Most radiation exposure comes from natural sources. These so-called "natural sources" include Radon, Internal, Terrestrial, and Cosmic. Among that, Radon proves to be the largest source of radiation. Radon is a naturally occurring radioactive gas that comes from the breakdown of uranium.
When energy is emitteds by a source and travels through a medium until it's absorbed by matter, radiation is occuring. We are exposed to radiation everyday, some sources of radiation are natural and other come from man-made elements. We are commonly exposed to Background radiation, from Earth itself (some minerals) and very few man-made objects. From this type of radiation comes the one we are the most exposed to emitted by Radon and Thoron (radioactive gases which are created when other naturally occurring elements undergo radioactive decay). This gases represent 37% of all the radiation we are commonly exposed to.
Natural selection is a simple mechanism that causes populations of living things to change over time. Organisms that are more adapted to their environment are more likely to survive and pass on the genes that aided their success.
