200,000 years ago, humans preferred to kip cozy

 Researchers in South Africa's Border Cave, a well-known archaeological site perched on a cliff between eSwatini (Swaziland) and KwaZulu-Natal in South Africa, have found evidence that people have been using grass bedding to create comfortable areas for sleeping and working on at least 200,000 years ago.

These beds, consisting of sheaves of grass of the broad-leafed Panicoideae subfamily were placed near the back of the cave on ash layers. The layers of ash was used to protect the people against crawling insects while sleeping. Today, the bedding layers are visually ephemeral traces of silicified grass, but they can be identified using high magnification and chemical characterisation.

The Border Cave study was conducted by a multidisciplinary team from the University of the Witwatersrand, South Africa, the CNRS (University of Bordeaux), and Université Côte d'Azur, France, the Instituto Superior de Estudios Sociales, Tucumán, Argentina, and the Royal Institute for Cultural Heritage, Belgium.

"We speculate that laying grass bedding on ash was a deliberate strategy, not only to create a dirt-free, insulated base for the bedding, but also to repel crawling insects," says Professor Lyn Wadley, principal researcher and lead author.

"Sometimes the ashy foundation of the bedding was a remnant of older grass bedding that had been burned to clean the cave and destroy pests. On other occasions, wood ash from fireplaces was also used as the clean surface for a new bedding layer."

Several cultures have used ash as an insect repellent because insects cannot easily move through fine powder. Ash blocks insects' breathing and biting apparatus, and eventually dehydrates them. Tarchonanthus (camphor bush) remains were identified on the top of the grass from the oldest bedding in the cave. This plant is still used to deter insects in rural parts of East Africa.

"We know that people worked as well as slept on the grass surface because the debris from stone tool manufacture is mixed with the grass remains. Also, many tiny, rounded grains of red and orange ochre were found in the bedding where they may have rubbed off human skin or coloured objects," says Wadley.

Modern hunter-gatherer camps have fires as focal points; people regularly sleep alongside them and perform domestic tasks in social contexts. People at Border Cave also lit fires regularly, as seen by stacked fireplaces throughout the sequence dated between about 200,000 and 38,000 years ago.

"Our research shows that before 200,000 years ago, close to the origin of our species, people could produce fire at will, and they used fire, ash, and medicinal plants to maintain clean, pest-free camps. Such strategies would have had health benefits that advantaged these early communities."

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Weight between young adulthood and midlife linked to early mortality

 A new Boston University School of Public Health (BUSPH) study finds that changes in weight between young adulthood and midlife may have important consequences for a person's risk of early death.

Published in JAMA Network Open, the study found that participants whose BMIs went from the "obese" range in early adulthood down to the "overweight" range in midlife halved their risk of dying during the study period, compared with individuals whose BMIs stayed in the "obese" range. On the other hand, weight loss after midlife did not significantly reduce participants' risk of death.

The researchers estimate that 12.4% of early deaths in the US may be attributable to having a higher body mass index (BMI) at any point between early- and mid-adulthood.

"The results indicate an important opportunity to improve population health through primary and secondary prevention of obesity, particularly at younger ages," says study corresponding author Dr. Andrew Stokes, assistant professor of global health at BUSPH.

"The present study provides important new evidence on the benefit of maintaining a healthy weight across the life course," says lead author Dr. Wubin Xie, a postdoctoral associate in global health at BUSPH.

The researchers used data from 1998 through 2015 for 24,205 participants from the National Health and Nutrition Examination Survey. The participant were 40-74 years old when they entered the study, and the data included participants' BMI at age 25, 10 years before they entered the study, and when they entered the study. The researchers then analyzed the relationship between BMI change and the likelihood that a participant died over the course of the observed period, controlling for other factors such as participants' sex, past and current smoking, and education level.

They found that study participants whose BMIs went from the "obese" range at age 25 down to the "overweight" range in midlife were 54% less likely to have died than participants whose BMIs stayed in the "obese" range. Instead, these participants with an "obese" to "overweight" trajectory had a risk of death closer to that of participants whose BMIs had been in the "overweight" range all along.

The researchers estimated that 3.2% of deaths in the study would have been avoided if everyone with a BMI in the "obese" range at age 25 had been able to bring their BMIs down to the "overweight" range by midlife. However, they noted that weight loss was rare overall, and only 0.8% of participants had BMIs that went from the "obese" to the "overweight" range.

The researchers did not find a similar reduction in risk of death for participants who lost weight later in their lives. They wrote that this may be because weight loss later in life is more likely to be tied to an aging person's worsening health.

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Syphilis may have spread through Europe before Columbus

 Syphilis is a sexually transmitted disease -- and while commonly dismissed due to the availability of modern treatments, it is in fact spreading at an alarming rate: Over the last decades, more than 10 million people around the world have been infected with the syphilis subspecies pallidum of the Treponema pallidum bacteria. Other treponematoses, such as yaws and bejel, are caused by other subspecies of Treponema pallidum. The origins of syphilis, which wreaked havoc in Europe from the late 15th to the 18th century, are still unclear. The most popular hypothesis so far holds Christopher Columbus and his sailors liable for bringing the disease to Europe from the New World.

Yaws already widespread in Europe

The new study indicates a fair possibility that Treponema pallidum already existed in Europe before Columbus ever set sails to America. The researchers found treponematoses in archaeological human remains from Finland, Estonia and the Netherlands. Both molecular dating of the ancient bacterial genomes and traditional radiocarbon dating of the samples were used to estimate the age of the pathogens causing these diseases. The results indicate that the genomes dated back to between the early 15th and 18th century.

In addition to the syphilis cases, the researchers found yaws in one of the individuals. Like syphilis, yaws is transmitted via skin contact, although rarely through sexual intercourse. Today, the disease is only found in tropical and subtropical regions. "Our data indicates that yaws was spread through all of Europe. It was not limited to the tropics, as it is today," says last author Verena Schünemann, professor of paleogenetics at the Institute of Evolutionary Medicine of the University of Zurich.

Genome of a previously unknown pathogen discovered

The research team also discovered something else: The skeleton found in the Netherlands contained a pathogen belonging to a new, unknown and basal treponemal lineage. This lineage evolved in parallel to syphilis and yaws but is no longer present as a modern-day disease. "This unforeseen discovery is particularly exciting for us, because this lineage is genetically similar to all present treponemal subspecies, but also has unique qualities that differ from them," says first author Kerttu Majander from UZH.

Because several closely related subspecies of Treponema pallidum existed throughout Europe, it is possible that the diseases persisted in overlapping regions, and sometimes infected the same patient. The spatial distribution in the northern periphery of Europe also suggests that endemic treponematoses had already spread widely in Europe in the early modern period.

Not just Columbus

"Using our ancient genomes, it is now possible for the first time to apply a more reliable dating to the treponema family tree," says Schünemann. The genetic analyses conducted in this study suggest that the predecessor of all modern Treponema pallidum subspecies likely evolved at least 2,500 years ago. For venereal syphilis in particular, the latest common ancestor existed between the 12th and 16th century.

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How people and ecosystems fit together on the Great Barrier Reef

 A world-first study examining the scales of management of the Great Barrier Reef has the potential to help sustain other ecosystems across the world.

Massive marine ecosystems like the Great Barrier Reef aren't just a vibrant home to fish, corals and other creatures, they are also an important source of people's food, livelihoods and recreation.

The new study suggests the way people are managed when undertaking various activities within the marine park -- like fishing, boating, and scientific research -- could serve as an exemplary model for sustainably managing other ecosystems that humans use.

"There is plenty of evidence to suggest that the Great Barrier Reef is managed at appropriate scales within its boundaries," said lead author Professor Graeme Cumming, incoming Director of the ARC Centre of Excellence for Coral Reef Studies.

The reef served as a case study for mapping and measuring different scale matches between people and ecosystems. Prof Cumming explains the concept of scale matches using a backyard garden as an example of an ecosystem.

"For a house with a garden, you already have permission to manage that garden -- to mow the lawn and trim the trees inside your fences. To look after all the parts of it. That's a scale match," Prof Cumming said.

He says being able to manage only a flower bed within the garden is a small-scale match. "If you only have permission to manage the flower bed in your garden, you can manage the flowers, but your lawn and trees become unkempt. The weeds and pests affecting the flowers may come from an adjacent part of the garden, which you'd then have no control over," he said.

The Great Barrier Reef Marine Park Authority (GBRMPA) manages the entire marine park. Some permits, such as permission to access areas by boat as part of a commercial operation, may cover most of the park.

GBRMPA also manages smaller scale permits within the marine park boundaries -- small-scale matches that work best for activities like commercial tourism, lobster fisheries or the installation of certain structures like jetties or moorings.

The study found the permits issued for human activities generally occurred at larger scales than the particular individual marine features of interest, such as reefs or islands.

"The finding that people are managed at a broader scale than ecological variation suggests a general principle for permitting and management," Prof Cumming said. "In essence, people like to have choices about where they go and how they respond to change. This means that they prefer to operate at a broader spatial scale than the ecological features they are interested in, rather than the same scale."

The findings suggest this approach to managing people at broader rather than finer scales may be more effective. For small protected areas, increasing the size of the permissible area may even be critical.

However, GBRMPA can't manage the ecosystem's biggest impact, which lies outside park boundaries: climate change.

"Broad scale problems, like climate change, can only be managed with broad scale solutions, like global action," Prof Cumming said. "This is a scale mismatch because these impacts come from well outside the marine park boundaries."

GBRMPA also don't have control over what happens on the land directly adjacent to the reef. Not being able to stop pollutants and pesticides in storm water reaching the reef is another scale mismatch.

Prof Cumming says comparing the results of this study to similar data from other marine parks, including those that are recognised as dysfunctional, will help determine if the management of the Great Barrier Reef Marine Park is unusual or typical.

 Read more at Science Daily

New catalyst efficiently turns carbon dioxide into useful fuels and chemicals

 As levels of atmospheric carbon dioxide continue to climb, scientists are looking for new ways of breaking down CO2 molecules to make useful carbon-based fuels, chemicals and other products. Now, a team of Brown University researchers has found a way to fine-tune a copper catalyst to produce complex hydrocarbons -- known as C2-plus products -- from CO2 with remarkable efficiency.

In a study published in Nature Communications, the researchers report a catalyst that can produce C2-plus compounds with up to 72% faradaic efficiency (a measure of how efficiently electrical energy is used to convert carbon dioxide into chemical reaction products). That's far better than the reported efficiencies of other catalysts for C2-plus reactions, the researchers say. And the preparation process can be scaled up to an industrial level fairly easily, which gives the new catalyst potential for use in large-scale CO2 recycling efforts.

"There had been reports in the literature of all kinds of different treatments for copper that could produce these C2-plus with a range of different efficiencies," said Tayhas Palmore, the a professor of engineering at Brown who co-authored the paper with Ph.D. student Taehee Kim. "What Taehee did was a set of experiments to unravel what each of these treatment steps was actually doing to the catalyst in terms of reactivity, which pointed the way to optimizing a catalyst for these multi-carbon compounds."

There have been great strides in recent years in developing copper catalysts that could make single-carbon molecules, Palmore says. For example, Palmore and her team at Brown recently developed a copper foam catalyst that can produce formic acid efficiently, an important single-carbon commodity chemical. But interest is increasing in reactions that can produce C2-plus products.

"Ultimately, everyone seeks to increase the number of carbons in the product to the point of producing higher carbon fuels and chemicals," Palmore said.

There had been evidence from prior research that halogenation of copper -- a reaction that coats a copper surface with atoms of chlorine, bromine or iodine in the presence of an electrical potential -- could increase a catalyst's selectivity of C2-plus products. Kim experimented with a variety of different halogenation methods, zeroing in on which halogen elements and which electrical potentials yielded catalysts with the best performance in CO2-to-C2-plus reactions. He found that the optimal preparations could yield faradaic efficiencies of between 70.7% and 72.6%, far higher than any other copper catalyst.

The research helps to reveal the attributes that make a copper catalyst good for C2-plus products. The preparations with the highest efficiencies had a large number of surface defects -- tiny cracks and crevices in the halogenated surface -- that are critical for carbon-carbon coupling reactions. These defect sites appear to be key to the catalysts' high selectivity toward ethylene, a C2-plus product that can be polymerized and used to make plastics.

Ultimately, such a catalyst will aid in large-scale recycling of CO2. The idea is to capture CO2 produced by industrial facilities like power plants, cement manufacturing or directly from air, and convert it into other useful carbon compounds. That requires an efficient catalyst that is easy to produce and regenerate, and inexpensive enough to operate on an industrial scale. This new catalyst is a promising candidate, the researchers say.

 Read more at Science Daily

Recalling memories from a third-person perspective changes how our brain processes them

 Adopting a third-person, observer point of view when recalling your past activates different parts of your brain than recalling a memory seen through your own eyes, according to a new paper.

"Our perspective when we remember changes which brain regions support memory and how these brain regions interact together," explained Peggy St Jacques, assistant professor in the Faculty of Science'sDepartment of Psychology and co-author on the paper.

Specifically, the results show that recalling memories from an observer-like perspective, instead of through your own eyes, leads to greater interaction between the anterior hippocampus and the posterior medial network.

"These findings contribute to a growing body of research that show that retrieving memories is an active process that can bias and even distort our memories," added St Jacques.

"Adopting an observer-like perspective involves viewing the past in a novel way, which requires greater interaction among brain regions that support our ability to recall the details of a memory and to recreate mental images in our mind's eye."

Adopting an observer-like perspective may also serve a therapeutic purpose, explained St Jacques. "This may be an effective way of dealing with troubling memories by viewing the past from a distance and reducing the intensity of the emotions we feel."

This work builds on St Jacques' previous research on visual perspective in memory, which found that the perspective from which we recall a memory can influence how we remember them over time.

From Science Daily

How stars form in the smallest galaxies

 The question of how small, dwarf galaxies have sustained the formation of new stars over the course of the Universe has long confounded the world's astronomers. An international research team led by Lund University in Sweden has found that dormant small galaxies can slowly accumulate gas over many billions of years. When this gas suddenly collapses under its own weight, new stars are able to arise.

There are around 2,000 billion galaxies in our Universe and, while our own Milky-Way encompasses between 200 and 400 billion stars, small dwarf galaxies contain only a thousand times less. How stars are formed in these tiny galaxies has long been shrouded in mystery.

However, in a new study published in the research journal Monthly Notices of the Royal Astronomical Society, a research team led from Lund University has established that dwarf galaxies are capable of lying dormant for several billion years before starting to form stars again.

"It is estimated that these dwarf galaxies stopped forming stars around 12 billion years ago. Our study shows that this can be a temporary hiatus," says Martin Rey, an astrophysicist at Lund University and the leader of the study.

Through high-resolution computer simulations, the researchers demonstrate that star formation in dwarf galaxies ceased as a result of the heating and ionisation from the strong light of newborn stars. Explosions of so-called white dwarfs -- small faint stars made of the core that remains when normal-sized stars die -further contribute in preventing the star formation process in dwarf galaxies.

"Our simulations show that dwarf galaxies are able to accumulate fuel in the form of gas, which eventually condenses and gives birth to stars. This explains the observed star formation in existing faint dwarf galaxies that has long puzzled astronomers," states Martin Rey.

The computer simulations used by the researchers in the study are amongst the most expensive that can be carried out within physics. Each simulation takes as long as two months and requires the equivalent of 40 laptop computers operating around the clock. The work is continuing with the development of methods to better explain the processes behind star formation in our Universe's smallest galaxies.

Read more at Science Daily

Hubble finds that Betelgeuse's mysterious dimming is due to a traumatic outburst

 Observations by NASA's Hubble Space Telescope are showing that the unexpected dimming of the supergiant star Betelgeuse was most likely caused by an immense amount of hot material ejected into space, forming a dust cloud that blocked starlight coming from Betelgeuse's surface.

Hubble researchers suggest that the dust cloud formed when superhot plasma unleashed from an upwelling of a large convection cell on the star's surface passed through the hot atmosphere to the colder outer layers, where it cooled and formed dust grains. The resulting dust cloud blocked light from about a quarter of the star's surface, beginning in late 2019. By April 2020, the star returned to normal brightness.

Betelgeuse is an aging, red supergiant star that has swelled in size due to complex, evolving changes in its nuclear fusion furnace at the core. The star is so huge now that if it replaced the Sun at the center of our solar system, its outer surface would extend past the orbit of Jupiter.

The unprecedented phenomenon for Betelgeuse's great dimming, eventually noticeable to even the naked eye, started in October 2019. By mid-February 2020, the monster star had lost more than two-thirds of its brilliance.

This sudden dimming has mystified astronomers, who scrambled to develop several theories for the abrupt change. One idea was that a huge, cool, dark "star spot" covered a wide patch of the visible surface. But the Hubble observations, led by Andrea Dupree, associate director of the Center for Astrophysics | Harvard & Smithsonian (CfA), Cambridge, Massachusetts, suggest a dust cloud covering a portion of the star.

Several months of Hubble's ultraviolet-light spectroscopic observations of Betelgeuse, beginning in January 2019, yield a timeline leading up to the darkening. These observations provide important new clues to the mechanism behind the dimming.

Hubble captured signs of dense, heated material moving through the star's atmosphere in September, October, and November 2019. Then, in December, several ground-based telescopes observed the star decreasing in brightness in its southern hemisphere.

"With Hubble, we see the material as it left the star's visible surface and moved out through the atmosphere, before the dust formed that caused the star to appear to dim," Dupree said. "We could see the effect of a dense, hot region in the southeast part of the star moving outward.

"This material was two to four times more luminous than the star's normal brightness," she continued. "And then, about a month later, the south part of Betelgeuse dimmed conspicuously as the star grew fainter. We think it is possible that a dark cloud resulted from the outflow that Hubble detected. Only Hubble gives us this evidence that led up to the dimming."

The team's paper will appear online Aug. 13 in The Astrophysical Journal.

Massive supergiant stars like Betelgeuse are important because they expel heavy elements such as carbon into space that become the building blocks of new generations of stars. Carbon is also a basic ingredient for life as we know it.

Tracing a Traumatic Outburst

Dupree's team began using Hubble early last year to analyze the behemoth star. Their observations are part of a three-year Hubble study to monitor variations in the star's outer atmosphere. Betelgeuse is a variable star that expands and contracts, brightening and dimming, on a 420-day cycle.

Hubble's ultraviolet-light sensitivity allowed researchers to probe the layers above the star's surface, which are so hot -- more than 20,000 degrees Fahrenheit -- they cannot be detected at visible wavelengths. These layers are heated partly by the star's turbulent convection cells bubbling up to the surface.

Hubble spectra, taken in early and late 2019, and in 2020, probed the star's outer atmosphere by measuring magnesium II (singly ionized magnesium) lines. In September through November 2019, the researchers measured material moving about 200,000 miles per hour passing from the star's surface into its outer atmosphere.

This hot, dense material continued to travel beyond Betelgeuse's visible surface, reaching millions of miles from the seething star. At that distance, the material cooled down enough to form dust, the researchers said.

This interpretation is consistent with Hubble ultraviolet-light observations in February 2020, which showed that the behavior of the star's outer atmosphere returned to normal, even though visible-light images showed that it was still dimming.

Although Dupree does not know the outburst's cause, she thinks it was aided by the star's pulsation cycle, which continued normally though the event, as recorded by visible-light observations. The paper's co-author, Klaus Strassmeier, of the Leibniz Institute for Astrophysics Potsdam, used the institute's automated telescope called STELLar Activity (STELLA), to measure changes in the velocity of the gas on the star's surface as it rose and fell during the pulsation cycle. The star was expanding in its cycle at the same time as the upwelling of the convective cell. The pulsation rippling outward from Betelgeuse may have helped propel the outflowing plasma through the atmosphere.

Dupree estimates that about two times the normal amount of material from the southern hemisphere was lost over the three months of the outburst. Betelgeuse, like all stars, is losing mass all the time, in this case at a rate 30 million times higher than the Sun.

Betelgeuse is so close to Earth, and so large, that Hubble has been able to resolve surface features -- making it the only such star, except for our Sun, where surface detail can be seen.

Hubble images taken by Dupree in 1995 first revealed a mottled surface containing massive convection cells that shrink and swell, which cause them to darken and brighten.

A Supernova Precursor?

The red supergiant is destined to end its life in a supernova blast. Some astronomers think the sudden dimming may be a pre-supernova event. The star is relatively nearby, about 725 light-years away, which means the dimming would have happened around the year 1300. But its light is just reaching Earth now.

"No one knows what a star does right before it goes supernova, because it's never been observed," Dupree explained. "Astronomers have sampled stars maybe a year ahead of them going supernova, but not within days or weeks before it happened. But the chance of the star going supernova anytime soon is pretty small."

Dupree will get another chance to observe the star with Hubble in late August or early September. Right now, Betelgeuse is in the daytime sky, too close to the Sun for Hubble observations. But NASA's Solar Terrestrial Relations Observatory (STEREO) has taken images of the monster star from its location in space. Those observations show that Betelgeuse dimmed again from mid-May to mid-July, although not as dramatically as earlier in the year.

Read more at Science Daily

Young children would rather explore than get rewards

 Young children will pass up rewards they know they can collect to explore other options, a new study suggests.

Researchers found that when adults and 4- to 5-year-old children played a game where certain choices earned them rewards, both adults and children quickly learned what choices would give them the biggest returns.

But while adults then used that knowledge to maximize their prizes, children continued exploring the other options, just to see if their value may have changed.

"Exploration seems to be a major driving force during early childhood -- even outweighing the importance of immediate rewards," said Vladimir Sloutsky, co-author of the study and professor of psychology at The Ohio State University.

"We believe it is because young children need to explore to help them understand how the world works."

And despite what adults may think, kids' search for new discoveries is anything but random. Results showed children approached exploration systematically, to make sure they didn't miss anything.

"When adults think of kids exploring, they may think of them as running around aimlessly, opening drawers and cupboards, picking up random objects," Sloutsky said

"But it turns out their exploration isn't random at all."

Sloutsky conducted the study with Nathaniel Blanco, a postdoctoral researcher in psychology at Ohio State. Their results were published online recently in the journal Developmental Science.

The researchers conducted two studies. One study involved 32 4-year-olds and 34 adults.

On a computer screen, participants were shown four alien creatures. When participants clicked on each creature, they were given a set number of virtual candies.

One creature was clearly the best, giving 10 candies, while the others gave 1, 2 and 3 candies, respectively. Those amounts never changed for each creature over the course of the experiment.

The goal was to earn as much candy as possible over 100 trials. (The children could turn their virtual candies into real stickers at the end of the experiment.)

As expected, the adults learned quickly which creature gave the most candies and selected that creature 86 percent of the time. But children selected the highest-reward creature only 43 percent of the time.

And it wasn't because the children didn't realize which choice would reap them the largest reward. In a memory test after the study, 20 of 22 children correctly identified which creature delivered the most candy.

"The children were not motivated by achieving the maximum reward to the extent that adults were," Blanco said. "Instead, children seemed primarily motivated by the information gained through exploring."

But what was interesting was that the children didn't just click randomly on the creatures, Sloutsky said.

When they didn't click on the option with the highest reward, they were most likely to go through the other choices systematically, to ensure they never went too long without testing each individual choice.

"The longer they didn't check a particular option, the less certain they were on its value and the more they wanted to check it again," he said.

In a second study, the game was similar but the value of three of the four choices was visible -- only one was hidden. The option that was hidden was randomly determined in each trial, so it changed nearly every time. But the values of all four choices never changed, even when it was the hidden one.

Like in the first experiment, the 37 adults chose the best option on almost every trial, 94 percent of the time. That was much more than the 36 4- and 5-year-old children, who selected the highest-value option only 40 percent of the time.

When the hidden option was the highest-value option, adults chose it 84 percent of the time, but otherwise they almost never selected it (2 percent of the time).

Children chose the hidden option about 40 percent of the time -- and it didn't matter if it was the highest value one or not.

"The majority of the children were attracted to the uncertainty of the hidden option. They wanted to explore that choice," Sloutsky said.

However, there were some individual differences in children, he noted. A few children, for example, acted much like adults and nearly always chose the highest-value option. In the second experiment, a few children almost always avoided the hidden option.

These variations may have to do with different levels of cognitive maturation in children, he said.

But it appears that all children go through a phase where systematic exploration is one of their main goals.

"Even though we knew that children like to run around and investigate things, we're now learning that there is a lot of regularity to their behavior," Sloutsky said.

Read more at Science Daily

Ancient genomes suggest woolly rhinos went extinct due to climate change, not overhunting

 The extinction of prehistoric megafauna like the woolly mammoth, cave lion, and woolly rhinoceros at the end of the last ice age has often been attributed to the spread of early humans across the globe. Although overhunting led to the demise of some species, a study appearing August 13 in the journal Current Biology found that the extinction of the woolly rhinoceros may have had a different cause: climate change. By sequencing ancient DNA from 14 of these megaherbivores, researchers found that the woolly rhinoceros population remained stable and diverse until only a few thousand years before it disappeared from Siberia, when temperatures likely rose too high for the cold-adapted species.

"It was initially thought that humans appeared in northeastern Siberia fourteen or fifteen thousand years ago, around when the woolly rhinoceros went extinct. But recently, there have been several discoveries of much older human occupation sites, the most famous of which is around thirty thousand years old," says senior author Love Dalén, a professor of evolutionary genetics at the Centre for Palaeogenetics, a joint venture between Stockholm University and the Swedish Museum of Natural History. "So, the decline towards extinction of the woolly rhinoceros doesn't coincide so much with the first appearance of humans in the region. If anything, we actually see something looking a bit like an increase in population size during this period."

To learn about the size and stability of the woolly rhinoceros population in Siberia, the researchers studied the DNA from tissue, bone, and hair samples of 14 individuals. "We sequenced a complete nuclear genome to look back in time and estimate population sizes, and we also sequenced fourteen mitochondrial genomes to estimate the female effective population sizes," says co-first author Edana Lord, a PhD student at the Centre for Palaeogenetics.

By looking at the heterozygosity, or genetic diversity, of these genomes, the researchers were able to estimate the woolly rhino populations for tens of thousands of years before their extinction. "We examined changes in population size and estimated inbreeding," says co-first author Nicolas Dussex, a postdoctoral researcher at the Centre for Palaeogenetics. "We found that after an increase in population size at the start of a cold period some 29,000 years ago, the woolly rhino population size remained constant and that at this time, inbreeding was low."

This stability lasted until well after humans began living in Siberia, contrasting the declines that would be expected if the woolly rhinos went extinct due to hunting. "That's the interesting thing," says Lord. "We actually don't see a decrease in population size after 29,000 years ago. The data we looked at only goes up to 18,500 years ago, which is approximately 4,500 years before their extinction, so it implies that they declined sometime in that gap."

The DNA data also revealed genetic mutations that helped the woolly rhinoceros adapt to colder weather. One of these mutations, a type of receptor in the skin for sensing warm and cold temperatures, has also been found in woolly mammoths. Adaptations like this suggest the woolly rhinoceros, which was particularly suited to the frigid northeast Siberian climate, may have declined due to the heat of a brief warming period, known as the Bølling-Allerød interstadial, that coincided with their extinction towards the end of the last ice age.

"We're coming away from the idea of humans taking over everything as soon as they come into an environment, and instead elucidating the role of climate in megafaunal extinctions," says Lord. "Although we can't rule out human involvement, we suggest that the woolly rhinoceros' extinction was more likely related to climate."

The researchers hope to study the DNA of additional woolly rhinoceroses that lived in that crucial 4,500-year gap between the last genome they sequenced and their extinction. "What we want to do now is to try to get more genome sequences from rhinos that are between eighteen and fourteen thousand years old, because at some point, surely they must decline," says Dalén. The researchers are also looking at other cold-adapted megafauna to see what further effects the warming, unstable climate had. "We know the climate changed a lot, but the question is: how much were different animals affected, and what do they have in common?"

 Read more at Science Daily