eli5: What’s the process behind cancer, and why do bigger animals get it less?
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Cancer is “haywire” cells. When a random mutation turns off growth control, the self-destruct mechanism and also still gets recognized as a healthy cell by the immune system it multiplies and grows without limit.
How that happens: cells are controlled by their DNA. If the DNA gets damaged (for example by some chemical, or by radiation) there is a low chance it causes exactly the kind of effect that trigger cancerous growth.
Why big animals get it less: they have more cells and get older, so their overall cancer risk should be a lot higher. And that’s kinda the reason why it got lower, there was more evolutionary pressure to evolve cancer resistant cells (If your DNA leads to cancer after 3 years on average that’s not an issue for a rat, but for an elephant that’s the end of that bloodline, so only the most cancer resistant elephants pass on their genes)
That can happen in multiple ways. For example cells can be simply more robust to changes, I.E. cell growth being controlled by more than one DNA section. But also by the immune system being better and recognizing cells that have issues.
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