Evolution of Radioresistance on Earth: From Single-Cell Organisms to Humans

The evolution of species on the Earth occurred under conditions of continuous low-level irradiation from extraterrestrial X-rays and charged particles. Furthermore, continuous emission of radiation from beneath the planet’s surface including radium and radon products added to the background radiation. How these basic evolutionary events relate to the modern clinical use of radiation for diagnosis and therapy is important to understand. How they relate to radiation exposure to humans during space travel and under conditions of nuclear reactor accidents or the unthinkable detonation of a fission/fusion bomb is a topic of recent concern. The formation of the planet Earth occurred, in all likelihood, before the arrival of water delivery through a meteor and most likely preceded by the formation of the magnetosphere, which channels charged particles including galactic cosmic irradiation and solar protons to the poles. Life evolved on the planet through the creation of nucleic acids and led to single-cell organisms, which evolved over billions of years. The process of natural selection led to land animals, mammals, and eventually humans. The mechanism for the biological response to ionizing irradiation included the creation of DNA repair genes and genes for antioxidant molecules, which led to conditions for stable reproduction. The number of genes responsible for radiation resistance and their interaction with one another is a subject of current research.