Asteroid enthusiasts, rejoice! Thursday, June 30 is your day to remind the world that humankind is just one impact with a space rock away from annihilation (or, at the least, a very bad day).

Asteroid Day, started in 2015, brings together scientists, artists and concerned citizens to raise awareness of the hazards of asteroid impacts and build support for solutions that might avert disaster from the skies. Events are planned at museums, science centers and other locations around the world.

The date coincides with the anniversary of the most powerful impact in recorded history, when a roughly 40-meter-wide asteroid crashed near Tunguska, Siberia, in 1908. The run-in flattened about 2,000 square kilometers of forest and released about 185 times the energy of the atomic bomb detonated over Hiroshima. Estimates vary, but such collisions happen roughly once every several hundred to 1,000 years.

Homo naledi, currently the best-known and most mysterious fossil species in the human genus, may be considerably younger than previously thought, a new investigation suggests.

Evolutionary trees of ancient hominids statistically reconstructed from skull and tooth measurements indicate that H. naledi lived around 912,000 years ago, say paleoanthropologist Mana Dembo of Simon Fraser University in Burnaby, Canada, and her colleagues. That’s a provisional estimate, since researchers have yet to date either H. naledi’s bones or the sediment in which some of its remains were excavated.
The new statistical age estimate, described by Dembo’s group in the August Journal of Human Evolution, challenges proposals that H. naledi’s remains come from early in Homo evolution. Researchers who first studied H. naledi bones retrieved from an underground cave in South Africa noted similarities of the skull and several other body parts to early Homo species dating to between 2.5 million and 1.5 million years ago (SN: 10/3/15, p. 6).

A comparison of H. naledi skull measurements to those of 10 other hominid species, conducted by paleoanthropologist J. Francis Thackeray of the University of the Witwatersrand in Johannesburg, reached the same conclusion. H. naledi lived roughly 2 million years ago, Thackeray proposed in the November/December 2015 South African Journal of Science.

Dembo disagrees. Her team tested which of 60,000 possible evolutionary trees best fit skull and tooth measurements of H. naledi, 20 other hominid species, gorillas and chimpanzees. The new analysis keeps H. naledi in the genus Homo. But it’s still unclear which of several hominid species — including Homo sapiens, Homo floresiensis (or “hobbits”) and Australopithecus sediba (SN: 8/10/13, p. 26) — is most closely related to the South African species.

Dembo’s team found no signs that bones assigned to H. naledi represent a variant of Homo erectus, as some scientists have argued. H. erectus originated about 1.8 million years ago in Africa and rapidly spread to West Asia. But Dembo’s statistical model assumes that H. erectus skulls and teeth vary in shape throughout Africa and Asia much less than they actually do, says paleoanthropologist Christoph Zollikofer of the University of Zurich. Bones assigned to H. naledi most likely represent a form of H. erectus, he argues.

Further statistical comparisons that include measurements of limb and trunk bones may help to clarify H. naledi’s evolutionary relationships, Dembo says.
Based on geological dates for all hominids except H. naledi, the researchers also calculated the rate at which each species’ skull and tooth features evolved over time. Those results enabled the researchers to estimate H. naledi’s age.

“Homo naledi might be less than a million years old,” Dembo says. She considers that estimate “reasonably robust,” since ages calculated for other hominids in the analysis often fell close to dates gleaned from fossil and sediment studies. In a few cases, though, statistical and geological age estimates differed by 800,000 years or more.

A relatively young age for H. naledi expands the number of Homo species that survived well into the Stone Age, Dembo says. Small-brained H. naledi would have existed at the same time as larger-brained Homo species in Africa, just as small-brained H. floresiensis lived at the same time as larger-brained H. sapiens and H. erectus in Southeast Asia (SN: 7/9/16, p. 6).

If that scenario holds up, H. naledi may have made roughly 1-million-year-old stone tools that have been found in southern Africa, Dembo says.

“A young date for Homo naledi shouldn’t be unexpected,” says paleoanthropologist Matthew Tocheri of Lakehead University in Thunder Bay, Canada. At least some H. naledi bones appear not to have fossilized, he notes, consistent with a more recent age.

While Dembo’s statistical approach to hominid evolution shows promise, “a good geological date for H. naledi will trump the new date,” Tocheri adds.

Paleoanthropologist Bernard Wood of George Washington University in Washington, D.C., doesn’t think Dembo’s approach can accurately date H. naledi. But humanlike hands, feet and teeth of the South African hominid support the possibility that it lived about 1 million years ago, Wood says.

Two H. naledi researchers — John Hawks of the University of Wisconsin–Madison and Witwatersrand’s Lee Berger — still suspect the South African species lived at least 1.8 million years ago, based on its skeletal similarities to H. erectus. But a possible age of about 900,000 years for the cave finds, as proposed by Dembo, would be consistent with H. naledi or closely related species having survived in Africa for a million years or more, Hawks and Berger write in the current Transactions of the Royal Society of South Africa.

In our teens and 20s, many of us feel unstoppable. But after age 30, everyday life starts to get a little harder. Knees ache, hangovers last two days, younger family members begin to outrun us and we can’t remember what we did with our keys. With aches, pains and busy schedules, exercise can be a low priority, especially when it won’t necessarily help our waistlines. But exercising as we age can help preserve muscle mass so we can go the distance. It can even help us remember our keys.

After we hit 35, most of us just aren’t as strong or as fast as we used to be. “In normal aging there are a lot of physiological things that happen that decrease performance over the years,” explains Myriam Paquette, an exercise physiologist at Laval University in Quebec City. She notes that the maximum amount of oxygen we can use (VO2 max) and our overall muscle mass decrease, and, along with them, the strength and power they provide.

Exercise training can keep some of these effects at bay. “As soon as you hit 35 or 40, you need to start doing resistance [exercise],” says John Hawley, an exercise physiologist at Australian Catholic University in Sydney. “You muscles are being remodeled constantly. “As the muscle gets older … it gets resistant to building up.” So the older people get, the harder they have to work to get — and keep — their gains.

For VO2 max, decreases in maximum oxygen can mean decreased athletic performance. But “if people do high intensity training, that can be delayed five to 10 years,” says Michael Joyner, a physiologist at the Mayo Clinic in Rochester, Minn.

Enough exercise can even keep older athletes racing with the pros — as long as they run far enough. Sian Allen and Will Hopkins at the Sports Performance Research Institute New Zealand in Auckland gathered studies of peak competitive performance and found that for elite athletes, peak performance age increased as distance increased. Athletes who compete in short swimming events tended to peak at 20, while ultra-distance cyclists peaked at 39, they reported in the June 2015 Sports Medicine. Some of this may be for social reasons, Joyner notes — until the past few decades, distance events didn’t have the focus or coaching (or funding) that is characteristic of sprint distances.

Older athletes may not be at peak VO2 max and muscle mass, but they can take advantage of something only age provides — experience. “Being able to react to changes in conditions, mental resilience, pacing strategies, these are things you are able to accumulate,” Allen says. She suggests that learning and experience may assist people competing at later ages across longer distances, “As opposed to shorter distances that…[are] more raw expression of power.”

Age also takes a toll on the brain. This isn’t just for the retirees: Word recall, spatial reasoning and even processing speed can begin to decline in the early 30s. One of the brain benefits of exercise is an increase in the birth of new brain cells. As we get older, exercise proves protective both for brain structure and function. Sedentary people show decreases in white and gray matter as they age. Physical activity, even walking 72 blocks per week, helps preserve gray matter in older adults in areas such as the hippocampus — a brain area important for memory. Keeping up aerobic activity also improves cognitive control in middle-aged and older people — including tasks such as planning and working memory.
Some of this might be associated with the fact that keeping up aerobic activity means retaining VO2 max, says Takashi Tarumi, an exercise physiologist at the University of Texas Southwestern Medical Center in Dallas. Middle-aged endurance athletes with higher VO2 max also have better brain blood flow. That better blood flow is associated with better performance in memory and attention tasks — key to remembering where exactly you put those keys. Tarumi and his colleagues published their results in a 2013 study in the Journal of Hypertension.

While working out for weight loss or a beach body may be an exercise primarily in frustration, exercise is far from fruitless. It’s an investment toward stronger muscles and better endurance — whether for marathons or getting up the stairs. And staving off cognitive decline is probably well worth a few hours in the gym.

When asked the right way, a savvy bird species steers African hunter-gatherers to honey. All it takes is a loud trill followed by a grunt that sounds like “brrr-hm.”

Birds known as greater honeyguides (Indicator indicator) lead hunter-gatherers in Mozambique to honey-rich bees’ nests after hearing humans make this signature call, say evolutionary ecologist Claire Spottiswoode of the University of Cambridge and her colleagues. In exchange, the birds get human-aided access to perilous-to-reach food, the scientists report in the July 22 Science.

The new study provides the first solid evidence of two-way, collaborative communication between humans and a nonhuman animal in the wild. In some parts of the world, dolphins help fishermen herd fish into nets. But it’s unclear whether these dolphins respond to specific calls from fishermen.

Honeyguides associate Yao hunter-gatherers’ distinctive honey-hunting call with successful joint food hunts, Spottiswoode says. The birds respond to this call by making a loud chattering sound to alert humans to their presence. Honeyguides then fly from tree to tree until reaching one with a bees’ nest.
Although the wax-eating birds regularly scope out locations of bees’ nests in their home ranges, getting beeswax out of nests is dangerous. “Angry bees can and do sting honeyguides to death,” Spottiswoode says.

Yao honey hunters cut down trees containing bees’ nests nestled high up in crevices and smoke the insects out with flaming bundles of twigs and leaves. After removing honeycombs from nests, the Yao leave beeswax behind for their avian helpers and even put wax chunks on beds of leaves to reward honeyguides.

Written accounts of honeyguide-led expeditions to bees’ nests date to as early as 1588. But ax-like stone implements and human-made fires date to 1 million years ago or more (SN: 7/9/16, p. 10). So humans and honeyguides may have hunted together for at least that long, says Harvard University biological anthropologist Richard Wrangham.

In different parts of Africa, honeyguides respond to local honey-hunting calls of human groups, Spottiswoode suspects. A team led by Yale University biological anthropologist Brian Wood has found that Hadza honey hunters in Tanzania make a whistling sound to attract honeyguides. Other hunter-gatherers speak or shout words to call honeyguides, Wood says.
Unlike Yao honey hunters, the Hadza bury or burn much of the wax in bees’ nests. Hadza honey seekers believe this keeps honeyguides hungry and motivates them to lead further hunts. Wood’s team estimates that 8 to 10 percent of the Hadza’s diet comes from honeyguide-led hunts.

The new study “carefully documents one cultural tradition in how people and honeyguides interact,” Wood says.
Spottiswoode’s group conducted fieldwork in October 2013 and September and October 2015. The researchers tracked movements of six honeyguides fitted with radio transmitters. Overall, 73 of 97 bird-led honey hunts found at least one bees’ nest. During the study, nearly three-quarters of 149 bees’ nests found by the Yao involved honeyguide assistance.

In another experiment, Spottiswoode accompanied two Yao honey hunters on 72 searches for bees’ nests, each lasting 15 minutes. While they walked, a portable speaker played recordings every seven seconds either of a Yao honey hunter making the “brrr-hm” sound, a Yao individual saying words such as “honeyguide” or their own name, or a ring-necked dove’s song or excitement call.

Honeyguides joined 30 experimental searches. About two-thirds of searches that featured “brrr-hm” calls drew honeyguides’ assistance (although they did not always locate a bees’ nest). One-quarter of hunts that used recordings of words and one-third of those that played dove sounds received honeyguides’ help.

Spottiswoode’s team calculates that honey hunters who played the “brrr-hm” sound more than tripled their chances of actually finding a bees’ nest during 15-minute searches, compared with honey hunters who played Yao words or dove sounds.

Spottiswoode and Wood plan to investigate whether young honeyguides learn from adult birds to pay attention to humans’ honey-hunting calls and to lead humans to bees’ nests.

In the space business, weight and size are what run up the bills. So imagine the appeal of a telescope that’s a tenth to as little as a hundredth as heavy, bulky and power hungry as the conventional instruments that NASA and other government agencies now send into space. Especially alluring is the notion of marrying the time-tested technology called interferometry, used in traditional observatories, with the new industrial field of photonics and its almost unimaginably tiny optical circuits.

Say hello to SPIDER, or Segmented Planar Imaging Detector for Electro-optical Reconnaissance.
But its inventors believe that, once demonstrated at full-scale, SPIDER will replace standard telescopes and long-range cameras in settings where room is scarce, such as on planetary probes and reconnaissance satellites.

Researchers at the Lockheed Martin Advanced Technology Center in Palo Alto, Calif., with partners in a photonics lab at the University of California, Davis, have described work on SPIDER for several years at specialty conferences. In January, they revealed their progress with a splash to the public in a press release and polished video.

Somewhat like a visible-light version of a vast field of radio telescopes, but at a radically smaller scale, a SPIDER scope’s surface would sparkle with hundreds to thousands of lenses about the size found on point-and-shoot cameras. The instrument might be a foot or two across and only as thick as a flat-screen TV.

Transit system for light
SPIDER probably won’t be equivalent to a large instrument such as the Hubble Space Telescope, but it could be a smaller, lighter alternative to modest telescopes and long-range cameras. Experts tend to rank telescopes by their aperture — the size of the bucket that catches light or other such radiation. The wider the bucket’s mouth, the higher the resolution. Ordinarily, behind the bucket’s maw is an extensive framework for massive lenses, mirrors and heating or cooling systems. Hubble’s aperture spans 2.4 meters; its power-generating solar panels enlarge it to the size and weight of a winged city bus. Even a compact telescope with a saucer-sized lens might have more than a kilogram of equipment stretched behind its face for a third of a meter or so.
Alan Duncan, a senior fellow at Lockheed Martin’s Advanced Technology Center, has devoted much of his career to space and reconnaissance imaging. He often focuses on interferometry, a method astronomers have long used to combine electromagnetic waves — both radio and visible — from several different telescopes. The results, with the help of computers, are images more sharply focused than from any of the smaller telescopes or radio dishes. Yet even with the leverage of conventional interferometry, Duncan struggled to slash the SWaP: size, weight and power demand.

His ambitions leapt at the Photonics West 2010 meeting in San Francisco. He learned that IBM researchers had a supercomputer design that would need relatively little energy to cool its electronic innards. They proposed finely laced channels through which data-filled beams of light would travel to deliver the computer’s output data. The setup would require a fraction of the energy of standard, integrated electronic chips that use metal wiring.
Duncan stared at the skeins of optical channels and the millions of junctions portrayed on the screen during the IBM talk. He recalls seeing “about as many optical interconnects as a digital camera has pixels.” (A point-and-shoot camera’s pictures can have several megapixels, or millions of individual dots.) He imagined turning IBM’s tactic on its head. “They create photons in the chip, impose information on them and send them out to be decoded. What if you captured the light waves on the outside?” Duncan says. “The photons already have the [image] information you want.… You have to decode it inside the device. The decoder is the interferometer.”

The IBM people had not designed an interferometer, of course, but their optical circuitry seemed sophisticated enough to be adaptable to interferometry. Duncan figured that the fast-growing photonics industry already had or would soon invent fabrication solutions that his suddenly imagined telescope could use. Already, photonics companies were selling machines to create transparent channels or waveguides only a few millionths of a meter wide.

Considerably smaller than the fibers bundled into fiber-optic cables that carry data across continents and under oceans, photonic waveguides are made by finely focused, pulsating laser beams. As the beams scan along inside silicon-based photonic integrated circuits, or PICs, they leave behind close-packed strings in molten silicon that swiftly merge and cool. The resulting trails of transparency are superb transit systems for light, and they can be laser-incised in any pattern desired. Similar wizardry can shrink the scale of other optical gadgetry, such as filters to sort the signals by color, or the interferometry gadgetry to mix signals from different lenses in a SPIDER scope.

Decoding fringes
Interferometry does not produce pictures the way a conventional telescope does. Telescopes refract a scene’s incoming light through lenses or bounce it off of mirrors. The lenses or mirrors are shaped so that light beams, or photons, from a given part of a scene converge on a corresponding place on a photo-sensitive surface such as an image chip of a digital camera, similar to the retina of an eye.

Interferometry, instead, gathers signals from pairs of receivers — sometimes many pairs — all aimed at the same scene. It combines the signals to reveal the slight differences in the phases and strengths of the radio, light or other waves. The separate wave trains, or signals, are projected on a screen in an interferometry chamber as patterns of light and dark fringes where the signals from the paired receivers reinforce or counteract each other. The fringes, somewhat resembling checkout counter bar codes, carry a distinct, encoded hint of the difference in the viewed object as seen from the receivers’ offset positions in the aperture. With enough measurements of fringes from enough pairs of waves gathered by enough small receivers, a computer can deduce a picture that is as sharp as from a telescope with a lens as wide as the distance between the most widely spaced lenses, for example, on a SPIDER’s face.
Building a tiny version of this using photonics requires separate sets of waveguides for different colors or “spectral bins.” The more bins used, the more accurately an object can be portrayed. But each such layer of complexity aggravates the chore of fabrication.
So even a bare-bones SPIDER may need thousands of waveguides. Advanced SPIDERs may have millions of them. As far as Duncan knows, SPIDER would be the most complicated interferometer ever made.

Spycraft and space views
After his epiphany, Duncan began working with Lockheed colleagues, chiefly technology expert Richard L. Kendrick. Computed simulations convinced them that their mini-interferometer should work. In 2012, Lockheed Martin filed for a patent — granted in late 2014 — naming the two men as the inventors. Reflecting the company’s defense ties, the document provides a hypothetical application: SPIDER in a proposed, high-altitude Pentagon recon drone called Vulture, perhaps built into the curved bottom of a wing.

Initial simulations showed how SPIDER’s pictures of one satellite taken from another, or of buildings as seen from space, compare with pictures by standard long-range cameras. Interferometric images, due to the complex calculations using the equations of Fourier transforms, often have extra flares and streaks. Nonetheless, to a layman’s eye, the simulated SPIDER images look about the same as equivalent ones from standard lens or mirror telescopes.

If SPIDER pans out, its inventors imagine uses beyond spycraft. NASA is planning a mission to orbit Jupiter’s moon Europa (SN Online: 5/26/15). The SPIDER team calculates that, given the same space that has already been assigned to a conventional imager, SPIDER’s instrument could inspect 10 times the terrain at 17 times better resolution. SPIDER should be able to have a wider array of lenslets — or receivers — take pictures at points farther from Europa on the craft’s elliptical orbit and should have a wider field of view.

One proposed design for the first fully operable, but spartan, SPIDER is to have 37 radial blades, each backed by a single photonic chip with 14 lenslets along one edge. The whole model would be about the size of a dinner plate. Eventually, a SPIDER might be built on the face of a single chip of similar or larger size. This would allow more lenslets to be fitted, and permit waveguides to pair them up from anywhere in the aperture. Upshot: more “eyes” packed into the same space.
The Lockheed group has begun to fabricate test components in partnership with a photonics laboratory led by Ben Yoo, professor of electrical and computer engineering at UC Davis. DARPA, the Department of Defense’s agency for funding advanced research, granted about $2 million for prototype photonic integrated circuits and other gear to test the idea’s feasibility.

The technical challenges are extreme. Each tiny lenslet could need 200 or more separate waveguides leading from its focal area to the interferometers. For a fairly simple SPIDER scope, that would mean tens of thousands of waveguides coursing through the chips’ insides — perhaps fabricated many layers deep. So far, the researchers have built prototype components with only four lenslets, too few to get images.

Skeptics and a crusader
At least one top authority says the scheme is nonsense. Others are more amused than critical. Michael Shao, an MIT-trained astronomer and project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., has extensive experience with interferometry. He calls the concept of SPIDER “fundamentally sound,” but adds that it will require such extensive optical plumbing on a photonic scale that the sheer complexity “would scare a lot of folks away.” If the SPIDER team makes it work, great. “But it is a lot of work to save a little space.”

Peter Tuthill, an astronomer at the University of Sydney in Australia, leads one of the world’s busiest interferometry groups. His team has augmented such large conventional ground-based telescopes as the Keck Observatory in Hawaii with auxiliary interferometers. His group also designed an interferometer to be included on the James Webb Space Telescope, planned successor to the Hubble. After looking over the SPIDER proposal, he declared by e-mail, “I think the argument made that this can be somehow cheaper, simpler, lower mass and higher performance than conventional optics appears not to pass the laugh test.”

The extremely large number of waveguides in the SPIDER design, he added, would leave the signal strength per waveguide too feeble — hence vulnerable to swamping by noise in the system. “In short, I don’t think (the SPIDER team members) are waiting for technology to enable their platform. I think they are waiting for a miracle that defies physics.”

Duncan just smiles when he hears Tuthill’s opinion. Even if technical difficulties delay or quash this initial SPIDER project, he is confident somebody will step in and surmount any barriers. “It will happen,” he says.

Like an interplanetary parfait, the dwarf planet Ceres appears to have layers.

A pliable outer shell of minerals, ices and salts encapsulates a core of solid rock, a new study suggests. This first peek inside Ceres — courtesy of NASA’s Dawn spacecraft — can help researchers explain some mysteries on the surface and provide insight into the many ways planets and asteroids might be assembled. Ryan Park, a planetary scientist at the Jet Propulsion Laboratory in Pasadena, Calif., and colleagues report the findings online August 3 in Nature.
“Before we got to Ceres, we didn’t know what the interior looked like,” Park says. “Its evolution is more complex than what we envisioned.”

Ceres is the largest body in the asteroid belt, the field of rocks that lies between the orbits of Mars and Jupiter. The Dawn spacecraft has been orbiting Ceres since March 6, 2015, its second stop after spending 14 months at the asteroid Vesta (SN: 4/4/15, p. 9). As Dawn loops around Ceres, slight changes in the speed of the spacecraft — deviations of less than 0.1 millimeters per second — reveal the dwarf planet’s gravity field. By combining these measurements with images that show the overall shape of Ceres, the researchers deduced how mass is spread out inside. The core has a density similar to some meteorites; the shell (roughly 70 to 190 kilometers thick) is about two-thirds as dense.
Mountains on Ceres appear to float on a deformable layer of minerals and volatile elements that easily evaporate, Park and collaborators report. If Ceres were completely solid, then gravity over a mountain would be stronger than the surrounding terrain because of the increased mass. But gravity on Ceres doesn’t vary with topography, the researchers find. This suggests that mountains and hills displace mass beneath the surface, “like how a boat floats on water,” says Park. To keep the underlying layer slightly flexible, the temperature inside Ceres must be warm relative to the surface. That heat could come from radioactive decay or be left over from when Ceres assembled itself over 4 billion years ago.
This segregation of material — a solid core topped with a malleable crust — can help researchers learn about the environment in which Ceres formed, says Simone Marchi, a planetary scientist at the Southwest Research Institute in Boulder, Colo. Densities within these layers can lead to estimates of how much ice and radioactive material lies buried beneath the surface, he says — abundances which depend on how far from the sun Ceres was born.

Understanding the internal structure could also be key to solving a mystery: No craters on Ceres are wider than about 280 kilometers, which is odd given what researchers know about the population of rocks that should have slammed into it (SN: 9/5/15, p. 8). Something probably eroded those craters, though it’s not yet clear what. Marchi speculates that the erosion has something to do with Ceres’ internal evolution and composition.

Aside from getting an idea of how Ceres is put together, the findings can be applied to other worlds both in our solar system and around other stars, says Peter Thomas, a planetary scientist at Cornell University. Insight from Ceres adds “a whole new dimension of things that may not have been imagined before,” he says. “How many different kinds of objects — planets, dwarf planets, asteroids — can you get?”

Primates may have some high-flying relatives. Colugos, small mammals that glide from treetop to treetop in forests throughout Southeast Asia, have an evolutionary history that’s long been debated. Their teeth look similar to tree shrews’ teeth, while other skull and genetic features resemble those of primates. (Past studies have even linked colugos to bats and other insect-eating mammals.)

In an effort to settle the debate, William Murphy, a geneticist at Texas A&M University in College Station, and colleagues have deciphered the genome of a male Sunda colugo (Galeopterus variegatus) from West Java, Indonesia. Comparing colugo DNA with 21 other mammal genomes, the team found that colugos are most closely related to primates, while tree shrews took different evolutionary paths to arrive at similar traits. There are also changes in genes related to vision and gliding that are unique to colugos, the researchers report August 10 in Science Advances.
Genetic data from colugos preserved in museums also show that the animals are more diverse than suspected. While only two species have been described in the wild, the team found at least seven separate genetic lineages, which may represent individual species.

A large study of human genetic variation finds more than 7 million spots where one person’s DNA can differ from another’s. Analyses of such variants, compiled from cataloging the genes from more than 60,000 people, are already offering doctors helpful insights into diseases such as schizophrenia and some heart conditions.

Researchers from the Exome Aggregation Consortium first presented their analysis of the ExAC database online at bioRxiv.org last year (SN: 12/12/15, p. 8). Now, the project is getting its official debut in the Aug. 18 Nature.
An exome is just the protein-producing genes in a person’s genetic instruction book, or genome. Researchers from nearly two dozen studies around the world pooled exome data they had collected from 60,706 people, nearly 10 times more data than any previous study of human genetic variation. The people in the study were far more racially and ethnically diverse than any previous study as well, and included both people with various diseases and healthy people.

Any one person carries tens of thousands of DNA variants, said Daniel MacArthur, a geneticist at Massachusetts General Hospital in Boston, in a telephone press briefing. The ExAC team found that, on average, one in every eight DNA bases (the information-encoding chemical building blocks of DNA) differs among people. In total, the researchers recorded more than 7.4 million DNA variants, most of them changes in single DNA bases.

ExAC researchers released the data in 2014 for other scientists to use. Already these data have contributed to the day-to-day interpretation of genetic information in the clinic, says Eliezer Van Allen, a medical oncologist at Harvard Medical School. “It gives a new look into the drivers of human genetic diversity.”

A companion paper published August 17 in Nature Genetics, for instance, found that people are missing some genes or have extra copies of other genes. On average, people have 0.81 deleted genes and 1.75 duplicated genes. The analysis echoed previous studies in showing that people with schizophrenia are more likely to have such missing or duplicated genes, particularly genes important in the brain.
It’s a relief to researchers that the paper confirms the results of previous schizophrenia studies, says Jennifer Mulle, a psychiatric geneticist at Emory University in Atlanta who was not involved in the work. “We all breathe a collective sigh of relief that this thing we thought to be true continues to be true,” she says.
Now, the challenge is to figure out what all of the variations mean.

Two independent studies suggest that the ExAC data could give doctors and researchers a clearer picture of the gene changes that contribute to heart conditions known as cardiomyopathies.

As DNA sequencing studies, which decipher people’s genetic makeup, became more common in the last 10 years, researchers amassed a growing number of rare DNA variants implicated in causing the heart diseases. “There was always a lot of doubt cast about whether these [variants] were real or not,” says Roddy Walsh, a geneticist at Imperial College London.

Walsh and colleagues used the ExAC data and DNA data from 7,855 cardiomyopathy patients to reevaluate the likelihood that a particular variant would cause a heart problem. Finding a variant in heart patients that is rarely seen in people without the disease suggests the variant could be causing the disease. But if the variant appears just as often in the general population that don’t have cardiomyopathies as in patients, it is unlikely to cause disease.

Of the people in ExAC, 11.7 percent carry variants associated with hypertrophic cardiomyopathy, Walsh and colleagues report August 17 in Genetics in Medicine. That’s far more people than expected for a rare inherited heart condition, which strikes about one in 500 people. Those data and other evidence suggest that many of the variants implicated in the disease are actually benign, the researchers say.

ExAC data alone aren’t enough to rule out a potentially disease-causing variant, says Benjamin Meder, a cardiologist at Heidelberg University Hospital in Germany. Researchers don’t know the full medical history of the ExAC volunteers. Some may have undetected cases of cardiomyopathy, or others may have been misdiagnosed as having the disease, which could throw off the results, he says. It’s important to clearly define who has a disease and who doesn’t before conducting genetic studies, Meder says. “This paper does it the wrong way around.” Still, he says the study does offer some valuable insights into the genetics of heart problems.

Misdiagnosing a genetic disease can negatively affect entire families, says Isaac Kohane, a biomedical informaticist at Harvard Medical School. For instance, people related to a young person who collapses on the basketball court and is found to carry a rare variant associated with the heart condition may also be screened for the genetic variant. Family members carrying the disease-associated variant may be treated for a condition they don’t have.

Such misdiagnosis is much more likely for African-Americans, Kohane and colleagues report August 17 in the New England Journal of Medicine. Five variants previously associated with hypertrophic cardiomyopathy kept popping up again and again in the general population most of whom do not have the heart condition, Kohane’s team found. Those variants are far too common to cause a rare genetic disorder; 2.9 to 27.1 percent of black Americans were found to carry at least one copy of the variants, while 0.02 to 2.9 percent of white Americans had one of the variants.

Kohane and colleagues now say the variants are benign. The mistake could have been avoided if researchers had included even a few black Americans in their studies, most of which involved people of European descent who carry only a fraction of the genetic diversity found people with recent African ancestry. The researchers calculate that the ExAC data, with its great genetic diversity, could rule out many benign variants including ones carried by 0.1 percent of the population.

COLUMBIA, Mo. — If you find a daddy longlegs in your house, don’t be scared. “Daddy longlegs are actually pretty docile animals when it comes to interacting with humans,” says evolutionary biologist Kasey Fowler-Finn, who studies the arachnids at St. Louis University. Specifically, she studies daddy longlegs sex. She is using this common group of arachnids (they’re not spiders) to explore how mating behaviors can be shaped by evolutionary forces.

Daddy longlegs — which can be found in forests, in leaf litter, on tree trunks and, of course, in your garage in eastern North America — are a group of harvestmen with elongated legs. And like all harvestmen, their second pair of legs, which is used in sensory exploration instead of walking, is particularly long.

But what makes daddy longlegs especially interesting is what happens when they mate. “Most of us just think ‘ew’ when we see them, but they have this really fascinating suite of [mating] behaviors,” Fowler-Finn said July 31 at the 53rd Annual Conference of the Animal Behavior Society. “The same basic stuff happens with all species in the clade, but the details vary quite a bit.”

The mating ritual starts with individuals bumping into each other (scientists don’t yet know how males and females find one another). “Then shortly thereafter, males will attempt to engage the females in what’s called a ‘mating embrace,’” Fowler-Finn said. “They hook their pedipalps [a type of appendage on the front of the arachnid] behind the female’s sensory legs … and then there’s a bunch of back and forth between males and females that varies in duration across species.” Mating can last for 15 seconds in some species, and three to four hours in others. The male then delivers a nuptial gift and his ejaculate, and the pair separates.

There can be a lot of aggression during all of this, with males and females biting each other and even losing legs during mating. And this, too, can vary from species to species. Leiobunum vittatum encounters, for instance, are almost always violent, while L. aldrichi matings are aggressive only about half of the time.

L. aldrichiis one of Fowler-Finn’s favorites. “The male actually grabs the female’s second leg … and then they shake them by one leg,” she said. “And, in fact, this is so particular to the second leg that males who initially grab other legs on the female will continue to search until they find that second leg. So there’s something really cool going on here.” What that might be, though, is a mystery.

Fowler-Finn is still working out whether characteristics of the various daddy longlegs species can predict their mating styles. But she noted that she and her colleagues are finding a lot of variation in behavior not just across species but also by geographic area. She suspects that as she and her team describe these differences, they are going to find evidence for plenty of new species to scare the arachnophobes out there.

Bonobos — chimpanzees’ sister species — don’t get the credit they deserve as tool users.

Bonobos in a sanctuary’s protected forests in the Democratic Republic of Congo crack nuts with stones nearly as well as wild chimps in other parts of Africa do, researchers report online August 26 in the American Journal of Primatology. Wild bonobos have rarely been observed using tools and have never been reported to pound open nuts with stones (SN: 9/19/15, p. 22).

All 18 adult and adolescent bonobos tracked during April and May 2015 cracked oil palm nuts with stones of various sizes that researchers had placed near oil palm trees, says a team led by Johanna Neufuss of the University of Kent in England. Bonobos chose pounding stones well-suited to busting palm oil nutshells. These animals employed 15 grips to hold nut-cracking stones, including 10 grips not previously observed in nonhuman primates.