The stability of the genome is defined by the cells machinery of repair, damage tolerance, and checkpoint pathways that counteracts DNA damage. One hypothesis proposed by Gioacchino Failla in 1958[37] is that damage accumulation to the DNA causes aging. The hypothesis was developed soon by physicist Leó Szilárd.[38] This theory has changed over the years as new research has discovered new types of DNA damage and mutations, and several theories of aging argue that DNA damage with or without mutations causes aging.[39]