Coevolution of cooperative lifestyles and low cancer incidence in mammals

Why cancer is so prevalent among mammals, despite the fact that some species evolved resistance mechanisms, remains an open question. We hypothesized that cancer incidence might have been fine-tuned by evolution. Using public databases, we show that species with cooperative habits have lower cancer risk. By developing a novel mathematical model we provide a mechanistic explanation: a higher incidence of cancer in older and less reproductive individuals can lead to counterintuitive increases in population size within competitive contexts. The phenomenon of a population increasing in response to a decrease in its per capita survival rate is called the hydra effect, a process never explored in the field of cancer before. Therefore, cancer can be considered as a selected mechanism of biological obsolescence in competitive species.