Franklin W. Stahl, in collaboration with Matthew Meselson, discovered direct evidence for the semiconservative nature of deoxyribonucleic acid (DNA) replication in bacteria. In experiments, Stahl and Meselson showed that when a double stranded DNA molecule is duplicated, the double strands are separated and a new strand is copied from each parent strand forming two new double stranded DNA molecules. The new double stranded DNA molecules contain one conserved parent strand and one new daughter strand. Therefore, the replication of a DNA molecule is semiconservative: it retains some of the original material while creating some new material. The understanding of the semiconservative nature of DNA in replication was a major advancement in the field of molecular biology.

Franklin William Stahl, the youngest of three children, was born in Boston, Massachusetts, to Oscar Stahl, an equipment specialist with New England Telephone and Telegraph, and Eleanor Condon Stahl, a homemaker. Stahl...