An earlier version of this story had the wrong start time. The correct start time is 6 p.m.

Which is more influential to a child: her biological heritage or the environment in which she lives and grows? The question is perennial and one that scientists have attempted to understand through the study of twins.

It's matter of particular interest to Gary Swan, the director of SRI's Center for Health Sciences, who will give a talk called "Twins: Unlocking the Secrets of Nature-Nurture Interactions" at 6 p.m. Tuesday, Sept. 8.

This free event takes place at Cafe Scientifique, a monthly talk for the general public at the headquarters of SRI International at Middlefield Road and Ringwood Ave. in Menlo Park.

For more than 20 years, Mr. Swan has studied twins for insights on conditions such as nicotine addiction, obesity and blood pressure. The studies have "improved our understanding" of the environmental and genetic factors associated with coronary heart disease, cancer susceptibility, addiction and memory in aging, he said in an interview.

Mr. Swan also leads SRI's Center for Research on Independent Aging.

For more information, go to www.cafescientifique.org.