Twenty-one people have died and another six are missing as of Sunday evening after heavy rainfall hit Xi’an, Northwest China’s Shaanxi Province, and caused mountain floods and mudslides on Friday evening. 

Due to the impact of short-duration heavy rain, mountain floods and mudslides struck a village in Chang’an district in Xi’an around 6 pm on Friday. The disaster has damaged two houses occupying a total area of 300 square meters, destroyed three sections and slightly damaged 21 sections on the National Highway 210, damaged three electric power supply infrastructures and left 900 households out of power, according to Xi’an Bureau of Emergency Management. 

Xi’an city immediately set up an on-site command center, organized a total of 14 rescue teams including firefighting and police departments with more than 980 personnel, and deployed over 1,100 units of equipment and tools including life detectors, satellite phones, excavators, and search and rescue dogs, working around the clock to carry out search and rescue as well as disaster relief operations.

As of Sunday evening, 186 residents have been relocated and resettled, three severely damaged sections of the National Highway 210 have been restored, 21 slightly damaged road sections are under reinforcement, communication services have been restored in 49 affected areas, and power supply has been restored to 855 households.

The city is making every effort to seize the critical period for rescue operations, continuing to search for missing individuals restlessly, as well as remove risks to prevent the occurrence of secondary disasters.  

Preliminary investigations showed that two houses in the village were washed away, a with nearby roads, bridges, power supplies and other infrastructures damaged, leaving local residents partially cut off with the outside world. 

Local media reported that as of Sunday Morning, four people had been confirmed dead, while 14 others remain missing. 

The Xi'an detachment of the armed police force in Shaanxi deployed more than 100 personnel to the impacted area. Preliminary search and rescue operations remain underway. 

As of Sunday morning, rescue forces have transferred 81 residents and 11 vehicles to safe locations, and are assisting with the search and recovery of four deceased villagers, with emergency workers scanning an area 65 kilometers in length along a nearby river.  

According to a local villager surnamed Li (pseudonym), flooding and mudslides began following one or two hours of heavy rain on Friday afternoon. Two dwellings swept away by flood waters operated agritourism business, but there was yet to be confirmation whether guests were inside during flooding. 

Local fire department, police and emergency management authorities are working to coordinate rescue efforts. 

Upon receiving the report, China's Ministry of Emergency Management has dispatched a working group to the disaster site to assist with rescue and response efforts and have also mobilized a local fire and rescue team consisting of 207 personnel to carry out rescue operations.

A team of scientists has built a heat engine out of a single atom.

Heat engines, like steam engines or internal combustion engines, convert heat into motion. To create the minuscule engine, physicist Johannes Roßnagel of University of Mainz and colleagues heated and cooled a calcium ion with an electric field and a laser, causing it to move and do a tiny amount of work. They report their results in the April 15 Science.

Read more about this and other scaled-down engines in “Ultrasmall engines bend second law of thermodynamics.”

Many preschoolers take a surprisingly long and bumpy mental path to the realization that people can have mistaken beliefs — say, thinking that a ball is in a basket when it has secretly been moved to a toy box. Traditional learning curves, in which kids gradually move from knowing nothing to complete understanding, don’t apply to this landmark social achievement and probably to many other types of learning, a new study concludes.

Kids ranging in age from 3 to 5 often go back and forth between passing and failing false-belief tests for several months to more than one year, say psychologist Sara Baker of the University of Cambridge and her colleagues. A small minority of youngsters jump quickly from always failing to always passing these tests, the scientists report October 20 in Cognitive Psychology.
“If these results are replicated, it will surprise a lot of researchers that there is such a low level of sudden insight into false beliefs,” says psychologist Malinda Carpenter, currently at the Max Planck Institute for Evolutionary Anthropology in Leipzig. Early childhood researchers generally assume that preschoolers either pass or fail false-belief tests, with a brief transition between the two, explains Carpenter, who did not participate in the new study. Grasping that others sometimes have mistaken beliefs is a key step in social thinking.

False-belief understanding may start out as something that can be indicated nonverbally but not described. Human 2-year-olds and even chimpanzees tend to look toward spots where a person would expect to find a hidden item that only the children or apes have seen moved elsewhere (SN Online: 10/6/16).

Numerous investigations suggest that neurologically healthy kids between ages 3 and 5 consciously appreciate when others have formed mistaken beliefs. But those studies report average scores on false-belief tests for groups of preschoolers. That leaves unexamined how individual kids progress — or not — as mind readers.

Baker’s team generated individual scoring profiles for 52 children repeatedly assessed for false-belief understanding between ages 3 and 5. Trials occurred over roughly one to two years. Two types of false-belief tasks were alternately presented about every two to six weeks, either at a preschool, in a lab or at a child’s home.

In one task, an experimenter used pictures to help describe a situation in which someone moves an object from one location to another once a friend leaves — say, taking a ball from a basket and putting it in a toy box. Children were asked where the friend would later look for the object.
In a second task, children observed a container’s unexpected contents, such as a sock in a crayon box or a toy cow in an egg carton. Kids reported what they originally thought was inside the container and what another person would think is inside it.

Nine children, including some of the youngest ones, passed their first three trials. All except one of the nine continued to pass trials at a high rate. The remaining 43 children failed at least one of the first three trials. A statistical analysis calculated the likelihood that a series of scores for a particular child reflected gains, losses or no change in false-belief understanding.

Five of the 43 children achieved rapid insights into false beliefs, consistently passing trials immediately after a string of failed trials. Another 22 youngsters showed different patterns of improvement, such as going from a 12 percent likelihood of passing trials to a 50 percent chance by the study’s end. None of them moved gradually and steadily from failing to passing false belief tests. Smooth learning curves are statistical illusions created by averaging group scores, the researchers suspect.

Four kids started out failing false-belief tests and showed no signs of improvement over time. Another 10 children sometimes passed and sometimes failed throughout the study. Statistical profiles were inconclusive for two children.

Related findings, although based on group statistics, nonetheless suggest that grade-schoolers shift among various problem-solving strategies when learning mathematical concepts (SN: 3/17/01, p. 172). Baker’s statistical method could enhance the study of how individual children develop math skills and other forms of reasoning, says psychologist Rose Scott of the University of California, Merced.

One of the most pressing and perplexing questions parents have to answer is what to do about screen time for little ones. Even scientists and doctors are stumped. That’s because no one knows how digital media such as smartphones, iPads and other screens affect children.

The American Academy of Pediatrics recently put out guidelines, but that advice was based on a frustratingly slim body of scientific evidence, as I’ve covered. Scientists are just scratching the surface of how screen time might influence growing bodies and minds. Two recent studies point out how hard these answers are to get. But the studies also hint that the answers might be important.

In the first study, Julia Ma at the University of Toronto and colleagues found that, in children younger than 2, the more time spent with a handheld screen, such as a smartphone or tablet, the more likely the child was to show signs of a speech delay. Ma presented the work May 6 at the 2017 Pediatric Academic Societies Meeting in San Francisco.

The team used information gleaned from nearly 900 children’s 18-month checkups. Parents answered a questionnaire about their child’s mobile media use and then filled out a checklist designed to identify heightened risk of speech problems. This checklist is a screening tool that picks up potential signs of trouble; it doesn’t offer a diagnosis of a language delay, points out study coauthor Catherine Birken, a pediatrician at The Hospital for Sick Children in Toronto.

Going into the study, the researchers didn’t have expectations about how many of these toddlers were using handheld screens. “We had very little clues, because there is almost no literature on the topic,” Birken says. “There’s just really not a lot there.”

It turns out that about 1 in 5 of the toddlers used handheld screens, and those kids had an average daily usage of about a half hour. Handheld screen time was associated with potential delays in expressive language, the team found. For every half hour of mobile media use, a child’s risk of language delay increased by about 50 percent.

“The relationship is not that strong,” Birken says, and those numbers come with big variations. Still, a link exists. And finding that association means there’s a lot more work to do, Birken says. In this study, researchers looked only at time spent with handheld screens. Future studies could investigate whether parents watching along with a child, the type of content or even time of day might change the calculation.

A different study, published April 13 in Scientific Reports, looked at handheld digital device use among young children and its relationship to sleep. As a group, kids from ages 6 months to 3 years who spent more time using mobile touch screen devices got less sleep at night.
Parent surveys filled out online indicated that each hour of touch screen use was linked to 26.4 fewer minutes of night sleep and 10.8 minutes more sleep during the day. Extra napping time “may go some way to offset the disturbed nighttime sleep, but the total sleep time of high users is still less than low users,” says study coauthor Tim Smith, a cognitive psychologist at Birkbeck, University of London. Each additional hour of touch screen use is linked to about 15 minutes less sleep over 24 hours.

By analyzing 20 independent studies, an earlier study found a similar link between portable screen use and less sleep among older children. The new results offer “a consistent message that the findings from older children translate into those younger,” says Ben Carter of King’s College London, who was a coauthor on the study of older children.

So the numbers are in. Daily doses of Daniel Tiger’s Neighborhood on a mobile device equals 7.5 minutes less sleep and a 50 percent greater risk of expressive language delay for your toddler, right? Well, no. It’s tempting to grab onto these numbers, but the science is too preliminary. In both cases, the results show that the two things go together, not that one caused the other.

It may be a long time before scientists have answers about how digital technology affects children. In the meantime, you can follow the American Academy of Pediatrics’ recently updated guidelines, which discourage screens (except for video chatting) before 18 months of age and for all children during meals or in bedrooms.

We now live in a world where smartphones are ever-present companions, a saturation that normalizes the sight of small screens in tiny hands. But I think we should give that new norm some extra scrutiny. The role of mobile devices in our kids’ lives — and our own — is something worth thinking about, hard.

The largest marsupial to ever walk the Earth just got another accolade: It’s also the only marsupial known to migrate seasonally.

Diprotodon optatum was a massive wombat-like herbivore that lived in what’s now Australia and New Guinea during the Pleistocene, until about 40,000 years ago. Now, an analysis of one animal’s teeth suggests that it undertook long, seasonal migrations like those made by zebras and wildebeests in Africa.

Animals pick up the chemical element strontium through their diet, and it leaves a record in their teeth. The ratio of different strontium isotopes varies from place to place, so it can provide clues about where an animal lived. Strontium isotope ratios in an incisor from one D. optatum revealed a repeating pattern. That suggests the animal migrated seasonally — it moved around, but generally hit up the same rest stops each year, researchers report September 27 in the Proceedings of the Royal Society B.

It’s the first evidence to show a marsupial — living or extinct — migrating in this way, says study coauthor Gilbert Price, a paleoecologist at the University of Queensland in Brisbane, Australia. It’s not clear exactly why this mega-marsupial might have migrated, but an analysis of the carbon isotopes in its teeth suggests it ate a fairly limited diet. So it might have migrated to follow food sources that popped up seasonally in different places, the authors suggest.

Pluto has no rings — New Horizons triple-checked. An exhaustive search for rings and dust particles around the dwarf planet before, during and after the spacecraft flew past Pluto in 2015 has come up empty.

“It’s a very long paper to say we didn’t find anything,” says team member Tod Lauer of the analysis, posted online September 23 at arXiv.org. But the nonresult could help scientists understand the contents of the outer solar system — and help plan New Horizons’ next encounter. The spacecraft is now on a course to a space rock in the Kuiper Belt, another 1.5 billion kilometers past Pluto.
Before New Horizons arrived at Pluto, the possible existence of rings was an urgent matter of safety. Hitting a particle as small as a sand grain could have damaged the spacecraft.

Searches with the Hubble Space Telescope in 2011 and 2012 turned up two previously unknown moons orbiting Pluto — Kerberos and Styx (SN: 11/28/15, p. 14) — and zero rings. Even so, many researchers expected to encounter rings, or at least some debris. The four outer planets in the solar system have rings, as do other small bodies in the solar system, like the tiny planetoid 10199 Chariklo (SN: 5/3/14, p. 10). And some studies suggest that Pluto probably had rings at one point in its past, left over from the collision that formed its largest moon, Charon.

Nine weeks before New Horizons’ closest approach to Pluto, a team jokingly called the “crow’s nest” acted much like a ship’s lookout for potential hazards, says Lauer, an astronomer with the National Optical Astronomy Observatory in Tucson, Ariz. The group examined images taken with the spacecraft’s Long Range Reconnaissance Imager camera, looking for ring particles reflecting sunlight or spots that moved against a starry background from one set of images to the next. Nothing turned up.

The team declared the spacecraft’s trajectory safe, and New Horizons flew sailed safely past Pluto on July 14, 2015 (SN Online: 7/15/15). After the flyby, the team turned New Horizons around to look back at Pluto, and towards the sun. This was a much better position to look for rings, as dust particles would pop into view when backlit by the sun like motes of dust in the light from a window.

“If you really want to know for sure whether there’s any dust there, the viewing geometries where you’re looking past the dust with the sun in the background, that’s the gold standard,” says Matthew Tiscareno of the SETI Institute in Mountain View, Calif., who studied Saturn’s rings with the Cassini spacecraft but was not involved in New Horizons.
It took the better part of a year for all the data from New Horizons to return to Earth, and several months after that to analyze it, but the team is now ready to call it: The rings really aren’t there — or at least they’re too diffuse to see.

That’s somewhat surprising, Lauer says. But the chaotic gravity of Pluto’s family of moons might make it too hard for rings to find stable orbits. Or the slight pressure generated by light particles streaming from the sun could constantly blow would-be ring particles away.

It’s also possible there just wasn’t that much dust there to begin with. New Horizons saw fewer craters on Pluto and Charon than expected, which could mean there are fewer small bodies at that distance from the sun smacking into Pluto and its moons and kicking up dust.

That could be good news for New Horizons’ next act. After five months in hibernation, the spacecraft woke up on September 11 and has set its sights on a smaller, weirder and more distant object: a space rock about 30 kilometers long called 2014 MU69 (SN Online: 7/20/17). Initial observations suggest it might be a double object, with two bodies orbiting closely or touching lightly.

New Horizons will fly past MU69 on January 1, 2019. In the meantime, the team is looking for hazards along the route. “We’re going to do a similar effort to what we did with Pluto,” Lauer says. “We’re going to get in the crow’s nest and get out our binoculars, as it were, and see if we’re going to be okay.”

What looks like a spider, but with a segmented rear plus a long spike of a tail, has turned up in amber that’s about 100 million years old.

Roughly the size of a peppercorn (not including the tail, which stretches several times the body length), this newly described extinct species lived in forests in what is now Myanmar during the dinosaur-rich Cretaceous Period.

Spiders as their own distinctive group had evolved long before. Whether this tailed creature should be considered a true spider (of the group Araneae) is debatable though, researchers acknowledge February 5 in two studies in Nature Ecology & Evolution. In one of the papers, the fossils’ chimeric mash-up of traits both spidery and nonspidery inspired Bo Wang of the Chinese Academy of Sciences in Nanjing and colleagues to name the species Chimerarachne yingi.
C. yingi indeed has some anatomy that, among living animals, would be unique to spiders, says Gonzalo Giribet of Harvard University, a coauthor of the other paper. The fossils have what look like little structures that could have exuded spider silk, as well as distinctive male spider sex organs. Called pedipalps, these modified legs have no direct connection to a sperm-producing organ. Spiders need to load them before mating, for instance by ejaculating a sperm droplet and dipping pedipalps in it, so the structures can deliver the sperm a bit like a syringe.

But the abdomen-like end of a true spider’s body isn’t segmented and certainly doesn’t have a tail. Giribet and his colleagues’ analysis puts C. yingi in an ancient sister group of spiders. That’s startling in itself, Giribet says, because researchers have speculated that this Uraraneida group had gone extinct much earlier. So, spider or not, C. yingi remains intriguing.

A genetic hack to make photosynthesis more efficient could be a boon for agricultural production, at least for some plants.

This feat of genetic engineering simplifies a complex, energy-expensive operation that many plants must perform during photosynthesis known as photorespiration. In field tests, genetically modifying tobacco in this way increased plant growth by over 40 percent. If it produces similar results in other crops, that could help farmers meet the food demands of a growing global population, researchers report in the Jan. 4 Science.
Streamlining photorespiration is “a great step forward in efforts to enhance photosynthesis,” says Spencer Whitney, a plant biochemist at Australian National University in Canberra not involved in the work.

Now that the agricultural industry has mostly optimized the use of yield-boosting tools like pesticides, fertilizers and irrigation, researchers are trying to micromanage and improve plant growth by designing ways to make photosynthesis more efficient (SN: 12/24/16, p. 6).

Photorespiration is a major roadblock to achieving such efficiency. It occurs in many plants, such as soybeans, rice and wheat, when an enzyme called Rubisco — whose main job is to help transform carbon dioxide from the atmosphere into sugars that fuel plant growth — accidentally snatches an oxygen molecule out of the atmosphere instead.

That Rubisco-oxygen interaction, which happens about 20 percent of the time, generates the toxic compound glycolate, which a plant must recycle into useful molecules through photorespiration. This process comprises a long chain of chemical reactions that span four compartments in a plant cell. All told, completing a cycle of photorespiration is like driving from Maine to Florida by way of California. That waste of energy can cut crop yields by 20 to 50 percent, depending on plant species and environmental conditions.Streamlining photorespiration is “a great step forward in efforts to enhance photosynthesis,” says Spencer Whitney, a plant biochemist at Australian National University in Canberra not involved in the work.

Now that the agricultural industry has mostly optimized the use of yield-boosting tools like pesticides, fertilizers and irrigation, researchers are trying to micromanage and improve plant growth by designing ways to make photosynthesis more efficient (SN: 12/24/16, p. 6).

Photorespiration is a major roadblock to achieving such efficiency. It occurs in many plants, such as soybeans, rice and wheat, when an enzyme called Rubisco — whose main job is to help transform carbon dioxide from the atmosphere into sugars that fuel plant growth — accidentally snatches an oxygen molecule out of the atmosphere instead.

That Rubisco-oxygen interaction, which happens about 20 percent of the time, generates the toxic compound glycolate, which a plant must recycle into useful molecules through photorespiration. This process comprises a long chain of chemical reactions that span four compartments in a plant cell. All told, completing a cycle of photorespiration is like driving from Maine to Florida by way of California. That waste of energy can cut crop yields by 20 to 50 percent, depending on plant species and environmental conditions.
Using genetic engineering, researchers have now designed a more direct chemical pathway for photorespiration that is confined to a single cell compartment — the cellular equivalent of a Maine-to-Florida road trip straight down the East Coast.

Paul South, a molecular biologist with the U.S. Department of Agriculture in Urbana, Ill., and colleagues embedded genetic directions for this shortcut, written on pieces of algae and pumpkin DNA, in tobacco plant cells. The researchers also genetically engineered the cells to not produce a chemical that allows glycolate to travel between cell compartments to prevent the glycolate from taking its normal route through the cell.
Unlike previous experiments with human-designed photorespiration pathways, South’s team tested its photorespiration detour in plants grown in fields under real-world farming conditions. Genetically altered tobacco produced 41 percent more biomass than tobacco that hadn’t been modified.
“It’s very exciting” to see how well this genetic tweak worked in tobacco, says Veronica Maurino, a plant physiologist at Heinrich Heine University Düsseldorf in Germany not involved in the research, but “you can’t say, ‘It’s functioning. Now it will function everywhere.’”

Experiments with different types of plants will reveal whether this photorespiration fix creates the same benefits for other crops as it does for tobacco. South’s team is currently running greenhouse experiments on potatoes with the new set of genetic modifications, and plans to do similar tests with soybeans, black-eyed peas and rice.

The vetting process for such genetic modifications to be approved for use on commercial farms, including more field testing, will probably take at least another five to 10 years, says Andreas Weber, a plant biochemist also at Heinrich Heine University Düsseldorf who coauthored a commentary on the study that appears in the same issue of Science. In the meantime, he expects that researchers will continue trying to design even more efficient photorespiration shortcuts, but South’s team “has now set a pretty high bar.”

THE WOODLANDS, Texas — Grains of dust from the edge of the solar system could be finding their way to Earth. And NASA may already have a handful of the debris, researchers report.

With an estimated 40,000 tons of space dust settling in Earth’s stratosphere every year, the U.S. space agency has been flying balloon and aircraft missions since the 1970s to collect samples. The particles, which can be just a few tens of micrometers wide, have long been thought to come mostly from comets and asteroids closer to the sun than Jupiter (SN Online: 3/19/19).

But it turns out that some of the particles may have come from the Kuiper Belt, a distant region of icy objects orbiting beyond Neptune, NASA planetary scientist Lindsay Keller said March 21 at the Lunar and Planetary Science Conference. Studying those particles could reveal what distant, mysterious objects in the Kuiper Belt are made of, and perhaps how they formed (SN Online: 3/18/19).

“We’re not going to get a mission out to a Kuiper Belt object to actually collect [dust] samples anytime soon,” Keller said. “But we have samples of these things in the stratospheric dust collections here at NASA.”
One way to find a dust grain’s home is to probe the particle for microscopic tracks where heavy charged particles from solar flares punched through. The more tracks a grain has, the longer it has wandered in space — and the more likely it originated far from Earth, says Keller, who works at the Johnson Space Center in Houston.

But to determine precisely how long a dust grain has spent traveling space, Keller first needed to know how many tracks a grain typically picks up per year. Measuring that rate required a sample with a known age and known track density — criteria met only by moon rocks brought back on the Apollo missions. But the last track-rate estimate was done in 1975 and with less precise instruments than are available today.
So Keller and planetary scientist George Flynn of SUNY Plattsburgh reexamined that same Apollo rock with a modern electron microscope. They found that the rate at which rocks pick up flare tracks was about 20 times lower than the previous study estimated.

That means it takes longer for dust flakes to pick up tracks than astronomers assumed. When Keller and Flynn counted the number of tracks in 14 atmospheric dust grains, the pair found that some of the particles must have spent millions of years out in space — far too long to have come just from between Mars and Jupiter.

Grains specifically from the Kuiper Belt would have wandered 10 million years to reach Earth’s stratosphere, the researchers calculated. That’s “pretty solid evidence that we’re collecting Kuiper Belt dust right here,” Keller says.
Four of the particles contained minerals that had to have formed through interactions with liquid water. That’s surprising; the Kuiper Belt is thought to be too cold for water to be liquid.

“Many of these particles, if they in fact are from the Kuiper Belt, tell you that some of the minerals in Kuiper Belt objects formed in the presence of liquid water,” Keller says. The water probably came from collisions between Kuiper Belt objects that produced enough heat to melt ice, he says.

“I think it’s incredible if Lindsay Keller has shown that he has pieces of Kuiper Belt dust in his lab,” says planetary scientist Carey Lisse of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. But more work needs to be done to confirm that the dust really came from the Kuiper Belt, he says, and wasn’t just sitting on an asteroid for millions of years. “Lindsay needs to get a lot more samples,” Lisse says. “But I do think he’s on to something.”

Lisse works on NASA’s New Horizons mission, which found plenty of dust in the outer solar system and measured its abundance near Pluto when the spacecraft flew past the dwarf planet in 2015. Based on those results, he finds it unsurprising that some of that dust has made it to Earth. But it is “really cool,” he says. “We can actually try to figure out what the Kuiper Belt is made of.”

Editor’s note: This story was updated April 8, 2019, to correct that the newly calculated flare track rate was about 20 times lower than the rate calculated in 1975, not two orders of a magnitude lower.

A new member of the human genus has been found in a cave in the Philippines, researchers report.

Fossils with distinctive features indicate that the hominid species inhabited the island now known as Luzon at least 50,000 years ago, according to a study in the April 11 Nature. That species, which the scientists have dubbed Homo luzonensis, lived at the same time that controversial half-sized hominids named Homo floresiensis and nicknamed hobbits were roaming an Indonesian island to the south called Flores (SN: 7/9/16, p. 6).
In shape and size, some of the fossils match those of corresponding bones from other Homo species. “But if you take the whole combination of features for H. luzonensis, no other Homo species is similar,” says study coauthor and paleoanthropologist Florent Détroit of the French National Museum of Natural History in Paris.

If the find holds up to further scientific scrutiny, it would add to recent fossil and DNA evidence indicating that several Homo lineages already occupied East Asia and Southeast Asian islands by the time Homo sapiens reached what’s now southern China between 80,000 and 120,000 years ago (SN: 11/14/15, p. 15). The result: an increasingly complicated picture of hominid evolution in Asia.

Excavations in 2007, 2011 and 2015 at Luzon’s Callao Cave yielded a dozen H. luzonensis fossils at first — seven isolated teeth (five from the same individual), two finger bones, two toe bones and an upper leg bone missing its ends, the scientists say. Analysis of the radioactive decay of uranium in one tooth suggested a minimum age of 50,000 years. Based on those fossils, a hominid foot bone found in 2007 in the same cave sediment was also identified as H. luzonensis. It dates to at least 67,000 years ago.
had molars that were especially small, even smaller than those of hobbits, with some features similar to modern humans’ molars. The hominid also had relatively large premolars that, surprisingly, had two or three roots rather than one. Hominids dating to several hundred thousand years ago or more, such as Homo erectus , typically had premolars with multiple roots. H. luzonensis finger and toe bones are curved, suggesting a tree-climbing ability comparable to hominids from 2 million years ago or more.
It’s unclear whether H. luzonensis was as small as hobbits, Détroit says. The best-preserved hobbit skeleton comes from a female who stood about a meter tall. Based on the length of the Callao Cave foot bone, Détroit’s team suspects that H. luzonensis was taller than that, although still smaller than most human adults today.

As with hobbits, H. luzonensis’ evolutionary origins are unknown. Scientists think that hobbits may have descended from seagoing H. erectus groups, and perhaps H. luzonensis did too, writes paleoanthropologist Matthew Tocheri of Lakehead University in Thunder Bay, Canada, in a commentary published with the new report. Evidence suggests that hominids reached Luzon by around 700,000 years ago (SN Online: 5/2/18). So H. erectus may have also crossed the sea from other Indonesian islands or mainland Asia to Luzon and then evolved into H. luzonensis with its smaller body and unusual skeletal traits, Détroit speculates, a process known as island dwarfing.

But some scientists not involved in the research say it’s too soon to declare the Luzon fossils a brand-new Homo species. Détroit’s group, so far, has been unable to extract ancient DNA from the fossils. So “all [evolutionary] possibilities must remain open,” says archaeologist Katerina Douka of the Max Planck Institute for the Science of Human History in Jena, Germany.

The mosaic of fossil features that the team interprets as distinctive, for instance, may have been a product of interbreeding between two or more earlier Homo species, creating hybrids, but not a new species.

Or perhaps a small population of, say, H. erectus that survived on an isolated island like Luzon for possibly hundreds of thousands of years simply acquired some skeletal features that its mainland peers lacked, rather than evolving into an entirely new species, says paleoanthropologist María Martinón-Torres.

Those questions make the new fossils “an exciting and puzzling discovery,” says Martinón-Torres, director of the National Research Centre on Human Evolution in Burgos, Spain.

If the unusual teeth and climbing-ready hand and foot bones found at Callao Cave occurred as a package among Luzon’s ancient Homo crowd, “then that combination is unique and unknown so far” among hominids, Martinón-Torres says. Only a more complete set of fossils, ideally complemented by ancient DNA, she adds, can illuminate whether such traits marked a new Homo member.