Why Don’t Big Animals Get Cancer?

(Last Updated On: April 24, 2020)

Why Don’t Big Animals Get Cancer?

Why Don’t Big Animals Get Cancer?

Cancer. We’re all pretty familiar with what it is and none of us like it. We might not know everything about cancer, but we do know that humans aren’t the only things on Earth that can suffer from it. At the same time, there are some animals we never hear about getting cancer, like whales or elephants. There’s a reason for that–they don’t really suffer from cancer. And if they do, they suffer from it way less than us humans do. So why don’t big animals get cancer? 


If you’re not familiar with cancer beyond “it’s really bad for you,” we’ll do a quick rundown of what it is and what it does to you. 

As a part of being alive, your cells have to multiply. They don’t last forever after all, and they need to be replaced. If you’re still growing, which a sizable amount of people are, you 100% don’t have the same amount of cells in your body as you did when you were a baby.

What we’re saying is that mitosis is a very important function for you to keep functioning. Such is life that this process can be… Buggy to put it one way. That’s essentially what cancer is. When your cells aren’t dividing, they’re doing their jobs. But sometimes they decide they no longer want to do their jobs, and they just want to do the dividing part. 

Normally the body has fail-safes against this, part of it is apoptosis. Your cells more or less commit suicide when something’s a little off with them, so they don’t make more of themselves and spread imperfections. If you’ve photocopied the same picture over and over and over again, you kind of know what we’re talking about.

Even so, potential cancer cells are often nipped in the bud by the immune system. Of course, with the average person having like 30 trillion cells, things go wrong. Thus, cancer.

Cancer in Animals

As interesting as it would be to go through the weird ways cancer can manifest in tons of other animals, that’s a topic for another day.

Quick side note: clams can get cancer contagiously. Yes, two clams chilling next to each other can just… Give each other cancer.

Compared to other animals, our cells are roughly the same size. Your pet dog just has a lot less cells than you–by virtue of being smaller. Same goes for bigger animals. A blue whale just has a lot more–some estimates put blue whale cell counts in the tens of quadrillions. 

Given what we said earlier, cancer is essentially a numbers game. With so many cells doing so many things per day, eventually something will go wrong. Even with fail-safes in place, things slip though, mistakes are made. So logically, you’d conclude that more cells doing more things increases the likelihood for mistakes to be made. 

Increased likelihood for mistakes means an increased likelihood for cancer, right?

And conversely, smaller animals with less cells and shorter lifespans should get less cancer–since they have less cells to make mistakes, and less time for those cells to make mistakes, right?

Peto’s Paradox

Except that’s not the case at all. Humans and mice, despite having vastly different sizes and average lifespans, get cancer roughly the same amount–on average. But blue whales and other large animals simply don’t get cancer.

Thus, we come to Peto’s Paradox.

Big Animals Evolved to Avoid Cancer

Perhaps large animals are more likely to get cancer. They just evolved to… Not get it. Most organisms have tumor suppression genes buried in their cells. These suppressive genes are what make cells kill themselves or get detected when mutations go awry. For example the suppression gene TP53. Us humans have 1 copy of this gene.

By contrast, elephants have a whopping 20 copies. On top of that are another 19 genes that indirectly support the suppression process.

While this doesn’t make elephants and other large animals immune to cancer, it does mean that their bodies are far more equipped to deal with it naturally. Quite literally, an elephant cell has to have far more imperfections than a human or rat cell before it’s a problem the body has to destroy.

Big Animals Are too Big to Care

Since all animals have essentially the same-sized cells, it takes roughly the same amount of time to generate a tumor of, let’s say, 1 pound. No we’re not saying tumors get this big, it’s for conceptualization–bear with us.

1 pound is like 10% of your 10 pound housecat, which would make 10% of their total weight cancer. Alternatively, it’s just 1% of your mass as a 100 pound human. Suffice to say, the same tumor affects two different sized animals differently. 

If cancer grows at similar rates, but takes longer to affect larger animals, perhaps they’re just too big for the cancer to ever get large enough to cause problems. 

Big Animals Get Cancer on their Cancer

No seriously. Tumors can get tumors. They’re called hypertumors. You did not read us wrong.

Cancer cells make tumors when there are a lot of them grouped together, and tumors feed off of your body’s resources. That’s really what tumors are. They’re just a bunch of freeloaders mooching off of your body’s blood supply and all that. 

If you’ve ever had direct or indirect experience with cancer, you probably know that tumors can get… Rather large. Which is where hypertumors come in.

Since cancer cells are borne of imperfections and mutations, and they must also replicate–just as non cancer cells do. Which means cancer cells can also generate imperfect mutations. One key difference is that they’re likely to mutate a lot more, given that all they do is mooch and multiply. 

So what happens when a cancer cell mutates so far it becomes a new type of cancer? Well sometimes you get a huge problem. Unless this new cancer starts mooching off of the original cancerous mass. Your tumor, just got a tumor.

Because these two tumors are now in conflict with each other, they might just kill each other off, allowing the body to proceed as normal. 

So it’s possible that big animals are absolutely cancer-ridden. They’re just so cancer-ridden their cancer gets cancer so their cancer goes away. 

Know your cancers? Pick out the deadliest ones here.

About the Author:

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Kyler is a content writer at Sporcle living in Seattle, and is currently studying at the University of Washington School of Law. He's been writing for Sporcle since 2019; sometimes the blog is an excellent platform to answer random personal questions he has about the world. Most of his free time is spent drinking black coffee like water.