Carl Zimmer

The number of birds in the United States and Canada has fallen by 29% since 1970, scientists reported Thursday. There are 2.9 billion fewer birds taking wing now than there were 50 years ago.

The analysis, published in the journal Science, is the most exhaustive and ambitious attempt yet to learn what is happening to avian populations. The results have shocked researchers and conservation organizations.

In a statement Thursday, David Yarnold, president and chief executive of the National Audubon Society, called the findings “a full-blown crisis.”

Experts have long known that some bird species have become vulnerable to extinction. But the new study, based on a broad survey of more than 500 species, reveals steep losses even among such traditionally abundant birds as robins and sparrows.

There are likely many causes, the most important of which include habitat loss and wider use of pesticides. “Silent Spring,” Rachel Carson’s prophetic 1962 book about the harms caused by pesticides, takes its title from the unnatural quiet settling on a world that has lost its birds: “On the mornings that had once throbbed with the dawn chorus of robins, catbirds, doves, jays, wrens, and scores of other bird voices, there was now no sound.”

Kevin Gaston, a conservation biologist at the University of Exeter, said that new findings signal something larger at work: “This is the loss of nature.”

Common bird species are vital to ecosystems, controlling pests, pollinating flowers, spreading seeds and regenerating forests. When these birds disappear, their former habitats often are not the same.

“Declines in your common sparrow or other little brown bird may not receive the same attention as historic losses of bald eagles or sandhill cranes, but they are going to have much more of an impact,” said Hillary Young, a conservation biologist at the University of California, Santa Barbara, who was not involved in the new research.

A team of researchers from universities, government agencies and nonprofit organizations collaborated on the new study, which combined old and new methods for counting birds.

For decades, professional ornithologists have been assisted by an army of devoted amateur bird-watchers who submit their observations to databases and help carry out surveys of bird populations each year.

In the new study, the researchers turned to those surveys to estimate the populations of 529 species between 2006 and 2015.

Those estimates include 76% of all bird species in the United States and Canada, but represent almost the entire population of birds. (The species for which there weren’t enough data to make firm estimates occur only in small numbers.)

The researchers then used bird-watching records to estimate the population of each species since 1970, the earliest year for which there is solid data.

“This approach of combining population abundance estimates across all species and looking for an overall trend is really unprecedented,” said Scott Loss, a conservation biologist at Oklahoma State University who was part of the new study.

While some species grew, the researchers found, the majority declined — often by huge numbers.

“We were stunned by the result — it’s just staggering,” said Kenneth V. Rosenberg, a conservation scientist at Cornell University and the American Bird Conservancy, and lead author of the new study.

“It’s not just these highly threatened birds that we’re afraid are going to go on the endangered species list,” he said. “It’s across the board.”

Weather radar offered another way to track bird populations. Rosenberg and his colleagues counted birds recorded on radar at 143 stations across the United States from 2007 to 2018. They focused on springtime scans, when birds were migrating in great numbers.

The team measured a 14% decline during that period, consistent with the drop recorded in the bird-watching records.

“If we have two data sets showing the same thing, it’s a home run,” said Nicole Michel, a senior quantitative ecologist at the Audubon Society who was not involved in the study.

Among the worst-hit groups were warblers, with a population that dropped by 617 million. There are 440 million fewer blackbirds than there once were.

Rosenberg said he was surprised by how widespread the population drop was. Even starlings — a species that became a fast-breeding pest after its introduction to the United States in 1890 — have dwindled by 83 million birds, a 49% decline.

Europe is experiencing a similar loss of birds, also among common species, said Gaston, of the University of Exeter. “The numbers are broadly comparable,” he said.

The new study was not designed to determine why birds are disappearing, but the results — as well as earlier research — point to some likely culprits, Rosenberg said.

Grassland species have suffered the biggest declines by far, having lost 717 million birds. These birds have probably been decimated by modern agriculture and development.

“Every field that’s plowed under, and every wetland area that’s drained, you lose the birds in that area,” Rosenberg said.

In addition to habitat loss, pesticides may have taken a toll. A study published last week, for example, found that pesticides called neonicotinoids make it harder for birds to put on weight needed for migration, delaying their travel.

The researchers found some positive signs. Bald eagles are thriving, for example, and falcon populations have grown by 33%. Waterfowl are on the upswing.

For the most part, there’s little mystery about how these happy exceptions came to be. Many recovering bird species were nearly wiped out in the last century by pesticides, hunting and other pressures. Conservation measures allowed them to bounce back.

“In those cases, we knew what the causes were and we acted on that,” Rosenberg said. “They’re models of success.”

But some thriving populations are harder to explain.

Tiny warbler-like birds called vireos are booming, with 89 million more birds than in 1970 — a jump of 53%. Yet warblers, which share the same habitats as vireos, have suffered a 37% decline.

“I have no idea why vireos are doing well,” Rosenberg said. “I’d love to do a study of vireos and discover what their secret is.”

The sheer scale of the bird decline meant that stopping it would require immense effort, said Young, of the University of California, Santa Barbara. Habitats must be defended, chemicals restricted, buildings redesigned. “We’re overusing the world, so it’s affecting everything,” she said.

The Audubon Society is calling for protection of bird-rich habitats, such as the Great Lakes and the Colorado River Basin, as well as for upholding the Migratory Bird Treaty Act, which the Trump administration is trying to roll back.

The society and other bird advocacy groups also suggest things that individuals can do. They urge keeping cats inside, so they don’t kill smaller birds. Vast numbers of birds die each year after flying into windows; there are ways to make the glass more visible to them.

To some birders, the study’s findings confirmed a dreaded hunch.

Beverly Gyllenhaal, 62, a retired cookbook author, and her husband, Anders, have spotted 256 species in parks in the eastern United States. But when she visited her mother in North Carolina in recent years, it seemed there weren’t as many birds as she recalled from her childhood there.

And when she talks to people around the United States on her birding travels, many say the same thing. “Oftentimes people will tell you, ‘It’s nothing like it used to be,’” she said.

The estimated losses have left her appalled. “If the cardinals and the blue jays and the sparrows aren’t doing well,” she said, “that’s really scary.”

This article originally appeared in

(Matter)

Birds Are Vanishing From North America

In a laboratory at the Stanford University School of Medicine, the mice are seeing things. And it’s not because they’ve been given drugs.

With new laser technology, scientists have triggered specific hallucinations in mice by switching on a few neurons with beams of light. The researchers reported the results Thursday in the journal Science.

The technique promises to provide clues to how the billions of neurons in the brain make sense of the environment. Eventually the research also may lead to new treatments for psychological disorders, including uncontrollable hallucinations.

“This is spectacular — this is the dream,” said Lindsey Glickfeld, a neuroscientist at Duke University, who was not involved in the new study.

In the early 2000s, Karl Deisseroth, a psychiatrist and neuroscientist at Stanford, and other scientists engineered neurons in the brains of living mice to switch on when exposed to a flash of light. The technique is known as optogenetics.

In the first wave of these experiments, researchers used light to learn how various types of neurons worked. But Deisseroth wanted to be able to pick out any individual cell in the brain and turn it on and off with light.

So he and his colleagues designed a new device: Instead of just bathing a mouse’s brain in light, it allowed the researchers to deliver tiny beams of red light that could strike dozens of individual brain neurons at once.

To try out this new system, Deisseroth and his colleagues focused on the brain’s perception of the visual world. When light enters the eyes — of a mouse or a human — it triggers nerve endings in the retina that send electrical impulses to the rear of the brain.

There, in a region called the visual cortex, neurons quickly detect edges and other patterns, which the brain then assembles into a picture of reality.

The scientists inserted two genes into neurons in the visual cortices of mice. One gene made the neurons sensitive to the red laser light. The other caused neurons to produce a green flash when turned on, letting the researchers track their activity in response to stimuli.

The engineered mice were shown pictures on a monitor. Some were of vertical stripes, others of horizontal stripes. Sometimes the stripes were bright, sometimes fuzzy. The researchers trained the mice to lick a pipe only if they saw vertical stripes. If they performed the test correctly, they were rewarded with a drop of water.

As the mice were shown images, thousands of neurons in their visual cortices flashed green. One population of cells switched on in response to vertical stripes; other neurons flipped on when the mice were shown horizontal ones.

The researchers picked a few dozen neurons from each group to target. They again showed the stripes to the mice, and this time they also fired light at the neurons from the corresponding group. Switching on the correct neurons helped the mice do better at recognizing stripes.

Then the researchers turned off the monitor, leaving the mice in darkness. Now the scientists switched on the neurons for horizontal and vertical stripes, without anything for the rodents to see. The mice responded by licking the pipe, as if they were actually seeing vertical stripes.

Anne Churchland, a neuroscientist at Cold Spring Harbor Laboratory who was not involved in the study, cautioned that this kind of experiment can’t reveal much about a mouse’s inner experience.

“It’s not like a creature can tell you, ‘Oh, wow, I saw a horizontal bar,’ ” she said.

Churchland said that it would take more research to better understand why the mice behaved as they did in response to the flashes of red light. Did they see the horizontal stripes more clearly, or were they less distracted by misleading signals?

One of the most remarkable results from the study came about when Deisseroth and his colleagues narrowed their beams of red light to fewer and fewer neurons. They kept getting the mice to lick the pipe as if they were seeing the vertical stripes.

In the end, the scientists found they could trigger the hallucinations by stimulating as few as two neurons. Thousands of other neurons in the visual cortex would follow the lead of those two cells, flashing green as they became active.

Clusters of neurons in the brain may be tuned so that they’re ready to fire at even a slight stimulus, Deisseroth and his colleagues concluded — like a snowbank poised to become an avalanche.

But it doesn’t take a fancy optogenetic device to make a few neurons fire. Even when they’re not receiving a stimulus, neurons sometimes just fire at random.

That raises a puzzle: If all it takes is two neurons, why are we not hallucinating all the time?

Maybe our brain wiring prevents it, Deisseroth said. When a neuron randomly fires, others may send a signal to quiet down.

Glickfeld speculated that attention may be crucial to triggering the avalanche of neuronal action only at the right times. “Attention allows you to ignore a lot of the background activity,” she said.

Deisseroth hopes to see what other hallucinations he can trigger with light. In other parts of the brain, he might be able to cause mice to perceive more complex images, such as the face of a cat. He might be able to coax neurons to create phantom sounds, or even phantom smells.

As a psychiatrist, Deisseroth has treated patients who have suffered from visual hallucinations. In his role as a neuroscientist, he’d like to find out more about how individual neurons give rise to these images — and how to stop them.

“Now we know where those cells are, what they look like, what their shape is,” he said. “In future work, we can get to know them in much more detail.”

This article originally appeared in <a href="https://www.nytimes.com/2019/07/18/science/mice-brain-hallucinations.html" id="c613659a-2622-3a9f-a1e9-7cd9c83023ea">The New York Times</a>.

Why Are These Mice Hallucinating? Scientists Are in Their Heads

<h1>(Science Times): At 3 o’clock in the afternoon on Sept. 4, 1882, the electrical age began. The Edison Illuminating Co. switched on its Pearl Street power plant, and a network of copper wires came alive, delivering current to a few dozen buildings in the surrounding neighborhood.</h1>

One of those buildings housed The New York Times. As night fell, reporters at The Times gloried in the steady illumination thrown off by Thomas Edison’s electric lamps. “The light was soft, mellow, and grateful to the eye, and it seemed almost like writing by daylight,” they reported in an article the next day.

But nature invented the electrical grid first, it turns out. Even in 1882, thousands of miles of wires were already installed in the ground in the New York region — in meadows, in salt marshes, in muddy river bottoms. They were built by microbes, which used them to shuttle electricity.

Electroactive bacteria were unknown to science until a couple of decades ago. But now that scientists know what to look for, they’re finding this natural electricity across much of the world, even on the ocean floor. It alters entire ecosystems, and may help control the chemistry of the Earth.

“Not to sound too crazy, but we have an electric planet,” said John Stolz, a microbiologist at Duquesne University in Pittsburgh.

In the mid-1980s, Stolz was helping to study a baffling microbe fished out of the Potomac River by his colleague Derek Lovley. The microbe, Geobacter metallireducens, had a bizarre metabolism. “It took me six months to figure out how to grow it in the lab,” said Lovley, now a microbiologist at the University of Massachusetts at Amherst.

Like us, Geobacter feed on carbon compounds. As our cells break down these compounds to generate energy, they strip off free electrons and transfer them to oxygen atoms, producing water molecules. Geobacter couldn’t use oxygen, however, because it lived at the bottom of the Potomac, where the element was in short supply.

Instead, Geobacter transfers its electrons to iron oxide, or rust, Lovley and his colleagues discovered. The process helps turn rust into another iron compound, called magnetite.

The finding left the scientists with a puzzle. We humans draw oxygen into our cells to use it, but Geobacter does not import rust. So the microbe must somehow get the electrons out of its cell body and attach them to rust particles. How?

The researchers struggled for years to find the answer. Stolz eventually turned to other microbes to study. But Lovley soldiered on. Over the years, he and his colleagues have come across Geobacter in many places far beyond the Potomac. They’ve even encountered the bacteria in oil drilled from deep underground. “It’s basically found everywhere,” Lovley said.

In the early 2000s, Lovley’s team discovered that Geobacter could sense rust in its neighborhood. The microbe responded by sprouting hairlike growths.

Maybe each of those growths, known as a pilus, was actually a wire that latched onto the rust, Lovley thought. Electrons could flow from the bacterium down the wire to the receptive rust. “It seemed like a wild idea at the time,” Lovley said.

But he and his team found several clues suggesting that the pilus is indeed a living wire. In one experiment, when Geobacter was prevented from making pili, the bacteria couldn’t turn rust to magnetite. In another, Lovley and his colleagues plucked pili from the bacteria and touched them with an electrified probe. The current swiftly shot down the length of the hairs.

Subsequent research revealed that Geobacter can deploy its wires in different ways to make a living. Not only can it plug directly into rust, it can also plug into other species of microbes.

The partners of Geobacter welcome the incoming flow of electrons. They use the current to power their own chemical reactions, which convert carbon dioxide into methane.

Discoveries like these raised the possibility that other bacteria might be dabbling in electricity. And in recent years, microbiologists have discovered a number of species that do.

“When people are able to dig down at the molecular level, we’re finding major differences in strategy,” said Jeff Gralnick of the University of Minnesota. “Microbes have solved this issue in several different ways.”

In the early 2000s, a Danish microbiologist named Lars Peter Nielsen discovered a very different way to build a microbial wire. He dug up some mud from the Bay of Aarhus and brought it to his lab. Putting probes in the mud, he observed the chemical reactions carried out by its microbes.

“It developed in a very weird direction,” Nielsen recalled.

At the base of the mud, Nielsen observed a buildup of a foul-smelling gas called hydrogen sulfide. That alone was not surprising — microbes in oxygen-free depths can produce huge amounts of hydrogen sulfide. Normally, the gas rises to the surface, where oxygen-breathing bacteria can break most of it down.

But the hydrogen sulfide in the Aarhus mud never made it to the surface. About an inch below the top of the mud, it disappeared; something was destroying it along the way.

After weeks of perplexity, Nielsen woke up one night with an idea. If the bacteria at the bottom of the mud broke hydrogen sulfide without oxygen, they would build up extra electrons. This reaction could only take place if they could get rid of the electrons. Maybe they were delivering them to bacteria at the surface.

“I imagined it could be electric wires, and I could explain all of this,” he said.

So Nielsen and his colleagues looked for wires, and they found them. But the wires in the Aarhus mud were unlike anything previously discovered.

Each wire runs vertically up through the mud, measuring up to 2 inches in length. And each one is made up of thousands of cells stacked on top of each other like a tower of coins. The cells build a protein sleeve around themselves that conducts electricity.

As the bacteria at the bottom break down hydrogen sulfide, they release electrons, which flow upward along the “cable bacteria” to the surface. There, other bacteria — the same kind as on the bottom, but employing a different metabolic reaction — use the electrons to combine oxygen and hydrogen and make water.

Cable bacteria are not unique to Aarhus, it turns out. Nielsen and other researchers have found them — at least six species so far — in many places around the world, including tidal pools, mud flats, fjords, salt marshes, mangroves and sea grass beds.

And cable bacteria grow to astonishing densities. One square inch of sediment may contain as much as eight miles of cables. Nielsen eventually learned to spot cable bacteria with the naked eye. Their wires look like spider silk reflecting the sun.

Electroactive microbes are so abundant, in fact, that researchers now suspect that they have a profound impact on the planet. The bioelectric currents may convert minerals from one form to another, for instance, fostering the growth of a diversity of other species. Some researchers have speculated that electroactive microbes may help regulate the chemistry of both the oceans and the atmosphere.

“To me, it’s a strong reminder of how ready we are to ignore things we cannot imagine,” Nielsen said.

Electroactive Bacteria for Hire

Much about these microbes remains murky, and subject to debate. In April, Nikhil S. Malvankar, a physicist at Yale University, and his colleagues challenged Lovley’s finding that Geobacter use pili as wires.

Their research indicates that bacteria use a different structure to pump electrons. It’s a wire built from building blocks called cytochromes. Individual cytochromes are important for moving electrons around inside cells. But until now no one knew they could be stacked into a conductive wire.

“There never had been a material like this before,” Malvankar said.

Sarah Glaven, a research biologist at the U.S. Naval Research Laboratory who was not involved in the new study, said she found it compelling. “Totally believe it,” she said. “The question is, is it just part of the puzzle?”

It’s possible that Geobacter uses both structures to move electrons, Glaven said. Or maybe one serves a different function, and just happens to conduct electricity in the hands of a scientist.

The answers to such questions matter deeply to scientists, who are tinkering with electroactive bacteria to develop new kinds of technology.

At Cornell University, Buz Barstow and his colleagues are investigating the possibility of wiring bacteria to solar panels. The panels would capture sunlight and generate a stream of electrons. The electrons would stream down microbial wires to a species of bacteria called Shewanella, which would use the energy to convert sugar into fuel.

It’s still a distant dream. For now, Barstow is trying to work out the basic biology by which Shewanella moves electrons from its wires to the molecules it uses for its metabolism. But he is so taken with the elegance of electroactive bacteria that he figures it’s worth a shot. “You’re talking to someone who has drunk the Kool-Aid,” he said.

Other researchers are looking into using these filaments as sensors. For instance, a wristband with embedded wires might monitor people’s health by delivering electric current when it detects chemical changes in sweat. Lovley and his colleagues are genetically engineering Geobacter to add molecular hooks to their pili so they snag certain molecules.

Among the many advantages that living wires may have is that they would be easier on the environment than the man-made kind. “It takes a lot of energy and nasty chemicals to make a lot of those electronic materials, and then none of them are biodegradable,” Lovley said.

Bacteria, by contrast, can build wires from little more than sugar. And when it comes time to throw wires away, they become food for other microbes.

Nielsen, who now directs the Center for Electromicrobiology at the University of Aarhus in Denmark, said he was avoiding the technology rush for now. There is still too much to learn about the microbes themselves. “Once we find out what these wires are made from and how they work,” he said, “a lot of potential applications may show up.”

This article originally appeared in <a href="https://www.nytimes.com/2019/07/01/science/bacteria-microbes-electricity.html" link="null" target="_blank">The New York Times</a>.

One of those buildings housed The New York Times. As night fell, reporters at The Times gloried in the steady illumination thrown off by Thomas Edison’s electric lamps. “The light was soft, mellow, and grateful to the eye, and it seemed almost like writing by daylight,” they reported in an article the next day.

Organically wired through bacteria

A team of scientists reported Wednesday that the fossil belonged to a 160,000-year-old Denisovan, a member of a lineage of mysterious, Neanderthal-like humans that disappeared about 50,000 years ago.

The fossil is the first evidence of this species found outside the Denisova Cave in Siberia, buttressing the theory that these relatives of modern humans once lived across much of central and eastern Asia.

“I’m very excited — we have a Denisovan that’s somewhere else than Denisova,” said Bence Viola, a paleoanthropologist at the University of Toronto who was not involved in the new study. “We’d known about Denisovans for 10 years and hadn’t found them anywhere else.”

The new fossil demonstrates that Denisovans were remarkably hardy, able to endure harsh conditions on the Tibetan plateau, at an elevation of 10,700 feet, with only simple stone tools.

The find also suggests that these Denisovans may have evolved genetic adaptations to high altitudes and that living Tibetans may have inherited those genes thanks to interbreeding between Denisovans and modern humans in prehistoric times.

In the 1970s, Russian researchers began excavating Denisova Cave in Siberia. Over the years, they found a wealth of bones. A few looked like they might have come from humans or an extinct human relative.

Hoping for clues, the archaeologists sent some of the bones to the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, whose experts excel at retrieving DNA from fossils.

Some of the bones contained Neanderthal DNA, it turned out. But in 2010, Max Planck researchers discovered that one finger bone held different genes from an unknown human lineage.

Over the past decade, scientists have discovered more Denisovan teeth and bone fragments, including a chunk of a skull. Denisovans appeared to have lived in the cave, off and on, from 287,000 years ago to about 50,000 years ago.

Judging from their DNA, Denisovans shared a common ancestor with Neanderthals about 400,000 years ago. They interbred with Neanderthals and with our own species. Today, people in East Asia, Australia, the Pacific islands and the Americas all carry some Denisovan DNA.

The spread of Denisovan DNA in living humans strongly suggested that they may have lived throughout East and Southeast Asia. And maybe not just there: This month, a team of researchers argued that a population of Denisovans reached New Guinea and interbred further with modern humans.

But year after year, no one could find a Denisovan fossil outside the Siberian cave.

In 2010, Dongju Zhang, an archaeologist at Lanzhou University in China, began studying the Tibetan jaw, which had been languishing in storage at her institution.

Right away, she could tell it was humanlike — but not human. “We all have chins, but this doesn’t have one,” Zhang said in an interview.

Eventually, she located the cave in Tibet where the jaw had been discovered. Monks at a nearby temple told her they regularly found human remains on their visits.

“They said they were half-bone and half-stone,” Zhang said.

When she and her colleagues made a small excavation in the cave, they found ancient tools, a sign of human occupation.

She emailed photos of the jaw to Jean-Jacques Hublin, a paleoanthropologist at the Max Planck Institute. Intrigued, he traveled to China to examine the fossil, and soon he and Zhang had begun a collaboration with other experts to learn more.

Chuan-Chou Shen and Tsai-Luen Yu of National Taiwan University handled the task of figuring out how old it was. The jaw still had bits of rock stuck to it, and these contained uranium. By measuring the uranium’s decay into thorium, Shen and Yu were able to estimate the bone’s age.

The jaw turned out to be at least 160,000 years old, by far the oldest evidence of humans on the Tibetan plateau. Its antiquity also supported the scientists’ hunch that it did not belong to our own species.

DNA could reveal its true identity. But Qiaomei Fu, a geneticist at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, found that no genetic material had survived.

Fortunately, other biological molecules can be found in fossils. At Max Planck, Frido Welker, a molecular anthropologist, discovered ancient proteins in the jawbone’s teeth.

The proteins were not from modern humans; instead, they were a match to Denisovan DNA from Siberia.

With the new discovery and other recent finds, a picture of the Denisovans has grown clearer. Everything about their heads seems to have been big, from their giant molars to their thick jaws to their massive brain cases. Viola speculated adults may have weighed well over 200 pounds.

“I’d assume they’d be very large and robust individuals,” he said. “These are like football players.”

The discovery of Denisovans living at high altitude is intriguing for another reason: Tibetans today share a special genetic link to Denisovans.

When most people travel to high elevations, they respond to the low level of oxygen by making extra hemoglobin in their red blood cells.

“That’s bad, because it makes your blood thick,” said Emilia Huerta-Sanchez, a population geneticist at Brown University who was not involved in the new study.

But many Tibetans don’t make extra hemoglobin, thanks to an unusual version of a gene they carry called EPAS1. In 2014, Huerta-Sanchez and her colleagues discovered that this unusual gene came from Denisovans.

How did Denisovans end up with a gene that promotes health at high altitudes? And how did it end up becoming so common in Tibetans but so rare in other people?

Until scientists find DNA from Tibetan Denisovans, the history won’t be clear, Huerta-Sanchez said.

“We don’t know the order of events,” she said. “But Denisovans are such a mysterious group that anything we learn is exciting.”

In recent decades, Chinese paleontologists have found a number of puzzling bones that are almost human and are tens or hundreds of thousands of years old.

Researchers now may compare them to the Tibetan jaw and search the fossils for ancient proteins.

“Denisovans are already somewhere in a museum drawer,” Welker predicted. “We just haven’t been able to link them together yet.”

This article originally appeared in <a id="4cd4e87c-3dd4-4916-85d9-c945c5626465" href="https://www.nytimes.com/2019/05/01/science/denisovans-tibet-jawbone-dna.html">The New York Times</a>.

Denisovan Jawbone Discovered in a Cave in Tibet

(Matter): In 1980, a Buddhist monk in Tibet entered a sacred cave to pray. On the floor, he found half of a human jawbone, studded with two teeth.

Denisovan Jawbone discovered in a cave in Tibet

In a cave in the Philippines, scientists have discovered a new branch of the human family tree.

At least 50,000 years ago, an extinct human species lived on what is now the island of Luzon, researchers reported Wednesday. It’s possible that Homo luzonensis, as they’re calling the species, stood less than 3 feet tall.

The discovery adds growing complexity to the story of human evolution. It was not a simple march forward, as it once seemed. Instead, our lineage assumed an exuberant burst of strange forms along the way.

Our species, Homo sapiens, now inhabits a comparatively lonely world.

“The more fossils that people pull out of the ground, the more we realize that the variation that was present in the past far exceeds what we see in us today,” said Matthew Tocheri, a paleoanthropologist at Lakehead University in Canada, who was not involved in the discovery.

In the early 2000s, Armand Salvador Mijares, a graduate student at the University of the Philippines, was digging at Callao Cave, on Luzon, for traces of the first farmers on the Philippines. Soon, he decided to dig a little deeper.

Researchers on the Indonesian island of Flores had discovered the bones of an extraordinary humanlike species about 60,000 years old. The scientists named it Homo floresiensis.

Some features were similar to ours, but in other ways Homo floresiensis more closely resembled other hominins (the term scientists use for modern humans and other species in our lineage).

Homo floresiensis was able to make stone tools, for example. But the adults stood only 3 feet high and had tiny brains. This strange combination led to debates about who, exactly, were their ancestors.

The oldest fossils of hominins, dating back over 6 million years, have all been found in Africa. For millions of years, hominins were short, small-brained, bipedal apes.

Starting about 2.5 million years ago, one lineage of African hominins began to evolve new traits — a flatter face, bigger brains and a taller body, among other features. These hominins were the first known members of our own genus, Homo.

Only later, about 1.8 million years ago, do the first fossils of Homo appear outside of Africa. One common species was Homo erectus, a species that spread to East and Southeast Asia. The youngest Homo erectus fossils, discovered in Indonesia, may be just 143,000 years old.

Our own lineage kept evolving in Africa. Homo sapiens emerged about 300,000 years ago, and only 100,000 years ago did we start leaving the continent. By 50,000 years ago, our species had reached Australia. (Some researchers believe that date should be pushed back to 65,000 years ago.)

One hypothesis, then, is that Homo floresiensis evolved from Homo erectus. So here was the question for Philippine archaeologists: Could hominins have reached Luzon as well as Flores?

“That inspired me to go back and go deep,” Mijares, now a professor at the University of the Philippines, said in an interview.

In 2007, he returned to Callao Cave. As his team dug into the cave floor, the researchers hit a layer of bones. At first, Mijares was disappointed by the fossils, which mostly belonged to deer and other mammals.

But when Philip Piper, an archaeologist at the University of the Philippines, sorted through the finds, he noticed one that resembled a human foot bone. It was small, Mijares said, “and there was something weird about it.” But not much more could be learned from one bone.

In 2011, on another dig, he and his colleagues found more humanlike fossils, including teeth, part of a femur and hand bones. In 2015, they found two more molars, which they dated to at least 50,000 years ago.

All told, the fossils came from three individuals. And they were remarkable.

The teeth had a peculiar shape. Some front teeth had three roots, for example, whereas those of our species usually only have one. And the teeth were tiny.

“These adult teeth are smaller than any hominin known,” said Debbie Argue, a paleoanthropologist at Australian National University not involved in the study. “Could it be that these teeth belonged to adults that were even smaller than Homo floresiensis?”

The researchers did not find enough bones to estimate how tall Homo luzonensis stood. But they do display their own strange mix of traits. One toe bone, for example, looks nearly identical to those of early hominins living in Africa more than 3 million years ago.

“The combination of features is like nothing we have seen before,” said María Martinón-Torres, the director of Spain’s National Research Center on Human Evolution, who was not involved in the new study.

Taken together, Mijares and his colleagues concluded, the evidence pointed to a new species of Homo.

Drawing such a conclusion from a few bones is risky, acknowledged Huw Groucutt, a paleoanthropologist at the Max Planck Institute for Chemical Ecology.

Nevertheless, “I think the argument for a new species does look pretty convincing in this case,” he said.

Homo erectus may have been the ancestor of the tiny hominins on both Flores and Luzon — perhaps swept to the islands by storms, clinging to trees. It may even be possible that Homo luzonensis descended from hominins that came to Luzon hundreds of thousands of years earlier.

Last year, another team of scientists digging in a different cave on Luzon found the bones of a butchered rhinoceros. Near those remains, they also discovered stone tools dating back 700,000 years.

At the very least, the two studies indicate there were hominins on Luzon 700,000 years ago and 50,000 years ago. The question now is whether they belonged to the same population.

“I think it’s likely the same lineage,” said Gert van den Bergh, an archaeologist at the University of Wollongong in Australia and co-author of last year’s study. Over the next several hundred thousand years, he speculated, Homo erectus shrank as it adapted to life on Luzon.

Tocheri disagreed with that interpretation.

“I don’t really buy into the idea that it’s island-dwarfed Homo erectus,” he said. Instead, he suggests, the tiny island hominins had tiny ancestors — perhaps small hominins in Africa that expanded to Asia and wound up on Flores and Luzon, taking refuge from bigger hominins.

“But it begs the question,” Tocheri added. “If we’re finding these things way over there, there’s got to be a record of them all the way across the continent leading back to Africa.”

Sorting through these possibilities will demand more fossils of Homo luzonensis — and perhaps fossils from some of the many islands off the coast of Southeast Asia.

“I see it as an amazing opportunity to see several parallel experiments in human evolution on these islands,” van den Bergh said.

This article originally appeared in <a id="d974b2d1-e1c8-4391-8b54-eb1818ddae6e" href="https://www.nytimes.com/2019/04/10/science/homo-luzonensis-philippines-evolution.html">The New York Times</a>.

(Science Times) ; (Matter)

A new bloom on the tree of humanity

Starting in March 2015, astronaut Scott Kelly spent 340 days aboard the International Space Station. A team of scientists tracked his body’s responses to long-term spaceflight in painstaking detail. They simultaneously tracked his identical twin brother, Mark, on Earth.

On Thursday, the scientists began publishing the huge trove of results from the so-called NASA Twins Study — 90 pages, all told, and that’s just the first installment. Here’s a guide to what they’ve found ... so far.

— Space travel changes the body.

Scientists tracked a huge range of measurements in the NASA Twins Study, from Scott Kelly’s performance on cognition tests to levels of gene activity in his cells. Many of the molecular tests had never been carried out on astronauts before.

The exams required Kelly to draw his own blood and to send fresh samples back to Earth in a Soyuz supply craft. Within 48 hours, researchers were analyzing the samples at NASA labs.

Carl Zimmer

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