Wait, What?! Elephants Should Be Riddled with Cancer—But They’re Not

by Jon Scaccia March 6, 2025

Let’s play a game of logic: If cancer is caused by cells making mistakes when they divide, then bigger animals—who have more cells—should get more cancer, right? A whale has millions of times more cells than a mouse, so shouldn’t it be a walking tumor factory?

For decades, scientists thought they had this figured out. More cells, more risk, more cancer. But then they looked at the numbers, and…something weird happened. Elephants? Low cancer rates. Whales? Practically immune. Even humans—compared to other species our size—don’t get as much cancer as we should. This bizarre contradiction became known as Peto’s paradox, and for years, it stumped scientists.

Now, new research just delivered a shocking twist: Maybe Peto’s paradox was never real in the first place!

What the Science Says: Bigger Really Does Mean More Cancer

A group of researchers tackled this question head-on, analyzing cancer rates across four major groups of land vertebrates: mammals, birds, reptiles, and amphibians. Their conclusion? Turns out, the original paradox might not hold up after all. When you look at a huge dataset of different species, the pattern is clear: larger animals do, in fact, have higher cancer rates.

This might sound like a ‘duh’ moment, but previous studies had such small sample sizes that the real trend got buried under statistical noise. The new research, using powerful evolutionary models and big data, uncovered something even cooler: while bigger animals do get more cancer, species that evolved to be big over time have developed better cancer defenses.

In other words, size alone doesn’t doom an animal—it’s how fast and how recently they got big that seems to matter most.

Evolution’s Cancer-Fighting Superpowers

Think of it like this: If you take a human and suddenly make them the size of a blue whale, their risk of cancer would skyrocket. Their cells weren’t designed to handle that many divisions. But whales? They’ve had millions of years to tweak their biology, strengthening their defenses against cancer along the way.

The researchers found that as mammals and birds evolved larger body sizes, they also evolved mechanisms to slow down or prevent uncontrolled cell growth. Some species, like elephants, carry multiple copies of tumor-fighting genes like TP53, giving them an extra layer of protection. Bats, despite their small size, have evolved similar defenses thanks to their long lifespans and high metabolism.

This means evolution isn’t just about getting bigger—it’s about getting smarter at handling the biological baggage that comes with size.

What Does This Mean for Humans?

This research isn’t just a fun fact about elephants and whales—it could actually help us fight cancer in humans. Scientists are already studying how large animals suppress tumors in hopes of translating those mechanisms into treatments for people. If we can figure out how elephants or whales resist cancer so well, we might unlock new ways to prevent and treat the disease in humans.

But there’s also a cautionary tale here. Human lifespans and body sizes have been increasing dramatically in recent centuries, much faster than evolution typically works. Unlike elephants, we haven’t had millions of years to fine-tune our cancer defenses. Could that mean our modern lifestyles are outpacing our biology’s ability to keep us safe? Scientists are asking that very question.

The Big Takeaway

So, does size equal cancer? Kind of. Peto’s paradox turns out to be more of a misunderstanding than an actual rule—larger animals do get more cancer, but those that evolved to be big over long periods of time have built-in defenses. It’s not just about how many cells you have; it’s about how well your body manages them.

This study challenges old assumptions and opens new doors for cancer research. If evolution has already figured out how to beat cancer in some animals, maybe we can, too.\

Let’s Explore Together!

What do you think? Could we one day use elephant genes to fight human cancer? If you could pick an animal superpower, would it be cancer resistance or something else entirely? Drop your thoughts in the comments and share this article with your favorite science-loving friend!

Fight for Science:

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