Kepler's 'Alien Megastructure' Star to Spill SETI Secrets?

The star KIC 8462852 — informally known as Tabby's Star — has been the focus of the worlds' attention for months now, and for good reason. Its strange behavior could be a sign that there's a super-advanced alien civilization carrying out the mother of all engineering projects in orbit. But the mysterious dips in observed light from the star could alternatively just be a huge swarm of comets or some other as-yet-to-be-understood stellar phenomenon.

Although astronomers are generally skeptical that there really is an extraterrestrial civilization constructing a starlight-blocking megastructure only 1,480 light-years from Earth, the Breakthrough Listen SETI (Search for Extraterrestrial Intelligence) project is committing radio telescope time of one of the most powerful observatories on the planet to at least test the intelligent alien hypothesis.

The project is a part of the $100 million Breakthrough Prize Foundation that's funded by Russian entrepreneur Yuri Milner and backed by British theoretical physicist Stephen Hawking and Facebook founder Mark Zuckerberg.

Starting Wednesday (Oct. 26), a team of astronomers will use the renowned 100-meter Green Bank Telescope (pictured above) that is located deep in a radio-silent corner of West Virginia to study Tabby's Star. For eight hours per night for three nights over the next two months, a special instrument attached to the huge radio telescope will be used to carry out an unprecedented observation campaign of the star.

"The Breakthrough Listen program has the most powerful SETI equipment on the planet, and access to the largest telescopes on the planet," said Andrew Siemion, director of the Berkeley SETI Research Center and co-director of Breakthrough Listen, in a statement. "We can look at it with greater sensitivity and for a wider range of signal types than any other experiment in the world."

Although other projects have tried to eavesdrop on the star before, SETI campaigns have typically been limited by the number of radio frequencies that can be recorded simultaneously and the amount of time committed to just one star in the sky. This new instrument is able to record a huge amount of data across a range of frequencies at the same time, potentially allowing us to detect the radio transmissions from any transmitting intelligent aliens at Tabby's Star.

"The Green Bank Telescope is the largest fully steerable radio telescope on the planet, and it's the largest, most sensitive telescope that's capable of looking at Tabby's star given its position in the sky," said Siemion. "We've deployed a fantastic new SETI instrument that connects to that telescope, that can look at many gigahertz of bandwidth simultaneously and many, many billions of different radio channels all at the same time so we can explore the radio spectrum very, very quickly."

It's estimated that up to one petabyte of data may be collected over the observing run — that's enough data to fill a thousand computer hard drives (assuming each can store one terabyte). The researchers say that it could be over a month before we know whether or not a signal was detected because it will take a long time to process all the observations.

With Siemion, Tabetha Boyajian, from Louisiana State University, and visiting UC Berkeley astronomer Jason Wright will be heading the study. Boyajian was the first to report on KIC 8462852's peculiar light-curve in September 2015, which was initially flagged by citizen scientists participating in the Planet Hunters project. Tabby's Star is so-named in honor of Boyajian.

The project asks for the help of the public to look at candidate exoplanet transits from NASA's Kepler Space Telescope. Kepler has confirmed hundreds of worlds orbiting other stars by detecting the dip in brightness of a star (described by the star's "light-curve") by an exoplanet passing in front — an event known as a "transit." And the transit signal produced by Tabby's star was as dramatic as it was bizarre.

Typically, an exoplanet signal might dim a star's light by around 2%. But several of the irregular transits of Tabby's Star caused the starlight to drop by up to 22%. This means that something very big must be passing in front. What's more, it seems the star's brightness has been dimming for hundreds of years according to historical astronomical records, only adding to the intrigue. Although several ideas have been put forward to explain the signal, the key one being the possibility of a huge cloud of comets drifting in front of the star, all have fallen short of fully explaining the Kepler observation.

Read more at Discovery News

Cavemen Hunted Ice Age Lions to Extinction for Their Pelts

Evidence is mounting that humans played a primary role in the extinction of European cave lions, with new research finding that cavemen hunted the big cats for their pelts not too long before the lions disappeared from the face of the Earth.

One pelt once even decorated part of the cave site floor of La Garma in northern Spain, probably for symbolic and ritualistic purposes. Its remains, dating to about 16,000 years ago, are described in PLOS ONE.

The skin of animals was most commonly used to make clothing, "but this was not a common pelt," Marián Cueto of the University of Cantabria, Spain, told Seeker. "It comes from a lion, a very dangerous animal and surely one that was really difficult to hunt, so it probably had an important role as a trophy."

She went on to say that many societies, both past and present, viewed lions as symbols of power.

All that's left of the pelt are the lion's claws, which retain marks consistent with human modification of the overall pelt.

"We have observed cut-marks made by a silex (ground stone) instrument in all of them, indicating they separated the claws from the rest of the foot," Cueto explained. "These cut-marks are very clear and show expertise in skinning lions. They had knowledge of the anatomy: where to cut in the exact place."

Early Europeans could not have ignored cave lions, since female lions inhabited caves to raise their cubs and no doubt encountered people from time to time. Humans also hunted reindeer and other cave lion prey.

Cueto and her team suspect that, as the human population increased in Europe, they pushed out the cave lions in multiple ways, including killing them. Humans also contributed to the extinction of other iconic Ice Age animals. At least 177 large mammals, including the cave lion, went extinct as this era drew to a close. They include woolly mammoths, saber-tooth cats, mastodons and giant sloths.

The European cave lion bit the dust even earlier -- around 14,000 years ago -- so our hunting of them likely sped up the extinction.

No one knows just what these long-gone lions looked like. As Cueto said, "It's not easy describing the fur of an animal extinct in the Pleistocene because we have only recovered its skeleton."

The cave lion's skeleton is bigger but otherwise identical to modern lions, so scientists assume the animals would have looked pretty similar.

She added, however, that cave lions were included in cave paintings. Drawings of lions appear on the walls of caves at Chauvet (France), for example. Prehistoric figurines from Vogelherd Cave (Germany) also exist.

Read more at Discovery News

Some Alien Worlds Could Have 'Too Much' Water for Life

As with everything in life, too much of a good thing can be bad — and that logic now seems to apply to alien life, too.

Since Proxima Centauri b (or just Proxima b) was discovered in August, countless imaginings as to what the small, Earth-sized planet would look like up-close have captivated the media. Is the planet truly Earth-like with mountains, oceans, lush green continents and an atmosphere in just the right proportions to support extraterrestrial life? Or is it actually a dry, barren hellhole being constantly irradiated by its star? It could go either way.

As Proxima b was only detected by its gravitational influence on Proxima Centauri — the small exoplanet's orbit causes the tiny star to wobble — we only know its mass and orbital period. But these two characteristics are exciting. Not only is Proxima b of approximate Earth-mass, it also orbits within the star's habitable zone, the region surrounding a star that is neither too hot or too cold for liquid water to exist on the surface.

On Earth, where there's liquid water, there's life. So if Proxima b has water on its surface, it might also be in a liquid state, so there's certainly some excitement surrounding the possibility that the world may also play host to life. But so far, we have absolutely zero evidence that water is even there, so its life-giving potential is purely speculative.

Now, in new research by astrophysicists at the University of Bern, they've tackled this problem with planetary evolution models and found that red dwarf stars may preferentially host small, rocky worlds. Not only that, these worlds would likely contain large quantities of water.

"Our models succeed in reproducing planets that are similar in terms of mass and period to the ones observed recently," said Yann Alibert, of the Center of Space and Habitability (CSH) at the University of Bern, in a statement. "Interestingly, we find that planets in close-in orbits around these type of stars are of small sizes. Typically, they range between 0.5 and 1.5 Earth radii with a peak at about 1.0 Earth radius. Future discoveries will tell if we are correct!"

From this study, which has been accepted for publication in the journal Astronomy & Astrophysics, these small alien worlds also evolved with huge quantities of water. For 90% of the exoplanets simulated, their total mass consisted of over 10% water. Considering Earth is only 0.02% water, the simulated red dwarf exoplanets are veritable ocean planets!

At first glance, this might seem like an incredible opportunity for advanced life forms to evolve on planets in red dwarf systems. After all, red dwarfs are among the most ancient of stars in our galaxy and have a predicted lifespan of longer than the age of the universe (14 billion years). Life on Earth only sprung into being 3 billion years ago when our sun was young; life on red dwarf worlds could evolve over epic timescales by comparison.

And now it seems that, according to established planetary formation theories, these ancient worlds could have a plentiful supply of water? Well, the mind boggles.

But a huge supply of water on small exoplanets orbiting red dwarfs may not necessarily be a good thing. "While liquid water is generally thought to be an essential ingredient, too much of a good thing may be bad," said study co-author Willy Benz.

Read more at Discovery News

Philippines Island of Mindanao a Biodiversity Hot Spot

The Caraga region of northeast Mindanao, an island in the southern Philippines, has been identified as the top biodiversity hot spot for amphibians and reptiles in the country, the region boasting more species, for an area of its size, than any other in the Philippines.

That's according to researchers who have just documented 126 species in the area — including an array of frogs, snakes, lizards, turtles and crocodiles — in a new study in the online journal ZooKeys.

The island, with a history of environment loss, thanks largely to illegal logging in the timber-rich location, made for a challenging study subject, in terms of species location and documentation.

"Mindanao is a place where, unfortunately, the original forest cover was more than 85 percent, but now it's down to 6 percent original forest, and 15 percent is second-growth vegetation," said study co-author Rafe Brown, University of Kansas curator-in-charge of herpetology, in a statement.

"Mindanao has extensive mineral resources and forests with valuable timber," Brown explained. "Tropical rainforest soils are also very fertile, making the lowlands attractive to agribusiness. There's been conflict over those resources for hundreds of years."

Nonetheless, Brown and his colleagues forged on. Their efforts to explore the region paid off, to the tune of cataloging 49 lizards, 40 frogs, 35 snakes, a crocodile and a freshwater turtle.

And what efforts. It's one thing to ponder the number of species and another to actually have to go find them.

"We typically dig around tree trunks looking for animals that live underground," Brown said. "We search rivers and streams, turning over rocks, splitting open decaying logs looking for lizards or frogs. We climb trees, looking for tree-dwelling lizards, or place pitfall traps in the ground to catch lizards and small snakes that live in the leaf litter. We also use sticky traps like people use to catch pests in homes."

Here are a few of the critters Brown and his colleagues documented:

A white-lined water snake (Rhabdophis auriculata auriculata):

A frilled tree frog (Kurixalus appendiculatus):

And this cool, two-spotted flying lizard (Draco bimaculatus):

"The biodiversity is so high in this one pocket of northeast Mindanao, largely because the ranges of so many species in the archipelago overlap in this one area," said Brown. "We knew it was really diverse, but we didn't have a sense of this one area being the bull's-eye, the epicenter of this diversity."

Read more at Discovery News

A Massive Underground Find Revises the Tree of Life

So many new subterranean bacteria groups have just been found that the tree of life required a major revision.

The discovery of 47 new bacterial groups has just been reported from a single aquifer in Colorado, providing a vivid reminder of just how much life exists in the still mysterious subterranean world below our feet.

When added to 35 other new bacterial groups that were documented last year, the findings -- published in the journal Nature Communications -- double the number of the planet's known bacterial groups. As a result, dozens of new branches have just been added to the tree of life, essentially requiring a major revision of that all-encompassing diagram.

All of the known major bacterial groups are represented by wedges in this circular 'tree of life.'

"We did not initially expect anything like the diversity that was encountered at the site," co-author Jill Banfield told Seeker, explaining that she and her team started working on the Rifle aquifer along the Colorado River in west central Colorado "over a decade ago with the objective of studying microbes that remove uranium contamination from groundwater."

Banfield is a senior faculty scientist in Berkeley Lab's Climate & Ecosystem Sciences Division and a UC Berkeley professor. As the years went on at the research site near Rifle, Colo., she and her team noticed how complex and interconnected the microbial world there was -- so they developed the research site into a model system to study underground microbiology.

The researchers found so many new microbes that they struggled over how to name them. The prior study mentioning the 35 other groups drew from past Microbiology Award winners. For this latest research, they "decided to honor well-regarded microbiologists from around the world," Banfield said. "We made sure to strike a gender balance to ensure that women were given their due."

Genome-editing pioneer Jennifer Doudna inspired Candidatus doudnabacteria, for example.

To detect such tiny microbes, the scientists sent soil and water samples to the Joint Genome Institute for sequencing. The high-tech method isolates and purifies DNA from environmental samples, and then sequences 1 trillion base pairs of DNA at a time. Banfield's lab developed tools to analyze the data, permitting the reconstruction of the genomes of more than 2,500 microbes.

The underground microbes may be tiny, but they are more important than most of us probably think.

Lead author Karthik Anantharaman told Seeker that they are involved in many essential processes, such as breaking down the components of fertilizers. Nitrate from fertilizers can enter groundwater, where it may lead to the production of one of the most potent greenhouse gases, nitrous oxide, if certain microbes are inactive.

As for how microbes deal with fertilizers and other substances, Anantharaman explained that one microbe's waste is another microbe's food. This creates a tightly interconnected system.

"It is striking," he said, "that microbes need teamwork to complete tasks. It is precisely this lack of effective teamwork that can throw processes off sync and lead to release of greenhouse gases like nitrous oxide."

Read more at Discovery News

Violent Volcanic Eruptions on Jupiter Moon Io Mapped

Io's volcanism is unmatched by any other rocky body in the solar system. As Jupiter's innermost and third-largest moon, it is at the mercy of the gas giant's powerful tides. As a result, it is constantly erupting, unleashing incredibly powerful explosions, spewing molten rock all over its tortured surface.

Now, astronomers have been able to gather observations of the 2,000 mile-wide Io with two of the world's most powerful telescopes, watching it burn over two years.

"On a given night, we may see half a dozen or more different hot spots," said Katherine de Kleer, of UC Berkeley who led the 29 months of near-infrared observations using the 10-meter Keck II and the 8-meter Gemini North telescopes atop Mauna Kea in Hawaii. It is perhaps a little poetic that Mauna Kea is also a volcano, albeit a dormant one. "Of Io's hundreds of active volcanoes, we have been able to track the 50 that were the most powerful over the past few years."

As Io orbits Jupiter, slight changes in the moon's orbital distance can cause pretty dramatic changes in the tidal forces it experiences, causing friction from tidal heating. This mechanism delivers a huge amount of energy to Io's interior, keeping it in a molten state and driving perpetual volcanism.

During a flyby of Io in 1999, NASA's Jupiter mission Galileo captured this true-color observation of volcanic Io. Note the lack of impact craters; the surface of Io is constantly being renewed by fresh layers of lava.

By observing Io for so long, de Kleer's team was able to test some of the theoretical models that are thought to best describe the moon's eruptions. According to theory, the majority of the eruptions should be located either near the poles or the equator and, as Io is tidally locked to Jupiter, the pattern of volcanoes should be symmetrical between the forward-facing and rear-facing (to the direction of its orbit) hemispheres.

But on analyzing 100 days-worth of observations between August 2013 and December 2015, they found a surprising number of powerful, but short-lived eruptions all occurred on the rear-facing hemisphere and at higher latitudes than longer-lived eruptions.

"The distribution of the eruptions is a poor match to the model predictions," de Kleer said in a statement, "but future observations will tell us whether this is just because the sample size is too small, or because the models are too simplified. Or perhaps we'll learn that local geological factors play a much greater role in determining where and when the volcanoes erupt than the physics of tidal heating do."

Io, as seen in near-infrared wavelengths, exhibits a huge number of volcanic eruptions.

Another interesting finding focused on Loki Patera, Io's longest-living volcano that is believed to be a vast lake of molten lava. Every 2 years or so, it is believed the lava lake's cooling crust overturns, much like lava lakes that are found on Earth, triggering an intense brightening, and sending a wave of heat emissions around the lake. This causes destabilization and sinking of more crust and further heating.

Read more at Discovery News

Preferentially Earth-sized planets with lots of water

Artist’s impression of Earth-sized planets orbiting a red dwarf star.

Computer simulations by astrophysicists at the University of Bern of the formation of planets orbiting in the habitable zone of low mass stars such as Proxima Centauri show that these planets are most likely to be roughly the size of Earth and to contain large amounts of water.

In August 2016, the announcement of the discovery of a terrestrial exoplanet orbiting in the habitable zone of Proxima Centauri stimulated the imagination of the experts and the general public. After all this star is the nearest star to our sun even though it is ten times less massive and 500 times less luminous. This discovery together with the one in May 2016 of a similar planet orbiting an even lower mass star (Trappist-1) convinced astronomers that such red dwarfs (as these low mass stars are called) might be hosts to a large population of Earth-like planets.

How could these objects look like? What could they be made of? Yann Alibert and Willy Benz at the Swiss NCCR PlanetS and the Center of Space and Habitability (CSH) at the University of Bern carried out the first computer simulations of the formation of the population of planets expected to orbit stars ten times less massive than the sun.

"Our models succeed in reproducing planets that are similar in terms of mass and period to the ones observed recently," Yann Alibert explains the result of the study that has been accepted for publication as a Letter in the journal "Astronomy and Astrophysics." "Interestingly, we find that planets in close-in orbits around these type of stars are of small sizes. Typically, they range between 0.5 and 1.5 Earth radii with a peak at about 1.0 Earth radius. Future discoveries will tell if we are correct!" the researcher adds.

Ice at the bottom of the global ocean

In addition, the astrophysicists determined the water content of the planets orbiting their small host star in the habitable zone. They found that considering all the cases, around 90% of the planets are harbouring more than 10% of water. For comparison: Earth has a fraction of water of only about 0,02%. So most of these alien planets are literally water worlds in comparison! The situation could be even more extreme if the protoplanetary disks in which these planets form live longer than assumed in the models. In any case, these planets would be covered by very deep oceans at the bottom of which, owing to the huge pressure, water would be in form of ice.

Water is required for life as we know it. So could these planets be habitable indeed? "While liquid water is generally thought to be an essential ingredient, too much of a good thing may be bad," says Willy Benz. In previous studies the scientists in Bern showed that too much water may prevent the regulation of the surface temperature and destabilizes the climate. "But this is the case for Earth, here we deal with considerably more exotic planets which might be subjected to a much harsher radiation environment, and/or be in synchronous " he adds.

Following the growth of planetary embryos

To start their calculations, the scientists considered a series of a few hundreds to thousands of identical, low mass stars and around each of them a protoplanetary disk of dust and gas. Planets are formed by accretion of this material. Alibert and Benz assumed that at the beginning, in each disk there were 10 planetary embryos with an initial mass equal to the mass of the Moon. In a few day's computer time for each system the model calculated how these randomly located embryos grew and migrated. What kind of planets are formed depends on the structure and evolution of the protoplanetary disks.

Read more at Science Daily

The universe is expanding at an accelerating rate, or is it?

The universe may not be expanding at an accelerating rate, as previously thought, but rather, at a constant rate, suggests new research.

Five years ago, the Nobel Prize in Physics was awarded to three astronomers for their discovery, in the late 1990s, that the universe is expanding at an accelerating pace.

Their conclusions were based on analysis of Type Ia supernovae -- the spectacular thermonuclear explosion of dying stars -- picked up by the Hubble space telescope and large ground-based telescopes. It led to the widespread acceptance of the idea that the universe is dominated by a mysterious substance named 'dark energy' that drives this accelerating expansion.

Now, a team of scientists led by Professor Subir Sarkar of Oxford University's Department of Physics has cast doubt on this standard cosmological concept. Making use of a vastly increased data set -- a catalogue of 740 Type Ia supernovae, more than ten times the original sample size -- the researchers have found that the evidence for acceleration may be flimsier than previously thought, with the data being consistent with a constant rate of expansion.

The study is published in the Nature journal Scientific Reports.

Professor Sarkar, who also holds a position at the Niels Bohr Institute in Copenhagen, said: 'The discovery of the accelerating expansion of the universe won the Nobel Prize, the Gruber Cosmology Prize, and the Breakthrough Prize in Fundamental Physics. It led to the widespread acceptance of the idea that the universe is dominated by "dark energy" that behaves like a cosmological constant -- this is now the "standard model" of cosmology.

'However, there now exists a much bigger database of supernovae on which to perform rigorous and detailed statistical analyses. We analysed the latest catalogue of 740 Type Ia supernovae -- over ten times bigger than the original samples on which the discovery claim was based -- and found that the evidence for accelerated expansion is, at most, what physicists call "3 sigma." This is far short of the "5 sigma" standard required to claim a discovery of fundamental significance.

'An analogous example in this context would be the recent suggestion for a new particle weighing 750 GeV based on data from the Large Hadron Collider at CERN. It initially had even higher significance -- 3.9 and 3.4 sigma in December last year -- and stimulated over 500 theoretical papers. However, it was announced in August that new data shows that the significance has dropped to less than 1 sigma. It was just a statistical fluctuation, and there is no such particle.'

There is other data available that appears to support the idea of an accelerating universe, such as information on the cosmic microwave background -- the faint afterglow of the Big Bang -- from the Planck satellite. However, Professor Sarkar said: 'All of these tests are indirect, carried out in the framework of an assumed model, and the cosmic microwave background is not directly affected by dark energy. Actually, there is indeed a subtle effect, the late-integrated Sachs-Wolfe effect, but this has not been convincingly detected.

'So it is quite possible that we are being misled and that the apparent manifestation of dark energy is a consequence of analysing the data in an oversimplified theoretical model -- one that was in fact constructed in the 1930s, long before there was any real data. A more sophisticated theoretical framework accounting for the observation that the universe is not exactly homogeneous and that its matter content may not behave as an ideal gas -- two key assumptions of standard cosmology -- may well be able to account for all observations without requiring dark energy. Indeed, vacuum energy is something of which we have absolutely no understanding in fundamental theory.'

Read more at Science Daily

How snakes lost a blueprint for making limbs

This image depicts mouse embryos with the ZRS from cobra or python inserted into their genomes, replacing the normal gene regulator. Their truncated limb development is visible in the comparative bone scans.

Snakes lost their limbs over 100 million years ago, but scientists have struggled to identify the genetic changes involved. A Cell paper publishing October 20 sheds some light on the process, describing a stretch of DNA involved in limb formation that is mutated in snakes. When researchers inserted the snake DNA into mice, the animals developed truncated limbs, suggesting that a critical stretch of DNA lost its ability to support limb growth during snake evolution.

"This is one of many components of the DNA instructions needed for making limbs in humans and, essentially, all other legged vertebrates. In snakes, it's broken," says Axel Visel, a geneticist at the Lawrence Berkeley National Laboratory and senior author on the paper. "It's probably one of several evolutionary steps that occurred in snakes, which, unlike most mammals and reptiles, can no longer form limbs."

Today's serpents have undergone one of the most dramatic body plan changes in the evolution of vertebrates. To study the molecular roots of this adaptation, Visel and his colleagues started looking at published snake genomes, including the genomes from basal snakes such as boa and python, which have vestigial legs -- tiny leg bones buried in their muscles -- and advanced snakes, such as viper and cobra, which that have lost all limb structures. Within these genomes, they focused specifically on a gene called Sonic hedgehog, or Shh, involved in many developmental processes -- including limb formation. The researchers delved further into one of the Shh gene regulators, a stretch of DNA called ZRS (the Zone of Polarizing Activity Regulatory Sequence) that was present but had diverged in snakes.

To determine the consequences of these mutations, the researchers used CRISPR, a genome-editing method, to insert the ZRS from various other vertebrates into mice, replacing the mouse regulator. With the ZRS of other mammals, such as humans, the mice developed normal limbs. Even when they inserted the ZRS from fish, whose fins are structurally very different from limbs, the mice developed normal limbs. However, when the researchers replaced the mouse ZRS with the python or cobra version, the mice went on to develop severely truncated forelimbs and hindlimbs.

"Using these new genomic tools, we can begin to explore how different evolutionary versions of the same enhancer affect limb development and actually see what happens," says Visel. "We used to be mostly staring at sequences and speculating about molecular evolution, but now, we can really take these studies to the next level."

To identify the mutations in the snakes' ZRS that were responsible for its inactivation during snake evolution, the researchers took a closer look at the evolutionary history of individual sequence changes. By comparing the genomes of snakes and other vertebrates, they identified one particularly suspicious 17 base-pair deletion that only occurred in snakes; this deletion removed a stretch of the ZRS that has a key role in regulating the Shh gene in legged animals.

The research team turned back the evolutionary clock, restoring the missing 17 base pairs in an artificially created hybrid version of the python ZRS, and tested the edited DNA in mice. Those that carried this evolutionarily "resurrected" ZRS in their genome, replacing their normal regulator, developed normal legs. However, Visel cautions that the evolutionary events were probably more complex than just the one deletion: "There's likely some redundancy built into in the mouse ZRS. A few of the other mutations in the snake ZRS probably also played a role in its loss of function during evolution."

Read more at Science Daily

Ancient human history more complex than previously thought, researchers say

Primitive people (stock image). New research results suggest that throughout Eurasia, ancient populations interbred less than previously believed, and that -- contrary to previous findings -- the level of mixing with Neanderthals did not differ significantly between Europe and East Asia.

Relationships between the ancestors of modern humans and other archaic populations such as Neanderthals and Denisovans were likely more complex than previously thought, involving interbreeding within and outside Africa, according to a new estimator developed by geneticists. Findings were reported at the American Society of Human Genetics (ASHG) 2016 Annual Meeting in Vancouver, B.C.

In recent years, genetics has led to the revision of many assumptions about archaic populations, explained Ryan J. Bohlender, PhD, a postdoctoral researcher at the University of Texas MD Anderson Cancer Center and first author on the research. For example, the 2010 release of the Neanderthal genome led to the discovery that Neanderthals and the ancestors of modern Europeans interbred. A few years later, scientists discovered the existence of Denisovans, a population known of only through genetics, through a fossilized sample of DNA.

"My colleagues and I set out to find out what we might share with these ancient populations and how our histories interacted," Dr. Bohlender said. They developed an estimation tool to model these interactions based on parameters such as current estimates of population size and dates when populations separated -- how long ago they stopped interbreeding -- and look for inconsistencies with information known from genetic studies about the overlap between the modern human genome and those of ancient populations. Compared to previous estimators, this one made increased use of genetic data to cut down on statistical bias. The researchers then allowed estimates of population size and separation dates to vary in a series of simulations, in order to find out if adjusting these parameters better fit the genetic data.

"Using this process, we found that the population in Africa was likely about 50 percent larger than previously thought. We also found that an archaic-modern human separation date of 440,000 years ago was the best fit, suggesting that Neanderthals diverged from our lineage 100,000 years more recently than we thought," Dr. Bohlender said. "We got the same separation date using data from multiple modern human populations, which is a good sign."

In addition, their results suggest that throughout Eurasia, ancient populations interbred less than previously believed, and that -- contrary to previous findings -- the level of mixing with Neanderthals did not differ significantly between Europe and East Asia.

The findings bring up many new questions, including to what extent the new estimator can be trusted, why it produces results that differ from prevailing estimates, and how to reconcile these differences.

"Overall, our findings confirm the human family tree is more complicated than we think it is," Dr. Bohlender said. "For example, other archaic populations are likely to have existed, like the Denisovans, who we didn't know about except through genetics." They plan to try out simulations with multiple other populations, to see if this adds some clarity to the results.

Dr. Bohlender also believes that more detailed studies of African populations may shed some light. "Africans have been underrepresented in genetics research -- they're not as well studied as European and Asian populations, yet they are more diverse genetically than any other group," he said.

From Science Daily