Arquivo da tag: Antropologia física

Revolução neandertal (Folha de S.Paulo)

JC e-mail 4907, de 07 de março de 2014

Svante Pääbo, cientista que liderou o mapeamento do genoma do homem de Neandertal, conta em livro sua descoberta que abalou a antropologia

A história de como os humanos deixaram a África e povoaram o resto do mundo tem hoje seu foco em pesquisas sobre o DNA, deixando os fósseis –matéria-prima indispensável da antropologia– meio fora dos holofotes. Há quem questione se essa mudança é benéfica, mas é difícil desvincular essa revolução acadêmica do nome de um cientista: Svante Pääbo.

Em novo livro, o geneticista sueco radicado na Alemanha conta como essa mudança de perspectiva se instalou. Para tal, narra a história de seu principal objetivo científico, o sequenciamento do genoma do homem de Neandertal, a última criatura do gênero Homo a pisar na Terra antes de o Homo sapiens tomar o planeta inteiro para si.

Pääbo é o sujeito magricela que aparece em uma fotografia estampada em vários jornais em 7 de maio de 2010 na qual está olhando para um crânio de neandertal. Naquele dia, quando o cientista publicou a primeira versão do genoma do hominídeo extinto, teorias de evolução humana baseadas apenas na interpretação do formato de fósseis começaram a ter de ser alteradas para acomodar algumas revelações.

Aquela que chamou mais a atenção, sem dúvida, foi a de que H. sapiens e H. neanderthalensis legaram ao planeta os frutos de uma inusitada história de amor. Pessoas de etnias europeias ainda carregam no DNA cerca de 3% de ancestralidade neandertal.

O genoma desse hominídeo e a descoberta subsequente de uma linhagem totalmente nova do gênero Homo –os denisovanos, descritos por Pääbo com base no DNA extraído de um único osso de dedo– mostraram que a saída da África foi um processo bem mais complexo.

Achar DNA em ossos com dezenas de milhares de anos, porém, não era (e não é) coisa trivial. Pääbo, que se descreve como um sujeito paranoico por limpeza (para evitar contaminar amostras), também exigia de si repetir seus experimentos inúmeras vezes, cada vez que obtinha um bom resultado. Não poupa, por isso, criticas às revistas “Science” e “Nature” por terem publicado estudos que considera de baixo padrão.

Com o modesto título “Neanderthal Man”, o livro conta muito mais do que a história do sequenciamento de um genoma. Pääbo começou sua carreira acadêmica patinando entre disciplinas tão distintas quanto egiptologia e bioquímica. Seu ponto de virada foi a extração de DNA de uma múmia egípcia, estudo que realizou escondido de seu orientador de doutorado, usando uma amostra cedida por um museu da Alemanha Oriental. (O curador que cedeu o pedaço de múmia foi depois abordado pela Stasi, a polícia comunista.)

Uma boa parte do livro é dedicada a tecnicalidades de extração de DNA, apesar de as histórias de negociações para obtenção de fósseis serem mais interessantes.

No meio dos trabalhos de sequenciamento do neandertal, Pääbo conta sobre o racha com seu colaborador Ed Rubin, do Laboratório Nacional Lawrence Berkeley, que passou a competir diretamente por amostras de fósseis.

Além de intriga, há também um bocado de romance para o que se espera de um livro de ciência. Abertamente bissexual, Pääbo não se intimida em contar a história de um triângulo amoroso que envolveu sua mulher e outro cientista de seu instituto.

Nada disso, porém, é narrado mais passionalmente do que a epopeia científica do genoma do neandertal, que mudou a noção sobre o que significa ser humano.

(Rafael Garcia/Folha de S.Paulo)
http://www1.folha.uol.com.br/fsp/cienciasaude/155225-revolucao-neandertal.shtml

Humanity’s forgotten return to Africa revealed in DNA (New Scientist)

20:00 03 February 2014 by Catherine Brahic

Call it humanity’s unexpected U-turn. One of the biggest events in the history of our species is the exodus out of Africa some 65,000 years ago, the start ofHomo sapiens‘ long march across the world. Now a study of southern African genes shows that, unexpectedly, another migration took western Eurasian DNA back to the very southern tip of the continent 3000 years ago.

According to conventional thinking, the Khoisan tribes of southern Africa, have lived in near-isolation from the rest of humanity for thousands of years. In fact, the study shows that some of their DNA matches most closely people from modern-day southern Europe, including Spain and Italy.

Because Eurasian people also carry traces of Neanderthal DNA, the finding also shows – for the first time – that genetic material from our extinct cousin may be widespread in African populations.

The Khoisan tribes of southern Africa are hunter-gatherers and pastoralists who speak unique click languages. Their extraordinarily diverse gene pool split from everyone else’s before the African exodus.

Ancient lineages

“These are very special, isolated populations, carrying what are probably the most ancient lineages in human populations today,” says David Reich of Harvard University. “For a lot of our genetic studies we had treated them as groups that had split from all other present-day humans before they had split from each other.”

So he and his colleagues were not expecting to find signs of western Eurasian genes in 32 individuals belonging to a variety of Khoisan tribes. “I think we were shocked,” says Reich.

The unexpected snippets of DNA most resembled sequences from southern Europeans, including Sardinians, Italians and people from the Basque region (see “Back to Africa – but from where?“). Dating methods suggested they made their way into the Khoisan DNA sometime between 900 and 1800 years ago – well before known European contact with southern Africa (see map).

Archaeological and linguistic studies of the region can make sense of the discovery. They suggest that a subset of the Khoisan, known as the Khoe-Kwadi speakers, arrived in southern Africa from east Africa around 2200 years ago. Khoe-Kwadi speakers were – and remain – pastoralists who make their living from herding cows and sheep. The suggestion is that they introduced herding to a region that was otherwise dominated by hunter-gatherers.

Khoe-Kwadi tribes

Reich and his team found that the proportion of Eurasian DNA was highest in Khoe-Kwadi tribes, who have up to 14 per cent of western Eurasian ancestry. What is more, when they looked at the east African tribes from which the Khoe-Kwadi descended, they found a much stronger proportion of Eurasian DNA – up to 50 per cent.

That result confirms a 2012 study by Luca Pagani of the Wellcome Trust Sanger Institute in Hinxton, UK, which found non-African genes in people living in Ethiopia. Both the 2012 study and this week’s new results show that the Eurasian genes made their way into east African genomes around 3000 years ago. About a millennium later, the ancestors of the Khoe-Kwadi headed south, carrying a weaker signal of the Eurasian DNA into southern Africa.

The cultural implications are complex and potentially uncomfortably close to European colonial themes. “I actually am not sure there’s any population that doesn’t have west Eurasian [DNA],” says Reich.

“These populations were always thought to be pristine hunter-gatherers who had not interacted with anyone for millennia,” says Reich’s collaborator, linguist Brigitte Pakendorf of the University of Lyon in France. “Well, no. Just like the rest of the world, Africa had population movements too. There was simply no writing, no Romans or Greeks to document it.”

Twist in tale

There’s one more twist to the tale. In 2010 a research team – including Reich – published the first draft genome of a Neanderthal. Comparisons with living humans revealed traces of Neanderthal DNA in all humans with one notable exception: sub-Saharan peoples like the Yoruba and Khoisan.

That made sense. After early humans migrated out of Africa around 60,000 years ago, they bumped into Neanderthals somewhere in what is now the Middle East. Some got rather cosy with each other. As their descendants spread across the world to Europe, Asia and eventually the Americas, they spread bits of Neanderthal DNA along with their own genes. But because those descendants did not move back into Africa until historical times, most of this continent remained a Neanderthal DNA-free zone.

Or so it seemed at the time. Now it appears that the Back to Africa migration 3000 years ago carried a weak Neanderthal genetic signal deep into the homeland. Indeed one of Reich’s analyses, published last month, found Neanderthal traces in Yoruba DNA (Nature, DOI: 10.1038/nature12886).

In other words, not only is western Eurasian DNA ancestry a global phenomenon, so is having a bit of Neanderthal living on inside you.

Journal reference: PNAS, DOI: 10.1073/pnas.1313787111

Back to Africa – but from where?

Reich and his colleagues found that DNA sequences in the Khoisan people most closely resemble some found in people who today live in southern Europe. That, however, does not mean the migration back to Africa started in Italy or Spain. More likely, the migration began in what is now the Middle East.

We know that southern Europeans can trace their ancestry to the Middle East. However, in the thousands of years since they – and the ancestors of the Khoisan – left the region, it has experienced several waves of immigration. These waves have had a significant effect on the genes of people living in the Middle East today, and and means southern Europeans are much closer to the original inhabitants of the Levant than modern-day Middle Easterners.

Skull Fossil Suggests Simpler Human Lineage (New York Times)

The 1.8-million-year-old skull was found during a dig in the Republic of Georgia. Georgian National Museum

By 

Published: October 17, 2013

After eight years spent studying a 1.8-million-year-old skull uncovered in the Republic of Georgia, scientists have made a discovery that may rewrite the evolutionary history of our human genus Homo.

A Simpler Family Tree?

A skull discovered in the Republic of Georgia may indicate that early species in the genus Homo, right, are actually more closely related members of a single evolutionary lineage.

 

An artist’s rendition of what the original owner of Skull 5 may have looked like.

Skull 5, which was discovered alongside the remains of four other hominids in Dmanisi, Georgia. Courtesy of Guram Bumbiashvili, Georgian National Museum

An aerial view of the Dmanisi excavation site (foreground) and a medieval town. Fernando Javier Urquijo

It would be a simpler story with fewer ancestral species. Early, diverse fossils — those currently recognized as coming from distinct species like Homo habilis, Homo erectus and others — may actually represent variation among members of a single, evolving lineage.

In other words, just as people look different from one another today, so did early hominids look different from one another, and the dissimilarity of the bones they left behind may have fooled scientists into thinking they came from different species.

This was the conclusion reached by an international team of scientists led by David Lordkipanidze, a paleoanthropologist at the Georgian National Museum in Tbilisi, as reported Thursday in the journal Science.

The key to this revelation was a cranium excavated in 2005 and known simply as Skull 5, which scientists described as “the world’s first completely preserved adult hominid skull” of such antiquity. Unlike other Homo fossils, it had a number of primitive features: a long, apelike face, large teeth and a tiny braincase, about one-third the size of that of a modern human being. This confirmed that, contrary to some conjecture, early hominids did not need big brains to make their way out of Africa.

The discovery of Skull 5 alongside the remains of four other hominids at Dmanisi, a site in Georgia rich in material of the earliest hominid travels into Eurasia, gave the scientists an opportunity to compare and contrast the physical traits of ancestors that apparently lived at the same location and around the same time.

Dr. Lordkipanidze and his colleagues said the differences between these fossils were no more pronounced than those between any given five modern humans or five chimpanzees. The hominids who left the fossils, they noted, were quite different from one another but still members of one species.

“Had the braincase and the face of Skull 5 been found as separate fossils at different sites in Africa, they might have been attributed to different species,” a co-author of the journal report, Christoph Zollikofer of the University of Zurich, said in a statement. Such was often the practice of researchers, using variations in traits to define new species.

Although the Dmanisi finds look quite different from one another, Dr. Zollikofer said, the hominids who left them were living at the same time and place, and “so could, in principle, represent a single population of a single species.” He and his Zurich colleague, Marcia Ponce de León, conducted the comparative analysis of the Dmanisi specimens.

“Since we see a similar pattern and range of variation in the African fossil record,” Dr. Zollikofer continued, “it is sensible to assume that there was a single Homo species at that time in Africa.” Moreover, he added, “since the Dmanisi hominids are so similar to the African ones, we further assume that they both represent the same species.”

But what species? Some team members simply call their finds “early Homo.” Others emphasized the strong similarities to Homo erectus, which lived between two million and less than one million years ago. Tim D. White, a paleoanthropologist at the University of California, Berkeley, called it “the most primitive H. erectus yet known,” noting that “it is more similar than any other yet found to early Homo from eastern Africa,” a group of hominids estimated to have lived 2.3 million years ago.

All five of the skulls and skeletal bones were found in underground dens, suggesting grisly scenes from the perilous lives these early Homos led. They resided among carnivores, including saber-toothed cats and an extinct giant cheetah. All five of the individuals had probably been attacked and killed by the carnivores, their carcasses dragged into the dens for the after-hunt feast, with nothing left but dinner scraps for curious fossil hunters.

Dr. White and other scientists not involved in the research hailed the importance of the skull discovery and its implications for understanding early Homo evolution. In an article analyzing the report, Science quoted Ian Tattersall of the American Museum of Natural History in New York as saying that the skull “is undoubtedly one of the most important ever discovered.”

A few scientists quibbled that the skull looks more like Homo habilis or questioned the idea that fossils in Africa all belong to Homo erectus, but there was broad recognition that the new findings were a watershed in the study of evolution. “As the most complete early Homo skull ever found,” Dr. White wrote in an e-mail, “it will become iconic for Dmanisi, for earliest Homo erectus and more broadly for how we became human.”

Dr. White, who has excavated hominid fossils in Ethiopia for years, said he was impressed with “the total evidentiary package from the site that is the really good news story here.” Further, he said, he hoped the discovery would “now focus the debate on evolutionary biology beyond the boring ‘lumpers vs. splitters’ ” — a reference to the tendencies of fossil hunters to either lump new finds into existing species or split them off into new species.

In their report, the Dmanisi researchers said the Skull 5 individual “provides the first evidence that early Homo comprised adult individuals with small brains but body mass, stature and limb proportions reaching the lower range limit of modern variation.”

Skeletal bones associated with the five Dmanisi skulls show that these hominids were short in stature, but that their limbs enabled them to walk long distances as fully upright bipeds. The shape of the small braincase distinguished them from the more primitive Australopithecus genus, which preceded Homo and lived for many centuries with Homo in Africa.

Language and Tool-Making Skills Evolved at the Same Time (Science Daily)

Sep. 3, 2013 — Research by the University of Liverpool has found that the same brain activity is used for language production and making complex tools, supporting the theory that they evolved at the same time.

Three hand axes produced by participants in the experiment. Front, back and side views are shown. (Credit: Image courtesy of University of Liverpool)

Researchers from the University tested the brain activity of 10 expert stone tool makers (flint knappers) as they undertook a stone tool-making task and a standard language test.

Brain blood flow activity measured

They measured the brain blood flow activity of the participants as they performed both tasks using functional Transcranial Doppler Ultrasound (fTCD), commonly used in clinical settings to test patients’ language functions after brain damage or before surgery.

The researchers found that brain patterns for both tasks correlated, suggesting that they both use the same area of the brain. Language and stone tool-making are considered to be unique features of humankind that evolved over millions of years.

Darwin was the first to suggest that tool-use and language may have co-evolved, because they both depend on complex planning and the coordination of actions but until now there has been little evidence to support this.

Dr Georg Meyer, from the University Department of Experimental Psychology, said: “This is the first study of the brain to compare complex stone tool-making directly with language.

Tool use and language co-evolved

“Our study found correlated blood-flow patterns in the first 10 seconds of undertaking both tasks. This suggests that both tasks depend on common brain areas and is consistent with theories that tool-use and language co-evolved and share common processing networks in the brain.”

Dr Natalie Uomini from the University’s Department of Archaeology, Classics & Egyptology, said: “Nobody has been able to measure brain activity in real time while making a stone tool. This is a first for both archaeology and psychology.”

The research was supported by the Leverhulme Trust, the Economic and Social Research Council and the British Academy. It is published in PLOS ONE.

Journal Reference:

  1. Natalie Thaïs Uomini, Georg Friedrich Meyer. Shared Brain Lateralization Patterns in Language and Acheulean Stone Tool Production: A Functional Transcranial Doppler Ultrasound StudyPLoS ONE, 2013; 8 (8): e72693 DOI: 10.1371/journal.pone.0072693

Female Anthropologists Harassed (The Scientist)

[Why the photo of Maasai people? -RT]

A new survey finds a high incidence of sexual harassment and rape among women doing anthropological field work.

By Jef Akst | April 15, 2013

The Maasai tribe in Kenya. WIKIMEDIA, MATT CRYPTO

More than 20 percent of female bioanthropologists who took part in a new survey are victims of “physical sexual harassment or unwanted sexual contact” in the course of their scientific research, primarily at the hand of superior professional colleagues, even their own mentors.

After talking to a friend that had been raped by a colleague, anthropologist Kathryn Clancy of the University of Illinois, Urbana-Champaign decided to look into the matter further.  “It was like a slap in the face to learn that this was happening to my friends,” Clancy told ScienceInsider.

She began posting anonymous stories of sexual harassment, shared with her by her female colleagues, on the Scientific American blog Context and Variation. The stories began to draw comments of other researchers’ harassment stories. “This is definitely not limited to just my discipline,” Clancy told ScienceInsider—nor is it limited to females, she found.

To get a better handle on the frequency with which such harassment occurs, Clancy and colleagues conducted a (still ongoing) online survey, asking scientists to report on their field-work experiences. Preliminary results, presented Saturday (April 13) at the American Association of Physical Anthropologists (AAPA) annual meeting in Knoxville, Tennessee, indicated that about 30 percent of both men and women reported the occurrence of verbal abuse “regularly” or “frequently” at field sites. And 21 percent of women reported having experienced physical sexual harassment or unwanted sexual contact; one out of 23 men also reported such abuse.

Notably, fewer than 20 percent of the reported cases of harassment involved the local community; rather, most of the abuse came from other researchers, primarily those further along in their careers. But why are such experiences so rarely reported?

“Quitting a field site, not completing and publishing research, and/or loss of letters of recommendation can have potent consequences for academic careers,” collaborator Katie Hinde of Harvard University told ScienceInsider. “Taken together, these factors result in a particularly vulnerable population of victims and witnesses powerless to intervene. As a discipline, we need to recognize and remedy that an appreciable non-zero number of our junior colleagues, particularly women, are having to endure harassment and a hostile work environment in order to be scientists.”

What We Learned About Humanity in 2012 (Live Science)

Charles Choi, LiveScience Contributor

Date: 27 December 2012 Time: 10:03 AM ET

A skull of the Red Deer Cave People, possibly a previously unknown human species.Mysterious fossils of what may be a previously unknown human species were uncovered in caves in China. The hominins lived some time between 11,500 and 14,500 years ago, meaning they would have shared the landscape with modern humans when China’s earliest farmer were first appearing. Discovered at what is called Red Deer Cave in southwest China, the hominins have been dubbed the Red Deer Cave People. A skull of the possibly new hominin, shown here. CREDIT: Darren Curnoe. 

The controversial extinct human lineage known as “hobbits” gained a face this year, one of many projects that shed light in 2012 on the history of modern humans and their relatives. Other discoveries include the earliest known controlled use of fire and the possibility that Neanderthals or other extinct human lineages once sailed to the Mediterranean.

Here’s a look at what we learned about ourselves through our ancestors this year.

We’re not alone

A trove of discoveries this year revealed a host of other extinct relatives of modern humans. For instance, researchers unearthed 3.4-million-year-old fossils of a hitherto unknown species that lived about the same time and place as Australopithecus afarensis, a leading candidate for the ancestor of the human lineage. In addition, fossils between 1.78 million and 1.95 million years old discovered in 2007 and 2009 in northern Kenya suggest that at least two extinct human species lived alongside Homo erectus, a direct ancestor of our species. Moreover, fossils only between 11,500 and 14,500 years old hint that a previously unknown type of human called the “Red Deer Cave People” once lived in China.

Bones were not all that scientists revealed about modern humans’ extinct relatives in 2012. For instance, scientists finally put a face on the hobbit, a nickname for a controversial human lineage. Anthropologist Susan Hayes at the University of Wollongong in Australia reconstructed the appearance of the 3-foot (1-meter) tall, 30-year-old female member of the extinct humans officially known as Homo floresiensis, which were first discovered on the remote Indonesian island of Flores in 2003. [Image Gallery: A Real Life ‘Hobbit’]

DNA extracted from a recently discovered extinct human lineage known as the Denisovans — close relatives of Neanderthals — also revealed new details about this group, which once interbred with modern humans. The Denisovan genome that was sequenced belonged to a little girl with dark skin, brown hair and brown eyes, and displayed about 100,000 recent changes in our genome that occurred after the split from the Denisovans. A number of these changes influenced genes linked with brain function and nervous system development, leading to speculation that we may think differently from the Denisovans.

Genetic analysis also suggested the only modern humans whose ancestors did not interbreed with Neanderthals were apparently sub-Saharan Africans. These findings are just one tidbit regarding the closest extinct relatives of modern humans that was revealed this year. Scientists also found that the unusually powerful right arms of Neanderthals might not have been due to a spear-hunting life as was previously suggested, but rather one often spent scraping animal skins for clothes and shelters. Archaeologists also suggested that Neanderthals and other extinct human lineages might have been ancient mariners, venturing to the Mediterranean Islands millennia before researchers think modern humans arrived at the isles.

Humans’ tool use

Ancient artifacts revealed this year also have shown how tool use has helped humanity reshape the world — and perhaps inadvertently reshape humanity as well.

For instance, ash and charred bone, the earliest known evidence of controlled use of fire, reveal that human ancestors may have used fire 1 million years ago, 300,000 years earlier than thought, suggesting that human ancestors as early as Homo erectus may have begun using fire as part of their way of life. Controlled fires and cooked meat may have influenced human brain evolution, allowing our ancestors to evolve to have larger, more calorie-hungry brains and bodies.

Discoveries involving ancient weapons also revealed that humans learned to make and use these tools far earlier than scientists thought. For instance, what may be ancient stone arrowheads or lethal tools for hurling spearssuggest humans innovated relatively advanced weapons about 70,000 years ago, while a University of Toronto-led team of anthropologists found evidence that humans in South Africa used stone-tipped weapons for hunting 500,000 years ago, which is 200,000 years earlier than previously suggested.

Even the seemingly innocuous discovery this year of the first direct signs of cheesemakingfrom 7,500-year-old potsherds from Poland might help reveal how animal milk dramatically shaped the genetics of Europe. Most of the world, including the ancestors of modern Europeans, is lactose intolerant, unable to digest the milk sugar lactose as adults. However, while cheese is a dairy product, it is relatively low in lactose. Transforming milk into a product such as cheese that is friendlier to lactose-intolerant people might have helped promote the development of dairying among the first farmers of Europe. The presence of dairying over many generations may then, in turn, have set the stage for the evolution of lactase tolerance in Europe. As such, while cheese might just seem to be a topping on pizza or a companion to wine, it might have changed Western digestive capabilities.

Other clues regarding the diet of ancient relatives also emerged. For example, 2-million-year-old fossils suggest humans’ immediate ancestor may have lived off a woodland dietof leaves, fruits and bark, instead of a menu based on the open savanna, as other extinct relatives of humanity did. In addition, fragments of a 1.5-million-year-old skull from a child recently found in Tanzania suggest that later members of the human lineage weren’t just occasional carnivores but regular meat eaters, findings that help build the case that meat-eating helped the human lineage evolve large brains.

Humans still evolving

When it comes to the future of humanity, research this year added to accumulating evidence that natural forces of evolution continue to shape humanity. Church records of nearly 6,000 Finns born between 1760 and 1849 showed that despite humans radically altering their environments with behavior such as farming, human patterns of survival and reproduction were comparable with those of other species.

One researcher at Stanford University has even suggested that humans are getting dumber over time, having lost the evolutionary pressure to be smart once we started living in densely populated settlements several millennia ago. However, other scientists dispute this notion, pointing at geniuses such as Stephen Hawking, and suggest that rather than losing our intelligence, people have diversified, resulting in a number of different types of smarts today.

Fluctuating Environment May Have Driven Human Evolution (Science Daily)

Dec. 24, 2012 — A series of rapid environmental changes in East Africa roughly 2 million years ago may be responsible for driving human evolution, according to researchers at Penn State and Rutgers University.

“The landscape early humans were inhabiting transitioned rapidly back and forth between a closed woodland and an open grassland about five to six times during a period of 200,000 years,” said Clayton Magill, graduate student in geosciences at Penn State. “These changes happened very abruptly, with each transition occurring over hundreds to just a few thousand years.”

According to Katherine Freeman, professor of geosciences, Penn State, the current leading hypothesis suggests that evolutionary changes among humans during the period the team investigated were related to a long, steady environmental change or even one big change in climate.

“There is a view this time in Africa was the ‘Great Drying,’ when the environment slowly dried out over 3 million years,” she said. “But our data show that it was not a grand progression towards dry; the environment was highly variable.”

According to Magill, many anthropologists believe that variability of experience can trigger cognitive development.

“Early humans went from having trees available to having only grasses available in just 10 to 100 generations, and their diets would have had to change in response,” he said. “Changes in food availability, food type, or the way you get food can trigger evolutionary mechanisms to deal with those changes. The result can be increased brain size and cognition, changes in locomotion and even social changes — how you interact with others in a group. Our data are consistent with these hypotheses. We show that the environment changed dramatically over a short time, and this variability coincides with an important period in our human evolution when the genus Homo was first established and when there was first evidence of tool use.”

The researchers — including Gail Ashley, professor of earth and planetary sciences, Rutgers University — examined lake sediments from Olduvai Gorge in northern Tanzania. They removed the organic matter that had either washed or was blown into the lake from the surrounding vegetation, microbes and other organisms 2 million years ago from the sediments. In particular, they looked at biomarkers — fossil molecules from ancient organisms — from the waxy coating on plant leaves.

“We looked at leaf waxes because they’re tough, they survive well in the sediment,” said Freeman.

The team used gas chromatography and mass spectrometry to determine the relative abundances of different leaf waxes and the abundance of carbon isotopes for different leaf waxes. The data enabled them to reconstruct the types of vegetation present in the Olduvai Gorge area at very specific time intervals.

The results showed that the environment transitioned rapidly back and forth between a closed woodland and an open grassland.

To find out what caused this rapid transitioning, the researchers used statistical and mathematical models to correlate the changes they saw in the environment with other things that may have been happening at the time, including changes in the Earth’s movement and changes in sea-surface temperatures.

“The orbit of the Earth around the sun slowly changes with time,” said Freeman. “These changes were tied to the local climate at Olduvai Gorge through changes in the monsoon system in Africa. Slight changes in the amount of sunshine changed the intensity of atmospheric circulation and the supply of water. The rain patterns that drive the plant patterns follow this monsoon circulation. We found a correlation between changes in the environment and planetary movement.”

The team also found a correlation between changes in the environment and sea-surface temperature in the tropics.

“We find complementary forcing mechanisms: one is the way Earth orbits, and the other is variation in ocean temperatures surrounding Africa,” Freeman said. The researchers recently published their results in the Proceedings of the National Academy of Sciences along with another paper in the same issue that builds on these findings. The second paper shows that rainfall was greater when there were trees around and less when there was a grassland.

“The research points to the importance of water in an arid landscape like Africa,” said Magill. “The plants are so intimately tied to the water that if you have water shortages, they usually lead to food insecurity.

“Together, these two papers shine light on human evolution because we now have an adaptive perspective. We understand, at least to a first approximation, what kinds of conditions were prevalent in that area and we show that changes in food and water were linked to major evolutionary changes.”

The National Science Foundation funded this research.

*   *   *

How climate shifts in Africa sparked human evolution (MSNBC)

Scientists say landscape transitions may have forced early humans to think on their feet

Image: Nutcracker Man

Nicolle Rager Fuller / NSF. The first specimen of Paranthropus boisei, also called Nutcracker Man, was reported by Mary and Louis Leakey in 1959 from a site in Olduvai Gorge, Tanzania.

By Charles Choi – LiveScience Contributor

updated 12/26/2012 2:16:27 PM ET

At Olduvai Gorge, where excavations helped to confirm Africa was the cradle of humanity, scientists now find the landscape once fluctuated rapidly, likely guiding early human evolution.

These findings suggest that key mental developments within the human lineage may have been linked with a highly variable environment, researchers added.

Olduvai Gorge is a ravine cut into the eastern margin of the Serengeti Plain in northern Tanzania that holds fossils of hominins — members of the human lineage. Excavations at Olduvai Gorge by Louis and Mary Leakey in the mid-1950s helped to establish the African origin of humanity.

The Great Drying? 

To learn more about the roots of humanity, scientists analyzed samples of leaf waxes preserved in lake sediments at Olduvai Gorge, identifying which plants dominated the local environment around 2 million years ago. This was about when Homo erectus, a direct ancestor of modern humans who used relatively advanced stone tools, appeared.

“We looked at leaf waxes, because they’re tough, they survive well in the sediment,” researcher Katherine Freeman, a biogeochemist at Pennsylvania State University, said in a statement.

After four years of work, the researchers focused on carbon isotopes — atoms of the same element with different numbers of neutrons — in the samples, which can reveal what plants reigned over an area. The grasses that dominate savannas engage in a kind of photosynthesis that involves both normal carbon-12 and heavier carbon-13, while trees and shrubs rely on a kind of photosynthesis that prefers carbon-12. (Atoms of carbon-12 each possess six neutrons, while atoms of carbon-13 have seven.)

Scientists had long thought Africa went through a period of gradually increasing dryness — called the Great Drying — over 3 million years, or perhaps one big change in climate that favored the expansion of grasslands across the continent, influencing human evolution. However, the new research instead revealed “strong evidence for dramatic ecosystem changes across the African savanna, in which open grassland landscapes transitioned to closed forests over just hundreds to several thousands of years,” researcher Clayton Magill, a biogeochemist at Pennsylvania State University, told LiveScience. [Know Your Roots? Take Our Human Evolution Quiz]

The researchers discovered that Olduvai Gorge abruptly and routinely fluctuated between dry grasslands and damp forests about five or six times during a period of 200,000 years.

“I was surprised by the magnitude of changes and the rapid pace of the changes we found,” Freeman told LiveScience. “There was a complete restructuring of the ecosystem from grassland to forest and back again, at least based on how we interpret the data. I’ve worked on carbon isotopes my whole career, and I’ve never seen anything like this before.”

Losing water 

The investigators also constructed a highly detailed record of water history in Olduvai Gorge by analyzing hydrogen isotope ratios in plant waxes and other compounds in nearby lake sediments. These findings support the carbon isotope data, suggesting the region experienced fluctuations in aridity, with dry periods dominated by grasslands and wet periods characterized by expanses of woody cover.

“The research points to the importance of water in an arid landscape like Africa,” Magill said in a statement. “The plants are so intimately tied to the water that if you have water shortages, they usually lead to food insecurity.”

The research team’s statistical and mathematical models link the changes they see with other events at the time, such as alterations in the planet’s movement. [50 Amazing Facts About Earth]

“The orbit of the Earth around the sun slowly changes with time,” Freeman said in statement. “These changes were tied to the local climate at Olduvai Gorge through changes in the monsoon system in Africa.”

Earth’s orbit around the sun can vary over time in a number of ways — for instance,Earth’s orbit around the sun can grow more or less circular over time, and Earth’s axis of spin relative to the sun’s equatorial plane can also tilt back and forth. This alters the amount of sunlight Earth receives, energy that drives Earth’s atmosphere.

“Slight changes in the amount of sunshine changed the intensity of atmospheric circulation and the supply of water,” Freeman said. “The rain patterns that drive the plant patterns follow this monsoon circulation. We found a correlation between changes in the environment and planetary movement.”

The team also found links between changes at Olduvai Gorge and sea-surface temperatures in the tropics.

“We find complementary forcing mechanisms — one is the way Earth orbits, and the other is variation in ocean temperatures surrounding Africa,” Freeman said.

These findings now shed light on the environmental shifts the ancestors of modern humans might have had to adapt to in order to survive and thrive.

“Early humans went from having trees available to having only grasses available in just 10 to 100 generations, and their diets would have had to change in response,” Magill said in a statement. “Changes in food availability, food type, or the way you get food can trigger evolutionary mechanisms to deal with those changes. The result can be increased brain size and cognition, changes in locomotion and even social changes — how you interact with others in a group.”

This variability in the environment coincided with a key period in human evolution, “when the genus Homo was first established and when there was first evidence of tool use,” Magill said.

The researchers now hope to examine changes at Olduvai Gorge not just across time but space, which could help shed light on aspects of early human evolution such as foraging patterns.

Magill, Freeman and their colleague Gail Ashley detailed their findings online Dec. 24 in two papers in the Proceedings of the National Academy of Sciences.

Human hands evolved for punching (Discovery News)

Analysis by Jennifer Viegas

Wed Dec 19, 2012 06:16 PM ET

Fist

Credit: iStockPhoto

Human hands evolved so that men could make fists and fight, and not just for manual dexterity, new research finds.

The study, published in the Journal of Experimental Biology, adds to a growing body of evidence that humans are among the most aggressive and violent animals on the planet.

“With the notable exception of bonobos, great apes are a relatively aggressive group of mammals,” lead author David Carrier told Discovery News. “Although some primatologists may argue that chimpanzees are the most aggressive apes, I think the evidence suggests that humans are substantially more violent.”

Carrier points out that while chimpanzees physically batter each other more frequently than humans, rape appears to be less common in chimpanzees, and torture and group-against-group forms of violence, such as slavery, are not documented in the animals.

“Chimpanzees are also known to engage in raiding welfare in which one group largely eliminates a neighboring group, but this is not comparable in scope to the genocide that has characterized human history,” added Carrier, a University of Utah biology professor.

For this latest study, he and co-author Michael Morgan, a medical student, conducted three experiments. First, they analyzed what happened when men, aged from 22 to 50, hit a punching bag as hard as they could. The peak stress delivered to the bag — the force per area — was 1.7 to 3 times greater with a fist strike compared with a slap.

“Because you have higher pressure when hitting with a fist, you are more likely to cause injury to tissue, bones, teeth, eyes and the jaw,” Carrier said.

The second and third experiments determined that buttressing provided by the human fist increases the stiffness of the knuckle joint fourfold. It also doubles the ability of the fingers to transmit punching force, mainly due to the force transferred from the fingers to the thumb when the fist is clenched.

In terms of the size and shape of hand anatomy, the scientists point out that humans could have evolved manual dexterity with longer thumbs, but without the fingers and palms getting shorter.

Gorilla hands are closer in proportion to human hands than are other apes’ hands, but they and no other ape — aside from us — hits with a clenched fist.

The researchers additionally point out that humans use fists during threat displays. There is also a difference in body size between males and females, particularly evident with hands and arms. This, Carrier said, is “consistent with the hand being a weapon.”

Human males tend to be more physically violent than women, with men being ten times more likely to commit homicide than females in the U.S., Carrier said. But the research, nonetheless, applies to women as well.

“The bottom line is that women need to fight and defend themselves too,” Morgan told Discovery News. “Women need to fight off attackers and defend themselves from rape.”

Defending children may even help to explain human hand anatomy, since both men and women are often driven to protect their offspring, in addition to fighting with others over territory, resources and for other reasons.

“It can be argued that modern man exists in a world devoid of the evolutionary and selective pressures to which aggression was a beneficial trait,” Morgan said. “Our aggressive behavior remains, but no longer serves an evolutionary purpose.”

New DNA Analysis Shows Ancient Humans Interbred with Denisovans (Scientific American)

A new high-coverage DNA sequencing method reconstructs the full genome of Denisovans–relatives to both Neandertals and humans–from genetic fragments in a single finger bone

By Katherine Harmon  | Thursday, August 30, 2012

denisovan genome finger boneFRAGMENT OF A FINGER: This replica of the Denisovan finger bone shows just how small of a sample the researchers had to extract DNA from.Image: Image courtesy of Max Planck Institute for Evolutionary Anthropology

Tens of thousands of years ago modern humans crossed paths with the group of hominins known as the Neandertals. Researchers now think they also met another, less-known group called the Denisovans. The only trace that we have found, however, is a single finger bone and two teeth, but those fragments have been enough to cradle wisps of Denisovan DNA across thousands of years inside a Siberian cave. Now a team of scientists has been able to reconstruct their entire genome from these meager fragments. The analysis adds new twists to prevailing notions about archaic human history.

“Denisova is a big surprise,” says John Hawks, a biological anthropologist at the University of Wisconsin–Madison who was not involved in the new research. On its own, a simple finger bone in a cave would have been assumed to belong to a human, Neandertal or other hominin. But when researchers first sequenced a small section of DNA in 2010—a section that covered about 1.9 percent of the genome—they were able to tell that the specimen was neither. “It was the first time a new group of distinct humans was discovered” via genetic analysis rather than by anatomical description, said Svante Pääbo, a researcher at the Max Planck Institute (M.P.I.) for Evolutionary Anthropology in Germany, in a conference call with reporters.

Now Pääbo and his colleagues have devised a new method of genetic analysis that allowed them to reconstruct the entire Denisovan genome with nearly all of the genome sequenced approximately 30 times over akin to what we can do for modern humans. Within this genome, researchers have found clues into not only this group of mysterious hominins, but also our own evolutionary past. Denisovans appear to have been more closely related to Neandertals than to humans, but the evidence also suggests that Denisovans and humans interbred. The new analysis also suggests new ways that early humans may have spread across the globe. The findings were published online August 30 in Science.

Who were the Denisovans?
Unfortunately, the Denisovan genome doesn’t provide many more clues about what this hominin looked like than a pinky bone does. The researchers will only conclude that Denisovans likely had dark skin. They also note that there are alleles “consistent” with those known to call for brown hair and brown eyes. Other than that, they cannot say.

Yet the new genetic analysis does support the hypothesis that Neandertals and Denisovans were more closely related to one another than either was to modern humans. The analysis suggests that the modern human line diverged from what would become the Denisovan line as long as 700,000 years ago—but possibly as recently as 170,000 years ago.

Denisovans also interbred with ancient modern humans, according to Pääbo and his team. Even though the sole fossil specimen was found in the mountains of Siberia, contemporary humans from Melanesia (a region in the South Pacific) seem to be the most likely to harbor Denisovan DNA. The researchers estimate that some 6 percent of contemporary Papuans’ genomes come from Denisovans. Australian aborigines and those from Southeast Asian islands also have traces of Denisovan DNA. This suggests that the two groups might have crossed paths in central Asia and then the modern humans continued on to colonize the islands of Oceania.

Yet contemporary residents of mainland Asia do not seem to posses Denisovian traces in their DNA, a “very curious” fact, Hawks says. “We’re looking at a very interesting population scenario”—one that does not jibe entirely with what we thought we knew about how waves modern human populations migrated into and through Asia and out to Oceania’s islands. This new genetic evidence might indicate that perhaps an early wave of humans moved through Asia, mixed with Denisovans and then relocated to the islands—to be replaced in Asia by later waves of human migrants from Africa. “It’s not totally obvious that that works really well with what we know about the diversity of Asians and Australians,” Hawks says. But further genetic analysis and study should help to clarify these early migrations.

Just as with modern Homo sapiens, the genome of a single individual cannot tell us exactly what genes and traits are specific to all Denisovans. Yet, just one genome can reveal the genetic diversity of an entire population. Each of our genomes contains information about generations far beyond those of our parents and grandparents, said David Reich, a researcher at the Massachusetts Institute of Technology–Harvard University Broad Institute and a co-author on the paper. Scientists can compare and contrast the set of genes on each chromosome—passed down from each parent—and extrapolate this process back through the generations. “You contain a multitude of ancestors within you,” Reich said, borrowing from Walt Whitman.

The new research reveals that the Denisovans had low genetic diversity—just 26 to 33 percent of the genetic diversity of contemporary European or Asian populations. And for the Denisovans, the population on the whole seems to have been very small for hundreds of thousands of years, with relatively little genetic diversity throughout their history.

Curiously, the researchers noted in their paper, the Denisovan population shows “a drastic decline in size at the time when the modern human population began to expand.”

Why were modern humans so successful whereas Denisovans (and Neandertals) went extinct? Pääbo and his co-authors could not resist looking into the genetic factors that might be at work. Some of the key differences, they note, center around brain development and synaptic connectivity. “It makes sense that what pops up is connectivity in the brain,” Pääbo noted. Neandertals had a similar brain size–to-body ratio as we do, so rather than cranial capacity, it might have been underlying neurological differences that could explain why we flourished while they died out, he said.

Hawks counters that it might be a little early to begin drawing conclusions about human brain evolution from genetic comparisons with archaic relatives. Decoding the genetic map of the brain and cognition from a genome is still a long way off, he notes—unraveling skin color is still difficult enough given our current technologies and knowledge.

New sequencing for old DNA
The Denisovan results rely on a new method of genetic analysis developed by paper co-author Matthias Meyer, also of M.P.I. The procedure allows the researchers to sequence the full genome by using single strands of genetic material rather than the typical double strands required. The technique, which they are calling a single-stranded library preparation, involves stripping the genetic material down to individual strands to copy and avoids a purification step, which can lose precious genetic material.

The finger bone—just one disklike phalanx—is so small that it does not contain enough usable carbon for dating, the researchers note. But by counting the number of genetic mutations in a genome and comparing them with other living relatives, such as modern humans and chimpanzees, given assumed rates of mutations since breaking with a last common ancestor, “for the first time you can try to estimate this number into a date and provide molecular dating of the fossil,” Meyer said. With the new resolution, the researchers estimate the age of the bone to 74,000 to 82,000 years ago. But that is a wide window, and previous archaeological estimates for the bone are a bit younger, ranging from 30,000 to 50,000 years old. These genetic estimations are also still in limbo because of ongoing debate about the average rate of genetic mutations over time, which could skew the age. “Nevertheless,” the researchers noted in their paper, “the results suggest that in the future it will be possible to determine dates of fossils based on genome sequences.”

This new sequencing approach can be used for any DNA that is too fragmented to be read well through more traditional methods. Meyer noted that it could come in handy for analysis of both ancient DNA and contemporary forensic evidence, which also often contains only fragments of genetic material.

Hawks is excited about the new sequencing technology. It is also helpful to have a technology developed specifically for the evolutionary field, he notes. “We’re always using the new techniques from other fields, and this is a case where the new technique is developed just for this.”

Hawks himself has heard from the researchers that have worked with the Denisovan samples that “the Denisovan pinky is just extraordinary” in terms of the amount of DNA preserved in it. Most bone fragments would be expected to contain less than 5 percent of the individual’s endogenous DNA, but this fortuitous finger had a surprising 70 percent, the researchers noted in the study. And many Neandertal fragments have been preserved in vastly different states—many are far worse off than this Denisovan finger bone.

The new sequencing approach could also improve our understanding of known specimens and the evolutionary landscape as a whole. “It’s going to increase the yield from other fossils,” Hawks notes. Many of the Neandertal specimens, for example, have only a small fraction of their genome sequenced. “If we can go from 2 percent to the whole genome, that opens up a lot more,” Hawks says. “Going back further in time will be exciting,” he notes, and this new technique should allow us to do that. “There’s a huge race on—it’s exciting.”

The Denisovans might be the first non-Neandertal archaic human to be sequenced, but they are likely not going to be the last. The researchers behind this new study are already at work using the new single-strand sequencing technique to reexamine older specimens. (Meyer said they were working on reassessing old samples but would not specify which specimens they were studying—the mysterious “hobbit” H. floresiensis would be a worthy candidate.) Pääbo suggests Asia as a particularly promising location to look for other Denisovan-like groups. “I would be surprised if there were not other groups to be found there in the future,” he said.

Taking this technique to specimens from Africa is also likely to yield some exciting results, Hawks says. Africa, with its rich human evolutionary history, holds the greatest genetic diversity. The genomes of contemporary pygmy and hunter–gatherer tribes in Africa, for example, have roughly as many differences as do those of European modern humans and Neandertals. So “any ancient specimen that we find in Africa might be as different from us as Neandertals,” Hawks says. “Anything we find from the right place might be another Denisovan.”

Man’s best friends: How animals made us human (New Scientist)

31 May 2011 by Pat Shipman
Magazine issue 2814.

Video: How animals made us human

Our bond with animals goes far deeper than food and companionship: it drove our ancestors to develop tools and language

TRAVEL almost anywhere in the world and you will see something so common that it may not even catch your attention. Wherever there are people, there are animals: animals being walked, herded, fed, watered, bathed, brushed or cuddled. Many, such as dogs, cats and sheep, are domesticated but you will also find people living alongside wild and exotic creatures such as monkeys, wolves and binturongs. Close contact with animals is not confined to one particular culture, geographic region or ethnic group. It is a universal human trait, which suggests that our desire to be with animals is deeply embedded and very ancient.

On the face of it this makes little sense. In the wild, no other mammal adopts individuals from another species; badgers do not tend hares, deer do not nurture baby squirrels, lions do not care for giraffes. And there is a good reason why. Since the ultimate prize in evolution is perpetuating your genes in your offspring and their offspring, caring for an individual from another species is counterproductive and detrimental to your success. Every mouthful of food you give it, every bit of energy you expend keeping it warm (or cool) and safe, is food and energy that does not go to your own kin. Even if pets offer unconditional love, friendship, physical affection and joy, that cannot explain why or how our bond with other species arose in the first place. Who would bring a ferocious predator such a wolf into their home in the hope that thousands of years later it would become a loving family pet?

I am fascinated by this puzzle and as a palaeoanthropologist have tried to understand it by looking to the deep past for the origins of our intimate link with animals. What I found was a long trail, an evolutionary trajectory that I call the animal connection. What’s more, this trail links to three of the most important developments in human evolution: tool-making, language and domestication. If I am correct, our affinity with other species is no mere curiosity. Instead, the animal connection is a hugely significant force that has shaped us and been instrumental in our global spread and success in the world.

The trail begins at least 2.6 million years ago. That is when the first flaked stone tools appear in the archaeological record, at Gona in the Afar region of Ethiopia (Nature, vol 385, p 333). Inventing stone tools is no trivial task. It requires the major intellectual breakthrough of understanding that the apparent properties of an object can be altered. But the prize was great. Those earliest flakes are found in conjunction with fossilised animal bones, some of which bear cut marks. It would appear that from the start our ancestors were using tools to gain access to animal carcasses. Up until then, they had been largely vegetarian, upright apes. Now, instead of evolving the features that make carnivores effective hunters – such as swift locomotion, grasping claws, sharp teeth, great bodily strength and improved senses for hunting – our ancestors created their own adaptation by learning how to turn heavy, blunt stones into small, sharp items equivalent to razor blades and knives. In other words, early humans devised an evolutionary shortcut to becoming a predator.

That had many consequences. On the plus side, eating more highly nutritious meat and fat was a prerequisite to the increase in relative brain size that marks the human lineage. Since meat tends to come in larger packages than leaves, fruits or roots, meat-eaters can spend less time finding and eating food and more on activities such as learning, social interaction, observation of others and inventing more tools. On the minus side, though, preying on animals put our ancestors into direct competition with the other predators that shared their ecosystem. To get the upper hand, they needed more than just tools and that, I believe, is where the animal connection comes in.

Two and a half million years ago, there were 11 true carnivores in Africa. These were the ancestors of today’s lions, cheetahs, leopards and three types of hyena, together with five now extinct species: a long-legged hyena, a wolf-like canid, two sabretooth cats and a “false” sabretooth cat. All but three of these outweighed early humans, so hanging around dead animals would have been a very risky business. The new predator on the savannah would have encountered ferocious competition for prizes such as freshly killed antelope. Still, by 1.7 million years ago, two carnivore species were extinct – perhaps because of the intense competition – and our ancestor had increased enough in size that it outweighed all but four of the remaining carnivores.

Why did our lineage survive when true carnivores were going extinct? Working in social groups certainly helped, but hyenas and lions do the same. Having tools enabled early humans to remove a piece of a dead carcass quickly and take it to safety, too. But I suspect that, above all, the behavioural adaptation that made it possible for our ancestors to compete successfully with true carnivores was the ability to pay very close attention to the habits of both potential prey and potential competitors. Knowledge was power, so we acquired a deep understanding of the minds of other animals.

Out of Africa

Another significant consequence of becoming more predatory was a pressing need to live at lower densities. Prey species are common and often live in large herds. Predators are not, and do not, because they require large territories in which to hunt or they soon exhaust their food supply. The record of the geographic distribution of our ancestors provides more support for my idea that the animal connection has shaped our evolution. From the first appearance of our lineage 6 or 7 million years ago until perhaps 2 million years ago, all hominins were in Africa and nowhere else. Then early humans underwent a dramatic territorial expansion, forced by the demands of their new way of living. They spread out of Africa into Eurasia with remarkable speed, arriving as far east as Indonesia and probably China by about 1.8 million years ago. This was no intentional migration but simply a gradual expansion into new hunting grounds. First, an insight into the minds of other species had secured our success as predators, now that success had driven our expansion across Eurasia.

Throughout the period of these enormous changes in the lifestyle and ecology of our ancestors, gathering, recording and sharing knowledge became more and more advantageous. And the most crucial topic about which our ancestors amassed and exchanged information was animals.

How do I know this? No words or language remain from that time, so I cannot look for them. I can, however, look for symbols – since words are essentially symbolic – and that takes me to the wealth of prehistoric art that appears in Europe, Asia, Africa and Australia, starting about 50,000 years ago. Prehistoric art allows us to eavesdrop on the conversations of our ancestors and see the topic of discussion: animals, their colours, shapes, habits, postures, locomotion and social habits. This focus is even more striking when you consider what else might have been depicted. Pictures of people, social interactions and ceremonies are rare. Plants, water sources and geographic features are even scarcer, though they must have been key to survival. There are no images showing how to build shelters, make fires or create tools. Animal information mattered more than all of these.

The overwhelming predominance of animals in prehistoric art suggests that the animal connection – the evolutionary advantages of observing animals and collecting, compiling and sharing information about them – was a strong impetus to a second important development in human evolution: the development of language and enhanced communication. Of course, more was involved than simply coining words. Famously, vervet monkeys have different cries for eagles, leopards and snakes, but they cannot discuss dangerous-things-that-were-here-yesterday or ask “what ate my sibling?” or wonder if that danger might appear again tomorrow. They communicate with each other and share information, but they do not have language. The magical property of full language is that it is comprised of vocabulary and grammatical rules that can be combined and recombined in an infinite number of ways to convey fine shades of meaning.

Nobody doubts that language proved a major adaptive advantage to our ancestors in developing complex behaviours and sharing information. How it arose, however, remains a mystery. I believe I am the first to propose a continuity between the strong human-animal link that appeared 2.6 million years ago and the origin of language. The complexity and importance of animal-related information spurred early humans to move beyond what their primate cousins could achieve.

As our ancestors became ever more intimately involved with animals, the third and final product of the animal connection appeared. Domestication has long been linked with farming and the keeping of stock animals, an economic and social change from hunting and gathering that is often called the Neolithic revolution. Domestic animals are usually considered as commodities, “walking larders”, reflecting the idea that the basis of the Neolithic revolution was a drive for greater food security.

When I looked at the origins of domestication for clues to its underlying reasons, I found some fundamental flaws in this idea. Instead, my analysis suggests that domestication emerged as a natural progression of our close association with, and understanding of, other species. In other words, it was a product of the animal connection.

Man’s best friend

First, if domestication was about knowing where your next meal was coming from, then the first domesticate ought to have been a food source. It was not. According to a detailed analysis of fossil skulls carried out by Mietje Germonpré of the Royal Belgian Institute of Natural Sciences in Brussels and her colleagues, the earliest known dog skull is 32,000 years old (Journal of Archaeological Science, vol 36, p 473). The results have been greeted with some surprise, since other analyses have suggested dogs were domesticated around 17,000 years ago, but even that means they pre-date any other domesticated animal or plant by about 5000 years (see diagram). Yet dogs are not a good choice if you want a food animal: they are dangerous while being domesticated, being derived from wolves, and worst of all, they eat meat. If the objective of domestication was to have meat to eat, you would never select an animal that eats 2 kilograms of the stuff a day.

A sustainable relationship

My second objection to the idea that animals were domesticated simply for food turns on a paradox. Farming requires hungry people to set aside edible animals or seeds so as to have some to reproduce the following year. My Penn State colleague David Webster explores the idea in a paper due to appear in Current Anthropology. He concludes that it only becomes logical not to eat all you have if the species in question is already well on the way to being domesticated, because only then are you sufficiently familiar with it to know how to benefit from taking the long view. This means for an animal species to become a walking larder, our ancestors must have already spent generations living intimately with it, exerting some degree of control over breeding. Who plans that far in advance for dinner?

Then there’s the clincher. A domestic animal that is slaughtered for food yields little more meat than a wild one that has been hunted, yet requires more management and care. Such a system is not an improvement in food security. Instead, I believe domestication arose for a different reason, one that offsets the costs of husbandry. All domestic animals, and even semi-domesticated ones, offer a wealth of renewable resources that provide ongoing benefits as long as they are alive. They can provide power for hauling, transport and ploughing, wool or fur for warmth and weaving, milk for food, manure for fertiliser, fuel and building material, hunting assistance, protection for the family or home, and a disposal service for refuse and ordure. Domestic animals are also a mobile source of wealth, which can literally propagate itself.

Domestication, more than ever, drew upon our understanding of animals to keep them alive and well. It must have started accidentally and been a protracted reciprocal process of increasing communication that allowed us not just to tame other species but also to permanently change their genomes by selective breeding to enhance or diminish certain traits.

The great benefit for people of this caring relationship was a continuous supply of resources that enabled them to move into previously uninhabitable parts of the world. This next milestone in human evolution would have been impossible without the sort of close observation, accumulated knowledge and improved communication skills that the animal connection started selecting for when our ancestors began hunting at least 2.6 million years ago.

What does it matter if the animal connection is a fundamental and ancient influence on our species? I think it matters a great deal. The human-animal link offers a causal connection that makes sense of three of the most important leaps in our development: the invention of stone tools, the origin of language and the domestication of animals. That makes it a sort of grand unifying theory of human evolution.

And the link is as crucial today as it ever was. The fundamental importance of our relationship with animals explains why interacting with them offers various physical and mental health benefits – and why the annual expenditure on items related to pets and wild animals is so enormous.

Finally, if being with animals has been so instrumental in making humans human, we had best pay attention to this point as we plan for the future. If our species was born of a world rich with animals, can we continue to flourish in one where we have decimated biodiversity?

Pat Shipman is adjunct professor of biological anthropology at Penn State University. Her book The Animal Connection: A new perspective on what makes us human is published by W. W. Norton & Company on 13 June