I don’t like the traditional explanation for why we don’t all get cancer. I understand it. The traditional explanation is that there’s a variety of checks in our DNA to prevent cancer from happening, as well as a robust immune response when it does happen. Anyone who gets cancer had to have cells that bypassed the checks, evaded the immune system, and overcame the metalevel control of DNA that doesn’t allow cells to bypass checks in the first place.
Some of your observations may be explained by the inverse relationship between size and rate of metabolism across species. The mitochondria of smaller animals work on overdrive -- mostly because the number of mitochondria scales with body volume, while heat loss scales with body surface, so small animals need to squeeze more energy per mitochondrion in order to maintain body temperature. With higher rate of metabolism, the reactions involved in respiration produce free radicals faster, which increases the probability of DNA damage in a given amount of time.
This argument is well explained in the pop science book "Power, Sex, Suicide" by Nick Lane.
Some of your observations may be explained by the inverse relationship between size and rate of metabolism across species. The mitochondria of smaller animals work on overdrive -- mostly because the number of mitochondria scales with body volume, while heat loss scales with body surface, so small animals need to squeeze more energy per mitochondrion in order to maintain body temperature. With higher rate of metabolism, the reactions involved in respiration produce free radicals faster, which increases the probability of DNA damage in a given amount of time.
This argument is well explained in the pop science book "Power, Sex, Suicide" by Nick Lane.