Meselson is the Thomas Dudley Cabot Professor of the Natural Sciences at Harvard University. He joined the faculty of Harvard in 1960 as an associate professor of molecular biology. He is also the co-director of the Harvard Sussex Program on Chemical Biological Warfare Armament and Arms Limitation. Meselson received a Ph.B. (1951) from the University of Chicago and a Ph.D. (1957) from the California Institute of Technology. His research is directed toward understanding why most animals and plants reproduce sexually and why most asexual lineages suffer early extinction. He has investigated the molecular biology of the replication, recombination, restriction, and repair of DNA, as well as the control of gene expression. In addition, Meselson has studied chemical and biological weapons and arms control. He has served as a consultant for a number of government agencies and has participated in numerous scientific studies that examine the effects of biological weapons.