Joshua Lederberg; Pioneer of Molecular Biology

During World War II, while enrolled at Columbia College, he joined the Navy's V-12 training program. He served as a hospital corpsman at the clinical pathology laboratory at St. Albans Naval Hospital on Long Island, N.Y.

After two years at Columbia's medical school, he left to collaborate with Edward L. Tatum at Yale University. Experimenting with the intestinal bacterium Escherichia coli, Dr. Lederberg demonstrated that certain strains of bacteria can undergo a sexual stage, in which they mate and exchange genes. This discovery, and the methods used to make it, had far-reaching scientific and medical implications.

Most immediately for Dr. Lederberg, it brought a doctoral degree from Yale in 1947. Only days before his scheduled return to medical school at Columbia, the 22-year-old was offered an assistant professorship in genetics at the University of Wisconsin.

While working at Wisconsin from 1947 to 1959, he made another breakthrough. He showed that bacterial genetic material can be exchanged by transduction -- when only fragments of chromosomes are transferred from cell to cell. Those bits of genetic material are incorporated into a virus and later become part of the genetic material of infected bacterial cells, thereby altering their makeup and explaining how bacteria of different species could gain resistance to the same antibiotic so quickly.

The Nobel Prize in medicine or physiology came in 1958, while he was the 33-year-old Medical Genetics Department chairman at Wisconsin. The other recipients of the prize that year were Tatum and George Beadle.

Dr. Lederberg had just accepted an offer to become the first chairman of the newly established Department of Genetics at Stanford University's School of Medicine. He moved to Rockefeller University in New York 20 years later and became the school's fifth president. He served there until 1990.

He had been a member of the National Academy of Science since 1957, and he received the Allan Newell Award from the Association for Computing Machinery in 1995 and was elected a director of the Council on Foreign Relations in 1996. He wrote a weekly editorial column on science and society for The Washington Post between 1966 and 1971. He had served on the Pentagon's Defense Science Board since 1979.

He joined a 1985 effort by the American scientific establishment to improve the technical sophistication of newly elected members of Congress. Nearly all the politicians played hooky, The Post reported.

His marriage to Esther Lederberg ended in divorce.

Survivors include his wife, Dr. Marguerite S. Lederberg of New York City; a daughter from his second marriage, Anne Lederberg of New York City; a stepson, David Kirsch of Chevy Chase; and two grandchildren.