Health & Science

Out of Africa, revised

A cache of ancient stone tools unearthed in the northern Arabian Peninsula could radically change our understanding of when and how our human ancestors left Africa. The consensus has been that Homo sapiens originated in Africa some 200,000 years ago and stayed there for roughly 140,000 years before dispersing via the Mediterranean coastline to the rest of the world. The 100,000- to 125,000-year-old tools that German archaeologist Hans-Peter Uerpmann of the University of Tübingen found, however, suggest that the exodus happened 50,000 years earlier, along a route that passed over the narrow Red Sea and across a then-verdant Arabia. But because no fossil skeletons were found with the hand axes, scrapers, and cutting implements at the Jebel Faya rock-shelter site, in the United Arab Emirates, there is no way to prove the tools belonged to our direct ancestors as opposed to hominid species that have since died out. “This is a huge milestone,” Jeffrey Rose, an archaeologist at the University of Birmingham in England, tells The New York Times, “but unfortunately it raises more questions than it answers.”

A walk to remember

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If you’re 55 or older, put down your crossword puzzle and take a stroll. Scientists have found that moderate aerobic activity can improve seniors’ memory by reversing the slow wasting away of a key part of the brain, which begins at around 50. “It used to be thought that aging was a one-way street that was going the wrong direction,” University of Illinois professor Arthur Kramer tells Science News, but his recent study proves “that’s not the case.” Kramer and colleagues recruited 120 sedentary adults between the ages of 55 and 80. Half got their heart rates up by walking for 40 minutes, three times a week; the other half did stretching and weight exercises instead. After a year, scientists scanned each walker’s brain and found that the hippocampus, where memories are formed, had grown by an average of 2 percent. By contrast, the stretchers’ hippocampi had shrunk 1.4 percent, as expected. Though more study is needed, Kramer says initial results indicate that a brisk jaunt several times a week can roll back the pace of age-related memory loss “by about two years.”

Bountiful Earths

Our galaxy, it turns out, is teeming with planets—and some of them probably resemble Earth, says Space.com. A new NASA survey conducted through its Kepler satellite has identified 1,235 possible planets outside our solar system, 54 of them in so-called habitable zones, where temperatures could allow liquid water—and, perhaps, life—to exist. The planet-hunting satellite, launched in March 2009, has already tripled the number of known planets by focusing its deep-space camera on stars in just 0.25 percent of the sky. That suggests that planets are commonplace, rather than exceptions. One distant solar system spotted by Kep­ler apparently has six planets. The data are “game-changing,” William Borucki, Kep­ler’s principal investigator, tells Space.com. “It’s just a tremendous amount of new knowledge.” Scientists will now focus on clues that indicate how Earth-like some of the “exoplanets” may be. “I want to know whether these planets have atmospheres,” says Borucki.

Nabokov’s theory of evolution

Novelist Vladimir Nabokov’s passion for studying butterflies yielded not only great books—he wrote Lolita during trips to net specimens—but also exemplary science. More than 65 years after he first posed a contested theory of evolution for his favorite butterfly group, the Polyommatus blues, a new study proves him right in every detail. “I was blown away,” lead author and Harvard University professor Naomi Pierce tells The New York Times. A self-taught expert, Nabokov became curator of lepidoptera at Harvard’s Museum of Comparative Zoology. His microscopic study of the sexual organs of various species of blues led him to speculate that differences among them had evolved in Asia before they traveled, in five separate waves, over the Bering Strait into the New World. Other scientists argued that the butterflies in the group were more closely related, and that their differences had evolved later, once they arrived in the Amazon. Pierce says modern DNA testing posthumously vindicates the author’s “amazing, bold hypothesis,” and she thinks he would be pleased. She cites his poem “On Discovering a Butterfly”: “I found it and I named it,” he wrote. “I want no other fame.”

Terrorism-alert plants

Could daisies detect explosives better than bomb-sniffing dogs? A hundred times better, say Colorado State University scientists who have genetically engineered greenery to turn white in the presence of tiny amounts of TNT. Because “plants can’t run and hide” in the natural world, lead author June Medford tells Wired, they’ve evolved an ability to rapidly alter their structure when they detect a threat. Medford’s team tweaked plants to be on guard against TNT, and to respond to it by draining chlorophyll from leaves. She says the DNA code they used could work for any type of plant and a range of explosives. Researchers still need to reduce plants’ reaction time, now a matter of hours, and to make the color change easier to spot. But the departments of Defense and Homeland Security, which have spent millions on the project, hope to deploy a foliage force in about three years.