Big Think Interview With Carl Zimmer | Big Think

Big Think Interview With Carl Zimmer

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Carl Zimmer:

Carl Zimmer is a science writer, lecturer, and frequent guest on such radio programs as Fresh Air and This American Life. His books include "Soul Made Flesh," "Evolution: The Triumph of an Idea," and "Parasite Rex." In addition to writing books, Zimmer contributes articles to The New York Times, as well as magazines including National Geographic, Time, Scientific American, Science, and Popular Science. He also writes an award-winning blog, The Loom. From 1994 to 1998 Zimmer was a senior editor at Discover, where he remains a contributing editor and writes a monthly column about the brain.

Zimmer is a lecturer at Yale University, where he teaches writing about science and the environment. He is also the first Visiting Scholar at the Science, Health, and Environment Reporting Program at New York University’s Arthur L. Carter Journalism Institute.

Zimmer is a Big Think Delphi Fellow.

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TRANSCRIPT:

Question: Can beneficial viruses be transmitted through the human genome?

Carl Zimmer: Well it’s just been recently that scientists have realized that actually viruses don’t just make us sick. They can actually sometimes end up in our genomes. In other words a virus sort of pastes itself into our own DNA and if that DNA happens to be in an egg or a sperm cell it can get carried down to the next generation, so that virus DNA goes along with our own DNA and it’s in our kids and this happens actually incredibly often, maybe not to everybody in every generation, but if you go over millions and millions of years it actually happens so often that we now have maybe 100,000 pieces of virus DNA in our genome and if you add it all up it’s huge, so about 1.2% of the human genome is made up of genes, things that encode for proteins, the stuff that we consider us. There is about 8.3% that’s a virus. In other words we’re probably about seven times more virus than we are human genes, which is kind of a weird way to thinking about yourself, so if you’re looking for your own idea of your own identity you know the human genome may not be the best place to look for it. You’re just looking at a bunch of viruses.

Now a lot of those viruses, once they get into the genome and they go down through generation after generation they mutate, the get crippled, they can’t make new copies of themselves after awhile and then after awhile a lot of them are just dead. They’re just sort of filler, but there are some cases where our own genomes over millions of years have actually domesticated some of this virus DNA, so what happens is that there is a mutation to one of these virus genes and it starts to switch on and actually make proteins that we can use. So for example ironically there are some proteins from viruses that will help cells defend against invading viruses, so we basically are taking these viruses in and we’re using them as kind of guard dogs to keep the wolves out because they will make proteins that will block receptors that these viruses might use to invade our cells. Another way that viruses have become a part of us is when we’re all embryos in the womb. Before we were born we were sitting inside our mothers and there was this nice placenta that was giving us food. The attachment where the placenta connects to the mother’s body in the uterus has some very special proteins that create the right kind of barrier to support the placenta there and they’re essential. They’re called centisan, and these proteins come from viruses. If you knock those virus genes out, say in a mouse, in an experiment that mouse cannot have babies. Its placenta won’t develop properly. So we really depend on viruses for our complete survival.

Question: What new discoveries are emerging from the study of viruses in the genome?

Carl Zimmer: Okay. Let’s see. So one of the big challenges now is to figure out just how many viruses there really are in the human genome. So far the estimate is 8.3% of our genome is virus, but it actually could be a lot higher. The problem is that over millions of years the viruses in our genome mutate more and more so the look less and less and less recognizable as viruses and so if there was a virus that infected our pre mammal ancestors like 250 million years ago, which it probably did, we can’t see it because it just looks totally random now. So it’s hard to work back that far in time. Our view of things gets fuzzy.

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