Archaeology – Page 2 – artdiamondblog.com

Species Shifting Their Range Due to Climate Change May Have Enabled the “Playing Around With Resources” That Invented Farming

(p. D6) In the 1990s, archaeologists largely concluded that farming in the Fertile Crescent began in Jordan and Israel, a region known as the southern Levant. “The model was that everything started there, and then everything spread out from there, including maybe the people,” said Melinda A. Zeder, a senior research scientist at the Smithsonian National Museum of Natural History.

But in recent years, Dr. Zeder and other archaeologists have overturned that consensus. Their research suggests that people were inventing farming at several sites in the Fertile Crescent at roughly the same time. In the Zagros Mountains of Iran, for example, Dr. Zeder and her colleagues have found evidence of the gradual domestication of wild goats over many centuries around 10,000 years ago.

People may have been cultivating plants earlier than believed, too.

In the 1980s, Dani Nadel, then at Hebrew University, and his colleagues excavated a 23,000-year-old site on the shores of the Sea of Galilee known as Ohalo II. It consisted of half a dozen brush huts. Last year, Dr. Nadel co-authored a study showing that one of the huts contained 150,000 charred seeds and fruits, including many types, such as almonds, grapes and olives, that would later become crops. A stone blade found at Ohalo II seemed to have been used as a sickle to harvest cereals. A stone slab was used to grind the seeds. It seems clear the inhabitants were cultivating wild plants long before farming was thought to have begun.

“We got fixated on the very few things we just happened to see preserved in the archaeological record, and we got this false impression that this was an abrupt change,” Dr. Zeder said. “Now we really understand there was this long period where they’re playing around with resources.”

Many scientists have suggested that humans turned to agriculture under duress. Perhaps the climate of the Near East grew harsh, or perhaps the hunter-gatherer population outstripped the supply of wild foods.

But “playing around with resources” is not the sort of thing people do in times of desperation. Instead, Dr. Zeder argues, agriculture came about as climatic changes shifted the ranges of some wild species of plants and animals into the Near East.

Many different groups began experimenting with ways of producing extra food, which eventually enabled them to start a new way of life: settling down in more stable social groups.

For the full story see:

Carl Zimmer. “The First Farmers.” The New York Times (Tuesday, October 18, 2016 [sic]): D1 & D6.

(Note: the online version of the story has the date Oct. 17, 2016 [sic], and has the title “How the First Farmers Changed History.”)

The 2015 study co-authored by Dani Nadel and mentioned above is:

Snir, Ainit, Dani Nadel, Iris Groman-Yaroslavski, Yoel Melamed, Marcelo Sternberg, Ofer Bar-Yosef, and Ehud Weiss. “The Origin of Cultivation and Proto-Weeds, Long before Neolithic Farming.” PLOS ONE 10, no. 7 (July 22, 2015): e0131422.

Common Ritualistic Human Sacrifice Detract from the Myth of the Past as Golden Age

(p. D2) One thing that’s definitely gotten better over time: not as much ritualistic human sacrifice.

. . .

The authors list some run-of-the-mill techniques for human sacrifice, but others they mention are more, let’s say, specific: being crushed under a newly built canoe, or being rolled off the roof of a house and then decapitated.

For the full story see:

Tatiana Schlossberg. “Hierarchies: A Grisly Social Order.” The New York Times (Tuesday, April 5, 2016 [sic]): D2.

(Note: ellipsis added.)

(Note: the online version of the story has the date April 4, 2016 [sic], and has the title “Why Some Societies Practiced Ritual Human Sacrifice.” Where the versions differ, in the passages quoted above I follow the more detailed account in the online version.)

The article quoted above references the following academic article:

Watts, Joseph, Oliver Sheehan, Quentin D. Atkinson, Joseph Bulbulia, and Russell D. Gray. “Ritual Human Sacrifice Promoted and Sustained the Evolution of Stratified Societies.” Nature 532, no. 7598 (April 4, 2016): 228-31.

Observations of Non-Credentialed Citizens Add to “Scientific” Knowledge

(p. D5) In 1811, a 12-year-old girl named Mary Anning discovered a fossil on the beach near her home in southwestern England — the first scientifically identified specimen of an ichthyosaur, a dolphin-like, ocean-dwelling reptile from the time of the dinosaurs. Two centuries later, less than 50 miles away, an 11-year-old girl named Ruby Reynolds found a fossil from another ichthyosaur. It appears to be the largest marine reptile known to science.

Ms. Reynolds, now 15, and her father, Justin Reynolds, have been fossil hunting for 12 years near their home in Braunton, England. On a family outing in May 2020 to the village of Blue Anchor along the estuary of the River Severn, they came across a piece of fossilized bone set on a rock.

“We were both excited as we had never found a piece of fossilized bone as big as this before,” Mr. Reynolds said. His daughter kept searching the beach, he added, “and it wasn’t long before she found another much larger piece of bone.”

They took home the fragments of bone, the largest of which was about eight inches long, and began their research. A 2018 paper provided a hint at what they’d found: In nearby Lilstock, fossil hunters had discovered similar bone fragments, hypothesized to be part of the jaw bone of a massive ichthyosaur that lived roughly 202 million years ago. However, the scientists who’d worked on the Lilstock fossil had deemed that specimen too incomplete to designate a new species.

Mr. Reynolds contacted those researchers: Dean Lomax, at the University of Bristol, and Paul de la Salle, an amateur fossil collector. They joined the Reynolds family on collecting trips in Blue Anchor, digging in the mud with shovels. Ultimately, they found roughly half of a bone that they estimate would have been more than seven feet long when complete.

. . .

Dr. Lomax said that this discovery also highlighted the importance of amateur fossil collectors. “If you have a keen eye, if you have a passion for something like that, you can make discoveries like this,” he said.

Ruby Reynolds said: “I didn’t realize when I first found the piece of ichthyosaur bone how important it was and what it would lead to. I think the role that young people can play in science is to enjoy the journey of exploring as you never know where a discovery may take you.”

For the full story see:

Kate Golembiewski. “Huge Ocean Reptile From Dinosaur Days.” The New York Times (Tuesday, April 30, 2024): D5.

(Note: ellipses added.)

(Note: the online version of the story has the date April 17, 2024, and has the title “An 11-Year-Old Girl’s Fossil Find Is the Largest Known Ocean Reptile.” Where there is a difference in wording between the versions, the passages quoted above follow the online version.)

Lomax co-authored an article with Justin Reynolds and Ruby Reynolds that described and named the huge ocean reptile:

Lomax, Dean R., Paul de la Salle, Marcello Perillo, Justin Reynolds, Ruby Reynolds, and James F. Waldron. “The Last Giants: New Evidence for Giant Late Triassic (Rhaetian) Ichthyosaurs from the UK.” PLOS ONE 19, no. 4 (2024): e0300289.

Humans’ Adaptive, Flexible Intelligence Evolved Where Climate “Change Was Dramatic, Frequent, Unpredictable and Stressful”

(p. C9) In “Origins: How Earth’s History Shaped Human History,” astrobiologist and professor of science communication Lewis Dartnell argues that “there is a clear causal chain taking us from the politics and socio-economic conditions of today, to their roots in historical agricultural systems, and then further back to the geological tapestry of the ground beneath our feet.”

. . .

The final sentence he offers as summation—“The Earth made us”—can be read two ways, capturing the parallel themes of “Origins.”

With emphasis on “us,” it refers to the origin of the genus Homo, a clade of naked apes giving rise to our species, H. sapiens, the greatest biological superpower of all time, one so potent that all others in our genus are extinct. Why did this emergence take place in the cradle of the East African Rift and nowhere else? And why did the arrival of our genus broadly coincide with the onset of high-frequency climatic swings about two million years ago? Mr. Dartnell concludes that this recently uplifted and intricately rifted landscape created a mosaic of habitats dominated by lakes that further amplified the climatic oscillations between dry-wet and hot-cool conditions. Change was dramatic, frequent, unpredictable and stressful. Thus “intelligence” became “the evolutionary solution to the problem of an environment that shifts faster than natural selection can adapt the body . . . driving . . . ever more flexible and intelligent behavior.”

For the full review, see:

Robert M. Thorson. “The Earth and Us.” The Wall Street Journal (Saturday, April 23, 2022 [sic]): C9.

(Note: ellipsis between paragraph, added; ellipses within paragraph, in original.)

(Note: the online version of the review has the date May 9, 2019 [sic], and has the title “‘Origins’ Review: The Earth and Us.”)

The book under review is:

Dartnell, Lewis. Origins: How Earth’s History Shaped Human History. New York: Basic Books, 2019.

9,000 Years Ago 10,000 Humans Lived in the City of Catalhoyuk

The Catalhoyuk section of Four Cities appears germane to the question: how long have humans more or less like us existed on earth? Apparently at least 9,000 years. But only in the last few hundred years have some humans flourished. The bigger question is: what novel economic system has allowed the the flourishers to leapfrog previous humans?

(p. 16) Nine thousand years ago, the people of Catalhoyuk, maybe 10,000 of them, lived in cuboid clay houses packed against one another above the Konya Plain of south-central Turkey. Their dwellings were uniform, suggesting a highly regulated society: one or two rooms, painted in white or with red ocher designs. You exited not via a front door but by climbing a ladder to the roof. Much of life was lived up there: cooking, socializing, ambling along sidewalks that ran across the top of the city.

Let me say that again in case you missed it: This was 9,000 years ago. In terms of human society, that is just an imponderable span of time. The oldest of the books of the Hebrew Bible date to roughly 3,000 years ago; the pyramids of Egypt go back about 5,000 years. These were not prehumans or near relatives. They were like us: complex, organized, alive to meaning and living at a time beyond reckoning.

. . .

At Catalhoyuk, Newitz hangs out with Ruth Tringham of the University of California, Berkeley, who has devoted years to humanizing the remnants of this city of the dim past by focusing on one skeleton, of a woman she has dubbed Dido. Dido replastered her walls regularly, kept her home swept clean, covered the floor in reed mats and decorated the place with art: clay figures of animals and stylized human females. In other words: much like us.

Catalhoyuk was founded by pioneers of urban living. “When the earliest construction began,” Newitz writes, “many people coming to live at Catalhoyuk were only a generation or two removed from nomadism.” It was brand-new, this fixed settlement thing, but it proved remarkably successful. By the time Dido was born, the city was about 600 years old. I’m tempted to repeat a number yet again. Think of the settled, structured history Dido could look back on. As evidence of her awareness of the past, Dido, like everyone else in town, buried her ancestors in her home, beneath her bed. Some were given a special honor: Their skulls sat in niches in the walls. Dido could enjoy the comfort of her forebears’ empty eye sockets following her as she went about her daily chores. In other words: not so much like us.

. . .

Perhaps looking back 9,000 years can yield practical guidance on how to move forward from where we are. For me, the effect of reading “Four Lost Cities” was more meditative. This is a long, long, long ride we are on. Much is beyond our control. Humanity trundles on.

For the full review, see:

Russell Shorto. “In Ruins.” The New York Times Book Review (Sunday, March 14, 2021 [sic]): 14.

(Note: ellipses added.)

(Note: the online version of the review has the date Feb. 25, 2021 [sic], and has the title “Searching for Our Urban Future in the Ruins of the Past.”)

The book under review is:

Newitz, Annalee. Four Lost Cities: A Secret History of the Urban Age. New York: W. W. Norton & Company, 2021.

Iberian Hunter-Gatherers Were More Sophisticated 9,500 Years Ago Than Previously Known

(p. 6) Hunter-gatherer societies on the Iberian Peninsula were making sophisticated baskets with decorative geometric patterns 9,500 years ago, more than 2,000 years earlier than previously thought, researchers in Spain have reported.

. . .

Francisco Martínez-Sevilla, a researcher of prehistory at the University of Alcalá and the lead author of a paper outlining the findings that was published this week in Science Advances, explained that carbon-14 dating tests had been carried out on 76 objects that were found by 19th-century miners in the Cueva de los Murciélagos, a cave in southern Spain.

The objects, including Europe’s oldest pair of sandals, a wooden stick and mace and exquisitely crafted baskets woven from reed and esparto, were previously believed to have been made by Neolithic farmers.

But the carbon-14 testing carried out by Dr. Martínez-Sevilla’s research group, which has recently excavated human remains in the cave, showed that the best-preserved baskets were, in fact, crafted by hunter-gatherer communities in the Mesolithic era, 9,500 years ago. . . .

“My first reaction was, ‘Oh my God, that is not possible,’” Dr. Martínez-Sevilla said in a telephone interview, explaining how the discovery suggested that Mesolithic societies may have been more complex than previously imagined. “When we realized the magnitude of the findings, we published the paper with all the analysis in less than a year.”

For the full story, see:

Rachel Chaundler. “Artifacts Show Hunter-Gatherers Found Time to Weave, Too.” The New York Times, First Section (Sunday, October 1, 2023): 6.

(Note: ellipses added.)

(Note: the online version of the story was updated Oct. 3, 2023, and has the title “Hunter-Gatherers Were Making Baskets 9,500 Years Ago, Researchers Say.”)

The research discussed in the passages quoted above is published in the following academic article:

Martínez-Sevilla, Francisco, Maria Herrero-Otal, María Martín-Seijo, Jonathan Santana, José A. Lozano Rodríguez, Ruth Maicas Ramos, Miriam Cubas, Anna Homs, Rafael M. Martínez Sánchez, Ingrid Bertin, Rosa Barroso Bermejo, Primitiva Bueno Ramírez, Rodrigo de Balbín Behrmann, Antoni Palomo Pérez, Antonio M. Álvarez-Valero, Leonor Peña-Chocarro, Mercedes Murillo-Barroso, Eva Fernández-Domínguez, Manuel Altamirano García, Rubén Pardo Martínez, Mercedes Iriarte Cela, Javier L. Carrasco Rus, Carmen Alfaro Giner, and Raquel Piqué Huerta. “The Earliest Basketry in Southern Europe: Hunter-Gatherer and Farmer Plant-Based Technology in Cueva De Los Murciélagos (Albuñol).” Science Advances 9, no. 39 (2023): eadi3055.

Global Warming “Presents a Fleeting Opportunity for Glacial Archaeologists”

(p. 14) Espen Finstad was trudging through mud in the Jotunheimen mountains of eastern Norway this month when he happened upon a wooden arrow, bound with a pointed tip made of quartzite. Complete with feathers, it was so well-preserved that it looked as if it could have been lost just recently.

. . .

The find, which Mr. Finstad and his colleagues believe belonged to a reindeer hunter in the late Stone Age or early Bronze Age, is among thousands of artifacts and remains that have emerged from melting ice in recent years, as climate change thaws permafrost and glaciers around the world.

. . .

The thaw presents a fleeting opportunity for glacial archaeologists: They must find the historical treasures just as they emerge from the ice and before they are destroyed by the elements.

“We’re sort of in a race against time,” said Lars Holger Pilo, a glacial archaeologist and a colleague of Mr. Finstad’s. . . .

For more than a decade, their team, which runs the Secrets of the Ice project, has scoured mountain passes across the country. . . .

Since then, the team has discovered around 4,000 artifacts and remains, including a 1,000-year-old wooden whisk and Viking mitten, medieval horseshoes, Bronze Age skis and more than 150 arrows.

Similar work is taking place near Anchorage, Alaska, as well as in northeastern Siberia and Mongolia.

Among the most exciting finds have been Yuka, a 39,000-year-old baby Mammoth found in Siberia in 2010, and a 280-million-year-old tree fossil found in Antarctica in 2016. But the most famous of all is Ötzi — a 5,300-year-old iceman found in 1991 by hikers on the northern Italian border with Austria.

For the full story, see:

Livia Albeck-Ripka. “Melting Ice in Norway Reveals Ancient Arrow.” The New York Times, First Section (Sunday, September 24, 2023): 14.

(Note: ellipses added.)

(Note: the online version of the story has the date Sept. 23, 2023, and has the title “Ancient Arrow Is Among Artifacts to Emerge From Norway’s Melting Ice.”)

Stimulant Ephedrine Was Known and Used in Bronze Age

Ephedrine currently has a variety of medical uses, including as a decongestant.

(p. A4) Bronze Age humans have been credited with a number of civilizational advancements: the invention of irrigation, the wheel, writing systems and the ability to forge weapons and tools from the durable metal that lends the era its name.

Now, strands of human hair discovered in an ancient burial cave in Spain suggest another novelty: a proclivity for consuming psychoactive drugs.

. . .

The findings, published Thursday [April 6, 2023] in Scientific Reports of the journal Nature, provide the first direct evidence that ancient Europeans consumed psychoactive drugs much like their pre-Columbian brethren in Mesoamerica, the researchers said.

Elisa Guerra-Doce, the lead author of the study, said researchers were stunned by the results, especially because the cave interiors yielded no detectable signs of the drugs’ presence. A chemical analysis of the hair revealed evidence of three alkaloid substances known to produce altered states of consciousness: ephedrine, atropine and scopolamine.

The compounds themselves are produced by flora native to Minorca. Atropine and scopolamine, powerful hallucinogens, can be found in plants in the nightshade family, among them mandrake, henbane and thorn apple. Ephedrine, a stimulant, can be extracted from joint pine.

“These findings are so singular,” said Ms. Guerra-Doce, an expert in the anthropology of intoxication at the University of Valladolid in Spain. “Sometimes when people think about drugs, they think it’s a modern practice. These results tell a different story.”

. . .

The three compounds have a long history of human use. Ephedrine is a stimulant that provides bursts of energy and mental clarity, and it can stave off sleepiness. Atropine and scopolamine are powerful deliriants that can produce hallucinations and out-of-body experiences.

For the full story, see:

Andrew Jacobs. “Scientists See Bronze Age In New Light: It Was Trippy.” The New York Times (Friday, April 7, 2023): A4.

(Note: ellipses, and bracketed date, added.)

(Note: the online version of the story has the date April 6, 2023, and has the title “Tripping in the Bronze Age.”)

The academic paper mentioned in the passage quoted above is:

Guerra-Doce, E., C. Rihuete-Herrada, R. Micó, R. Risch, V. Lull, and H. M. Niemeyer. “Direct Evidence of the Use of Multiple Drugs in Bronze Age Menorca (Western Mediterranean) from Human Hair Analysis.” Scientific Reports 13, no. 1 (April 6, 2023): article #4782.

Caution in Interpreting Alternative Explanations of Ancient Artifacts

A few weeks ago, an article highlighted the finding of female bones in a burial along with a sword. It was interpreted that the sword belonged to a distinguished female warrior and was interpreted as evidence against patriarchal assumptions.

(p. D1) The epitaph on more than one Roman tombstone read: “A gang of doctors killed me.”

Medical remedies have improved since those times — no more smashed snails, salt-cured weasel flesh or ashes of cremated dogs’ heads — but surgical instruments have changed surprisingly little. Scalpels, needles, tweezers, probes, hooks, chisels and drills are as much part of today’s standard medical tool kit as they were during Rome’s imperial era.

Archaeologists in Hungary recently unearthed a rare and perplexing set of such appliances. The items were found in a necropolis near Jászberény, some 35 miles from Budapest, in two wooden chests and included a forceps, for pulling teeth; a curet, for mixing, measuring and applying medicaments, and three copper-alloy scalpels fitted with detachable steel blades and inlaid with silver in a Roman style. Alongside were the remains of a man presumed to have been a Roman citizen.

The site, seemingly undisturbed for 2,000 years, also yielded a pestle that, judging by the abrasion marks and drug residue, was probably used to grind medicinal herbs. Most unusual were a bone lever, for putting fractures back in place, and the handle of what appears to have been a drill, for trepanning the skull and extracting impacted weaponry from bone.

The instrumentarium, suitable for performing complex operations, provides a glimpse into the advanced medical prac-(p. D4)tices of first-century Romans and how far afield doctors may have journeyed to offer care. “In ancient times, these were comparatively sophisticated tools made of the finest materials,” said Tivadar Vida, director of the Institute of Archaeology at Eötvös Loránd University, or ELTE, in Budapest and leader of the excavation.

Two millenniums ago Jászberény and the county around it were part of the Barbaricum, a vast region that lay beyond the frontiers of the Empire and served as a buffer against possible outside threats. “How could such a well-equipped individual die so far from Rome, in the middle of the Barbaricum,” mused Leventu Samu, a research fellow at ELTE and a member of the team on the dig. “Was he there to heal a prestigious local figure, or was he perhaps accompanying a military movement of the Roman legions?”

. . .

The tool-laden grave was discovered last year at a site where relics from the Copper Age (4500 B.C. to 3500 B.C.) and the Avar period (560 to 790 A.D.) had been found on the surface. A subsequent survey with a magnetometer identified a necropolis of the Avars, a nomadic peoples who succeeded Attila’s Huns. Among the rows of tombs, the researchers uncovered the man’s grave, revealing a skull, leg bones and, at the foot of the body, the chests of metal instruments. “The fact that the deceased was buried with his equipment is perhaps a sign of respect,” Dr. Samu said.

That is not the only possibility. Dr. Baker said that she often cautioned her students about interpreting ancient artifacts, and asked them to consider alternative explanations. What if, she proposed, the medical tools were interred with the so-called physician because he was so bad at his practice that his family and friends wanted to get rid of everything associated with his poor medical skills? “This was a joke,” Dr. Baker said. “But it was intended to make students think about how we jump to quick conclusions about objects we find in burials.”

For the full story, see:

Franz Lidz. “Old Roman Medicine Wasn’t So Pleasant.” The New York Times (Tuesday, June 13, 2023): D1 & D4.

(Note: ellipsis added.)

(Note: the online version of the story also has the date June 13, 2023, and has the title “Scalpel, Forceps, Bone Drill: Modern Medicine in Ancient Rome.”)

Small-Brained Early Humans Buried Their Dead and Used Symbols

(p. A16) Discoveries from a subterranean cave system in South Africa are prompting paleoanthropologists to rethink what makes us human. New findings reveal a small-brained human relative known as Homo naledi buried its dead and carved symbols on walls inside the system. Both these behaviors were previously associated with our species or the big-brained Neanderthals with which we interbred.

“We’re looking at cultural behavior that is very human in a species that has a brain a third the size of ours,” said John Hawks, a University of Wisconsin-Madison paleoanthropologist and co-author of the research released Monday [June 5, 2023], which will soon be published in the journal eLife as reviewed preprints. “It is going against the idea that brain size is what made us human.”

. . .

“We’ve never had a creature that manifested the complexity of us that wasn’t us,” said Lee Berger, a paleoanthropologist and an explorer in residence at National Geographic who co-authored the new research. Homo naledi, he added, is “threatening to the very clearly defined narrative of the rise of human exceptionalism.”

For the full story, see:

Aylin Woodward. “Ape-Size-Brained Relative Upends Theories.” The Wall Street Journal (Tuesday, June 6, 2023): A16.

(Note: ellipsis, and bracketed date, added.)

(Note: the online version of the story was updated June 5, 2023, and has the title “New Homo Naledi Cave Discoveries Upend What We Know About Being Human.”)

The reference to the journal preprint mentioned above is:

Agustin, Fuentes, Kissel Marc, Spikins Penny, Molopyane Keneiloe, Hawks John, and R. Berger Lee. “Burials and Engravings in a Small-Brained Hominin, Homo Naledi, from the Late Pleistocene: Contexts and Evolutionary Implications.” bioRxiv (2023): 2023.06.01.543135.

Homo Sapiens’s Greater Genetic Diversity May Have Allowed Them to Adapt to Climate Change Faster than Neanderthals

(p. D5) Scientists have revealed a surprisingly complex origin of our species, rejecting the long-held argument that modern humans arose from one place in Africa during one period in time.

By analyzing the genomes of 290 living people, researchers concluded that modern humans descended from at least two populations that coexisted in Africa for a million years before merging in several independent events across the continent. The findings were published on Wednesday [May 24, 2023} in Nature.

“There is no single birthplace,” said Eleanor Scerri, an evolutionary archaeologist at the Max Planck Institute for Geoarchaeology in Jena, Germany, who was not involved in the new study. “It really puts a nail in the coffin of that idea.”

. . .

The researchers concluded that as far back as a million years ago, the ancestors of our species existed in two distinct populations. Dr. Henn and her colleagues call them Stem1 and Stem2.

About 600,000 years ago, a small group of humans budded off from Stem1 and went on to become the Neanderthals. But Stem1 endured in Africa for hundreds of thousands of years after that, as did Stem2.

If Stem1 and Stem2 had been entirely separate from each other, they would have accumulated a large number of distinct mutations in their DNA. Instead, Dr. Henn and her colleagues found that they had remained only moderately different — about as distinct as living Europeans and West Africans are today. The scientists concluded that people had moved between Stem1 and Stem2, pairing off to have children and mixing their DNA.

. . .

It’s possible that climate upheavals forced Stem1 and Stem2 people into the same regions, leading them to merge into single groups. Some bands of hunter-gatherers may have had to retreat from the coast as sea levels rose, for example. Some regions of Africa became arid, potentially sending people in search of new homes.

Even after these mergers 120,000 years ago, people with solely Stem1 or solely Stem2 ancestry appear to have survived. The DNA of the Mende people showed that their ancestors had interbred with Stem2 people just 25,000 years ago. “It does suggest to me that Stem2 was somewhere around West Africa,” Dr. Henn said.

. . .

Dr. Scerri speculated that living in a network of mingling populations across Africa might have allowed modern humans to survive while Neanderthals became extinct. In that arrangement, our ancestors could hold onto more genetic diversity, which in turn might have helped them endure shifts in the climate, or even evolve new adaptations.

“This diversity at the root of our species may have been ultimately the key to our success,” Dr. Scerri said.