A Lower High-Water Mark

Do Rain Forests Make Rain?
Long-standing assumption: rain forests are a consequence of heavy rainfall. New hypothesis: some forested regions may produce conditions that lead to heavy rainfall. This “biotic pump” model contends that a vast forest such as the Amazon draws in large amounts of water vapor. Evaporation and condensation of the acquired water lead to a local atmospheric pressure drop. That decrease causes rain and attracts more water vapor to the forest, in a continuous positive feedback loop. “This theory could explain why continental interiors with huge rain forests remain so moist,” says Wildlife Conservation Society researcher Douglas Sheil, who in an April Bioscience paper revived the biotic pump model, originally proposed in 2006 by Anastassia Makarieva and Victor Gorshkov, both at the Petersburg Nuclear Physics Institute in Russia. “It could also underline the dangers of widespread deforestation.” Though promising, the model needs more data regarding air circulation patterns and vegetation types to support it, Sheil notes. —Steve Mirsky

Ants: “I’m Not Dead Yet”
Ants are notoriously efficient undertakers, carrying off dead nestmates before the corpses can infect the colony with their pathogens. Some researchers had hypothesized that ants detected breakdown products in decomposing bodies, but a new study undermines that theory. Entomologists from the University of California, Riverside, found that Argentine ants could detect dead nestmates before decomposition could have taken hold. More telling, the team found that living ants produce two “I’m not dead yet” chemicals, called dolichodial and iridomyrmecin. The compounds curb necrophoresis, the removal of dead colony members by fellow workers. Both chemicals dissipate quickly after death, plummeting to below half strength in just 10 minutes, the researchers write in a paper published in the May 19 Proceedings of the National Academy of Sciences USA. —John Matson

Working on the Railroad

Temptation Zone
An imaging study reveals how the brains of some dieters stay disciplined and others give in to cravings. Researchers at the California Institute of Technology asked volunteers trying to slim down to pick a food toward which they felt neutral in terms of health and taste (many chose yogurt). They next scanned the dieters’ brains as they chose between this reference item and either healthy snacks, such as apples, or junk foods, such as candy bars. The team linked a brain region, the ventromedial prefrontal cortex, with the desire for tasty items, regardless of how unhealthy they might be. A separate area, the dorsolateral prefrontal cortex, was associated with self-control; dieters who had strong signals in this region chose the healthier food even if they did not think it tasted better. The findings, in the May 1 Science, present new targets that could help treat not only obesity but also addiction, wasteful spending, and other matters dealing with desire and restraint. —Charles Q. Choi

Humanity's Ground Zero
A massive new genetic study may have zeroed in on humanity’s starting point. By analyzing genetic sequences from 121 populations in Africa, 60 non-African populations and four African-American populations, researchers traced Africans back to 14 ancestral clusters originating at 12.5 degrees east latitude and 17.5 degrees south longitude, near the border of modern-day Angola and Namibia. Besides offering a far more specific understanding of human migrations, the study, in the May 22 Science, also promotes a better understanding of health and disease in many of these populations. —Katherine Harmon

What is Watson?
This software program will beat people on the game show Jeopardy! At least, that is what IBM hopes will happen with a supercomputer running a powerful semantics-crunching program dubbed Watson, which will have access to a knowledge database but no Internet connection. In following up on its human-beating chess computer Deep Blue, IBM says it has been refining Watson for almost two years and hopes to stage a series of sparring matches before a final showdown in 2010. —John Matson

Note: This article was originally printed with the title, "News Scan Briefs."