Episode 10 – Why is cancer so rare in whales?

Janine was helping some students with high school genetics when she came across some fascinating research suggesting that whales and other cetacean mammals hardly ever get cancer. She and Aleena were super intrigued and just had to know why, especially as there is such a strong history of cancer in their family. Meanwhile, Aleena tells us how she spent a recent Friday night exploring the ins and outs of Excel pivot tables, and Janine outlines her accidental experiment which proves once and for all that her new favourite pens are not magical at all.

What is peto’s paradox?

OK so get this: the larger an animal is, the more cells it has; and the more cells an animal has, the more chances there are for cells to turn cancerous. It’s just probability. So in theory we should see larger animals getting a lot more cancer than smaller animals. Except we don’t… It’s a similar story for animals that live for a really long time. The longer an animal lives the greater chance it has to develop cancer. So again we should see long-lived animals, like whales, get cancer more frequently than animals that live shorter lives. Except we don’t! That is Peto’s paradox. This and more about how different animals deal with the threat of cancer in this question and answer paper.

Tollis, M, Boddy, AM, & Maley, CC. (2017). Peto’s Paradox: how has evolution solved the problem of cancer prevention? BMC biology, 15 (1): 1-5.

So how exactly are whales resisting cancer?

Cetaceans include whales, dolphins and porpoises. They include the blue whale, and bowhead whale, which, respectively, are the biggest and longest lived mammals to ever exist on planet Earth (massive respect!) But guess what? They have some of the lowest incidences of cancer observed for all animals…

Essential tangent: the closest living relative to the whales is the hippopotamus (more here cos you know you need to know)!

So what’s the sitch? It turns out that cetaceans have a very high number of tumor-suppressor genes which appear to have increased in number through random duplication mutation events. This means that mistakes in DNA replication led to double-ups of these genes many, many times over evolutionary history. Since tumor-suppressor genes code for proteins that either prevent cancer or massively slow it down, it’s a very good thing to randomly end up with loads of them. There is also evidence of strong natural selection in that individuals with extra tumor-suppressor genes appear to have had a clear survival advantage over others. On the other hand, individuals, and also other species, who did not have so many tumor-suppressor genes, were at higher risk of cancer and these individuals and species were not as successful. If whales and cetaceans had not randomly evolved to have these extra tumor-suppressor genes, they may well have gone extinct and this episode would have been about something else entirely!

Tejada-Martinez, D, de Magalhães, JP, & Opazo, JC. (2021). Positive selection and gene duplications in tumour suppressor genes reveal clues about how cetaceans resist cancer. Proceedings of the Royal Society B, 288 (1945): 20202592.

Do the evolution

Essentially, the resistance to cancer that we see in cetaceans and some other animal groups is all down to evolution, baby (apologies to Pearl Jam: note that this classic banger has been stuck in Aleena’s head the entire time she spent prepping for this episode. Err… Aside from the title, it doesn’t have much to do with what we’re talking about, but don’t let that stop you from rocking out to it! And if you’re in the mood to reflect on the stupidity of humans, even better!)

What brought out our inner square?

Aleena confesses to spending a recent Friday night, while NOT in lockdown, leaning about Excel pivot tables. If you love data and haven’t discovered these then do yourself a favour and check this out. Who would have thought spreadsheets could get any more exciting, right? The same day she learned the difference between cupcakes and muffins. Essential knowledge for all.

Janine has been obsessed with her new erasable pens, and explained how she accidentally conducted an experiment: she placed a plate of hot food on her journal, which was filled with key to-do lists, but when she lifted up the plate, all of the lists had disappeared! Thankfully, and surprisingly, the lists slowly but surely reappeared before her very eyes, as the page cooled down. This proves that is is the heat delivered by friction that enables these pens to be erased… It’s science, not sorcery! Here is more about the exact science involved (apparently the ink will still reappear if the page is placed in a freezer! Cue second experiment…).

Photo by Todd Cravens on Unsplash

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