neandertal, ou que os habitantes do Tibete têm genes transmitidos pelos denisovanos para poder viver em grandes altitudes. Algo muito mais inquietante foi revelado pela análise genética das populações atuais da Nova Guiné: é possível que os denisovanos − um ramo irmão dos neandertais − tenham vivido até apenas 15.000 anos atrás, uma distância muito pequena em termos evolutivos.

A terceira grande descoberta dos últimos dias é quase detetivesca. Na análise de DNA conservado no solo da caverna de Denisova, na Sibéria, foi encontrado material genético dos humanos autóctones, os denisovanos, de neandertais e de sapiens em períodos tão próximos que poderiam até se sobrepor. Lá foram encontrados há três anos os restos do primeiro híbrido entre espécies humanas que se conhece: uma menina filha de uma neandertal e de um denisovano.

O paleoantropólogo Florent Detroit descobriu para a ciência outra dessas novas espécies humanas: o Homo luzonensis, que viveu em uma ilha das Filipinas há 67.000 anos e que apresenta uma estranha mistura de traços que poderiam ser o resultado de sua longa evolução em isolamento durante mais de um milhão de anos. É um pouco parecido com o que experimentou seu contemporâneo Homo floresiensis, ou “homem de Flores”, um humano de um metro e meio que viveu em uma ilha indonésia. Tinha um cérebro do tamanho do de um chimpanzé, mas se for aplicado a ele o teste de inteligência mais usado pelos paleoantropólogos, podemos dizer que era tão avançado quanto o sapiens, pois suas ferramentas de pedra eram igualmente evoluídas.

Imagem radiográfica da mandíbula do ‘Homo’ de Nesher Ramla descoberta em Israel.
Imagem radiográfica da mandíbula do ‘Homo’ de Nesher Ramla descoberta em Israel.Ariel Pokhojaev

A esses dois habitantes insulares se soma o Homo erectus, o primeiro Homo viajante que saiu da África há cerca de dois milhões de anos. Ele conquistou a Ásia e lá viveu até pelo menos 100.000 anos atrás. O oitavo passageiro desta história seria o Homo daliensis, um fóssil encontrado na China com uma mistura de erectus e sapiens, embora seja possível que acabe sendo incluído na nova linhagem do Homo longi.

“Não me surpreende que houvesse várias espécies humanas vivas ao mesmo tempo”, afirma Detroit. “Se considerarmos o último período geológico que começou há 2,5 milhões de anos, sempre houve diferentes gêneros e espécies de hominídeos compartilhando o planeta. A grande exceção é a atualidade, nunca havia existido apenas uma espécie humana na Terra”, reconhece. Por que nós, os sapiens, somos os únicos sobreviventes?

Para Juan Luis Arsuaga, paleoantropólogo do sítio arqueológico de Atapuerca, no norte da Espanha, a resposta é que “somos uma espécie hipersocial, os únicos capazes de construir laços além do parentesco, ao contrário dos demais mamíferos”. “Compartilhamos ficções consensuais como pátria, religião, língua, times de futebol; e chegamos a sacrificar muitas coisas por elas”, assinala. Nem mesmo a espécie humana mais próxima de nós, os neandertais, que criavam adornos, símbolos e arte, tinham esse comportamento. Arsuaga resume assim: “Os neandertais não tinham bandeira”. Por razões ainda desconhecidas, essa espécie se extinguiu há cerca de 40.000 anos.

Os sapiens não eram “estritamente superiores” a seus congêneres, opina Antonio Rosas, paleoantropólogo do Conselho Superior de Pesquisas Científicas da Espanha. “Agora sabemos que somos o resultado de hibridações com outras espécies, e o conjunto de características que temos foi o perfeito para aquele momento”, explica. Uma possível vantagem adicional é que os grupos sapiens eram mais numerosos que os neandertais, o que significa menos endogamia e melhor saúde das populações.

Detroit acredita que parte da explicação está na própria essência da nossa espécie sapiens, “sábio” em latim. “Temos um cérebro enorme que devemos alimentar, por isso precisamos de muitos recursos e, portanto, de muito território”, assinala. “O Homo sapiens teve uma expansão demográfica enorme e é bem possível que a disputa pelo território fosse muito dura para as demais espécies”, acrescenta.

María Martinón-Torres, diretora do Centro Nacional de Pesquisa sobre Evolução Humana, com sede em Burgos, acredita que o segredo seja a “hiperadaptabilidade”. “A nossa é uma espécie invasiva, não necessariamente mal-intencionada, mas somos como o cavalo de Átila da evolução”, compara. “Por onde passamos, e com nosso estilo de vida, diminui a diversidade biológica, incluindo a humana. Somos uma das forças ecológicas de maior impacto do planeta e essa história, a nossa, começou a se delinear no Pleistoceno [o período que começou há 2,5 milhões de anos e terminou há cerca de 10.000, quando o sapiens já era a única espécie humana que restava no planeta]”, acrescenta.

As descobertas dos últimos dias voltam a expor um problema crescente: os cientistas estão denominando cada vez mais espécies humanas. Tem sentido fazer isso? Para o paleoantropólogo israelense Israel Hershkovitz, autor da descoberta do Homo de Nesher Ramla, não. “Há muitas espécies”, afirma. “A definição clássica diz que duas espécies diferentes não podem ter filhos férteis. O DNA nos diz que sapiens, neandertais e denisovanos tiveram, por isso deveriam ser considerados a mesma espécie”, aponta.

“Se somos sapiens, então essas espécies que são nossos ancestrais por meio da miscigenação também são”, reforça João Zilhão, professor da Instituição Catalã de Pesquisa e Estudos Avançados na Universidade de Barcelona.

Essa questão é objeto de discórdia entre especialistas. “A hibridação é muito comum em espécies atuais, especialmente no mundo vegetal”, lembra José María Bermúdez de Castro, codiretor das pesquisas em Atapuerca. “Pode-se matizar o conceito de espécie, mas acho que não podemos abandoná-lo, porque é muito útil para podermos nos entender”, ressalta.

Escavações no sítio arqueológico de Nesher Ramla.
Escavações no sítio arqueológico de Nesher Ramla. Zaidner

Muitas nuances entram em jogo nessa questão. A evidente diferença entre sapiens e neandertais não é a mesma coisa que a identidade como espécie do Homo luzonensis, do qual só conhecemos alguns poucos ossos e dentes, ou dos denisovanos, dos quais a maioria das informações vem do DNA extraído de fósseis minúsculos.

“Curiosamente, apesar dos cruzamentos frequentes, tanto os sapiens como os neandertais foram espécies perfeitamente reconhecíveis e distinguíveis até o fim”, destaca Martinón-Torres. “Os traços do neandertal tardio são mais marcados que os dos anteriores, em vez de terem se apagado como consequência do cruzamento. Houve trocas biológicas, e talvez culturais também, mas nenhuma das espécies deixou de ser ela, distintiva, reconhecível em sua biologia, seu aspecto, suas adaptações específicas, seu nicho ecológico ao longo de sua história evolutiva. Acredito que esse é o melhor exemplo de que a hibridação não colide necessariamente com o conceito de espécie”, conclui. Seu colega Hershkovitz alerta que o debate continuará: “Estamos fazendo escavações em outras três cavernas em Israel onde encontramos fósseis humanos que nos darão uma nova perspectiva sobre a evolução humana”.