Joshua Lederberg (May 23, 1925 – February 2, 2008) was an American molecular biologist known for his work in genetics, artificial intelligence, and space exploration. He was just 33 years old when he won the 1958 Nobel Prize in Physiology or Medicine for discovering that bacteria can mate and exchange genes. He shared the prize with Edward L. Tatum and George Beadle who won for their work with genetics.
In addition to his contributions to biology, Lederberg did extensive research in artificial intelligence. This included work in the NASA experimental programs seeking life on Mars and the chemistry expert system Dendral.
Instead of returning to Columbia to finish his medical degree, Lederberg chose to accept an offer of an assistant professorship in genetics at the University of Wisconsin-Madison. He married Esther Miriam Zimmer, who went with him to Wisconsin. She received her doctorate there in 1950.
Lederberg and his graduate student Norton Zinder went on to show in 1952 that bacteriophages could transfer genetic information between bacteria in Salmonella. This process, called transduction, explained how bacteria of different species could gain resistance to the same antibiotic very quickly.
Esther Lederberg published a paper dealing with the discovery of lambda in 1950. This was followed in 1952 by papers written by Norton Zinder and Joshua Lederberg dealing with bacteriophage lambda.
During her time in Joshua Lederberg's laboratory, Esther Lederberg also discovered fertility factor F, later publishing with Joshua Lederberg and Luigi Luca Cavalli-Sforza. In 1956, the Society of Illinois Bacteriologists awarded Joshua Lederberg and Esther Lederberg the Pasteur Medal, for "their outstanding contributions to the fields of microbiology and genetics".
In 1957, Joshua Lederberg founded the Department of Medical Genetics at the University of Wisconsin-Madison.
In 1958, Joshua Lederberg received the Nobel Prize and moved to Stanford University where he was the founder and chairman of the Department of Genetics. He collaborated with Frank Macfarlane Burnet to study viral antibodies. With the launching of Sputnik in 1957, Lederberg became concerned about the biological impact of space exploration. In a letter to the National Academies of Sciences, he outlined his concerns that extraterrestrial microbes might gain entry to Earth onboard spacecraft, causing catastrophic diseases. He also argued that, conversely, microbial contamination of manmade satellites and probes may obscure the search for extraterrestrial life. He advised quarantine for returning astronauts and equipment and sterilization of equipment prior to launch. Teaming up with Carl Sagan, his public advocacy for what he termed exobiology helped expand the role of biology in NASA. In the 1960s, he collaborated with Edward Feigenbaum in Stanford's computer science department to develop DENDRAL.
Throughout his career, Lederberg was active as a scientific advisor to the U.S. government. Starting in 1950, he has been a member of various panels of the Presidential Science Advisory Committee. In 1979, he became a member of the U.S. Defense Science Board and the chairman of President Jimmy Carter's President's Cancer Panel. In 1989, he received National Medal of Science for his contributions to the scientific world. In 1994, he headed the Department of Defense's Task Force on Persian Gulf War Health Effects, which investigated Gulf War Syndrome.
In 2006, Lederberg was awarded the Presidential Medal of Freedom.
Lederberg married fellow scientist Esther Miriam Zimmer in 1946; they divorced in 1966. He married psychiatrist Marguerite Stein Kirsch in 1968. He was survived by Marguerite, their daughter, Anne Lederberg, and his stepson, David Kirsch.