Although researchers know that cancer risk increases as a person ages and gains weight, whales, the world’s largest mammals, do not experience this correlation. In fact, they are some of the animals least likely to get cancer. New research aims to find out why that is.
Cancer should be a near certainty for whales, the longest-living and largest mammals there are – but scientists are finding that cetaceans are excellent at protecting themselves against the deadly disease.
About Peto’s Paradox
Scientists have long puzzled over a phenomenon known as “Peto’s Paradox.”
The chance of a cancer developing increases with number of cell divisions and length of life, both of which favor the occurrence of cancer-inducing mutations. The large size of whales and elephants is because of a lot of cell divisions, and they also live much longer than most mammals—so you’d expect them to have more cancer. Yet they don’t; they have significantly lower rates than other mammals. This is known as Peto’s paradox.
The study team summarizes the paradox as: “Why do not larger organisms always have a higher risk of developing cancer than smaller ones?”
And why don’t whales get cancer?
Geneticists have found that some parts of the whale genome, especially genes concerned with cell proliferation and DNA repair, have evolved faster than others. Many forms of cancer in humans result from mutations in protective tumor-suppressor (TS) genes. The humpbacked whale genome has evolved multiple copies of these genes—maybe acting like backup if one or more of them mutate and lose their protective function.
That may give these animals a level of protection we don’t have. The extra protection afforded by these redundant genes is perhaps necessary for the animals to grow to such sizes; they perform a necessary “housekeeping” role. These animals’ unusually low level of cancer may be a side benefit of this.
So yes, this has excited a line of research looking into anticancer mechanisms in whales and other long-lived animals including sharks, bats, tortoises, and crocodilians.
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Video source: Wild Zilla