Obituary: Dr Franklin Stahl

Dr Franklin Stahl, a prominent molecular biologist whose work helped solidify the DNA double helix model, has died aged 95.

His landmark DNA replication experiment demonstrated how DNA strands separate and replicate, with one strand conserved and the other newly synthesised. Published in 1958, just four years after James Watson and Francis Crick put forward their DNA model, it provided evidence for the hypothesis that the pairing of bases could provide a copying mechanism.

'It has been termed the most beautiful experiment in biology, and rightfully so,' Dr Diana Libuda, associate professor of biology at the University of Oregon, where Dr Stahl spent much of his career, told the Washington Post.

The experiment involved growing E. coli bacteria sequentially in two different media, each enriched with either a 'heavy' (nitrogen-15) or 'light' (nitrogen-14) isotope. It showed that each new DNA molecule correspondingly contained a heavier and lighter strand, confirming that DNA replication is semi-conservative.

Born in 1929 in Needham, Massachusetts, Dr Stahl earned a biology degree from Harvard University, Massachusetts, in 1951 before completing a doctorate in genetics at the University of Rochester, New York.

Two serendipitous laboratory visits set him on the path that would make his name. The first, to Cold Spring Harbour Laboratory for a course in bacteriophages (viruses that prey on bacteria by injecting their DNA into them), piqued Dr Stahl's interest in the molecular mechanics of DNA. The second, to the Marine Biological Laboratory in Massachusetts for a molecular biology course (coincidentally taught by Watson and Crick), is where he met his 'beautiful experiment' collaborator, Dr Matthew Meselson.

After joining Dr Meselson at the California Institute of Technology, they collaborated on the interdisciplinary experiment – Dr Meselson bringing the idea for the experimental approach, and Dr Stahl the necessary mathematical skills.

Writing of his famous experiment, Dr Stahl once said: 'It set a standard for me in science which I don't know I can ever achieve again, but it's worth shooting for. Anytime I write a paper, I remember that one, and say… come as close as you can.'

In the years that followed, his work at the University of Oregon continued to pave the way for new generations of geneticists to make transformative discoveries – such as his elucidation of the process behind bacteriophage cloning.

Dr Stahl's wife, Mary Morgan, who became his research technician, co-wrote many of their papers and shared the discovery of the first DNA recombination hotspot – a place where DNA strands frequently exchange pieces of genetic material. She died in 1996, shortly before Dr Stahl retired.

His books 'The Mechanics of Inheritance' (1964) and 'Genetic Recombination: Thinking About It in Phage and Fungi' (1979) were founding contributions to public engagement on genetics. He received numerous accolades, including the MacArthur Foundation's 'genius grant', two Guggenheim fellowships and the Genetics Society of America's Thomas Hunt Morgan Medal for lifetime contributions.

Dr Stahl is survived by his son, daughter, and eight grandchildren.