In addition to the Nature Communications article, however, a more recent publication demonstrated that cancer incidence has no association with species' size and longevity, and that elephants have a mere 6.1% incidence of cancer, compared to 25% incidence in humans.(4) This > 4-fold lower occurrence In contrast to hydra, which evolved over 600 million years ago, elephants arose much more recently, around 50-60 million years ago (90% more recently on the evolutionary timescale). This low disease incidence associated with elephants possessing over 20 copies (i.e., 40 alleles) of the "master" tumor suppressor gene TP53 (protein name p53), and that the elephant p53 ortholog predominantly facilitates programmed cell death (“apoptosis”), compared to human p53, which favors cells’ repair of DNA damage.
Consistent with the elephant vs. human comparisons described above, it appears that in vertebrate animals, animal size is even negatively correlated with cancer incidence, and mutation rates (Figure 2). While this dichotomy ("Peto's paradox," first theorized by Richard Peto in 1977)(5) has persistently been held when considering cancer rates across species, it has not yet held true within the same species. For example, in the 25-year Whitehall study of 17,738 London public servants, when corrected for confounding factors such as tobacco use, found that cancer incidence positively correlated with height;(6) another assessment of 74,556 domesticated dogs demonstrated the lowest cancer risk in small dog breeds, and smaller animals within the same breed.(7)