3 ms·

One theory is that they actually get so many cancers that they fight each other and never reach the stage where they would become harmful for the Elephant. A go

• bradrn 5y ago
  Also discussed by Scott Alexander in some detail, near the end of a mostly unrelated post: https://slatestarcodex.com/2014/06/14/living-by-the-sword/ https://slatestarcodex.com/2014/06/14/living-by-the-sword/
• jjk166 5y ago
  Hypertumors aren't really a good explanation for Peto's Paradox. Yes, larger animals would need larger tumors to kill them, and larger tumors are more likely to develop hypertumors, but even if cancer didn't kill a large animal we'd still expect to see all those "small" tumors that haven't yet developed hypertumors. Further, Peto's paradox doesn't just apply to large organisms: small creatures get higher cancer rates. You'd expect there to be some threshold below which the odds of a hypertumor developing are incredibly low, and all organisms that can be killed by tumors smaller than this threshold would have a cancer incidence rate proportional to body mass. At the same time there should be some threshold where a hypertumor is basically guaranteed, above which cancer deaths would simply stop regardless of body mass. Instead, cancer rate is independent of body mass across the spectrum. Then, the lack of correlation between cancer rates and body mass only applies between species. Within a single species, animals with more body mass do have higher rates of cancer and vice versa. This is directly contradictory to what we'd expect if cancer suppression was a result of increased body mass. Finally, closely related to Peto's Paradox is the fact that longer lived species have lower per-cell division cancer rates than shorter lived species. Animals with different lifespans but of the same bodymass can be killed by tumors of the same size, so you need some explanation other than hypertumors (which occur as a function of the size of the tumor) to explain this observation. Evolutionary adaptations that limit cancer are both a simpler and better explanation for these observations. Every animal is going to have some threshold in its life by which it is likely to have passed on its genes, and another threshold beyond which it is unlikely to better pass down its genes. Any gene that kills you before the first threshold is going to be strongly selected against, any gene that keeps you alive after the second threshold isn't going to have much selective pressure supporting it. A mouse in the wild can successfully pass on its genes in 3 months and is unlikely to live past 18 months due to injury and predation. While mice under ideal conditions in captivity have lived for up to 6 years, a gene that helps mice suppress cancer when they're 5 years old isn't doing wild mice any favors. On the other end of the spectrum, blue whales take a minimum of 16 years to reach genetic breakeven, and realistically given their distribution it could easily take much longer. A mutation that causes a 5 year old whale to get fatal cancer will never get passed on to offspring. We should logically expect that any species will continue to evolve cancer defense mechanisms up until the point at which cancer is no longer the limiting factor for passing on their genes, at which point evolution stops selecting for further improvements.
  • crubier 5y ago
    This is a very strong point. It puts some rationalization behind my intuition that hyper tumors are not a correct explanation, it emphasizes the strength of the gene explanation and this consistent with OP’s article.
• MiddleEndian 5y ago
  https://www.youtube.com/watch?v=aI0euMFAWF8 https://www.youtube.com/watch?v=aI0euMFAWF8