The cellular paradox
In the 1970s, English statistician Richard Peto noticed a strange inconsistency. A human has about 1,000 times more cells than a mouse and lives dozens of times longer, creating vastly more opportunities for a cell to mutate and become cancerous. Yet, cancer rates in humans and mice are surprisingly similar. This became known as Peto's Paradox: across different species, cancer risk does not correlate with body size or lifespan.
Whales are an extreme example of this paradox. A blue whale has an estimated 1,000 times more cells than a human. The bowhead whale (Balaena mysticetus) can live for over 200 years, the longest of any mammal, and weighs over 80,000 kg. With so many cells dividing over such a long period, whales should face a much higher risk of cancer. Their existence proves they have evolved superior cancer suppression mechanisms. If they had the same cellular cancer risk as humans, the species would likely die out before they could reproduce.
Evolution's anti-cancer toolkit
Early research into Peto's Paradox focused on tumor-suppressor genes. Elephants, for instance, combat their high cell count with extra copies of a gene called TP53, which is famous for its role in destroying potentially cancerous cells. Humans have only one copy of TP53, while elephants possess at least 20. For a time, scientists assumed whales used a similar strategy.
However, whale genetics revealed a different approach. Many whale species, including sperm whales, only have one copy of the TP53 gene. Instead of simply adding more tumor-suppressor genes to kill off damaged cells, whales evolved ways to prevent the damage in the first place. Studies on bowhead whales show their cells are exceptionally efficient and accurate at repairing DNA double-strand breaks.
This enhanced repair capability is linked to elevated levels of specific proteins, particularly CIRBP and RPA2. In lab experiments, bowhead whale cells required fewer "hits," or mutations, to become cancerous than human cells did. This surprising result suggests the whale's primary strategy is not destroying damaged cells, a process that can deplete stem cells and accelerate aging, but rather repairing them with high fidelity. This "repair, don't replace" strategy may be a important factor in both their cancer resistance and their extraordinary longevity.