WEBVTT - Why Do Elephants Seldom Get Cancer?

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<v Speaker 1>Welcome to brain Stuff production of I Heart Radio. Hey

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<v Speaker 1>brain Stuff, Lauren Bobo bam here. You have no idea

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<v Speaker 1>what your DNA is up to right now. You might

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<v Speaker 1>not be able to see or feel it working, but

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<v Speaker 1>it is there, It never sleeps, and it's basically got

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<v Speaker 1>you hog tied. Your genetic material is an entire universe

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<v Speaker 1>of biological instructions, and a lot of the time they're

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<v Speaker 1>not even very good instructions. Your DNA could be making

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<v Speaker 1>coarse black hairs grow out of your palms right now,

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<v Speaker 1>or it could be nonchalantly protecting you from cancer. There's

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<v Speaker 1>no telling. Here's the thing, evolution doesn't have some great

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<v Speaker 1>plan for you personally, whether or not you have genes

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<v Speaker 1>that tell your palms to grow whiskers or your body

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<v Speaker 1>to fight cancer. That's mostly just happenstance, mostly, but from

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<v Speaker 1>time to time, DNA has been known to pull incredible

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<v Speaker 1>hail Mary's Take elephants, for instance, they very rarely get cancer.

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<v Speaker 1>An elephants cancer mortality rate is just under five percent.

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<v Speaker 1>For US humans it's between eleven and twenty five. Whales

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<v Speaker 1>have very low rates of cancer too. In fact, large

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<v Speaker 1>animals of all kinds seem to succumb to cancer way

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<v Speaker 1>less than one might imagine. This puzzled cancer researchers in

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<v Speaker 1>the nineteen fifties and sixties because the early understanding of

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<v Speaker 1>why cancer happens has to do with how many cells

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<v Speaker 1>an animal has, coupled with its longevity. Large and long

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<v Speaker 1>lived animals, scientists theorized, have lots of cells and more

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<v Speaker 1>time in which cells could potentially start doing their jobs wrong. Conversely,

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<v Speaker 1>small animals have fewer cells and generally don't live as

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<v Speaker 1>long as larger animals. Thus there are fewer chances and

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<v Speaker 1>less time for cells to mutate in the ways that

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<v Speaker 1>would result in cancer. This line of reasoning makes a

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<v Speaker 1>good bit of sense, right Yet in the nine seven these,

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<v Speaker 1>statistical epidemiologist Richard Peto observed that we don't see a

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<v Speaker 1>higher instance of cancer in humans than we do in mice,

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<v Speaker 1>even though human bodies contain a thousand times more cells

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<v Speaker 1>and we live thirty times as long. And so science

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<v Speaker 1>was introduced to Peto's paradox, the mystery that's bedeviled cancer

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<v Speaker 1>researchers for nearly half a century. Even though cancer reliably

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<v Speaker 1>shows up in larger individuals within a species more often

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<v Speaker 1>than in smaller ones. For instance, just a couple inches

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<v Speaker 1>of height on a human can significantly raise her chances

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<v Speaker 1>of getting some types of cancer. For whatever reason, huge

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<v Speaker 1>and long lived animals have cancer rates comparable to or

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<v Speaker 1>lower than our own. Because being humongous has evolved in

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<v Speaker 1>various animals countless times over the eons, there are probably

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<v Speaker 1>as many solutions to Peto's paradox as there are gigantic animals. However,

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<v Speaker 1>a study published in an August issue of Cell Reports

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<v Speaker 1>found the reason for Peto's paradox and elephants is in

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<v Speaker 1>reality completely bonkers genetically speaking. Previous research reported that African

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<v Speaker 1>savannah elephants have a whole bunch of copies of a

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<v Speaker 1>specific cancer fighting gene called t P fifty three. This

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<v Speaker 1>gene produces a protein that comb cells looking for potential

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<v Speaker 1>DNA damage. Humans and most other animals have only one

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<v Speaker 1>copy of this gene. Elephants, it happens, have twenty copies.

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<v Speaker 1>So t P fifty three lends the elephant a lot

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<v Speaker 1>of capacity to see that there is a problem, but

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<v Speaker 1>not really the ability to do anything about it. So

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<v Speaker 1>the University of Chicago research team rummaged around and the

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<v Speaker 1>elephant genome to see if they could find any clue

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<v Speaker 1>as to what would be carrying out the cell repairs

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<v Speaker 1>or cell destruction that gives elephants their cancer fighting powers,

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<v Speaker 1>and they found something pretty obvious. Elephants have between seven

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<v Speaker 1>and eleven copies of a type of gene known as

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<v Speaker 1>leukemia inhibitory factor, or l i F. The problem was

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<v Speaker 1>these copies were evolutionarily old, and many of them had

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<v Speaker 1>probably been useful to the elephants distant ancestors, but they

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<v Speaker 1>were so degraded that they were probably useless. But this

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<v Speaker 1>is where things start getting weird. For the article this

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<v Speaker 1>episode is based on how Stuff Work. Spoke with the

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<v Speaker 1>studies lead author one Manuel of as Quez, then a

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<v Speaker 1>graduate student in the Department of Human Genetics at the

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<v Speaker 1>University of Chicago. He said, well, what we actually found

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<v Speaker 1>was a copy of l i F l i F six,

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<v Speaker 1>which had integrated into the genome in the common ancestor

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<v Speaker 1>of elephants and manatees. Manatees still have this piece of DNA,

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<v Speaker 1>but it's what would traditionally consider junk. But elephants took

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<v Speaker 1>this junk DNA and right before law lost any in

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<v Speaker 1>all coding potential for the correct protein. It evolved a

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<v Speaker 1>new way of inducing its activation and expression into a

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<v Speaker 1>functional protein. Again, it was pure luck. So as a

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<v Speaker 1>last ditch attempt to cut down on the accumulation of

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<v Speaker 1>bad cells, the elephant's body resurrected a piece of DNA

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<v Speaker 1>that's capable of killing cells that have been flagged for

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<v Speaker 1>execution by t P fifty three due to DNA damage

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<v Speaker 1>and put it to work culling those cells. L i

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<v Speaker 1>F six kill cells by poking holes in the mitochondria,

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<v Speaker 1>the power plant of the cell, and you know it

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<v Speaker 1>could have gone wrong. What's amazing is that the elephant

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<v Speaker 1>was able to both reactivate the gene and control it

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<v Speaker 1>to tell l i F six to kill not every cell,

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<v Speaker 1>but just the ones that seemed the most dangerous. You

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<v Speaker 1>can't control your DNA, but sometimes it can come out

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<v Speaker 1>with some pretty good tricks you'd never even think of.

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<v Speaker 1>Today's episode is based on the article Zombie Jeane protects

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<v Speaker 1>Elephants from cancer on House Tofworks dot Com, written by

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<v Speaker 1>Jesslyn Shield. Brain Stuff is production of I Heart Radio

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<v Speaker 1>in partnership with housetuffworks dot Com, and it's produced by

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<v Speaker 1>Tyler Clang. Four more podcasts on my heart Radio, visit

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<v Speaker 1>the iHeart Radio app, Apple podcasts, or wherever you listen

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<v Speaker 1>to your favorite shows.