上海花千坊爱上海

A boy who lived in what’s now South Africa nearly 2,000 years ago has lent a helping genome to science. Using the long-gone youngster’s genetic instruction book, scientists have estimated that humans emerged as a distinct population earlier than typically thought, between 350,000 and 260,000 years ago.

The trick was retrieving a complete version of the ancient boy’s DNA from his skeleton to compare with DNA from people today and from Stone Age Neandertals and Denisovans. Previously documented migrations of West African farmers to East Africa around 2,000 years ago, and then to southern Africa around 1,500 years ago, reshaped Africans’ genetics — and obscured ancient ancestry patterns — more than has been known, the researchers report online September 28 in Science.
The ancient boy’s DNA was not affected by those migrations. As a result, it provides the best benchmark so far for gauging when Homo sapiens originated in Africa, evolutionary geneticist Carina Schlebusch of Uppsala University in Sweden and her colleagues conclude.

In line with the new genetically derived age estimate for human origins, another team has proposed that approximately 300,000-year-old fossils found in northwestern Africa belonged to H. sapiens (SN: 7/8/17, p. 6). Some researchers suspect a skull from South Africa’s Florisbad site, dated to around 260,000 years ago, qualifies as H. sapiens. But investigators often place our species’ origins close to 200,000 years ago (SN: 2/26/05, p. 141). There is broad consensus that several fossils from that time represent H. sapiens.

Debate over the timing of human origins will continue despite the new evidence from the child, whose remains came from previous shoreline excavations near the town of Ballito Bay, says Uppsala University evolutionary geneticist and study coauthor Mattias Jakobsson. “We don’t know if early Homo sapiens fossils or the Florisbad individual were genetically related to the Ballito Bay boy,” he says.

Thus, the precise timing of humankind’s emergence, and exact patterns of divergence among later human populations, remain unclear. Researchers have yet to retrieve DNA from fossils dating between 200,000 and 300,000 years old that either securely or possibly belong to H. sapiens.
However early human evolution played out, later mixing and mingling of populations had a big genetic impact. DNA evidence from more recent fossils, including those studied by Schlebusch’s group, increasingly suggests that Stone Age human groups migrated from one part of Africa to another and mated with each other along the way (SN: 10/20/12, p. 9), says Harvard Medical School evolutionary geneticist Pontus Skoglund. In the Sept. 21 Cell, he and his colleagues report that DNA from 16 Africans, whose remains date to between 8,100 and 400 years ago, reveals a shared ancestry among hunter-gatherers from East Africa to South Africa that existed before West African farmers first arrived 2,000 years ago.

That ancient set of common genes still comprises a big, varying chunk of the DNA of present-day Khoisan people in southern Africa, Skoglund’s group found. Earlier studies found that the Khoisan — consisting of related San hunter-gatherer and Khoikhoi herding groups — display more genetic diversity than any other human population.

Schlebusch’s team estimates that a genetic split between the Khoisan and other Africans occurred roughly 260,000 years ago, shortly after humankind’s origins and around the time of the Florisbad individual. Khoisan people then diverged into two genetically distinct populations around 200,000 years ago, the researchers calculate.

Ancient DNA in Schlebusch’s study came from seven individuals unearthed at six South African sites. Three hunter-gatherers, including the Ballito Bay boy, lived about 2,000 years ago. Four farmers lived between 500 and 300 years ago.

Comparisons to DNA from modern populations in Africa and elsewhere indicated that between 9 percent and 30 percent of Khoisan DNA today comes from an East African population that had already interbred with Eurasian people. Those East Africans were likely the much-traveled farmers who started out in West Africa and reached southern Africa around 1,500 years ago, the researchers propose.

For Chong Liu, asking a scientific question is something like placing a bet: You throw all your energy into tackling a big and challenging problem with no guarantee of a reward. As a student, he bet that he could create a contraption that photosynthesizes like a leaf on a tree — but better. For the now 30-year-old chemist, the gamble is paying off.

“He opened up a new field,” says Peidong Yang, a chemist at the University of California, Berkeley who was Liu’s Ph.D. adviser. Liu was among the first to combine bacteria with metals or other inorganic materials to replicate the energy-generating chemical reactions of photosynthesis, Yang says. Liu’s approach to artificial photosynthesis may one day be especially useful in places without extensive energy infrastructure.

Liu first became interested in chemistry during high school, and majored in the subject at Fudan University in Shanghai. He recalls feeling frustrated in school when he would ask questions and be told that the answer was beyond the scope of what he needed to know. Research was a chance to seek out answers on his own. And the problem of artificial photosynthesis seemed like something substantial to throw himself into — challenging enough “so [I] wouldn’t be jobless in 10 or 15 years,” he jokes.
Photosynthesis is a simple but powerful process: Sunlight helps transform carbon dioxide and water into chemical energy stored in the chemical bonds of sugar molecules. But in nature, the process isn’t particularly efficient, converting just 1 percent of solar energy into chemical energy. Liu thought he could do better with a hybrid system.
The efficiency of natural photosynthesis is limited by light-absorbing pigments in plants or bacteria, he says. People have designed materials that absorb light far more efficiently. But when it comes to transforming that light energy into fuel, bacteria shine.

“By taking a hybrid approach, you leverage what each side is better at,” says Dick Co, managing director of the Solar Fuels Institute at Northwestern University in Evanston, Ill.

Liu’s early inspiration was an Apollo-era attempt at a life-support system for manned space missions. The idea was to use inorganic materials with specialized bacteria to turn astronauts’ exhaled carbon dioxide into food. But early attempts never went anywhere.

“The efficiency was terribly low, way worse than you’d expect from plants,” Liu says. And the bacteria kept dying — probably because other parts of the system were producing molecules that were toxic to the bacteria.

As a graduate student, Liu decided to use his understanding of inorganic chemistry to build a system that would work alongside the bacteria, not against them. He first designed a system that uses nanowires coated with bacteria. The nanowires collect sunlight, much like the light-absorbing layer on a solar panel, and the bacteria use the energy from that sunlight to carry out chemical reactions that turn carbon dioxide into a liquid fuel such as isopropanol.

As a postdoctoral fellow in the lab of Harvard University chemist Daniel Nocera, Liu collaborated on a different approach. Nocera had been working on a “bionic leaf” in which solar panels provide the energy to split water into hydrogen and oxygen gases. Then, Ralstonia eutropha bacteria consume the hydrogen gas and pull in carbon dioxide from the air. The microbes are genetically engineered to transform the ingredients into isopropanol or another liquid fuel. But the project faced many of the same problems as other bacteria-based artificial photosynthesis attempts: low efficiency and lots of dead bacteria.
“Chong figured out how to make the system extremely efficient,” Nocera says. “He invented biocompatible catalysts” that jump-start the chemical reactions inside the system without killing off the fuel-generating bacteria. That advance required sifting through countless scientific papers for clues to how different materials might interact with the bacteria, and then testing many different options in the lab. In the end, Liu replaced the original system’s problem catalysts — which made a microbe-killing, highly reactive type of oxygen molecule — with cobalt-phosphorus, which didn’t bother the bacteria.

Chong is “very skilled and open-minded,” Nocera says. “His ability to integrate different fields was a big asset.”

The team published the results in Science in 2016, reporting that the device was about 10 times as efficient as plants at removing carbon dioxide from the air. With 1 kilowatt-hour of energy powering the system, Liu calculated, it could recycle all the carbon dioxide in more than 85,000 liters of air into other molecules that could be turned into fuel. Using different bacteria but the same overall setup, the researchers later turned nitrogen gas into ammonia for fertilizer, which could offer a more sustainable approach to the energy-guzzling method used for fertilizer production today.

Soil bacteria carry out similar reactions, turning atmospheric nitrogen into forms that are usable by plants. Now at UCLA, Liu is launching his own lab to study the way the inorganic components of soil influence bacteria’s ability to run these and other important chemical reactions. He wants to understand the relationship between soil and microbes — not as crazy a leap as it seems, he says. The stuff you might dig out of your garden is, like his approach to artificial photosynthesis, “inorganic materials plus biological stuff,” he says. “It’s a mixture.”

Liu is ready to place a new bet — this time on re-creating the reactions in soil the same way he’s mimicked the reactions in a leaf.

MINNEAPOLIS — Birds don’t need to be drenched in crude oil to be harmed by spills and leaks.

Ingesting even small amounts of oil can interfere with the animals’ normal behavior, researchers reported November 15 at the annual meeting of the Society of Environmental Toxicology and Chemistry North America. Birds can take in these smaller doses by preening slightly greasy feathers or eating contaminated food, for example.

Big oil spills, such as the 2010 Deepwater Horizon disaster, leave a trail of dead and visibly oily birds (SN: 4/18/15, p. 22). But incidents like last week’s 5,000-barrel spill from the Keystone pipeline — and smaller spills that don’t make national headlines — can also impact wildlife, even if they don’t spur dramatic photos.
To test how oil snacks might affect birds, researchers fed zebra finches small amounts of crude oil or peanut oil for two weeks, then analyzed the birds’ blood and behavior. Birds fed the crude oil were less active and spent less time preening their feathers than birds fed peanut oil, said study coauthor Christopher Goodchild, an ecotoxicologist at Oklahoma State University in Stillwater.

Oil-soaked birds will often preen excessively to try to remove the oil, sometimes at the expense of other important activities such as feeding. But in this case, the birds didn’t have any crude oil on their feathers, so the decrease in preening is probably a sign they’re not feeling well, the researchers say.

Exactly how the oil affects the birds’ activity levels isn’t clear. Researchers suspected that oil might deprive birds of oxygen by affecting hemoglobin, which carries oxygen in the blood. Blood tests didn’t turn up any evidence of damaged hemoglobin proteins but did find some evidence that oil-sipping birds might be anemic, Goodchild said. At the higher of two crude oil doses, birds’ blood contained less hemoglobin per red blood cell, a sign of anemia.
The findings, while preliminary, add to a growing pile of evidence that estimates of the number of animals impacted by oil spills might be too low. For instance, even a light sheen of oil on sandpipers’ wings makes it harder to fly, costing birds more energy, a different group of researchers reported earlier this year. That could affect everything from birds’ daily movements to long-distance migration.

Movies and other media are full of mixed messages about the risks and rewards of building machines with minds of their own. For every manipulative automaton like Ex Machina’s Ava (SN: 5/16/15, p. 26), there’s a helpful Star Wars droid. And while some tech titans such as Elon Musk warn of the threats artificial intelligence presents, others, including Mark Zuckerberg, dismiss the doomsayers.

AI researcher Toby Walsh’s Machines That Think is for anyone who has heard the hype and is seeking a critical assessment of what the technology can do — and what it might do in the future. Walsh’s conversational style is welcoming to nonexperts while his endnotes point readers to opportunities for deeper dives into specific aspects of AI.
Walsh begins with a history of AI, from Aristotle’s foundation of formal logic to modern facial-recognition systems. Excerpts from computer-composed poetry and tales of computers trouncing humans at strategy games (SN: 11/11/17, p. 13) are a testament to how far AI has come. But Walsh also highlights weaknesses, such as machine-learning algorithms’ reliance on so much data to master a single task.

This 30,000-foot view of AI research packs a lot of history, as well as philosophical and technical explanation. Walsh personalizes the account with stories of his own programming experiences, anecdotes about AI in daily life — like his daughter’s use of Siri — and his absolute, unapologetic love of puns.

Later in the book, Walsh speculates about technical hurdles that may curb further AI development and legal limits that society may want to impose. He also explores the societal impact that increasingly intelligent computers may have.
For instance, Walsh evaluates how likely various jobs are to be outsourced to AI. Some occupations, like journalist, will almost certainly be automated, he argues. Others, like oral surgeon, are probably safe. For future job security, Walsh recommends pursuing careers that require programming acumen, emotional intelligence or creativity.

AI also has the potential to revolutionize warfare. “Like Moore’s law, we are likely to see exponential growth in the capabilities of autonomous weapons,” Walsh writes. “I have named this ‘Schwarzenegger’s law’ to remind us of where it will end.” Walsh isn’t resigned to a Terminator-like future, though. If governments ban killer robots and arms developers use automation to enhance defensive equipment, he believes military AI could actually save many lives.

In fact, Walsh argues, all aspects of AI’s future impacts are in our hands. “Artificial intelligence can lead us down many different paths, some good and some bad,” he writes. “Society must choose which path to take.”