Harry Harris FRS, FCRP (30 September 1919 – 17 July 1994) was a British-born biochemist. His work showed that human genetic variation was not rare and disease-causing but instead was common and usually harmless. He was the first to demonstrate, with biochemical tests, that with the exception of identical twins we are all different at the genetic level. This work paved the way for many well-known genetic concepts and procedures such as DNA fingerprinting, the prenatal diagnosis of disorders using genetic markers, the extensive heterogeneity of inherited diseases, and the mapping of human genes to chromosomes.