The answer lies in how quickly the body size evolves. We discovered that birds and mammals that reached large sizes faster have reduced the prevalence of cancer. For example the common dolphin, Delphinus Delphis Developed to achieve his large body size – together with most other whales and dolphins (called slide tans) about three times faster than other mammals. Cetaceans, however, tend to have less cancer than expected.
Larger species are confronted with higher cancer risks, but those who reached that size, quickly developed mechanisms to reduce it, such as lower mutation speeds or improved DNA repair mechanisms. So instead of contradicting the rule of Cope, our findings refine them.
Larger bodies often evolve, but not so quickly in groups where the burden of cancer is higher. This means that the threat of cancer may have formed the pace of evolution.
People evolved relatively quickly to our current body size. Based on this, we would expect that people and bats have similar prevalence of cancer, because we evolved with a much faster speed. However, it is important to note that our results cannot explain the actual prevalence of cancer in people. That is also not an easy statistics to estimate.
Human cancer is a complicated story to unravel, with an abundance of types and many factors that influence their prevalence. For example, many people not only have access to modern medicine, but also different lifestyle that influence the risk of cancer. For this reason we have not included people in our analysis.
Fighting cancer
Insight into how species naturally evolve cancer defenses has important implications for human medicine. The naked Molrat, for example, is studied for its exceptionally low prevalence of cancer in the hope of discovering new ways to prevent or treat cancer in people. Only a few cancer cases have ever been observed in captive moles, so the exact mechanisms of their cancer resistance usually remain a mystery.
At the same time, our findings raise new questions. Although birds and mammals that were quickly developed, seem to have stronger anti-cancer mechanisms, amphibians and reptiles did not show the same pattern. Larger species had a higher prevalence of cancer, regardless of how quickly they evolved. This can be due to differences in their regenerative skills. Some amphibians, such as Salamanders, can regenerate entire limbs – a process that entails a lot of cell division, which could exploit cancer.
Setting cancer in an evolutionary context enabled us to reveal that its prevalence is increasing with body size. Studying this evolutionary arms race can unlock new insights into how nature fights cancer – and how we can do the same.
Joanna Baker, postdoctoral researcher in evolutionary biology, University of Reading and George Butler, Carriles Duvitals Fellow in Cancer Evolution, UCL. This article is re -published from the conversation under a license for Creative Commons. Read the original article.
