Why don’t whales get cancer?

Whales, dolphins and porpoises are the world’s largest and longest-living mammals – and they can resist cancer. 

Why these cetaceans and other large animals evade this scourge has long perplexed scientists, who reason that organisms with more cells should have a higher risk of cancerous mutations – a dilemma known as Peto’s paradox.

A molecular study, published in the Proceedings of the Royal Society B, has now found cetaceans have rapidly evolving genes that suppress tumours.

A team of international scientists from Chile, the UK and the US explored how natural selection drove the evolution of 1077 tumour suppressor genes in cetacean ancestors and compared them with those of 15 other mammal species, including humans.

Key Research points

  • Whales and dolphins are less susceptible to cancer than humans.
  • Molecular analysis showed they had a high rate of gene mutation.
  • This led to a high number of tumour suppressor genes.

The turnover of the genes – the rate at which they were gained and lost through mutation– was nearly 2.4 times higher in cetaceans than most other mammals, and highest in baleen whales (filter-feeding species that include blue, humpback and right whales).

The gene variants found in those mammals “could have favoured the evolution of their particular traits of anti-cancer resistance, gigantism and longevity,” write Daniela Tejada-Martinez, from the Universidad Austral de Chile, and co-authors.

The study found signs of positive selection in genes regulating DNA-damage, tumour spreading and immunity. It also found 71 genes with duplications associated with fighting cancer, such as DNA repair, metabolism, cell death and ageing and 11 duplicate genes associated with longevity. 

“Overall, these results provide evolutionary evidence that natural selection in tumour suppressor genes could act on species with large body sizes and extended lifespan,” the authors write, “providing novel insights into the genetic basis of disease resistance.”

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