On the horizon: news from the frontiers of science

Big Rats and Little Possums

For those who think Earth has already revealed all her secrets, think again: High up in New Guinea's Foja Mountains, scientists have discovered a new species of giant rat and pygmy marsupial. The animals are a sampling of what remains undiscovered in this biodiversity hot spot, and in Earth's vanishing pristine wildernesses in general, says Bruce Beehler, the expedition's leader and vice president for Pacific programs at Conservation International in Arlington, Va. "It really is an analog for how little we know about this particular mountain range," he says.

Situated on the tropical island's northwest corner, the Foja Mountains are separated from the island's more densely populated central cordillera by lowland jungle and marshland and have remained largely free of humans. The 3 lb. rodent, about five times bigger than the average sewer rat, wandered repeatedly through the explorers' camp in search of food, says Mr. Beehler. So isolated was the rat's home mountain range that the rodent had little fear of humans.

New Guinea, along with neighboring Australia, generally hosts few placental mammals, but many marsupials. Indeed, a newly discovered mini-marsupial, a possum, is one of the smallest known to science.

As for the rat, its ancestors probably settled on the island when temperatures were cooler and sea levels lower at some point during the Pleistocene – a period that spanned from 1.8 million to 10,000 years ago. Then, as the climate warmed, it likely moved to higher elevations, says Beehler. Facing little competition for the "big mammal" spot in its new environs, the rat "grew" over evolutionary time to occupy the niche.

Monkey math

Scientists have found that monkeys can solve some math problems as well as college students. The finding suggests that the human ability to do mathematics may rest on a hard-wired foundation shared with nonhuman primates.

Scientists have known for some time that animals can count and assess quantities – that three apples are better than one, for example. But they weren't sure if animals could add two quantities to produce a third. The study, appearing in the December issue of the journal PLoS Biology, indicates that rhesus macaque monkeys can.

Researchers presented monkeys with a variable number of dots on a computer screen. After flashing two dot-bearing screens, a third screen presented two boxes. One contained a number of dots equal to the sum of the first two screens; the second box had another quantity.

The simians, who received a reward for touching the correct box, chose the sum-containing box 76 percent of the time. College students, who were asked to solve the problem "by feel" rather than by counting (the screens flashed for a mere half second), chose the correct box 94 percent of the time.

"It tells us something about the evolution of math," says Jessica Cantlon, a postdoctoral researcher at Duke University in Durham, N.C., and lead author of the study. "We know that humans have sophisticated ways of thinking about numbers. But when you take language and symbols away from humans, it seems that there are these more primitive abilities lingering around."

Calamity for coral?

Rising levels of carbon dioxide in Earth's atmosphere could drive coral reefs, one of the planet's most diverse ecosystems, out of existence, scientists report in the Dec. 14 issue of the journal Science. The oceans absorb about one-third of the atmosphere's CO2. In the water, the gas forms carbonic acid, the same stuff used to give soda its fizz. More acidic oceans, combined with generally higher temperatures, make the minerals coral needs to grow its signature skeleton less available. Combined with overfishing and pollution, the stress could push coral reef systems over a "tipping point," according to the paper.

Currently at 380 parts per million (p.p.m.), the highest CO2 concentration of the past 740,000 years, atmospheric CO2 levels are predicted to reach 560 p.p.m. by century's end. If humanity does nothing to curb emissions, oceans may be too acidic for coral growth by mid-century, say the authors.

Australia's great barrier reef – the world's largest – has already shown a 20.6 percent decrease in growth during the past 16 years. (Although scientists can't attribute the reef's decreased vitality to higher CO2 with absolute certainty, the findings are consistent with predicted changes.) In some cases, scientists have observed that algae now prevail in ecosystems previously dominated by coral, a shift perhaps spurred by the oceans' changing chemistry.

But the greatest warning against a business-as-usual approach to human carbon emissions may come from Earth's past. Some 245 million years ago in the early Triassic period, atmospheric CO2 levels spiked to at least five times today's levels. The corresponding fossil record indicates that few calcified organisms inhabited the sea.