question: The Earth was highly radioactive four billion years ago when life emerged. Even today, all humans are bombarded by 20,000 radiation strikes each second. Although high radiation doses are hazardous, organisms have evolved not only to tolerate lower-dose radiation but also to benefit by it (hormesis). Hormesis is prevailing in all species in various respects. An example is that hibakusha (Japanese A-bomb survivors) have longer lifespans and have lower risk of cancer, on average. Many microbes thrive in deep subsurface regions by consuming radiation as a source of nutrition. Low-dose radiation (LDR) is effective at treating severely affected COVID-19 patients, but the invalid linear no-threshold model (LNT) hinders the full beneficial use of LDR.