2021 research reinforced that mating across groups drove human evolution

Evidence that cross-continental Stone Age networking events powered human evolution ramped up in 2021.

A long-standing argument that Homo sapiens originated in East Africa before moving elsewhere and replacing Eurasian Homo species such as Neandertals has come under increasing fire over the last decade. Research this year supported an alternative scenario in which H. sapiens evolved across vast geographic expanses, first within Africa and later outside it.

The process would have worked as follows: Many Homo groups lived during a period known as the Middle Pleistocene, about 789,000 to 130,000 years ago, and were too closely related to have been distinct species. These groups would have occasionally mated with each other while traveling through Africa, Asia and Europe. A variety of skeletal variations on a human theme emerged among far-flung communities. Human anatomy and DNA today include remnants of that complex networking legacy, proponents of this scenario say.

It’s not clear precisely how often or when during this period groups may have mixed and mingled. But in this framework, no clear genetic or physical dividing line separated Middle Pleistocene folks usually classed as H. sapiens from Neandertals, Denisovans and other ancient Homo populations.
“Middle Pleistocene Homo groups were humans,” says paleoanthropologist John Hawks of the University of Wisconsin–Madison. “Today’s humans are a remix of those ancient ancestors.”

New fossil evidence in line with that idea came from Israel. Braincase pieces and a lower jaw containing a molar tooth unearthed at a site called Nesher Ramla date to between about 140,000 and 120,000 years ago. These finds’ features suggest that a previously unknown Eurasian Homo population lived at the site (SN Online: 6/24/21), a team led by paleoanthropologist Israel Hershkovitz of Tel Aviv University reported. The fossils were found with stone tools that look like those fashioned around the same time by Middle Easterners typically classified as H. sapiens, suggesting that the two groups culturally mingled and possibly mated.

Interactions like these may have facilitated enough mating among mobile Homo populations to prevent Nesher Ramla inhabitants and other Eurasian groups from evolving into separate species, Hershkovitz proposed.

But another report provided a reminder that opinions still vary about whether Middle Pleistocene Homo evolution featured related populations that all belonged to the same species or distinct species. Researchers studying the unusual mix of features of a roughly 146,000-year-old Chinese skull dubbed it a new species, Homo longi (SN Online: 6/25/21). After reviewing that claim, however, another investigator grouped the skull, nicknamed Dragon Man, with several other Middle Pleistocene Homo fossils from northern China.

If so, Dragon Man — like Nesher Ramla Homo — may hail from one of many closely related Homo lines that occasionally mated with each other as some groups moved through Asia, Africa and Europe. From this perspective, Middle Pleistocene Homo groups evolved unique traits during periods of isolation and shared features as a result of crossing paths and mating.
Back-and-forth migrations by Homo groups between Africa and Asia started at least 400,000 years ago, discoveries in Saudi Arabia suggest (SN: 10/9/21 & 10/23/21, p. 7). Monsoon rains periodically turned what’s now desert into a green passageway covered by lakes, wetlands and rivers, reported archaeologist Huw Groucutt of the Max Planck Institute for the Science of Human History in Jena, Germany, and colleagues. Each of five ancient lake beds identified at a Saudi site once hosted hunter-gatherers who left behind stone tools.

Occupations occurred intermittently between about 400,000 and 55,000 years ago. By about 200,000 years ago, stone tools at one of the lake beds resembled those made around the same time by H. sapiens in northeastern Africa. Some of those Africans may have stopped for a bit in a green Arabia before trekking into southwestern Asia, Groucutt suggests.

Either H. sapiens or Neandertals made stone tools unearthed in the youngest lake bed. Neandertals inhabited parts of the Middle East by around 70,000 years ago and could have reached a well-watered Arabia by 55,000 years ago. If that’s what happened, Neandertals may have mated with H. sapiens already there, Groucutt speculates.

Although Arabian hookups have yet to be detected in ancient DNA, European Neandertals and H. sapiens mated surprisingly often around 45,000 years ago (SN: 5/8/21 & 5/22/21, p. 7), other scientists reported. DNA extracted from H. sapiens fossils of that age found in Bulgaria and the Czech Republic indicates that these ancient individuals possessed between about 2 percent and 4 percent Neandertal ancestry, a large amount considering H. sapiens migrants had only recently arrived in Europe.

So even after the Middle Pleistocene, networking among ancient Homo groups may have helped make us who we are today.

How AI can help forecast how much Arctic sea ice will shrink

In the next week or so, the sea ice floating atop the Arctic Ocean will shrink to its smallest size this year, as summer-warmed waters eat away at the ice’s submerged edges.

Record lows for sea ice levels will probably not be broken this year, scientists say. In 2020, the ice covered 3.74 million square kilometers of the Arctic at its lowest point, coming nail-bitingly close to an all-time record low. Currently, sea ice is present in just under 5 million square kilometers of Arctic waters, putting it on track to become the 10th-lowest extent of sea ice in the area since satellite record keeping began in 1979. It’s an unexpected finish considering that in early summer, sea ice hit a record low for that time of year.

The surprise comes in part because the best current statistical- and physics-based forecasting tools can closely predict sea ice extent only a few weeks in advance, but the accuracy of long-range forecasts falters. Now, a new tool that uses artificial intelligence to create sea ice forecasts promises to boost their accuracy — and can do the analysis relatively quickly, researchers report August 26 in Nature Communications.

IceNet, a sea ice forecasting system developed by the British Antarctic Survey, or BAS, is “95 percent accurate in forecasting sea ice two months ahead — higher than the leading physics-based model SEAS5 — while running 2,000 times faster,” says Tom Andersson, a data scientist with BAS’s Artificial Intelligence lab. Whereas SEAS5 takes about six hours on a supercomputer to produce a forecast, IceNet can do the same in less than 10 seconds on a laptop. The system also shows a surprising ability to predict anomalous ice events — unusual highs or lows — up to four months in advance, Andersson and his colleagues found.
Tracking sea ice is crucial to keeping tabs on the impacts of climate change. While that’s more of a long game, the advanced notice provided by IceNet could have more immediate benefits, too. For instance, it could give scientists the lead time needed to assess, and plan for, the risks of Arctic fires or wildlife-human conflicts, and it could provide data that Indigenous communities need to make economic and environmental decisions.

Arctic sea ice extent has steadily declined in all seasons since satellite records began in 1979 (SN: 9/25/19). Scientists have been trying to improve sea ice forecasts for decades, but success has proved elusive. “Forecasting sea ice is really hard because sea ice interacts in complex ways with the atmosphere above and ocean below,” Andersson says.
Existing forecast tools put the laws of physics into computer code to predict how sea ice will change in the future. But partly due to uncertainties in the physical systems governing sea ice, these models struggle to produce accurate long-range forecasts.

Using a process called deep learning, Andersson and his colleagues loaded observational sea ice data from 1979 to 2011 and climate simulations covering 1850 to 2100 to train IceNet how to predict the state of future sea ice by processing the data from the past.

To determine the accuracy of its forecasts, the team compared IceNet’s outputs to the observed sea ice extent from 2012 to 2020, and to the forecasts made by SEAS5, the widely cited tool used by the European Centre for Medium-Range Weather Forecasts. IceNet was as much as 2.9 percent more accurate than SEAS5, corresponding to a further 360,000 square kilometers of ocean being correctly labeled as “ice” or “no ice.”

What’s more, in 2012, a sudden crash in summer sea ice extent heralded a new record low extent in September of that year. In running through past data, IceNet saw the dip coming months in advance. SEAS5 had inklings too but its projections that far out were off by a few hundred thousand square kilometers.

“This is a significant step forward in sea ice forecasting, boosting our ability to produce accurate forecasts that were typically not thought possible and run them thousands of times faster,” says Andersson. He believes it’s possible that IceNet has better learned the physical processes that determine the evolution of sea ice from the training data while physics-based models still struggle to understand this information.

“These machine learning techniques have only begun contributing to [forecasting] in the last couple years, and they’ve been doing amazingly well,” says Uma Bhatt, an atmospheric scientist at the University of Alaska Fairbanks Geophysical Institute who was not involved in the new study. She also leads the Sea Ice Prediction Network, a group of multidisciplinary scientists working to improve forecasting.

Bhatt says that good seasonal ice forecasts are important for assessing the risk of Arctic wildfires, which are tied strongly to the presence of sea ice (SN: 6/23/20). “Knowing where the sea ice is going to be in the spring could potentially help you figure out where you’re likely to have fires — in Siberia, for example, as soon as the sea ice moves away from the shore, the land can warm up very quickly and help set the stage for a bad fire season.”

Any improvement in sea ice forecasting can also help economic, safety and environmental planning in northern and Indigenous communities. For example, tens of thousands of walruses haul out on land to rest when the sea ice disappears (SN: 10/2/14). Human disturbances can trigger deadly stampedes and lead to high walrus mortality. With seasonal ice forecasts, biologists can anticipate rapid ice loss and manage haul-out sites in advance by limiting human access to those locations.

Still, limitations remain. At four months of lead time, the system was about 91 percent accurate in predicting the location of September’s ice edge.IceNet, like other forecasting systems, struggles to produce accurate long-range forecasts for late summer due, in part, to what scientists call the “spring predictability barrier.” It’s crucial to know the condition of the sea ice at the start of the spring melting season to be able to forecast end-of-summer conditions.

Another limit is “the fact that the weather is so variable,” says Mark Serreze, director of the National Snow and Ice Data Center in Boulder, Colo. Though sea ice seemed primed to set a new annual record low at the start of July, the speed of ice loss ultimately slowed due to cool atmospheric temperatures. “We know that sea ice responds very strongly to summer weather patterns, but we can’t get good weather predictions. Weather predictability is about 10 days in advance.”

A blood test may help predict recovery from traumatic brain injury

Elevated blood levels of a specific protein may help scientists predict who has a better chance of bouncing back from a traumatic brain injury.

The protein, called neurofilament light or NfL for short, lends structural support to axons, the tendrils that send messages between brain cells. Levels of NfL peak on average at 10 times the typical level 20 days after injury and stay above normal a year later, researchers report September 29 in Science Translational Medicine. The higher the peak NfL blood concentrations after injury, the tougher the recovery for people with TBI six and 12 months later, shows the study of 197 people treated at eight trauma centers across Europe for moderate to severe TBI.

Brain scans of 146 participants revealed that their peak NfL concentrations predicted the extent of brain shrinkage after six months, and axon damage at six and 12 months after injury, neurologist Neil Graham of Imperial College London and his colleagues found.

These researchers also had a unique opportunity to check that the blood biomarker, which gives indirect clues about the brain injury, actually measured what was happening in the brain. In 18 of the participants that needed brain surgery, researchers sampled the fluid surrounding injured neurons. NfL concentrations there correlated with NfL concentrations in the blood.
“The work shows that a new ultrasensitive blood test can be used to accurately diagnose traumatic brain injury,” says Graham. “This blood test can predict quite precisely who’s going to make a good recovery and who’s going to have more difficulties.”

Study participants were adults and mostly male, so more work needs to be done to determine if these findings apply to women, children and people with mild TBI.

Finding a reliable biomarker for the severity and outlook of TBI, a head injury that disrupts brain function, could improve millions of lives. Studies of U.S. football players have brought attention to the injury (SN: 12/13/17), but it’s a far more widespread problem. Around 55 million people globally were living with a TBI in 2016, and there’s no one-size-fits-all treatment.

“No two traumatic brain injuries are alike,” says David Okonkwo, director of the Neurotrauma Clinical Trials Center at the University of Pittsburgh. Scientists have been looking for biomarkers of TBI injury such as NfL to develop injury-specific interventions, and Okonkwo says these new findings are promising for patients whose injury has damaged their axons.

“We have not had the tools to measure a specific injury type of an individual patient,” Okonkwo says. While this test probably is still a few years from use in U.S. clinics, other large research groups are looking for ways to use NfL and other blood-based biomarkers for diagnosing TBI and creating opportunities for intervention.

Astrophysicist writes about the stars for Spanish speakers

Paula Jofré
Astrophysicist
Universidad Diego Portales

Paula Jofré, featured in 2018, used the chemical composition of stars across the Milky Way like DNA to map the stars’ family tree. She recently filled in some details of the tree — and is filling a gap in the publishing world by writing a book about stars in Spanish.

What progress have you made on your stellar family tree?
In the first paper, the tree had three main branches. There was one that we could associate with a young thin disk, which is one of the populations in the Milky Way. Another was associated with an old, thick disk, which was the older component of the Milky Way. And then we had something in between…. Now, because we had more stars and more chemical elements and we made a better selection of which chemical elements to include, we could find that this strange population was actually an ancestor population of the thin disk. And one of the interpretations we had in the second paper [published in January in the Monthly Notices of the Royal Astronomical Society] was that they were produced all very quickly.

Other groups have found striking evidence of a galaxy that was merged into the Milky Way [billions of years ago]. And that [merging and mixing of gas] could have triggered what is called a star formation burst — lots of stars [forming] at the same time. So, it’s kind of exciting that we find in the tree a feature that could be attributed to a star formation burst … a few gigayears after the [merger of these two galaxies] that we know happened.

You’re also writing a popular book on stars. Can you tell me more about the book, Fósiles del cosmos: descifrando la historia de la Vía Láctea, or Fossils of the Cosmos: Deciphering the History of the Milky Way, and why you decided to write it?
It’s going to be published in November [in Chile]. It’s a book in Spanish for the public. I am teaching a class about stars in the Milky Way, a general astronomy class. And I’ve been finding that there is no proper literature in Spanish for the students.… The level is sometimes way too basic or too complex. So I wanted to write something for their level.

[The book] explains how stars create the chemical elements, what’s the role of Gaia [a satellite mission to map the galaxy], what’s the role of the Milky Way Mapper [another survey using Earth-based telescopes], about all these big surveys, why we care, what’s going on.

When I started writing it, of course, I started reading other books…. In all these general astronomy books, women are never highlighted. In my book, I have lots of quotes from 40 different women all around the world, working in my field.… I want to make the point that you can be a woman, you can be clever, you can dedicate yourself to something that is mentally challenging. You can be like any of these 40 women.

What’s the greatest challenge that you’ve faced since 2018?
The biggest challenge has been to promote hiring more women at the faculty level. Chile’s a very small country and they love new figures, young figures being highlighted by the United States. The moment I was in Science News,I became very popular [in Chile] very quickly. They needed the inspirational woman. And I kept saying, “I don’t want to be the only one. I want more women.”

I don’t know if you were aware of this collective Las Tesis; they made a dance for the social unrest that we had in Chile before the pandemic. It was a feminist movement that resonated for so many people in the world. The movement [says]: We want to be treated with respect, we want the same salary, we want the same opportunities, we want to feel safe on the streets.… But then, when you are fewer in academia, you’re not going to start jumping on the table and dancing, right? You have to argue … it’s difficult.

— Interview by Ashley Braun

Pluto’s dark side reveals clues to its atmosphere and frost cycles

Pluto’s dark side has come into dim view, thanks to the light of the dwarf planet’s moon.

When NASA’s New Horizons spacecraft flew past Pluto in 2015, almost all the images of the dwarf planet’s unexpectedly complex surface were of the side illuminated by the sun (SN: 7/15/15). Darkness shrouded the dwarf planet’s other hemisphere. Some of it, like the area near the south pole, hadn’t seen the sun for decades.

Now, mission scientists have finally released a grainy view of the dwarf planet’s dark side. The researchers describe the process to take the photo and what it tells them about how Pluto’s nitrogen cycle affects its atmosphere October 20 in the Planetary Science Journal.

Before New Horizons passed by Pluto, the team suspected the dwarf planet’s largest moon, Charon, might reflect enough light to illuminate the distant world’s surface. So the researchers had the spacecraft turn back toward the sun to take a parting peek at Pluto.
At first, the images just showed a ring of sunlight filtering through Pluto’s hazy atmosphere (SN: 7/24/15). “It’s very hard to see anything in that glare,” says planetary scientist John Spencer of the Southwest Research Institute in Boulder, Colo. “It’s like trying to read a street sign when you’re driving toward the setting sun and you have a dirty windshield.”

Spencer and colleagues took a few steps to make it possible to pull details of Pluto’s dark side out of the glare. First, the team had the spacecraft take 360 short snapshots of the backlit dwarf planet. Each was about 0.4 seconds long, to avoid overexposing the images. The team also took snapshots of the sun without Pluto in the frame so that the sun could be subtracted out after the fact.

Tod Lauer of the National Optical Astronomy Observatory in Tucson, Ariz., tried to process the images when he got the data in 2016. At the time, the rest of the data from New Horizons was still fresh and took up most of his attention, so he didn’t have the time to tackle such a tricky project.

But “it was something that just sat there and ate away at me,” Lauer says. He tried again in 2019. Because the spacecraft was moving as it took the images, each image was a little bit smeared or blurred. Lauer wrote a computer code to remove that blur from each individual frame. Then he added the reflected Charon light in each of those hundreds of images together to produce a single image.
“When Tod did that painstaking analysis, we finally saw something emerging in the dark there … giving us a little bit of a glimpse of what the dark pole of Pluto looks like,” Spencer says.

That the team got anything at all is impressive, says planetary scientist Carly Howett, also of the Southwest Research Institute and who is on the New Horizons team but was not involved in this work. “This dataset is really, really hard to work with,” she says. “Kudos to this team. I wouldn’t have wanted to do this.”

The image, Howett says, can help scientists understand how Pluto’s frigid nitrogen atmosphere varies with its decades-long seasons. Pluto’s atmosphere is controlled by how much nitrogen is in a gas phase in the air and how much is frozen on the surface. The more nitrogen ice that evaporates, the thicker the atmosphere becomes. If too much nitrogen freezes to the ground, the atmosphere could collapse altogether.
When New Horizons was there, Pluto’s south pole looked darker than the north pole. That suggests there was not a lot of fresh nitrogen frost freezing out of the atmosphere there, even though it was nearing winter. “The previous summer ended decades ago, but Pluto cools off pretty slowly,” Spencer says. “Maybe it’s still so warm [that] the frost can’t condense there, and that keeps the atmosphere from collapsing.”

There was a bright spot in the middle of the image, which could be a fresh ice deposit. That’s also not surprising, Howett says. The ices may still be moving from the north pole to the south pole as Pluto moves deeper into its wintertime.

“We’ve thought this for a long time. It makes sense,” she says. “But it’s nice to see it happening.”

This eco-friendly glitter gets its color from plants, not plastic

All that glitters is not green. Glitter and shimmery pigments are often made using toxic compounds or pollutive microplastics (SN: 4/15/19). That makes the sparkly stuff, notoriously difficult to clean up in the house, a scourge on the environment too.

A new, nontoxic, biodegradable alternative could change that. In the material, cellulose — the main building block of plant cell walls — creates nanoscale patterns that give rise to vibrant structural colors (SN: 9/28/21). Such a material could be used to make eco-friendly glitter and shiny pigments for paints, cosmetics or packaging, researchers report November 11 in Nature Materials.

The inspiration to harness cellulose came from the African plant Pollia condensata, which produces bright, iridescent blue fruits called marble berries. Tiny patterns of cellulose fibers in the berries’ cell walls reflect specific wavelengths of light to create the signature hue. “I thought, if the plants can make it, we should be able to make it,” says chemist Silvia Vignolini of the University of Cambridge.

Vignolini and colleagues whipped up a watery mixture containing cellulose fibers and poured it onto plastic. As the liquid dried into a film, the rodlike fibers settled into helical structures resembling spiral staircases. Tweaking factors such as the steepness of those staircases changed which wavelengths of light the cellulose arrangements reflected, and therefore the color of the film.

That allowed the researchers, like fairy-tale characters spinning straw into gold, to transform their clear, plant-based slurry into meter-long shimmery ribbons in a rainbow of colors. These swaths could then be peeled off their plastic platform and ground up to make glitter.
“You can use any type of cellulose,” Vignolini says. Her team used cellulose from wood pulp, but could have used fruit peels or cotton fibers left over from textile production.

The researchers need to test the environmental impacts of their newfangled glitter. But Vignolini is optimistic that materials using such natural ingredients have a bright future.