Share and Share Alike?

Chimps may be our closest relatives, but you wouldn't want to rely on one in a pinch. Apparently, they don't share the human willingness to do favors for others.

A team of scientists led by Joan B. Silk of the University of California at Los Angeles conducted two sets of experiments with chimps living in captivity in Texas and Louisiana to measure their propensity for altruism. More then two dozen were presented with an apparatus that gave them two options: They could choose to get food only for themselves, or they could get food in a way that also gave some to another chimp.

The chimps, though, were no more inclined to go for the option that gave food to another chimp even if they knew the other chimp and it was clear that being generous would cost them nothing.

"Humans are an unusually prosocial species -- we vote, give blood, recycle, give tithes and punish violators of social norms," the team wrote Thursday in the journal Nature. "Experimental evidence indicates that people willingly incur costs to help strangers in anonymous one-shot interactions, and that altruistic behavior is motivated, at least in part, by empathy and concern for the welfare of others."

Because chimps are so closely related to humans, live in social groups and collaborate in a variety of ways -- such as hunting for food, patrolling their territories and caring for injured comrades -- researchers suspected they would share the human penchant for altruism, as well.

The study results, however, may indicate that such behavior is "tied to sophisticated capacities for cultural learning, theory of mind, perspective taking and moral judgment," the researchers wrote.

-- Rob Stein

Vegetation Cut Tsunami Damage

Coastal areas sheltered by vegetation fared better during last year's Indian Ocean tsunami than those without it, a study in the Saturday issue of Science has found.

Led by Finn Danielsen at the Copenhagen-based Nordic Agency for Development and Ecology, researchers from Denmark, India, Malaysia, Britain, the United States, Japan and Indonesia examined the Cuddalore District in Tamil Nadu, India, to gauge how well mangrove-covered regions weathered the massive tsunami on Dec. 26, 2004.

Areas hit by the most damaging waves were not protected, the scientists wrote, but "further away, however, areas with coastal trees vegetation were markedly less damaged than areas without."

At the river mouth in Cuddalore, the "tsunami completely destroyed parts of a village. However, areas with mangroves and tree shelter belts were significantly less damaged than other areas."

Analytical models suggest that 30 trees per 120 square yards in a 109-yard-wide belt would reduce the maximum tsunami impact by more than 90 percent.

Between 1980 and 2000, human activity, including shrimp farming, reduced the area of mangroves by 26 percent in the five countries most affected by the tsunami.

"Sustainable use and management of coastal wetlands should be a [focus] in an effort to protect people against not only tsunamis, but also hurricanes and storms," Danielsen said in an interview.

-- Juliet Eilperin

Rise of Mammals Was in the Air

A rise in oxygen levels in the atmosphere about 50 million years ago may have been the evolutionary jolt that allowed mammals to grow larger and eventually dominate Earth.

That is the view of researchers who measured the isotope carbon-13 in deep-sea core samples spanning the past 205 million years. Carbon-13 is a byproduct of photosynthesis, by which plants convert water and carbon dioxide into carbohydrates, releasing oxygen into the atmosphere.

Knowing how much carbon-13 was in a deposit enabled scientists to determine the amount of atmospheric oxygen at the same time. The team found that oxygen, steady at 10 percent through the age of the dinosaurs, "spiked" to 17 percent 15 million years later and eventually rose above 20 percent, where it is now.

"We associate the spike with the rise of large . . . mammals," said team leader Paul Falkowski, a Rutgers University geobiologist. "You start to see 12- to 15-foot sloths in South America, gigantic ungulates [hoofed animals] and enormous mammals of all kinds." The team's findings were reported recently in the journal Science.

Large mammals "are the Hummers of the world," Falkowski said, needing lots of oxygen to metabolize food. Also, he said, "plumbing" is important. Larger mammals have fewer capillaries per unit of muscle mass than smaller ones, and need oxygen-rich blood to burn calories efficiently, he said.

Falkowski said the oxygen spike occurred when the continents were growing farther apart and large deposits of organic matter were being laid down on the edges of the Atlantic Ocean, soon to be buried by sediments. This large-scale carbon sequestration eventually became the oil fields of -- among others -- the Gulf Coast and the North Sea.

-- Guy Gugliotta

When a tsunami comes, it first hits the mangroves. When the mangroves have been destroyed or degraded, the coastline is more vulnerable to extreme events such as tsunamis.