However, given that cell division may lead to errors, larger animals should get more cancer. After all, bigger body, more cells/cell divisions, more possible mutations. Enter a paradox.
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If we look within species, there seems to be a positive correlation between cancer risk and body size. Larger individuals → increased risk. But, when we look across species, this correlation breaks down. An elephant does not get more cancer than a mouse. This apparent resistance of larger-sized species to cancer is known as Peto’s paradox, named after English statistician Richard Peto who first observed it in 1977.
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Evolution, it seems, has gifted the larger species some extra protection.
A new study now exposes some of those gifts by looking at the largest of animal groups: cetaceans. The whales.
The researchers went looking for clues in the genetic data of 7 species of cetacean (bottlenose dolphin, orca, beluga, Yangtze river dolphin, the sperm whale, common minke whale, and the bowhead whale). They also looked at 8 other species to have good points of comparison (cow, pig, dog, horse, microbat, human, mouse, and the African elephant).
They started with data on known tumor suppressor genes and then scoured the cetacean DNA for traces of those.
The scientist found evidence of positive selection for seven of the tumor-suppressing genes in whales: CXCR2 in all cetaceans and DAB2, ADAMTS8, DSC3, EPHA2, TMPRSS11A, ANXA1 specifically in baleen whales (which happen to be the largest of all whales). These genes are known to be involved (in humans) in cancers such as lung neoplasm, leukemia, teratocarcinoma, as well as in immune system disorders.
Another interesting finding was that cetaceans genes had a higher turnover rate, aka more gene loss and gain. This makes sense because the researchers also found more gene duplications. Extra gene copies give evolution more material to play with. (This turnover signal was strongest in the baleen whales as well.)
Evolution is cleverer than we are…
- More Here
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