Figure 1.

Evolution explains why cancer exists and also why it is not more common. (A) Cancer results from somatic selection at the cell level that favors neoplastic cells (red) over normal somatic cells (tan). (B) Cancer suppression results from selection at the organism level, favoring organisms that have traits (e.g., DNA repair, cell cycle checkpoints/apoptosis, and certain tissue architectures), which keep neoplastic cells in check (blue) while those individuals with traits that make them susceptible (pink) decrease in prevalence in the population.