Mutagens are chemicals or physical factors (such as radiation) that increase the rate of mutation in the cells of bacteria, plants, and animals (including humans). Most mutagens are of natural origin and are not just a modern phenomenon: even dinosaurs were susceptible to mutagens. Mutagens can be found in the food we eat, the air we breath, or the ground we walk on. Very small doses of a mutagen usually have little effect while large doses of a mutagen could be lethal.DNA in the nuclei of all cells encodes proteins that play important structural and functional (metabolic) roles in the cell. Mutagens typically disrupt the DNA of cells, causing changes in the proteins that the cell produces which can lead to abnormally fast growth (cancer), or even cell death. In rarer incidences mutagens can even cause protein changes that are beneficial to the cell.

The first mutagens...