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Is creeping abandon of human cancer defences evolutionarily favoured?
  • Alexander D. Rahm,
  • Pierre Pratley
Alexander D. Rahm
University of French Polynesia

Corresponding Author:alexander.rahm@upf.pf

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Pierre Pratley
KIT Royal Tropical Institute
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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. Chimpanzees, being closely related to humans, have a very low 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, and higher degrees of inbreeding would quite certainly have been detrimental to a tribe. And males of high social status can attract new reproductive partners again and again until an age that has seen several generations grow, which in case of a not-so-large tribe would have considerably narrowed down its genetic pool. Furthermore, lowering tumour suppression activities might save calories and hence benefit tribes with limited food production; and individuals suffering from cancer after female reproductive age could still have made contributions to parental/grandparental care, while no more being attractive as a reproductive partner. Is creeping abandon of human cancer defences evolutionarily favoured?