Science

Superficial explorers "evolve high levels of aggression in both games, whereas thorough explorers evolve to be consistently non-aggressive," the researchers wrote. The central principle in the shaping of animal personalities, they write, is that "the more an individual has to lose, the more risk averse it should be."

-- Christopher Lee

Low Testosterone, Shorter Lives

Men who have lower levels of testosterone may be at greater risk of dying early, according to new research.

A study of nearly 800 California men ages 50 to 91 found that those with the lowest testosterone levels had a 33 percent greater risk of death during the next 18 years than the men with higher levels.

"The new study is only the second report linking deficiency of this sex hormone with increased death from all causes over time and the first to do so in relatively healthy men," said Gail Laughlin of the University of California at San Diego School of Medicine, who presented the findings last week at a meeting of the Endocrine Society.

Testosterone levels tend to decline with age but vary widely, with many older men still having levels typically found in younger men. Low levels in the study were considered those at the lower limit of normal for young men.

The men in the study with low levels also tended to have more signs of inflammation, which has been associated with a variety of health problems.

Although the study might support the idea that taking testosterone supplements may benefit some men, the researchers cautioned against jumping to that conclusion. Lifestyle changes, such as losing weight and exercising, may work just as well and be safer.

"We are excited about these findings, which have important implications, but we are not ready to say that men should go out and get testosterone to prolong their lives," said Elizabeth Barrett-Connor, who helped conduct the research.

-- Rob Stein