The hypothesis that cancer arises from accumulated mutations can account for many findings. For example, the longer an organism lives, the more likely it is to have cancer, because theoretically it builds up more mutations over time. This has been supported by epidemiological studies that showed a vast increase in the number of cancer patients in many countries owing to an aging population.
Aside from longevity, another interesting issue is body size. One may assume that the bigger organisms are more likely to get cancer than smaller ones, because bigger bodies have more cells and thus more mutations. Although this idea sounds logical, it has been proven to be only partly true. Larger individuals do appear to have increased risk of cancer than smaller ones of the same species,. However, cross-species studies failed to support this hypothesis. No correlation was found between body size and the incidence of cancer between different species. For example, the incidence of cancer in humans is much higher than that in whales, which are about 100 times the size and about 1000 times the cell number of humans. In another example, humans and rodents have similar incidences of cancer despite the fact that they are enormously different in size.
One explanation scientists have for this paradox is that bigger-sized species are usually more resistant to carcinogenesis. They do so by developing many mechanisms, one of which is low metabolic rate. At lower metabolic rate the body produces fewer free radicals, which are an essential culprit that leads to cancer.
[1] Peto’s Paradox: evolution’s prescription for cancer prevention. Trends in Ecology and Evolution, April 2011, Vol. 26, No. 4.
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