Seriously, a bad sunburn could limit our ability to survive in the wild. I’ve had a few so bad I could barely move and I had a super high fever. Desn’t that happen to animals? How do they manage?
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Every answer so far is missing the key biological difference:
Every living cell contains mechanisms to error-check its DNA and correct many, but not all, errors that might occur.
DNA is held together with a type of chemical bond called a hydrogen bond, which is fairly weak. UV photons have enough energy to break these bonds, which is how UV damages DNA. Any time this happens where two thymine molecules are adjacent to one another, they can form a new chemical bond to each other, only a much stronger covalent bond.
In many animals, like reptiles, elephants and rhinoceroses, their DNA repair mechanism is able to fix this thymine-thymine covalent bond, saving UV-damaged skin cells.
However, in humans, our DNA repair mechanism has lost this ability, so when it encounters a thymine-thymine covalent bond, there’s no way to fix it. Instead, the cell receives a chemical signal that triggers apoptosis—the cell would rather die and be replaced by a healthy cell than risk becoming cancer. It’s this process of apoptosis and growing replacement skin cells that *is* a sunburn.
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