Are Viruses Alive? - with Carl Zimmer

thank you I'm gonna talk today about this this basic question uh our virus is alive um it's a it's a simple question in the sense that it is only three words but it's actually a very complicated one when you really dig into its meaning and it's very difficult to answer and and we're still trying to answer it today uh even though scientists have been trying for a very long time to to resolve it uh part of the problem with uh this question is that viruses uh are pretty new to science certainly viruses are not new to us um you know people knew for example that um dogs uh could become rabid and attack people and they'd have to be killed this disease rabies uh was certainly familiar to everyone but nobody knew that it was actually a virus that was growing inside the nerves of these dogs that caused them to have this new Behavior uh people experienced viruses themselves very personally in the sense that uh they might develop a fever become very sick start to cough and and might die and uh one of these diseases uh came to be known as influenza we think of influenza as the name of a virus but uh this name was not given to the virus uh because this name came about I believe in the 1500s this name is Italian for influence meaning that people thought that they got influenza through the influence of the Stars the the concept of a virus was totally uh lost to them um there was just no way to know um so so understanding viruses and what they really are was simply impossible uh for for most of human history in fact what's incredible is that uh that doctors and scientists could even start fighting viruses before they knew what they were uh so Edward Jenner in the late 1700s created a smallpox vaccine which was actually consisted of uh cow pox viruses that he would administer to people and that would actually create a protective immunity not just to the cow pox but to the related smallpox Jenner had no idea that he was dealing with two different kinds of viruses or viruses at all in fact the word viruses we use it when he was uh creating his vaccine that word did not really exist in fact it wasn't until the end of the 19th century that scientists got their first real inkling of viruses and they did not come from people or from dogs but actually from tobacco plants tobacco plants have a disease called tobacco Mosaic disease you can see here why because it creates this Mosaic pattern and tobacco farmers were to them this disease was one of their worst enemies and so with the rise of the germ theory of disease in the 1800s they were wondering well could this be a germ that causes this disease could it be bacteria for example or maybe a fungus well a scientist named Martinez by drink uh did a very interesting experiment um what he did was he took a sick tobacco leaf he mashed it up in water and he poured that fluid uh through a porcelain filter and the holes in the filter were so small that the water could get through but bacteria and fungi could not And yet when he took what seemed to be just clear water and injected it into another Leaf he made that tobacco plant sick as well and you could do the same thing to that second plant you could pass it through a filter and it could cause an infection in the next one so by drink argued that there was something infectious that was causing the disease but it wasn't bacteria it wasn't fungi it was something incredibly tiny tiny enough to get through these pores and he they could pass through a filter and he picked out the name virus for whatever this thing was um viruses the name has you know a very old uh history but it means things for example like a poison uh or even a seed he used this word now uh at the end of the 1800s just talk specifically about whatever it was that was making these tobacco leaves sick scientists started to find isolate other viruses as well so for example rabies they found the rabies virus very quickly uh they uh were able to to isolate uh the influenza virus by the 1930s so they were starting to see that different species in fact all species of animals plants even bacteria can be infected by viruses but they would use this filtering to find them I couldn't see them yet because they were just so small too small for the best microscopes of the day the first uh step towards seeing uh these viruses actually happened in the 1930s when the Nobel prize-winning scientist Wendell Stanley created a huge batch of tobacco mosaic virus that thing that makes the tobacco leaves sick and then what he did is he basically um effectively sort of cooked it down so that eventually all he was left with were pure virus and in fact what the viruses did was they locked together and crystallized in other words he created virus crystals now you can make crystals out of salt you can make even crystals out of proteins you can't make a crystal out of a tobacco plant you can't make people into crystals this is the kind of thing you do with with inanimate matter and yet here are these viruses that he could crystallize this is a picture of these crystals uh and he could Stanley could put these crystals you know up on a shelf just like salt for months and then take them off the shelf and he could throw them in water and now he had viruses that could infect tobacco plants just like by drink had done decades earlier so when he published these results in the 1930s it's it's it's really hard to convey just how much this blew people's minds and one of my forerunners at the New York Times in 1937 uh wrote a piece and the headline was viruses and life and this person wrote the import of these researches staggers the imagination viruses are neither dead nor alive they seem to lie on that shadowy Borderland where matter is ready to LEAP into life uh in fact this was so mind-blowing that uh another reporter came back to it in the 1940 in 1940 um asking the question can crystals live you know kind of a question that not many people had asked before when Dr W M Stanley of the Rockefeller institute's Princeton station crystallized the virus which produces the Mosaic disease of tobacco there was a great hullabaloo among the biologists and rightly so were these crystals alive apparently no more so than diamonds glass sand or other crystals with which we are familiar yet when virus crystals were put on a tobacco leaf the Mosaic disease spread like a slow fire over a whole field just as if it had been infected by living bacteria so if if you look at the way that uh these articles kind of set up life uh it's very hard to figure out what viruses are um on the one hand you've got life uh where you have things that are are growing and have other features in common and then on the other side you have I guess not life you have a diamond and you have these at least virus crystals um what they are when they're not crystals hard to say foreign so this this line This Borderland is that is that reporter called it that is the subject of of my new book live search the search for what it means to be alive this is the lovely uh British cover the British Edition has just come out recently and um and viruses play a big part in in my book I talk about lots of other things I talk about um you know the you know when when our own lives begin and when is when is the point that we die I talk about life on other planets I talk about strange animals like like tardigrades that live in the soil that can basically turn themselves into glass when you're in these strange Borderlands it's a weird place to be and this is very much the home of viruses so I'm going to talk today particularly about viruses and but first I want to sort of bring you up to speed from the 1930s you know we know a lot more about viruses now than we did say 80 years ago so Wendell Stanley you know he he could only see tobacco Mosaic viruses as crystals when lots and lots of viruses were packed together in these beautiful shapes uh however um scientists soon invented strong electron microscopes with which they could see tobacco Mosaic viruses and here they are so this is what scientists could see there's they're incredibly tiny far smaller than a human cell or or bacteria for example but as you can kind of make out these viruses are they look like stripes in fact they're little cylinders and it turned out as scientists put other micro mother viruses under the microscope that viruses have lots of different shapes so for example some of them look like soccer balls Ebola looks like a snake uh adenovirus to me looks like kind of like a satellite uh the TS virus which infects bacteria that looks like I don't know looks like a lunar lander maybe viruses come in in a fascinating range of shapes and sizes uh and uh and yet we call them all viruses because they have certain things in common Rosalind Franklin who is is perhaps most famous for her work on the structure of DNA actually before she did that DNA work she spent a lot of time looking at this tobacco mosaic virus this became one of the most important viruses in the history of science because scientists could build on the work of previous scientists and really start to get the first good look had any virus and an understanding what made it up and what Franklin's work was really important to help us understand was that viruses are really really different than cells in the sense that here you have tobacco mosaic virus and the blue and the Violet shapes there are alternating proteins they kind of get wrapped around like like kind of like a Napoleon pastry and sandwiched inside of them is a genetic molecule our genetic molecules are DNA which is double-stranded a lot of viruses use RNA which is single stranded and so that's wound inside of this protein shell so this this virus doesn't have any enzymes inside of it it doesn't have uh like a ribosome for example which is a factory for building new proteins it doesn't have any of that it's just this shell and the genes and that's it sir Peter Meadow who are uh aptly called a virus a piece of bad news wrapped up in a protein um and You know despite the different shapes that viruses can have this is the influenza virus for example that same structure is true for all of them so you again here you have a flu virus with a with a round shell uh which is studded by proteins and then inside of that you have RNA uh which is actually in little little segments as opposed to being like a continuous strand foreign way that new viruses come to be is is pretty much the same from virus to virus and again it's different than cellular life a virus itself does not grow and divide and become a new one if the viruses do not mate and have little baby viruses what happens is that viruses latch onto cells they fuse their genes go into the cells the cell makes proteins from those genes it makes new genes from the virus and then G new genes and proteins are packaged into new viruses that escape the cell that's it that's that is the virus life cycle we've gotten to the point now that um you know it's possible to take a virus like this one Sarge Kobe 2 the cause of covid-19 and in very little time figure it out down to the atomic level this is actually a model that Romeo Morrow and her colleagues put together at the University of Colorado San Diego this is a model they're building down to every single atom in the virus uh and so what you're seeing is that it has this round shape and then it has these Pros one kind of protein that studs its surface this is called the spike protein you may have heard of the spike protein because this is essentially the key that the virus uses to unlock our cells the spike protein as it changes shape it is able to attach to certain kinds of cells in our bodies first in our nose and then in our lungs and then in other organs uh and then it can fuse and dump its RNA into its host cell and then that cell then makes new coronaviruses so here here we've gone from you know viruses as this deep mystery of why dogs become rabid or why we get sick with the flu we've gone to viruses as things you can pass through filters we've seen them as crystals and now finally we can see them down in their atomic detail but viruses are still kind of mysterious to us even with all this information and again we're still struggling with this simple fundamental question now that we know about viruses at the level that we do in 2021 our viruses alive well what does it mean to be alive um you know I think we'd all agree for example that this snake that's rapid stuff around my neck is alive why you know what what is it what about what about it means that it's alive um you know it it it moves okay movement is interesting but you know a robot can move um it can eat it can metabolize that's very important in terms of life you know all living things have to get food in one form or another somehow and build organic molecules from them and break down other ones and get rid of them so metabolism is obviously something really important we feel to life reproduction is important as well uh and there are lots of different ways to reproduce maple trees which I have around my house in Connecticut in the United States uh do it in a particular way where uh you know pollen fertilizes seeds and then they produce these beautiful Samaras which then fall all over the place they clog my gutters they and they they sprout up into little volunteer saplings all over the place every year a single maple tree will just churn out thousands of these things although the vast majority of them will not survive to to be able to reproduce themselves but some of them do which is why we still have maple trees around for millions of years another feature of Life uh it unites us with things that at first might not really look alive at all so this is a slime mold it's a giant single-celled organism that lives on the forest floor you can see them for yourself with your naked eye when they are growing quickly um if you're wanting to know what to look for uh the name of one species is dogs vomit so that kind of gives you an idea of what to keep your eye out for this is a slime mold called phy serum and like other slime molds it's just a giant cell that sends out tentacles to find food in this case the food is oatmeal or more specifically the bacteria that grows on the flakes of oatmeal you can see one in the lower left hand corner that the slime mold has just reached uh so at the slime mold is going out and searching for food um and sending in all these tentacles as it finds food and is digesting them it keeps reworking its network of tentacles amazingly it can create a network of the shortest distance to connect these different uh pieces of food it's like solving a mathematical problem so here you have something that is taking in information from its surroundings and then coming up with behaviors to advance its own Survival based on what it learns so you know I so scientists who study slime molds will say like this is intelligence this is this is intelligence not in a sort of uh test taking way but an intelligence in a more fundamental way fundamental to life but what does that mean what does that all add up to this is a question that has is not at all new this is a quote from 1704 from a chemist named George Ernst Stahl who was wrestling with how to make sense of the scientific revolutions Innovations in terms of physics in terms of thinking of the world as matter in motion and trying to understand like well what makes life different we have a feeling that life is different from other things so we asked Above All Else consequently comes down to this to know what is life now in my book I uh demonstrate that um there there's not really a a good agreed on answer yet to that question there's no standard definition of life which is kind of weird imagine chemists for example not having an agreed on definition of an electron or a hydrogen like some yet somehow biologists managed to do lots of important work with Act without actually agreeing on what it is that they're studying um one of uh perhaps the most popular definitions that doesn't mean it's the right one but the one that you see very often is sometimes called the NASA definition of life this is a definition that uh was put together by a group of scientists in the 1990s uh they were brought by NASA together for a meeting where they were going to come up with a road map for looking for life on other planets and they very quickly realized that they had to agree on what it is they were looking for like what's the point of sending a really expensive spacecraft and maybe even people to go look for life when you don't even agree on what it is that you're actually looking for so they needed a working definition something that could get it could Advance research and so this is the definition they came up with life is a self-sustained chemical system capable of undergoing darwinian evolution it's concise you know as a writer I appreciate it like it's it's it does a lot with a little so let's think about viruses according to that definition just to start the conversation uh and so I want to focus on that last part of this definition uh capable of going undergoing darwinian evolution and I think you know we are living through that definition of life for viruses right now with the pandemic when the pandemic emerged in late 2019 in China scientists were quickly able to isolate the virus Stars Kobe 2 which causes covet 19. but um the spectacular Pace at which it took over the world and has turned uh Humanity's Collective existence upside down has a lot of people asking where did this come from how did this we didn't know about this virus before 2019 how is this possible um and you know there have been speculations that uh you know maybe scientists made it in a lab um scientists I talked to don't see very compelling evidence for that instead what they argue is that most likely what happened is that it spilled over from a virus that was infecting animals specifically bats and the evidence is all of the coronaviruses that infected bats today we've just scratched the surface of the huge diversity of coronaviruses that infect bats and you can draw a family tree of them this is uh this is the kind of evolutionary tree that Darwin Drew when he was developing his theory of evolution except now we can show with them how coronaviruses have spilled over so in 2002 we had SARS caused by another coronavirus on a different branch and more recently Stars Kobe 2 has spilled over coronaviruses can also go from bats into other animals as well like pangolins or mink and so on um so you know the the the details of precisely how this virus got from bats to people that's it's going to be it's going to take years of research to figure out if we ever do but the broad outlines are pretty clear here that over the course of centuries coronaviruses have been spilling over from bats perhaps other species as well into humans now once this new coronavirus got into our species and started uh spreading from person to person Evolution did not stop this is a family tree of of SARS Kobe 2 just from people and it you can see how it's branching out into these different lineages and these little dots Mark mutations that accumulate in those lineages so you have this raw material in terms of new mutations that can make evolution possible the first really clear evidence of this came at the end of December when a new variant it's called b117 then it's now called Alpha uh took over Britain suddenly uh this this variant was was dominant uh and soon it was spreading to other countries as well and becoming dominant there what made it dominant well this family tree here shows a whole bunch of mutations to to proteins like the spike that I mentioned before on the surface of the virus um which appear to have made them more fit in other words these viruses may have been able to evade our immune system better they may have been able to um potentially be able to grab on more tightly to cells they had an evolutionary advantage and so by looking at these mutations scientists would try to understand how it was that being 117 Alpha was wiping out all the other variants and then in turn uh Alpha has been wiped out by another variant Delta so receiving wave after wave of natural selection of darwinian evolution happening to these viruses that is making our lives very difficult so um are viruses capable of darawinian evolution I I hope I persuade you the answers emphatic yes but that's not the whole definition according to NASA something has to be a self-sustained chemical system they have to have metabolism that I mentioned they have to have homeostasis a way to to keep all the chemicals balanced in in a way that can enable something to stay alive do viruses have that no they don't uh and I did no one has ever found a virus that has like a full complement of the machinery for uh for these things inside of the virus inside of What's called the virion this this uh shell with the genes inside so uh a journalist once asked Gerald Joyce of the Salk Institute who was one of the people who came up with that working definition the NASA definition of Life what about viruses uh and he said according to the working definition a virus doesn't make the cut in other words a virus is not alive a lot of people who uh who would agree with him uh many virology taxonomists say like viruses are not living things but there are others who disagree uh one of them uh who has been arguing for this over the past decade is a scientist named Patrick Fortier and he doesn't uh use the NASA definition of life he argues here's a passage life and living processes are simply names or complex evolving forms of matter that are now present on our planet and so in this view of things viruses he welcomes in virus to life and living processes um for Terror has championed a an idea called the viral cell according to this concept when when a virus gets into a cell that cell is no longer what it was and so you have two different kinds of cells both of which are alive the viral cell is making new viruses as opposed to the uninfected cell he calls that a ribosell named after the ribosome which is that factory I mentioned that produces proteins so that virus cell that is that is the sort of the Incarnation of the virus that to for tear is most important and and he argues that it is it is alive that is a distinct form of life this is a wonderfully complex uh diagram from uh a recent article in nature which kind of shows you some of the key steps in in SARS Kobe 2's life cycle you know it's the same basic cycle as I told you about before virus goes in cell makes new viruses new viruses come out but what I wanted to focus on here um amongst all the details of how this works is this change in shape this change in structure that happens in the cell you see these bubbles here this is a a wild and amazing feature of an infection with SARS Kobe too these bubbles fill up the cell like that's the cell is not doing um much of its old work anymore it's it's not maintaining its own structures it's building these things these this is sort of this is a close-up uh based on microscopy of those bubbles they're double layered so here the layers are in yellow and blue and those green things inside those are all individual pieces of RNA those are virus genes new virus genes that the cell is making somehow they're getting into these little uh these little vesicles these little nurseries scientists don't know how they're getting in they don't know why they have to get in there but it's it's an essential part of that life cycle of the virus that the cell has to become this virus Factory um the little red things on the side of uh the vesicle you see in the lower left that's a channel that channel is encoded in a virus Gene and that appears to be either letting the RNA in or out of these bubbles it's still not clear clear what but but these this RNA that's being stored in these bubbles is then being used by the cell to make new viruses so this is really you know we're you know sarge cov2 is showing us for terror's idea of a virus cell in action and what that virus cell is doing is it's making new viruses and new virus cells and so the way Ford tariff puts it is whereas the dream of a normal cell is to produce two cells a dream of a viral cell is to produce a hundred or more new viral cells for Terra is a wonderfully poetic way of conveying his ideas um some scientists think that he takes a little too much poetic license but certainly as a writer myself I appreciate it and it's a very influential idea because we can see that you know these infected cells are are so radically different than a normal cell so I've given you um you know two points of view in in this in this debate our virus is alive or not um and this debate is not settled among scientists although each scientist will tell you and has told me that of course it's settled it's just it's my point of view and everyone else is wrong um which is usually a sign of a debate that's quite Lively and healthy and a long way from being over I would just give you two examples of this two emails I received literally on the very same day this was after I uh an excerpt of my book life's Edge appeared in the New York Times where I was talking about some of these issues um yeah and and these emails kind of show you that the the kind of battle that we're still in so a reader writes uh Dear Mr Zimmer I understand the need for a journalist writer to excite readers but really virologist I speak as one and now retired PhD professor emeritus and RNA virologist will tell you if you ask but they know quite well what the coronaviruses are and how they are structured and replicate because it has long been a very interesting family of viruses to study to say we don't know if viruses are alive is false and this old saw should not be used how does a virus reproduce without a host it cannot being alive means being able to replicate on one's own and that requires energy viruses do none of these okay that same day I got another email unsolicited from another scientist subject line viruses are alive ask any evolutionary microbiologist and the writer says my field of microbial ecology and evolution has come to peace with the virus the idea that viruses are alive viruses are alive under a life definition popularized by John Maynard Smith this is a very famous English evolutionary biologist life has the property that it can evolve adaptations by natural selection which viruses clearly do if you're going to fuss or with the physiology of how the viruses accomplish all these life-specific things then you're never going to find another system of Life on another planet so there you have it I am a writer I am I am writing about the the the situation as it is um and so I present to you sir the state of play but I am intrigued by uh people who sort of step back and think about sort of the philosophical foundations of this debate and in fact one of the my favorite passages comes from uh way back in 1937. um Norman Peery British virologist he did a lot of research on Tobacco mosaic virus I told you about before uh he wrote when one is asked whether a filter passing virus is living or dead the only sensible answer is I don't know we know a number of things it will do and a number of things it won't and if someone will Define the word living I will try to see how the viruses fit into the definition so in other words he's recognizing that the scientific experiments sort of depend on the concepts that we develop and then we can go and develop hypotheses and run experiments to see how well they hold up so this is this is a very important uh uh issue uh when it comes to life in general and with viruses in particular um you know we use the word life in in different ways sort of overlapping ways but sometimes uh we may be uh tripping ourselves up uh by getting stuck on certain ways of using the word so for example um we live on a living planet you know our planet is alive in the sense that it is home to lots of living things uh and those living things are not in isolation from each other but they are forming this ecological Network uh and so perhaps we should ask ourselves well do viruses belong to the living world and uh it's the answer is a most emphatic yes and scientists are really only starting to appreciate how emphatic a yes that answer is um for example um decades ago scientists thought that when it came to viruses oceans were basically sterile because viruses couldn't survive in seawater but when scientists in the night in the 1980s and 1990s develops technology to start to actually see viruses um like in this picture for example uh they saw lots of them so that you know a scoop of seawater might contain billions of viruses most of which were infecting the Abundant bacteria and single-celled organisms in the water so scientists started to come up with estimates for well how many viruses are in the water and it was just a staggering number and the viruses in the water hugely outnumbered uh all their hosts but it's not just Oceans Where you will find viruses um in in fact uh viruses are quite abundant in the ocean floor they're they're actually abundant in rock because there are bacteria that live in rock and viruses can get to them this is a cave of crystals a spectacular cave deep underground in Mexico and water comes out of the walls there there's some bacteria in those in that water and scientists have isolated viruses from the water this may seem an even less promising place to look for viruses this is in Antarctica but Lake vostok there's a real Lake it's just way way down underneath uh miles of ice uh and but there's but there's life down there and when scientists drill down to to try to get to that uh to to that Lake and see what's in there they find viruses all sorts of fascinating viruses um the virus in panel a is actually called a giant virus because it's far bigger than viruses that we used to know about they're as big as bacteria and in B and C these are actually viruses that infect the giant virus yes these are virus infecting viruses they're called zerophages and they turn out to be incredibly abundant and have been on Earth for billions of years as well inside of us there are lots of viruses as well some of them uh infect our own cells some of them like this phage in fact the bacteria that our bodies are home to uh the numbers of viruses inside our own body the scientists are still trying to add it up but it's a lot so you know in in a milliliter you know just less than a quarter of a teaspoon of cerebral spinal fluid um there will be roughly 10 000 uh viruses um then you get up to the billions of viruses uh you know in your mouth in your in in your lungs uh in in urine they're basically viruses everywhere inside of us um some of them are infecting our host cells even when we're healthy some and but the majority of them are infecting the trillions of bacteria that are inside of us so between our bodies between the soil between the caves between the oceans between the Arctic Antarctic Lakes how many viruses are there um well obviously scientists haven't counted them all but they have been able to make an estimate um and this is the number it's a one followed by 31 zeros it's a number so big it's kind of hard to know what to make of it um and so scientists have come up with some creative ways of of uh conceptualizing this so one way to think about is like okay let's take every virus and just stack them one on top of another if you how long how high would that that Tower be how far would it go you know would it go from the Earth to the Moon well yes but then it would go beyond who you would actually leave the solar system you'd actually leave our galaxy in fact uh again this is this is from the scientific literature I'm not making this up um if you stacked up those 10 to the 31st power viruses on Earth you would go 200 million light years that would take you past our neighbor our closest 65 galaxies so uh so that might give you a sense of just how many viruses there are on this planet all of which were produced by cells all of which have the potential to infect new hosts and the fact is there are lots of different kinds of viruses you know it's not just rabies and influenza um the fact is that when scientists go and they look at the genes of viruses they keep finding very different genes from the viruses they knew before so this is just one example of a study from a few years back where scientists said okay let's let's take a sample of saliva from people and let's just pull out all the genes that we can recognize belong to viruses and let's see if they match virus species that we already know so here the ones that we know about classified they're blue the ones we don't they're red so you can see from person to person the vast majority of these viruses are new to science they're species that do not have names and they're and they're very different from the viruses we do know about yeah scientists have have been slow historically speaking to really come to terms with the diversity of viruses most of the genetic diversity of all life is in viruses some people have speculated there might be trillions of species of viruses and yet you know perhaps the most influential book in recent decades about biodiversity the diversity of Life by Edward Wilson really doesn't give them much attention at all in fact none if you go back to the last page in the index you look for viruses uh you'll find vipers you'll find volcanoes but no viruses so hopefully you know in the you know the EO Wilsons of the future are going to be able to to make sense of this incredible diversity of viruses and what it means for life in general one thing it means is that actually viruses are actually very often pulling the strings in our ecosystems and I'll give you an example of what this means um there are viruses that infect photosynthetic bacteria and algae and the genes that they carry with them some of them actually are involved in photosynthesis so the virus goes into one of these hosts and the host starts making these photosynthesis genes from the virus and now this changes how its host cell captures sunlight and what it uses that energy for it starts to use it to to build new viruses there if you if you change the way that uh photosystem this happens you can optimize it for making new viruses as opposed to making new cells and so these uh host cells are are doing what photosynthetic things do they're taking in carbon dioxide and they're giving off oxygen so actually um there's a huge amount of these in infected bacteria photosynthetic bacteria in the ocean that are producing the oxygen that we breed any Chisholm that MIT has done a lot of important work in this area and roughly speaking um out of every 10 breaths of oxygen you take one of them was brought to you by viruses in other words viruses infecting these photosynthetic bacteria that are then producing oxygen using the viruses instruction book so so the the effect that viruses are having on life in general on Earth is profound and finally um the effect that they're having on ourselves as other living things is just as profound that's because viruses uh can get stuck in our genomes this is one way that's going to happen some cells some viruses will actually stick copies of their genes into our DNA so HIV does this a number of other viruses do this now if this happens when you have an infection um and in for example in your brain this leads to disease the virus is replicating and infecting new cells and making you sick but what happens if it gets into the germ line what if happens if these viruses end up in sperm and eggs well they can get passed down to the Next Generation because they're built in some of they're because their DNA is built into the genes that are being passed down so future Generations can inherit these virus genes along with the regular genes and they become part of the human genome this may sound crazy but this happens a lot in fact this happens uh regularly and has happened for Millions hundreds of millions of years this is an evolutionary tree showing us with our primate relatives and all those arrows show these different points at which different viruses installed their genes into our genome so these viruses their genes we share that we all share them we all have herb K we all have herb nine we all have uh Irving herb we have them all um and this has been happening over geological time this Arrow shows you where the the grant the Grand Canyon formed so this has been going on for for ages and it's an important part of our evolution one reason it's important is that just the simple fact that um our genome has a huge amount of viral DNA in it um they're about eight percent is is you can break it down in into clear virus Origins you can say well this came from this virus it's possible that maybe over half of the genome is made up of little fragments of those viruses that got copied because the crazy thing is that once these viruses get stuck in our genome they can still sometimes um break out have ourselves make a new copy of their genes and put that back in our genome so arguably over half of our genome has this kind of viral origin some of it is just along for the ride but as these pieces of viral DNA hop around things can happen this can be a source of new Evolution one of my favorite examples actually involves oranges there are actually blood oranges that are the result of a piece of a virus that infected or oranges so there's a a sequence called tcs2 and it acts as sort of a genetic switch of the virus in other words it's what the virus uses when it infects our cell it affects the oranges cells to um to get the cell to to read its genes and to make new viruses so some of these oranges got infected with this virus and a piece of that viruses genes this switch called tcs2 ended up next to a gene called Ruby and Ruby makes these these pigment molecules these color molecules um and it turns out now that these aren't these oranges uh they're very sensitive to cold when the temperature drops that causes this switch from a virus to switch on Ruby these are blood oranges so if you have a blood orange sometime thank viruses for them it's not just oranges it's all all sorts of animals plants uh bacteria where viruses are a huge source of evolutionary Innovation for ourselves there are many examples I could give you one of my favorite ones is the placenta um so there this picture here shows you how there's a layer in the placenta called the synotrophoblast which is a hideous name but you can see there how it's actually a layer that's made up of a fusion of cells so that it's basically kind of a sandwich of of the cellular material with with the different genes floating in them that's really important uh for our placentas to work an embryo that cannot form this layer cannot develop it's lethal and well how is it that these cells fuse to form the structure well it turns out it's a viral protein we call it sensitin uh and uh we our ancestors got it from a virus it's here shown in green it it goes to the surface of our cells and it clamps onto other proteins on other cells and it enables the cells to form a pore now now that this now the cell there's a continuity between the cells and the placenta this is essential none of us who would be here without this viruses protein so I I hope that uh you know I I hope that through my talk today I've sort of made you appreciate the the the the fascinating uh mystery of this question of our virus is alive and I guess I would argue that uh you know viruses are are deeply embedded in our own lives and we ourselves are deeply embedded in in a viral World a living world in which viruses are the most abundant uh living things and and Perhaps Perhaps the most important things arguably in life so if if viruses aren't alive I would argue well what is um and uh that is not the that does not uh settle the the question um I I think that in 10 years 20 years scientists will have new ways of looking at it uh and I look forward to to seeing what they have to say and I just want to thank everyone for for uh again coming to this talk for for listening to it and uh if you have any questions I'd be delighted to uh to take them foreign [Applause]

Channel: The Royal Institution

Views: 473,080

Keywords: Ri, Royal Institution, virus (type of infectious agent), carl zimmer, life's edge, virus, virology, vaccines, biology, microbiology, health, genetics

Id: Tryg5UCp6fI

Length: 53min 20sec (3200 seconds)

Published: Thu Nov 25 2021