Michael Klass discovered that lifespan of "C. elegans" could be altered by mutations, but Klass believed that the effect was due to reduced food consumption (caloric restriction). Thomas Johnson later showed that the 65% life extension effect was due to the mutation itself rather than due to caloric restriction. In 1993, Kenyon's discovery that a single-gene mutation (Daf-2) could double the lifespan of "C. elegans" and that this could be reversed by a second mutation in daf-16m, sparked an intensive study of the molecular biology of aging, including work by Leonard Guarente and David Sinclair. Kenyon's findings have led to the discovery that an evolutionarily conserved hormone signaling system influences aging in other organisms, perhaps also including mammals.