Early results of a study of sleeping habits suggest that sleeping with infants could prevent the sudden death that strikes 10,000 American babies a year.

"Human babies are the most vulnerable of all the primates," says anthropologist James J. McKenna of California's Pomona College and the University of California at Irvine. "And we separate ourselves in real physical ways from our infants at a very young age."

So young an age, McKenna suggests, that human infants may miss out on breathing cues they need as their breathings system mature.

Sudden infant death syndrome, or SIDS, occurs when babies stop breathing and die for no apparent reason. Ninety percent of the cases occur in babies younger than 6 months.

The problem appears to be unique to humans, McKenna says, and that may be because human breathing patterns change between the second and fourth months of life in preparation for speech.

McKenna's study, at the Irvine Sleep Center, monitors the breathing and other vital signs of a parent and baby as they sleep first in separate rooms, then in the same room, then in the same bed.

Preliminary evidence from the first mother and baby tested shows that the baby's breathing rhythm followed the mother's. This phenomenon, which may "remind" infants to breathe, was not found when they slept apart.

Until the advent of western urban living, babies usually slept with parents. "We consider sleeping with babies bizarre," McKenna says. But in fact, sleeping apart "is a very recent and novel change in behavior.