Obituary: Lee Segel

March 10, 2005


Lee Segel, 1932-2005

Lee Segel passed away on January 31, 2005. With his death, the applied mathematics community lost one of its finest practitioners, and the theoretical biology community lost a true pioneer who was still a leader at the cutting edge of so many subjects. And most importantly, the world community lost a true mensch, a compassionate and loving individual who inspired so many with his brilliance, his enthusiasm, his sense of humor, and his concern for others. Our hearts go out to his beloved Ruthie, his partner of half a century; to his children, Joel, Susie, Daniel, Michael, and their spouses; and to all of his grandchildren and other family members. Lee was a very special human being.

Theoretical and mathematical biology went through a critical transition in the 1970s, and Lee was one of the leaders in forging a marriage between mathematical theory and empirical fact; it was efforts such as his that all but obliged experimentalists to take notice of mathematical theory, and of the insights that were possible. His exceptional taste in choosing problems and his standards for good work will have an enduring influence, even beyond his numerous and brilliant specific contributions. The criteria for good theoretical biology that young scientists take for granted today were not always in evidence in the field. The early work could easily have left a legacy of irrelevance but for the efforts of a few scientists like Lee Segel, who recognized the primacy of the biology in determining what was worth doing.

Lee Segel was well established as an applied mathematician before he turned his attention to biology. He received a PhD from MIT in 1959, working with C.C. Lin. In 1960, he joined the outstanding faculty at Rensselaer Polytechnic Institute and began to publish fundamental work in continuum mechanics and related subjects. His first two beautiful books, Mathematics Applied to Deterministic Problems in the Natural Sciences (with C.C. Lin, 1974) and Mathematics Applied to Continuum Mechanics, remain cornerstones of applied mathematics courses throughout the world. Because of its preeminent position in the literature, the 1974 Lin and Segel book has become a classic; indeed, in 1988 SIAM distinguished it by making it the first volume in its Classics in Applied Mathematics series.

By the late 1960s, realizing how rich a treasure trove biology represented for mathematicians, Lee had begun to work seriously on problems in the field. He spent an important sabbatical at Cornell Medical School and the Sloan-Kettering Institute, where Sol Rubinow had created a superb unit in biomathematics, and where such mathematicians as Joe Keller and Hirsh Cohen were frequent visitors. Lee's two great early contributions, both with Evelyn Fox Keller, created frameworks for modeling bacterial chemotaxis, and for understanding related problems in the development of the cellular slime mold, a model system for studying development, multicellularity, and social biology. Lee quickly earned the respect of the leading experimentalists and theoreticians in these subjects, in particular John Bonner and Ted Cox at Princeton, and Howard Berg, then at Colorado. More than thirty years later, the Keller-Segel models remain the gold standards in these fields.

Lee's interests in biology knew no limits, but he was no dilettante; his later contributions to development, to ecology, to evolutionary biology, to immunology, and to neurosciences established him as one of the broadest yet deepest theoretical biologists of his generation.

Lee moved in 1973 from RPI to the Weizmann Institute, where he became dean of the Faculty of Mathematical Sciences and, later, chair of the Scientific Council. At both RPI and Weizmann, he mentored a diverse assemblage of outstanding young scientists who went on to join the ranks of the leaders of their fields. At Weizmann, an institution known for its excellence in experimental biology, he instituted a course on mathematical modeling, not for mathematicians but for biologists who had a year of calculus. The course, which he taught for about twenty years, led to his inspiring and insightful text Modeling Dynamic Phenomena in Molecular and Cellular Biology (1984). He was working on a sequel when his untimely death occurred.

His collaborators were legion, and anyone who ever worked with him will remember mainly how much fun it was. Lee laced every interaction with humor, and no pun was beneath him; many were subtle enough to make their way past editors into his published papers.

Lee had a tremendous sense of responsibility to family, students, and community. As editor of the Bulletin of Mathematical Biology, he transformed it from a marginal journal into one of the leading vehicles for new results. He was a central figure in the Gordon Research Conference in Theoretical Biology for decades, and played a key role in the development of the field. At Los Alamos National Laboratory, he was a summer consultant to the theoretical biology group from 1984 to 1999, and he was named Ulam Visiting Scholar for 1992-93; he also became a fixture at the Santa Fe Institute.

No single individual is more clearly identified with the face of theoretical and mathematical biology today. He was a dynamic and inspiring lecturer, and a brilliantly clear expositor. Although he was opposed to publishing "every sneeze," his publication record is equally daunting and inspiring. His expository style, indeed, made each of his papers a joy to read.

Above all, Lee was a wonderful friend, husband, and father. His deep roots in Judaism, which he shared in every aspect with Ruthie and his children, led him to emigrate to Israel, and pervaded his character and his essence. A deeply spiritual person, he made all who interacted with him feel comfortable in who they were. Never judgmental, he led by example. With his passing, a piece of all of us has died. The field will never seem the same.---Simon Levin, Princeton University, and James M. Hyman and Alan S. Perelson, Los Alamos National Laboratory.


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