Abstract
Among the animal species on which observations are available, humans have a uniquely high lifetime risk to suffer from cancer - over 38%, compared to less than 10% for all observed other species (except species suffering from environmental pollution). Peto's paradox shows that this cannot simply be explained by mathematical models which view cancer genesis as a stochastic process, with resulting risks polynomial in lifespan and body mass - whales have a longer lifespan and about 30 times the human body mass, however their cancer risk remains constant throughout their life rather than increasing sharply after female reproductive age as observed in humans. Rather, it is well documented in the literature that species-specific tumour suppression mechanisms allow for large lifespan and body mass. Data which was examined on chimpanzees, being closely related to humans, make it likely that there is a major difference between chimpanzee and human cancer risk, and hence the weakness of human cancer defence is likely to have resulted from the specific development of Homo sapiens. As this weakness appears past the reproductive years, a prominent hypothesis blames it to antagonistic pleiotropy. However, Homo sapiens having lived in small tribes during most of its development, natural selection is likely to also have acted at the level of tribes, which lets us derive our hypothesis, _is creeping abandon of human cancer defences evolutionarily favoured?_ from two alternative speculative scenarios. One of them is based on that lowering tumour suppression activities might save calories and hence benefit tribes with limited food production, the other one suggests that creeping abandon of cancer defences benefits genetical diversity.