Cellular change
Over time, all cells accumulate multiple genetic changes to their DNA sequence. These changes are often the result of radiation damage (ultraviolet light, cosmic rays, radioactivity) or exposure to low levels of toxic chemicals. As they occur at random, the majority will miss the 2% of coding (genetically active) DNA, and have no major effect on the organism. Other rarer mutations that result in useful adaptations may arise by the alteration of single amino acids of a particular protein. This can modify the three-dimensional structure of the protein which can raise, lower, or negate its normal activity. Other changes can result in either complete or partial deletion of genes (including gene control sequences) or a subtraction or duplication of genes resulting in potentially lower or higher amounts of a particular protein. In rare cases, a major rearrangement of the DNA in the nucleus may result in a completely novel hybrid gene. This is the mechanism of evolution at its simplest and if such genetic changes adversely affect a single-cellular organism it dies. Should an advantage be conferred, it will spread throughout a population and eventually become established.