Alcoholism may stem from using genes incorrectly, a study of hard-drinking rats suggests.

Rats bred either to drink heavily or to shun alcohol have revealed 930 genes linked to a preference for drinking alcohol, researchers in Indiana report August 4 in PLOS Genetics.

Human genetic studies have not found most of the genetic variants that put people at risk for alcoholism, says Michael Miles, a neurogenomicist at Virginia Commonwealth University in Richmond. The new study takes a “significant and somewhat novel approach” to find the genetic differences that separate those who will become addicted to alcohol from those who drink in moderation.
It took decades to craft the experiment, says study coauthor William Muir, a population geneticist at Purdue University in West Lafayette, Ind. Starting in the 1980s, rats bred at Indiana University School of Medicine in Indianapolis were given a choice to drink pure water or water mixed with 10 percent ethanol, about the same amount of alcohol as in a weak wine. For more than 40 generations, researchers selected rats from each generation that voluntarily drank the most alcohol and bred them to create a line of rats that consume the rat equivalent of 25 cans of beer a day. Simultaneously, the researchers also selected rats that drank the least alcohol and bred them to make a line of low-drinking rats. A concurrent breeding program produced another line of high-drinking and teetotaling rats.

For the new study, Muir and colleagues collected DNA from 10 rats from each of the high- and low-drinking lines. Comparing complete sets of genetic instructions from all the rats identified 930 genes that differ between the two lines.

Such a large number of genes, “shows how complex the genetic underpinnings of the drive to consume alcohol might be,” says Miles.

Often, human genetic studies known as genome-wide association studies, or GWAS, can’t determine which of many genes in a particular region of DNA is involved in a disease or addiction. But the Indiana researchers’ DNA data allowed them to pinpoint the exact genetic tweaks implicated in the rats’ drinking. “With GWAS, they’re just trying to get down to the gene — we’ve got it down to the parts of the genes,” Muir says.

That precision “is clearly an advance,” says John Crabbe, a neuroscientist at the Portland VA Medical Center in Oregon. “No one has gone into this much detail before in any alcohol-related trait.”
Most of the time, the genetic variant associated with drinking behavior wasn’t located within the part of the gene containing blueprints for a protein, the researchers discovered. Only four genes contained variants in their protein-producing parts. The majority of the differences were in surrounding DNA that regulates gene activity. Those changes could alter how much protein is produced from the genes, says study coauthor Feng Zhou, a neurobiologist at Indiana University School of Medicine. In turn, altering amounts of proteins could shift biochemical reactions important for determining behavior.

Until recently, scientists thought alcoholism and other problems stemmed from inheriting altered forms of genes that would produce faulty proteins. “Well, that game’s over,” says Crabbe. Now researchers realize that regulating gene activity is often just as important as changing the genes themselves.

The researchers don’t yet know whether the genes identified in the rats are the same ones that lead to drinking problems in people.

Understanding sea anemones’ exceptional healing abilities may help scientists figure out how to restore hearing.

Proteins that the marine invertebrates use to repair damaged cells can also repair mice’s sound-sensing cells, a new study shows. The findings provide insights into the mechanics of hearing and could lead to future treatments for traumatic hearing loss, researchers report in the Aug. 1 Journal of Experimental Biology.

“This is a preliminary step, but it’s a very useful step in looking at restoring the structure and function of these damaged cells,” says Lavinia Sheets, a hearing researcher at Harvard Medical School who was not involved in the study.
Tentacles of starlet sea anemones (Nematostella vectensis) are covered in tiny hairlike cells that sense vibrations in the water from prey swimming nearby. The cells are similar to sound-sensing cells found in the ears of humans and other mammals. When loud noises damage or kill these hair cells, the result can range from temporary to permanent hearing loss.

Anemones’ repair proteins restore their damaged hairlike cells, but landlubbing creatures aren’t as lucky. Glen Watson, a biologist at the University of Louisiana at Lafayette, wondered if anemones’ proteins — which have previously been shown to mend similar cells in blind cave fish — might also work in mammals.

Watson and colleagues mimicked traumatic hearing loss in mice hair cells by depriving them of calcium ions, which are crucial for maintaining cell structure and transmitting sounds. Within a few hours, the normally stiff, hairlike structures that detect sound “looked like spaghetti,” he says.
Researchers bathed the damaged hair cells in a cocktail of anemone repair proteins. After an hour, the cells showed remarkable improvement compared with untreated cells. Proteins rebuilt molecular tethers that bundle hair cells and act as gatekeepers for calcium ions. As a result, the cells absorbed more fluorescent dye — an indication of how well calcium flows into the cells.

What’s more, researchers identified a bevy of mice proteins that are analogs of anemones’ repair proteins. But mammalian versions work less effectively than anemone proteins, if at all. More research could point the way to one day harnessing human repair proteins, Sheets says.

Moving forward, Watson plans to investigate the ability of the anemones’ proteins to repair damaged cells in the ears of living mice. “If we could get to those hair cells before they commit to die and treat them, there’s a possibility we could reduce hearing loss,” he says.

When my friend Steve Finkel and I get together, the talk is almost always about bacteria. He and I are both huge fans, from different angles. I’m a spectator. He studies them (E. coli) in his lab at the University of Southern California. I used to work down the hall from him, so I’m sure that some of my enthusiasm for the tiny creatures can be blamed on him, along with USC’s out-of-control microbe-lover Ken Nealson (Shewanella oneidensis is his bug, among others).
Single-celled though they may be, bacteria and other microbes are far from simple. They can thrive in hostile spots — from the acidic, low-oxygen environment of the stomach to boiling hot springs or frozen tundra. Some even breathe rock (see Nealson’s bug). They can adapt rapidly in rough times, switching their metabolic scheme or just going dormant. Bacteria have many admirable qualities that many of us would want for our children: grit, perseverance, flexibility and seemingly limitless creativity (albeit mostly biochemical).

Their flexibility and creativity were on full display at a recent meeting, a few blocks away from the Science News offices (and the occasion for Finkel’s visit to Washington, D.C.). Reports from the meeting all involve science that takes advantage of the latest techniques for probing the bacterial experience — be that finding out how bacteria can survive without “essential” enzymes and how offensive attacks can actually give rise to bacterial cooperation. Now that bacterial genome sequencing is cheap, Finkel and fellow scientists can watch microbes evolve in the lab, in real time. Taking genetic snapshots along the way, scientists are building up a detailed picture of the genetic shifts that allow a new strain to become dominant in a given experiment. It is watching evolution in action, Finkel says, quite literally.

But microbes are organisms, much more than little sacks of evolving biochemistry. They have immune systems, of a sort. It was through studies of one bacterium’s antiviral defense that scientists first discovered what’s become the most versatile and headline-grabbing gene editor of all time: CRISPR/Cas9. These ingenious molecular scissors work within microbes to target viral DNA that has invaded bacteria and literally cut it to shreds. Harnessed and aimed at the DNA of other organisms, CRISPR/Cas9 has proved much easier to work with, cheaper and more precise than existing editing tools. It’s been wildly successful at precisely deleting genes, helping to reveal gene functions that have long remained hidden, as Tina Hesman Saey reports in “CRISPR gets a makeover.”

But even this wonder tool has its limits. So, as a legal battle over who owns the patent to the technique rages on, scientists (including the current patent holder) are already tweaking it, adjusting it, engineering it and searching for CRISPR-like alternatives, an effort Saey describes in her cover story. Some scientists are going back to the source (bacterial immune systems) to find new enzymes that might help build a library of precision gene-editing tools — one for each job.

That brings me back to why I love microbes — resilient, creative survivors that they are. Like the best humans, they are always coming up with new solutions.

A radio signal detected last year has sparked speculation that an advanced alien civilization is broadcasting from a relatively nearby planet. But recent scans have turned up nothing, suggesting the blip was a false alarm and nothing more than earthly interference.

In May 2015, astronomers detected a blast of radio waves coming from the direction of HD 164595, a sunlike star about 94 light-years away in the constellation Hercules. The signal, reported online August 27 on the blog Centauri Dreams, lasted just a few seconds and reached a peak power of about 750 millijansky — fairly strong by radio astronomy standards (1 jansky equals 10-26 watts per square meter per hertz). The researchers aren’t claiming that they found E.T., but they are asking other astronomers to monitor the star — home to a planet at least 16 times as massive as Earth — in case the signal repeats.
So far, all is quiet.

Scientists with the SETI Institute, whose mission is to seek out signs of extraterrestrial intelligence, turned the Green Bank Telescope in West Virginia toward HD 164595 on August 28 to scan for signals. “There was nothing there,” says Dan Werthimer, a SETI astronomer at the University of California, Berkeley. The original claim, however, “is consistent with someone pushing the button on a CB radio for a couple of seconds.”

Radio telescopes have to contend with interference from the civilization on this planet before picking out transmissions from our galactic neighbors. Earth-based satellites, power lines and cellphones all emit radio waves that can overwhelm cosmic signals. One type of radio chirp whose origin had eluded astronomers for years recently turned out to be coming from microwave ovens, a fact discovered when researchers at the Parkes observatory in Australia who were tracking the signal prematurely opened an oven door without waiting for the ding signal (SN: 5/16/15, p. 5).

“We see strong signals like this all the time,” says Werthimer. With enough information, such as frequency and location, researchers can usually figure out the cause of an incoming signal. But this latest finding, recorded at the RATAN-600 radio observatory near the Caucasus Mountains in Russia, is missing a lot of details that could help astronomers assess its origin. Without precise frequency measurements or statistics on how often the observatory detects comparable events, says Werthimer, it’s hard to tell how unusual this signal is.

The signal was detected around a frequency of 11 gigahertz. That suggests interference from telecommunication devices, says Italian astronomer Claudio Maccone, who was part of the discovery team. “This is precisely why many countries have to watch the star with different technologies,” he says. “By comparing results, we may be able to find the answer.” The long delay in sharing the results, he says, comes from a reluctance among his Russian colleagues to interact with Western researchers. “They are a closed community,” he says. “It’s an unfortunate circumstance.” The team will present the findings September 27 at a meeting of the International Academy of Astronautics in Guadalajara, Mexico.
If the signal didn’t originate on Earth, there are also plenty of natural cosmic sources. Jean Schneider, an astrophysicist at the Paris Observatory in Meudon, France, contends that a gravitational microlens might be responsible. Gravity from an object, such as a star or planet, can temporarily amplify light — including radio waves — received on Earth from other more distant bodies that the interloper passes in front of. Testing that idea would require meticulously tracking the movement of stars that lie in the direction of the radio signal, says Schneider, and seeing if anything could have lined up on the day of the detection.

The discovery is reminiscent of an infamous — and still unexplained — detection known as the “Wow!” signal, named after what astronomer Jerry Ehman wrote on a printout of the signal. Detected in 1977 at the Big Ear radio telescope in Delaware, Ohio, the Wow! signal was at least 70 times as powerful as the one at RATAN-600, lasted for about 72 seconds and appeared to originate in the constellation Sagittarius. Many ideas have been put forth about the signal’s origin, including comets in our solar system, Earth-orbiting space debris and, of course, extraterrestrials.

If aliens do reside around HD 164595, and they are trying to get our attention, they could do so with precisely aimed transmitters no more powerful than anything on Earth, Werthimer says. But if we eavesdropped on a signal that was blasting in all directions into space, then our neighbors are far more advanced than us; such a device would require tapping into the entire power output of their sun.

The fate of Africa’s elephants may be decided before the weekend is out. Members of the International Union for the Conservation of Nature World Conservation Congress, happening this week in Honolulu, will decide on Motion 7, whichwould call on the IUCN to encourage governments to shut down the ivory trade — and provide help in doing so. The hope is that ending the demand for ivory — and with it, hopefully, the large-scale elephant poaching that has been going on for more than a decade — would allow both savannah and forest elephants to recover. But two new studies show that the species have declined so much that, even after poaching ends, their populations will take decades to recover.

The first study presents results from the Great Elephant Census, the first-ever continent-wide effort to survey savannah elephants (Loxodonta africana), the more common of the two species of elephant in Africa. Wildlife researchers, conservation organizations and government agencies worked together to conduct aerial surveys of elephant herds in 18 African nations. They cataloged more than 350,000 elephants (not including the 22,700 counted in Namibia in 2015, or elephants in South Sudan and Central African Republic, which have yet to be counted). An estimated 84 percent of the animals were living in protected areas, the team reports August 31 in PeerJ.

While that may sound like a lot of elephants, the raw numbers are a bit misleading. That’s because not long ago there were so many more. The researchers estimate that 144,000 savannah elephants were lost between 2007 and 2014, with elephant numbers in the surveyed populations falling by about 8 percent per year largely due to poaching. If these populations continue to decline at that rate, their numbers would be halved every nine years, and smaller populations could be wiped out completely, the researchers warn.

And living in a protected area, like a park or nature reserve, doesn’t mean that the elephants are necessarily protected from poaching or conflict with humans. The Great Elephant Census team found high levels of elephant deaths, which could indicate poaching, in Tsavo East National Park in Kenya, Mozambique’s Niassa National Reserve and Rungwa Game Reserve in Tanzania. “Heightened antipoaching measures are needed in these and other protected areas to ensure that they do not become mere ‘paper parks’ for elephants,” the researchers write.

The situation may be worse for forest elephants (L. cyclotis), which scientists discovered only five years ago are a genetically distinct species. No one is quite sure how many forest elephants there are (the Great Elephant Census didn’t count them), but there are far fewer of these elephants than their savannah cousins. Like savannah elephants, forest elephants are dealing with losses from poaching, habitat loss and human conflict. A 2013 study estimated that they lost 62 percent of their numbers between 2002 and 2011, and a 2014 study estimated that as much as 10 to 18 percent of the forest elephant population disappears every year. And a new study finds that these elephants may be even less equipped than the savannah elephants to bounce back once poaching stops.
Because it has taken a long time to recognize that forest elephants are their own species, there isn’t a lot of basic biology known about them. But researchers collected data on more than 1,200 elephants that visited a forest clearing in the southwestern Central African Republic between 1990 and 2013, and have now used that data to make some startling observations about how forest elephants differ from savannah elephants. Their results appear August 31 in the Journal of Applied Ecology.

Biologically the two species of African elephants are fairly similar, but forest elephants have slowed down their reproduction. Female forest elephants can conceive when they are as young as 10 years — but most don’t. The elephants in the study reached sexual maturity as young as 13 and as old as 28 (the median was 23 years, compared with 12 for savannah elephants). And forest elephants breed only once every five to six years, compared with every three or four in savannah elephants. This means that a population of forest elephants would double in size at less than half the rate as savannah elephants.

The researchers suspect that this slow population growth is an outcome of living in the forest environment. Forest elephants rely on a diet of fruit, leaf matter and bark, but most forest growth happens at the treetops. So elephants are going to be limited in what and how much food they can find. “Low reproductive rates may in fact be the norm for large-bodied mammals in these rain forests,” the researchers write.

That wouldn’t be a problem except for the fact that their numbers are being driven lower and lower by poaching. The research team estimates that it could take 80 to 90 years for forest elephants to recover to their pre-poaching numbers — and that’s only if poaching stops. Savannah elephants would recover more quickly, but it would still take decades.

And that’s why the IUCN vote to potentially end the ivory trade is so important — because if we want to see elephants continue to roam Africa’s savannahs and forests, we need to stop the trade that is incentivizing people to kill them.

Anna Frebel can’t explain her fascination with the stars. It’d be like explaining why “berry purple-pink” is one of her favorite colors. “They are just a part of me,” says Frebel, an astronomer at MIT. “What’s going on with them and what they can tell us — there is something magical.”

Frebel’s fascination has led to the discovery of at least three record-breaking stars. Dating back roughly 13 billion years, the stars — all within the Milky Way galaxy — might be elders from the second generation of stars ever formed in the universe. She has also found that one of the tiny galaxies flitting around outside the Milky Way might be a fossil that has survived from not long after the Big Bang. The light from these ancient relics encodes stories about the birth of the first stars, the assembling of galaxies and the origin of elements essential to creating planets and life as we know i
“Anna has a really good track record of finding these amazing things,” says Alexander Ji, one of the three graduate students Frebel mentors at MIT. “She’s always finding things that change our understanding of the universe.”
As a young girl living in Germany, Frebel wanted to be an astronaut, but she passed on that dream when she learned about the centrifuge that whips trainees around to simulate launch acceleration. Not for her. She instead studied physics and astronomy, first at the University of Freiburg in Germany and then at the Australian National University in Canberra. Since then, Frebel, now 36, has earned a reputation as a “stellar archaeologist,” with the patience and perseverance to search through the universe’s most ancient debris.

Only someone with a galaxy’s worth of patience could sift through the tiny rainbows of light, the spectra, produced by thousands of stars, handpicking the specimens that might preserve clues to the conditions shortly after the first stars lit up the universe. And only a persistent person would spend more than two years pointing Australia’s 2.3-meter-wide Advanced Technology Telescope at 1,200 of the most promising candidates (“105 stars per night was my record,” she says) and eventually, with observations from other telescopes too, land on one star that was, for a while, among the oldest known.

She was first drawn to this research after hearing astronomer Norbert Christlieb, then a visiting researcher at the Australian National University, talk about his work on old stars. “It hit me: Oh my God, this project combines all my interests,” Frebel says. There were stars, chemistry, nuclear physics and the periodic table. “There are so many, for me, cool topics that come together.”

In combing through her stars, Frebel was looking for ones that contained hydrogen and helium — but little else. Most heavier elements up to iron are forged in the cores of stars, where atomic nuclei smash together. As the universe aged, its inventory of atoms such as carbon, silicon and iron steadily increased. The earliest stars, however, came on the scene when there were far fewer of these pollutants floating around.
Her efforts paid off in 2005 with a star branded HE 1327-2326, reported in

Nature

asthe most pristine star known at the time

. “She found one that took us closer back to the beginning of time as we know it,” says Frebel’s Ph.D. adviser, astronomer John Norris of Australian National. “It became clear to us early on that she was quite gifted.”

Her gifts netted her the Charlene Heisler Prize in 2007, given by the Astronomical Society of Australia for outstanding Ph.D. thesis. She has since won several recognitions, including the Annie Jump Cannon Award in 2010, given to notable young female researchers by the American Astronomical Society, for her “pioneering work in advancing our understanding of the earliest epochs of the Milky Way galaxy through the study of its oldest stars.”

Carbon seeding
The geriatric stars that Frebel finds are not perfectly pristine; they preserve in their atmospheres the chemical makeup of interstellar gas that had been seeded with a smidgen of heavy elements from the explosions of stars that came before. Chemical abundances in many of these stellar fossils are out of balance compared with modern stars. The fossil stars have much more carbon relative to iron, for example — carbon that had to have come from the debris of that very first crop of stars.

Frebel worked with theorists to show that excess carbon could have allowed successive generations of stars (and planets) to form, reporting the work in 2007 in Monthly Notices of the Royal Astronomical Society Letters. “I’ve always been interested in understanding the main message of the data,” she says, which leads her away from the telescope to computer simulations and theory. In this case, the message is that carbon “might have been the most important element in the universe.”

Gas needs to be cold, around –270° Celsius, just a few degrees above absolute zero, to clump and form stars. And carbon is an excellent coolant; its electrons are arranged in such a way to let it efficiently radiate energy. The first generation of stars didn’t have carbon’s help. They were probably slow to form and ended up as gargantuan fluffy orbs hundreds of times as massive as the sun. But once those stars exploded and seeded the cosmos with carbon, Frebel’s data suggest, subsequent generations of stars formed that would have looked more like the stars we see today.

Frebel likens her studies to watching her young son learn to walk and talk. “My overall interpretation is that the universe was still trialing things.”

Before she became a parent, she regularly went to one of the twin Magellan telescopes, 2,380 meters above sea level in the Chilean Atacama Desert. On long nights, while waiting for the telescope to soak up light from a star tens of thousands of light-years away, Frebel would feel the pull of the night sky. “I just lie on the ground and stare into the sky and get lost in the universe,” she says.

In recent years, Frebel has expanded her repertoire to include a horde of teeny galaxies that orbit the Milky Way and also serve as archaeological sites. “Now we can use not just one star,” she says. “We can use the entire galaxy as a fossil record.” One of these runts, called Segue 1, appears to be a remnant from the cosmic dawn and might be typical of the pieces that assembled into large galaxies like the Milky Way.

Frebel and her student Ji discovered that another dwarf galaxy, dubbed Reticulum II, contains clues about one of the mechanisms responsible for creating most of the elements heavier than iron. A long-ago smashup between two neutron stars once bombarded the gas in Reticulum II with neutrons, producing atoms, such as uranium, that can’t be formed in stellar cores. Similar run-ins in other galaxies might have helped build up the universe’s stockpile of heavy elements.

Frebel plans to continue her quest to understand the origin of atoms, stars and galaxies. Though the celestial bodies she studies are ancient, “my days never get old,” she says.

DENVER — Barnacles can tell a whale of a tale. Chemical clues inside barnacles that hitched rides on baleen whales millions of years ago could divulge ancient whale migration routes, new research suggests.

Modern baleen whales migrate thousands of kilometers annually between breeding and feeding grounds, but almost nothing is known about how these epic journeys have changed over time. Scientists can glean where an aquatic animal has lived based on its teeth. The mix of oxygen isotopes embedded inside newly formed tooth material depends on the region and local temperature, with more oxygen-18 used near the poles than near the equator. That oxygen provides a timeline of the animal’s travels. Baleen whales don’t have teeth, though. So paleobiologists Larry Taylor and Seth Finnegan, both of the University of California, Berkeley, looked at something else growing on whales: barnacles. Like teeth, barnacle shells take in oxygen as they grow.
Patterns of oxygen isotopes in layers of barnacle shells collected from modern beached whales matched known whale migration routes, Taylor said September 25 at the Geological Society of America’s annual meeting. Roughly 2-million-year-old barnacle fossils have analogous oxygen isotope changes, preliminary results suggest. Converting those changes into migration maps, however, will require reconstructing how oxygen isotopes were distributed long ago, Taylor said.

A South African flower catches flies with honey, or in this case, the smell of honeybees.

Several plant species lure potential pollinators with false promises of sweet nectar, sex or even rotting flesh. But Ceropegia sandersonii attracts its primary pollinator, Desmometopa flies, with the scent of fear. The flower mimics the chemical signals, or pheromones, released by alarmed western honeybees (Apis mellifera) during a predator attack. For flies that feast on the bees’ guts, it’s the perfect bait, Stefan Dötterl, a chemical ecologist at the University of Salzburg in Austria, and colleagues report online October 6 in Current Biology.
The team compared the compounds that make up the flower’s scent with pheromones released by the bees during simulated attacks. Not only did the two odors have several compounds in common, but the flies were strongly attracted to a mixture of a few of the shared compounds. That chemical cocktail has so far been observed only in the bees and C. sandersonii, the researchers say.

Before flies have a chance to wise up to the trickery, they become trapped inside the flower. The flies eventually escape about a day later, once the flower wilts, only to be duped by other flowers to finish the fertilizing task, Dötterl says.

PASADENA, Calif. — It’s hard being a comet sometimes. Comet 67P/Churyumov-Gerasimenko is developing stress fractures and might break apart in the next several hundred years.

Comet 67P is famous for its oddball shape. With two lobes joined together at a neck, it vaguely resembles an interplanetary peanut. The Rosetta spacecraft, which ended its 26-month visit to the comet in September (SN Online: 9/29/16), noticed a large crack in the neck in 2014. After the comet made its closest approach to the sun in August 2015, the fissure grew by several hundred meters and new cracks appeared.

The fractures appear to be developing as forces subtly bend the comet to and fro, Stubbe Hviid, a planetary scientist at the German Aerospace Center Institute of Planetary Research in Berlin, reported October 17 in a press conference at a meeting of the American Astronomical Society’s Division for Planetary Sciences. Hviid and colleagues combined maps from Rosetta with computer simulations of all the forces at work within the comet to determine how the cracks develop. They found that the two bulbous ends rock in opposite directions as the comet spins, flexing the neck and creating severe stress. Because the comet isn’t held together strongly — it’s a conglomeration of dust and ice not much stickier than snow, Hviid said — the neck is starting to break. After a few hundred more years, he said, the comet could fold itself in half as the two lobes snap apart and smoosh together.

VANCOUVER — Traces of long-lost human cousins may be hiding in modern people’s DNA, a new computer analysis suggests.

People from Melanesia, a region in the South Pacific encompassing Papua New Guinea and surrounding islands, may carry genetic evidence of a previously unknown extinct hominid species, Ryan Bohlender reported October 20 at the annual meeting of the American Society of Human Genetics. That species is probably not Neandertal or Denisovan, but a different, related hominid group, said Bohlender, a statistical geneticist at the University of Texas MD Anderson Cancer Center in Houston. “We’re missing a population or we’re misunderstanding something about the relationships,” he said.
This mysterious relative was probably from a third branch of the hominid family tree that produced Neandertals and Denisovans, an extinct distant cousin of Neandertals. While many Neandertal fossils have been found in Europe and Asia, Denisovans are known only from DNA from a finger bone and a couple of teeth found in a Siberian cave (SN: 12/12/15, p. 14).

Bohlender isn’t the first to suggest that remnants of archaic human relatives may have been preserved in human DNA even though no fossil remains have been found. In 2012, another group of researchers suggested that some people in Africa carry DNA heirlooms from an extinct hominid species (SN: 9/8/12, p. 9).

Less than a decade ago, scientists discovered that human ancestors mixed with Neandertals. People outside of Africa still carry a small amount of Neandertal DNA, some of which may cause health problems (SN: 3/5/16, p. 18). Bohlender and colleagues calculate that Europeans and Chinese people carry a similar amount of Neandertal ancestry: about 2.8 percent. Europeans have no hint of Denisovan ancestry, and people in China have a tiny amount — 0.1 percent, according to Bohlender’s calculations. But 2.74 percent of the DNA in people in Papua New Guinea comes from Neandertals. And Bohlender estimates the amount of Denisovan DNA in Melanesians is about 1.11 percent, not the 3 to 6 percent estimated by other researchers.

While investigating the Denisovan discrepancy, Bohlender and colleagues came to the conclusion that a third group of hominids may have bred with the ancestors of Melanesians. “Human history is a lot more complicated than we thought it was,” Bohlender said.

Another group of researchers, led by Eske Willerslev, an evolutionary geneticist at the Natural History Museum of Denmark in Copenhagen, recently came to a similar conclusion. Willerslev’s group examined DNA from 83 aboriginal Australians and 25 people from native populations in the Papua New Guinea highlands (SN: 10/15/16, p. 6). The researchers found Denisovan-like DNA in the study volunteers, the group reported October 13 in Nature. But the DNA is genetically distinct from Denisovans and may be from another extinct hominid. “Who this group is we don’t know,” Willerslev says. They could be Homo erectus or the extinct hominids found in Indonesia known as Hobbits (SN: 4/30/16, p. 7), he speculates.
But researchers don’t know how genetically diverse Denisovans were, says Mattias Jakobsson, an evolutionary geneticist at Uppsala University in Sweden. A different branch of Denisovans could be the group that mated with ancestors of Australians and Papuans.

Researchers know so little about the genetic makeup of extinct groups that it’s hard to say whether the extinct hominid DNA actually came from an undiscovered species, said statistical geneticist Elizabeth Blue of the University of Washington in Seattle. DNA has been examined from few Neandertal fossils, and Denisovan remains have been found only in that single cave in Siberia. Denisovans may have been widespread and genetically diverse. If that were the case, said Blue, the Papuan’s DNA could have come from a Denisovan population that had been separated from the Siberian Denisovans for long enough that they looked like distinct groups, much as Europeans and Asians today are genetically different from each other. But if Denisovans were not genetically diverse, the mysterious extinct ancestor could well be another species, she said.

Jakobsson says he wouldn’t be surprised if there were other groups of extinct hominids that mingled with humans. “Modern humans and archaic humans have met many times and had many children together,” he said.