The fundamental role of hormesis in evolution

Hormesis can be considered a major mechanism underlying Darwin's and Wallace's theory of evolution by natural selection. The ability of organisms to respond adaptively to low levels of exposure to environmental hazards in a manner that increases their resistance to more severe similar or different hazards is fundamental to the evolutionary process. The organisms that survive and reproduce are those best able to tolerate or avoid environmental hazards while competing successfully for limited energy (food) resources. Therefore many of the genes selected for their survival value encode proteins that protect cells against stress (heat-shock proteins, antioxidant enzymes, antiapoptotic proteins, etc.) or that mediate behavioral responses to environmental stressors (neurotransmitters, hormones, muscle cell growth factors, etc.). Examples of environmental conditions that can, at subtoxic levels, activate hormetic responses and examples of the genes and cellular and molecular pathways that mediate such adaptive stress responses are provided to illustrate how hormesis mediates natural selection.