SCIENCE

Notebook

Birthrate of Boys Is Declining

If you are thinking of having children and want to have a boy, you might want to book that romantic weekend getaway soon. Boys are getting harder to make, according to a new analysis.

Worldwide, a handful of extra boys have historically been born for every 100 girls. Boys are also more likely to die young, so it all works out by the time they start dating.

Devra Lee Davis of the University of Pittsburgh and her colleagues gathered data on U.S. birth ratios from the National Center for Health Statistics. From 1970 to 2001, they found, the number of boys born for every 100 girls dropped steadily from 105.5 to 104.6. Male births among U.S. whites dropped even more steeply, from 105.9 per 100 girls to 104.7.

The researchers found similar declines in Japan, another industrialized country with excellent birth records. They also found that the proportion of deaths among fetuses after the 20th week of pregnancy (before that, gender can be difficult to determine) has steadily risen in both countries. The data suggest that some, but not all, of the decline in male births is because of fetal loss. The remainder appears to be because of fewer males being conceived.

"The falling sex ratio coupled with the disproportionately male fetal deaths supports the hypothesis that males are being culled in some systematic fashion," they write in the June 1 issue of Environmental Health Perspectives, noting that studies have found similar trends in other countries.

The cause remains a mystery. Davis and her colleagues suspect that much of the shift is because of exposure to gender-bending pollutants, including certain plastics and metals that have been shown in laboratory experiments to preferentially harm male-producing sperm or to cause feminization of genetically male fetuses.

-- Rick Weiss

Wild Apes Often Walk Upright

Scientists have long theorized that humans' ape ancestors began walking on two legs after they descended from the trees and began living on the savannah. But after observing wild orangutans in Indonesia for one year, a British research team has found that those apes often walk on two legs as they hunt for fruit in the forest canopy.

The team found that the orangutans walked on all fours when moving on thick branches but often made their way on thinner branches by walking upright and using their arms primarily to maintain balance. While engaging in this "hand-assisted bipedalism," the team wrote last week in the journal Science, they often stood fully upright with their legs straight.

Co-author Robin Crompton of the University of Liverpool said the finding further blurs the distinction between early humans and apes, because signs of bipedalism have long been a key criterion for distinguishing human ancestors.

"If we're right, it means you can't rely on bipedalism to tell whether you're looking at a human or another ape ancestor," he said.

The researchers, who watched the orangutans on the island of Sumatra, analyzed 3,000 examples of movement. They concluded that standing on two legs sometimes gave the animals a distinct advantage by enabling them to gather fruit from thinner branches. Scientists generally believe that our ancestors left the trees and began walking on two legs millions of years ago, perhaps during periods when the forest canopy was thin because of long-term droughts.

-- Marc Kaufman