Matthew Stanley Meselson (born May 24, 1930) is a Harvard geneticist and molecular biologist who has investigated how DNA replicates, recombines, and is repaired in cells and how cells recognize and destroy foreign DNA. In the famous Meselson–Stahl experiment he showed that DNA is replicated semi-conservatively In addition, he, François Jacob, and Sydney Brenner were largely responsible for discovering the existence of messenger RNA.