Science News - February 17, 2007

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Chimpanzee

Stone Age

Finds in Africa rock prehistory of tools

Working along a riverbank in a West African rain forest, researchers have uncovered remnants from a chimpanzee stone age that started at least 4,300 years ago. The finds constitute the only evidence yet detected of prehistoric ape behavior.

Most of the more than 200 stone artifacts found at three sites in Taï National Park, Ivory Coast, were used by prehistoric chimps to crack open nuts, say archaeologist Julio Mercader of the University of Calgary in Alberta and his colleagues. The animals placed nuts on the flat surface of one rock and smashed the tough shells with another rock.

NUTCRACKER SWEET At a site in West Africa, a stone used by chimps to hammer open nuts around 4,300 years ago lies next to an excavator’s trowel.

“I’d predict that this type of simple bashing technology goes back to a common ancestor of chimps and humans around 6 million years ago,” Mercader says.

UNIV. CALGAR Y

His team presents its findings in an upcoming Proceedings of the National Academy of Sciences.

The researchers excavated a cluster of three sites in 2001 and 2003. Most of the

stone artifacts came from one location, known as Noulo. Radiocarbon measurements of burned wood in the soil produced the age estimate for the finds.

To see whether the artifacts could be distinguished as implements, Mercader and two of his coauthors, both well-recognized specialists in Stone Age tools, assessed a group of 90 stones, not knowing beforehand their origins: the West African sites, a 5,000-year-old human occupation in Canada, or a location in the Canadian Rockies where the stones had been modified only by geological forces. In almost all cases, the three examiners identified just the stones from the first two groups as being intentionally modified.

Turning to the full set of specimens from the three West African sites, the scientists concluded that most represent instances of one stone being hammered forcefully against another. Those rocks weighed from 1 kilogram to

9 kilograms (2.2 to 19.8 pounds).

The team also judged that people had apparently struck flakes off 28 of the stones. People probably visited the frequently flooded riverbank sites sporadically, Mercader posits.

Other clues suggest that chimps, rather than people, had used the unflaked stones,

For instance, large, heavy hammering stones at Noulo look like those that chimps at a nearby site use to crack nuts (SN: 3/30/02, p. 195). Both the old and modern sets of artifacts contain small pits and hollow depressions produced by bashing rocks together, as well as distinctive edge and corner damage.

Finally, starch grains extracted from 31 stones at the West African sites came predominantly from nuts typically eaten only by chimps, according to Mercader’s team. People living in that part of the rain forest mainly subsist on tubers, plants, and fruits. The sites yielded none of the pounding and grinding tools favored by foragers and farmers.

The new finds precede the emergence of farming villages in that part of Africa. Mercader notes that it’s possible that chimps imitated simple stone-tool practices of human foragers. Still, he suspects that the rock-bashing activity originated deep in prehistory.

Archaeologist Alison S. Brooks of George Washington University in Washington, D.C., agrees: “There is no reason why future work should not reveal evidence of even older chimpanzee sites.” Starch grains last well over 100,000 years, Brooks notes.

Although the new data make “a fairly solid case” for prehistoric nut cracking by chimps, the animals probably invented this stone-tool technique on their own rather than inheriting it from a common human-

chimp ancestor, remarks archaeologist John J. Shea of the State University of New York at Stony Brook. —B. BOWER

Clear the Way
Stenting opens jammed
arteries in the brain
QUOTE

By pushing a tiny mesh cylinder called a stent through blood vessels leading from the groin to the head, doctors can prop open narrowed arteries in the brain much as they do in the heart, several new studies show.

A brain artery that’s partially blocked because of atherosclerosis is a stroke waiting to happen. While blood thinners such as aspirin and warfarin can ease blood flow through narrowed brain vessels, roughly one-fifth of patients with severe narrowing who get these drugs still suffer a stroke or brain hemorrhage or die of a vascular problem within 2 years.

Seeking a better alternative, scientists have adapted stents to fit brain arteries, which are smaller and more fragile than the arteries serving the heart. Two studies

presented last week at the 2007 International Stroke Conference in San Francisco, along with a trial reported last year, indicate that the still-experimental brain stents might work as well or better than drugs and have fewer adverse effects.

In one of the studies reported in San Francisco, Chinese researchers placed bare metal stents in the brains of 213 people who had had a stroke or ministroke in response to atherosclerosis that had reduced the diameter of a brain artery by more than half. Only about 9 percent of the patients experienced a stroke in the stented artery during the 2 years following stent placement, says Wei-Jian Jiang, a cardiologist at Beijing Tiantan Hospital.

In another study, U.S. researchers analyzed data on 131 patients who had a brain artery 82 percent occluded, on average. Most had already suffered a stroke or ministroke. All received a newer, more flexible stent that springs open at the target site. The device reduced the average size of the occlusion to 20 percent, says study coauthor Osama O. Zaidat, a neurologist at the Medical College of Wisconsin in Milwaukee.

In a third study, published in the October 2006 Stroke, only 2 of 59 patients with severely narrowed brain arteries experienced strokes during the 4 months after they received drug-coated metal stents. There were few other complications, and almost all the stented arteries remained open, says study coauthor Tudor G. Jovin,