Evolutionary and biological foundations of malignant tumors

A hypothesis on evolutionary and biological foundations of malignant tumors is developed. It is suggested that malignant transformation is an inevitable facet of the process of senescence, consequent on the accumulation of somatic mutations. The rate of mutation accumulation is determined by an interplay of internal damage to DNA due to metabolic production of oxidative radicals, and effectiveness of DNA-repair mechanisms. The extent of production of oxidative radicals depends on the metabolism intensity which is determined genetically, and is related to the timing of sexual maturation. The timing of sexual maturation depends on the hazard to life of species members--in species exposed to more dangers, reproduction must be set to occur earlier, at the price of having less effective DNA-repair mechanisms. Target genes for malignant transformation are cellular oncogenes. The deaths due to malignant tumors may thus be considered 'one of the mechanisms of death due to aging'. Environmental carcinogens will only modify the incidence of a small fraction of certain tumor types, as other environmental factors modify the death incidence from other causes.