Fossils of a 4.1-million-year-old human ancestor in Ethiopia bolster the controversial idea that early members of our evolutionary family arose one species at a time rather than branching out into numerous species. (p. 227)

A newfound bacterium can cause illness in people who have a rare, inherited form of immune deficiency. (p. 227)

Two studies provide conflicting findings on estrogen therapy's effect on breast cancer risk, while a third study suggests that the hormone contributes to blood clot formation. (p. 228)

Worms from deep-sea vents prefer water at temperatures near the upper limit of what animals are known to survive. (p. 228)

Even though the carbon dioxide in Earth's atmosphere acts as a fertilizer for plants, the planet's vegetation won't be able to sequester large amounts of that greenhouse gas in the long term because it will quickly run out of other nutrients. (p. 229)

A recently discovered hormone may play a major role in triggering and maintaining hibernation. (p. 229)

By combining the power of two well-known reactions, chemists have devised a way to alter the length of linear carbon chains. (p. 229)

Xena, unofficially called the 10th planet, is the second-most-shiny known object in the solar system. (p. 230)

Hidden deep in their tissues, all plants probably have fungi that don't make them sick but still may have a big influence. (p. 231)

Scientists are still analyzing the magnitude 7.9 quake that struck San Francisco a century ago and, at the same time, are scrambling to estimate when the next large quake will strike the Bay Area. (p. 234)

Domesticated varieties of wheat emerged gradually in the prehistoric Near East over a roughly 3,000-year span. (p. 237)

Hummingbirds can keep track of when a particular flower has replenished its nectar and is worth visiting again. (p. 237)

New computer simulations of Mercury's violent formation account for the planet's abundance of heavy elements and also reveal that some of the debris generated by the collision could have found its way to Earth and Venus. (p. 237)

The newest spacecraft from Earth arrived at the Red Planet on March 10. (p. 237)

Although breakfasts tend to pack a lot of nutrition per typical calorie consumed, one in five U.S. residents skips this meal. (p. 238)

Fat cells exposed to brominated flame retardants undergo changes that would appear to foster obesity and type 2 diabetes. (p. 238)

Downing the human equivalent of two to four alcoholic drinks per day dramatically spurs the growth of cancers implanted in lab mice. (p. 238)

Rattlesnakes undergo a hibernation-like state to survive long periods of famine, while continuing to grow longer. (p. 238)

(p. 239)