How Energy Flow Shapes The Evolution of Life - Professor Nick Lane

yeah so I'm going to I'm going to try and be quite ambitious there's a problem it seems to me I think I can probably explain the questions better than I can explain the answers I'm not sure I really have the answers but I can I can try and put forward some interesting questions to you one of them is you might have the sense from looking around at life on earth that just about anything that can happen does happen it's out there somewhere or if you can imagine it it could be there even if it's not there there's there's really nothing constraining what genes can do what information can do so obviously it's not actually breaking the laws of physics you would have the sense that anything that can happen does happen and we now have from genes really detailed trees which show the connectedness of different animals so yes you're here these are all animals in this part of the tree and you can step back from there and this is you know the whole tree of life which is showing the interconnectedness of different organisms at least that's what it pretends to do it doesn't really do that and if you find this kind of diagram slightly freaky good because I do as well and I think most normal people would actually it's it's wrong in various ways quite interesting ways because it's a beautiful presentation of data but it's partly wrong in that it gives the sense being this kind of starburst shape that every inch of space has been explored already you know it doesn't give you the sense of the space over here that could be explored it's the presentation style of it the other thing which is interesting about it is down here bacteria and archaea hardly take up any part of that tree in fact most variation in the Tree of Life is in that bit yeah this is trivial the differences between animals and plants is trivial really all the variations down here most people are interested in plants and animals and so that's why they it's been expanded up the other thing which is misleading about this is it's a single gene this is not a tree of life this is a tree of a single gene and the sequence is being compared and you you work out you know how closely are things related by how many sequence differences are there and if you used a different gene you'd come up with a different tree it would look the same if you presented it that way but if you use whole genomes you come up with something that looks rather different and if we can step back from all of that this is a much older version but you kind of get a much better orientation from this this was put forward by carl woese in in the late 1970s and this particular version dates back to about 1990 but actually the tree I just showed you is based on the same gene as this and it's basically the same structure even though you can't see it it's the same structure as a so there are three what are called domains and this was a shocking discovery by bios because plants and animals are in that small corner of the tree over there this was another really Copernican revolution that you know we like to think that we're somewhat special at least as you know sentient animals perhaps we're unique but you know this kind of pushes into a small corner of the tree and actually all large plants and animals and anything that you can really see is in that small corner of the tree and almost all the variation is over here in things you can't even see bacteria and this group which you can see you look the same those bacteria they're called archaea we've actually known about some of them for four hundred years but we didn't realize that they're so genetically different and so you're beginning to get a different sense of the structure of life when you look at this and it's oh it's a cold one because it pushes us into into a corner where we don't really like to be very much but if you if you try and think rationally about it it's also an interesting one because the length of these branches gives you a rough guide to how much genetic variation there is in these groups so the longer the branches the more genetic variation there is and so what you can see from this is the bacteria and the Archaea have kind of explored the genetic space of life the information things that can be done they can do them this is why bacteria will grow on concrete or on battery acid or survive in space or whatever else they can do almost anything you can imagine they do but not all of those things only one of those things that are different bacteria would do something different and so they're amazingly ingenious they've explored all of this space and yet in their morphology and their appearance they've remained over four billion years tiny and simple they're not simple in their biochemistry but they're simple as we look at them down a microscope so they have explored all possible forms of information and yet something held them back they've remained small and simple and bacterial and something different was happening down this branch of the Tree of Life that gave rise to all large complex organisms and nobody can agree about what that was which I enjoy telling my students because it's a problem for them I can highlight where the answer might lie but I'd like to tell you know I like to try and get this across to the public as much as possible as well because we live in a managerial age where we try and say what the solutions going to be and then we do the research to get to the solution that's not how science works the fact is we really don't know a great deal about why life evolved the way it actually did and I also find it encouraging that some of the greatest biologists and the greatest thinkers of the 20th century can't agree among themselves either so Jacque mano wrote a famous book called chance and necessity in 1971 it's a wonderful book really at the dawn of molecular biology when people just understood what the genetic code was and and and and the fact that it was a strange random kind of code and and it's a fairly bleak book it's he thought we were alone in an empty universe it's really French existentialism that is bleakest and then a Stephen Jay Gould who wrote a wonderful book called wonderful life which kind of whines back the clock to the time with the Cambrian explosion when we first see fossil animals in the fossil record and said well what would happen if you were to kind of wind back there and then allow it to play for you and would we end up with with mammals would we end up with vertebrates or would we end up with weird things that you you know would we have terrestrial octopuses intelligent octopuses on land I don't know what would you get and his view was was really that the trajectory of evolution is essentially what he called contingent which is to say it fills space as it can and that there isn't a kind of structure to evolution that if you were back the clock and let it run forward again you'd end up with something completely different completely unpredictable on the other side of this of this divide here we have Christian de Duve and Simon Conway Morris who was actually that one of the heroes of a wonderful life of Stephen Jay Gould book but thinks very very differently about evolution he thinks in terms of convergent evolution that if you wind back the clock and let it play forwards again you'll end up with humans again and they're going to end up with you know hands with four fingers and an opposable thumbs and so on I don't know who's right I suspect it's probably in between the two but how do you begin to ask those questions to do as well thinks that effectively life is inevitable that any planet which is a wet rocky planet will seed life which will evolve towards greater complexity and something approximating to the complexity of humans it's only a matter of time so they can't agree and they're some of the greatest thinkers around and I find that so a very pleasant place to be because it allows me to really come anew from where I want to this is my take on the tree of life from the point of view of a bacterium we start four billion years ago and we see the first fossils of bacteria and their equivocal are they really fossil bacteria they look a lot like bacteria but you could argue all afternoon about whether they really are or whether they're just funny shapes in the rock that look like but there's quite a lot of evidence that suggests that there were things that were basically bacteria four billion years ago and it's basically because they look an awful lot like bacteria today so they've had four billion years and they haven't really changed they've been flatlining this whole time except for one moment when we see fairly abrupt appearance of complex life I'm not talking about the Cambrian explosion here I'm talking about probably a billion years before the Cambrian explosion where we suddenly see large else they called eukaryotic cells so plants animals fungi but also things like amoeba are eukaryotes so a lot of a lot of the variation within the eukaryotic part of the tree is at the level of single-celled algae and fungi and so on and they apparently arose just once in four billion years and I will talk about why that might be the case and towards the end I shall give a possible suggestion as to as to why it might be the case but the questions that I'd like to address the what kind of forces constrain the evolution of bacteria they appear to be constrained by something it's not information it's something else it's something perhaps to do with the structure of cells how'd they complex eukaryotic cells escape from this just once and can we say anything from looking at life on Earth about how life might be on other planets as well I think we probably can so really I think perhaps the intellectual godfather of any questions about what life is is Owen Schrodinger though great physicist who wrote a famous book seventy-five years ago this year in fact called what his life and really there were two questions that he framed in that book one of them is very familiar to most people it's he was the first person who talked about information really in biology he referred to the genome as a code script he didn't know what it was he didn't know it was even DNA he thought it was proteins but he talked about a code script and coding the entire pattern of an individual's future development and it's functioning in the mature state so it was genes that he really was was referring to even though he didn't know what they were at the time and his book was a direct inspiration to Watson and Crick and rosalind Franklin and the discovery of the DNA double helix the other thing he talked about though was energy or specifically entropy or what he called negative entropy or neg Anthropy which is really a measure of disorder and you know obviously living cells are appear at least to be a pretty ordered state and so he wondered well how do they get to be ordered and he realized that the genes control the order in some way but how do they do it in the broadest terms he said well cells are continually sucking order from the environment which to a biologist today is a very peculiar way of seeing the questioned but he had a footnote which helped me to understand what he was talkin and he said if I'd been catering for physicists alone I should have let the discussion turn on free energy instead now free energy just means energy which is which can do work so it's not just heating up the environment or something it can physically power the kind of contractions of muscles or all kinds of things at the level of cells where your enzymes are operating and doing a continuous powered job so really he's saying that the the essence of biology is information and energy flow that's putting it in more modern terms and energy flow you know everybody has been obsessed with genes ever since ever since Watson and Crick understandably so and they provide a tremendous power of insight into biology but they don't provide necessarily all the answers as I showed you the tree of life something else is constraining what evolution can do which is not just in information alone so how do cells actually work in terms of their energy these are mitochondria so mitochondria is will here later on they were bacteria once and we have thousands of them in our own cells so altogether in the human body in the order of well hundreds if not thousands of trillions whatever that number works out at millions of billions these are the what's called the christie membranes so this is where respiration is taking place so when we're burning food in oxygen happening in these membranes deep down inside cells and these are you know around about a thousand there are one about one micron in diameter and a micron is a thousandth of a millimeter so this is what's happening we're stripping electrons from food and we're passing them to oxygen so we have a current of electrons passing down this is the membrane so this is my cheap cartoon attempt to enjoy one of the christie membranes it's a barrier anyway and is insulated and there are very large complex protein sitting in this and they're passing these electrons down hopping down from Center to Center within these proto proteins we have what amounts to an electrical current which is flowing from food to oxygen and that electrical current is powering the extrusion these proteins are pumping protons so protons are the charged nuclei of hydrogen atoms so they're the very small particles across this membrane and we end up with what amounts to a reservoir of protons on one side of the membrane and this is a kind of a turbine which is generating energy for cells to store the ATP synthase so the situation as a whole really it's it's very much like a hydroelectric dam it's in concept it's it's very similar so the protons are equivalent to the reservoir itself the membrane is equivalent to the dam and the turbine the electrical turbine is equivalent to one of these proteins like this this is the ATP synthase and it is one of the most mesmerizing unbelievable proteins really I mean it you it is a rotating motor and when you start to wonder about how this kind of machinery evolved in the first place it does your head in it's a marvelous thing and I do worry about how these things arose in the first place and I'm going to try and give you some sense of how it might have happened not specifically for this protein but the context in which in which you might have arisen but this is the ATP synthase this is the turbine which is driving so ATP if you if you're not familiar with this is usually called the universal energy currency you can think of it as a kind of coin that goes in the slot machine and the slot machine does its things that it's an enzyme it does a particular job you put the coin in it does its job you put another coin in it does its job again so this is how cells work they're powered by machines using using effectively the the currency the ATP so this idea that it's kind of like your hydroelectric power scheme came from one of the most brilliant and eccentric Englishmen of the 20th century scientists Peter Mitchell and he put these ideas forward initially in 1961 this is somewhat before that that's in the late nineteen forties when he was in Cambridge with Jennifer moil who was a lifelong collaborator she was in fact a brilliant experimentalist Mitchell was a brilliant thinker and a rather cack-handed in the lab I'm told and so it was Jennifer Morel who really did all the experiments and Mitchell who did a lot of the thinking and Marlowe herself was was brilliant she was one of the first women to get a actually she was not awarded a degree in Cambridge they didn't award degrees to women in the 1940s but an equivalent I don't recall what the term is she had been she had been involved in cracking codes in the war and had been head of some division which again was very unusual for a woman to be in that position at that time the Nobel Prize went to Mitchell in the end by himself there's always arguments about how these things should be apportioned I don't know enough about it but I think if it were today it would have gone to both of them and science is really about experiments as much as it is about thinking is the combination of the two if it hadn't been for her experiments Mitchell's ideas would have really come to nothing anyway but Mitchell was a great thinker and he came at these questions about how cell respiration works from thinking about bacteria his real question on bacteria was how do they keep their insides different to their outsides it's a very simple basic question and one of those great questions that takes decades to answer and he gave a talk in Moscow in 1957 on the origin of life there was a whole conference on the origin of life and a lot of the people who were interested in that kind of question at the time were were there so JD banal and JBS Haldane they're all communists actually and they all went to Moscow and you know they were interested in Moscow in a materialist explanation for the world which is why a lot of the people who are working on those questions shared this materialist conception mitchell was there and he was far from being a materialist he was quite kind of almost spiritualist in his in his outlook but he said I cannot consider the organism without its environment from a formal point of view the two may be regarded as equivalent phases between which dynamic contact is maintained by the membranes that separate and linked them now virtually every definition of life that you will ever see is going to say this is what an organism is and the environment is something different and Mitchell really here is saying that the environment and the organism are two equivalent phases separated by a membrane it's a very different perception of what life is and if you're thinking about the origin of life then you're beginning to think about compartments and phases and things this kind of conception makes to me a lot more sense so it's not a satisfying definition of life but it certainly gives you a different perspective that the on opposite sides of a membrane which is a millionth of a millimeter in thickness you have two phases one is the inside of the cell the other is the outside of the cell they are different and the only way they can be different is if you actively pumping things out or bringing things in and that costs energy so how did the first cells do it well you can see it the clue is in methane so the cows produce massive amounts of methane they do it because they Harbor particular types of archaea so this representative this domain of life called methanogens we all have methanogens as well especially those of you who can light your own farts so so these are methanogens and what they're doing is is they're they're taking carbon dioxide and hydrogen and reacting them together to make methane and they're getting all the energy and all the carbon that they need to grow from that reaction alone so the methane is the waste product and it's just farted out I suppose but you'll all probably be aware that if you if we could make hydrogen and co2 reacts easily we could solve a lot of problems in the world so we already can split water we can effectively mimic photosynthesis splits water to produce hydrogen and oxygen which is what photosynthesis does we can forget about the oxygen or reacted directly with the hydrogen but no one is particularly interested in the hydrogen economy it's a difficult thing to do if you could react the hydrogen with co2 and make synthetic gasoline that would solve a lot of problems we can strip the co2 out of the atmosphere or at least remain a neutral state and you can make the entire plastics industry all energy and so on can be done from this reaction to my knowledge nobody has succeeded in doing it in an economic way perhaps they have and they're not telling us but the cells these methanogens they grow from that without any energy input at all so they can make it work economically and it's interesting to wonder how they do it well the way they actually do it is they need a proton gradient across the membrane that's to say they're doing exactly the same thing that we do in our mitochondria they're pumping protons across a membrane so on one side they've got a high proton concentration the other side they don't and they use that not to make ATP they do use it to make ATP but more importantly they use it to power the reaction between hydrogen and carbon dioxide and this is roughly what the issue is don't worry about this if it's going uphill you have to put energy in if he's going downhill you're getting energy out that's really all you need to take home from this but there's there's two lines on there and one right at the top you can see it says h CH oh that's formaldehyde so to go from carbon dioxide to methane you have to put energy in for the first couple of steps to get up to formaldehyde and then it's energetically downhill all the way so how do they that's the problem those that uphill bit is the difficulty with making hydrogen react with co2 there's a barrier to their reaction an energetic barrier and what the methanogens do is they lower that barrier and they lower it by using a proton gradient so how do they actually do it well to think about it is a very good way to think about the origin of life because these same conditions you find them in a particular type of hydrothermal vent we see natural proton gradients barriers between compartments lots of hydrogen gas and co2 and those cells are live in that kind of environment even today and so you can begin to think well how would how would the structure of this environment begin to help and it gives us an insight into how they might do it and also how we might do it so this particular type of vent we're only discovered about 10 15 years ago or so they don't look much let me just go back to that they don't look much like the familiar black smokers that most people have seen belching black smoke out of the top you I suppose you could call them white non-smokers there's no smoke coming out and their their carbonate rocks limestone rocks really aragonite in fact but they are very active and there's no there's no animal life around it in particular a few fish every now and then but but they're full of bacteria and archaea and the kind of cells that live there and this kind of environment we're fairly sure would have existed on the early Earth as well so the black smokers were not so certain about these these type of events would certainly have been present four billion years ago on the early Earth and they were first pointed out by this guy Mike Russell who's so kind of mad geologist he's he's a brilliant scientist but he enjoys winding people up I think and some of his ideas you know the origin of life is a really fractured feels and people come in from the background with chemistry for example or a background of geology or a background of biology or a background of genetics or you know people come from very different places and converge on these questions about the origin of life so it's not surprising that we don't agree with each other very much often we don't even speak the same language and I think most people are trying to learn to speak the same language but we can't agree even then what the real question is because it's a long way to go from simple chemical reactions to a replicating cell with all of this machinery which bit are you going to focus on you know we we're all interested in different aspects of really different problems all of which goes under this term origin of life so Mike Russell was talking about these kind of vents ten years before they were actually discovered and and the language he used was the language of geochemistry and it was really an unfamiliar language to most chemists working on the subject or to the biologists and you know I struggled a lot with his terms to begin with and then they discovered that Kelly in fact discovered this lost city vent that I just showed you the picture of ten years after he'd been talking about these vents as the best setting for the origin of life and suddenly he became famous almost overnight he became famous and this was a Photoshop job that nature did so NATO is one of the great science journals and they had a feature article on Mike's work and and dressed him up as Erasmus as the Renaissance man and they called him ney science man they saw us as in the birth of life and they've got he built a reactor at our JPL the Jet Propulsion Laboratory to try and study these conditions and here's a little bit of lost city event in the background he made a number of predictions as to what the important conditions were and the key ones really is that they should be very rich in hydrogen gas which is true and that there should be the walls of the ancient vents not the modern ones with the ancient ones should have contained catalytic iron sulfur minerals that also seems to be true but the main point that he was talking about is there were natural proton gradients because you have alkaline fluids which you really don't have many protons they're deficient in protons and a relatively acidic early ocean the lots of carbon dioxide full of protons and so the two were mingling them in inside these vents and you would have very steep proton gradients within the vents we don't really know how steep we don't know a great deal about these vents but you can at least imagine how it might work essentially what the methanogens are doing and how in in essence the the proton concentration changes the reactivity of both hydrogen and co2 in alkaline fluids hydrogen is more reactive it wants to offload its electrons on to something else and in acidic conditions co2 is more reactive it's going to accept the electrons because it can accept protons to balance the charges as well and so in if you've got two channels next to each other the the co2 in acid conditions is going to be more receptive to picking up electrons and protons and becoming an organic molecule and if you have hydrogen in an alkaline channel it really wants to be rid of its electrons and and the protons will react with the hydroxide ions to make water which is thermodynamically very favored but if they mix then of course you you've lost that you've lost the structure you've lost the barrier you don't have a pH difference anymore and so you've lost everything it's the structure that really matters and it's the structure that we have here and these minerals that we think you would have found in these ancient vents and you find today in methanogens of the iron sulfur minerals and their semiconducting so you could imagine at least that the hydrogen would pass electrons onto this barrier and across the barrier onto co2 and that it's equivalent to a cell membrane and it's the same structure as a cell membrane and this is how methanogens might do it well you could call that a wild bit of imagination or you could call it a hypothesis hypothesis I think Peter Medawar said is a rush leap into the unknown but at least it's testable that's what makes it science and so we built a little reactor it's a very humble reactor really and it doesn't work very well but we've we've been playing with this for a few years now and we've decided that we need to build a better one uh-huh we need to make it smaller we're actually now building a microfluidic version of this but I'm only showing you this version for two reasons one of them we can precipitate the right kind of minerals inside these little vents structures here and the second one is we're trying to simulate the conditions where we have hydrogen in alkaline fluids on the inside with a semiconducting barrier and co2 in acidic fluids on the other side and that should drive the formation of organic matter and this is formaldehyde which is the top of that curve that I showed you a few minutes ago this is the hardpoint so we're not especially interested in formaldehyde but if you can make that you can make anything and this is only two hours so under those conditions we're seeing a substantial rise in formaldehyde the trouble with this is trying to keep the conditions under any form of control and so we're trying to try to do it better we've not even published that yet so I'm not going to talk about that but I'd like to think what are the consequences if big if what I'm telling you is true that life started in these hydrothermal vents and they started there because the structure of these vents favors the reaction between hydrogen and co2 the proton gradients across membranes or across barriers because that's still how cells work and cells now get their hydrogen from almost anywhere so in photosynthesis this splits water in there the hydrogen is extracted from water and its cobbled onto co2 to make organic molecules but the basic reaction is hydrogen reacting with co2 in in oxygenic photosynthesis where the waste product is oxygen but there's other types of photosynthesis you can use hydrogen sulfide as an electron donor you take the hydrogen out of it you leave the sulfur behind you cover it on to co2 or you're growing like a methanogens in the event that hydrogen is bubbling out of the ground you simply probably on to co2 life all across earth is based on the reaction between hydrogen and co2 and and you know we go around eating things but we're entirely dependent on the primary producers the plants and the bacteria which are basically reacting hydrogen with co2 and hydrogen and co2 don't react except under these rather these rather careful conditions where you have structure the same kind of structure that we see in cells so how common are those conditions like you to be on the early Earth we think that they would have been basically all the way across the seafloor because it's a reaction between rock and water so this is this if you've imagined this is the sea floor and then down beneath in the crust underneath the sea floor these green rocks here of rich in minerals like olivine so olivine is iron magnesium rich rock mostly found in the mantle of the earth today which is why you don't see so many reactions like this anymore but 4 billion years ago there wasn't really such a difference between the mantle and the crust and so we think these reactions would happen almost everywhere the water percolates down to depths of 5 or 6 kilometers beneath the crust and will react with these rocks so if you were to take a lump of olivine and put it in a bucket of water you probably get one bubble in about a week's time it's not something you know it's not an experiment you want to do for the kids but at the higher temperatures and pressures down at the bottom of the sea floor it really is bubbling with with hydrogen gas it's a pretty vigorous reaction and that's really all it takes it's the reaction between water and rock to produce strongly alkaline fluids rich in hydrogen gas it's an exothermic reaction which means it's producing Heat and so these are buoyant warm fluids which percolate back up and when they get to the seafloor they react with the the waters of the ocean the minerals in the in the ocean to precipitate as these vents so the reaction between rock and water is down below the sea floor but the vents themselves are up at the sea floor so they should happen on any wet rocky planet and there's actually quite a lot of lovely suggestions from across our own solar system that they do happen so Mars there's there's traces of methane thought to be traces of methane on Mars where does it come from the wishful thinkers hope it comes from life it's possible it does but it's more likely that it comes from exactly this same process of rocks reacting with water there is water on Mars still mostly frozen and mostly beneath the surface but you're likely to produce hydrogen and methane for exactly the same reasons and we see on Enceladus for example or Europa which are moons icy moons with frozen oceans but underneath the frozen ocean on Enceladus and on Europa it seems that there is a rather large ocean larger than the Earth's oceans and these plumes that you can see here are escaping from the surface of Enceladus and they are very alkaline pH 10 or there abouts and rich in hydrogen gas and methane and so the only thing that we know of the only geological process we know of that could produce an ocean that was that alkaline and that rich in hydrogen would be this same process it's called serpentinization but it's the reaction between olivine and water to produce a mineral called serpent tonight which is why it's called serpentinization so even in our own solar system there are at least three worlds where this process is actively going on and this is really one of the places that NASA would most like to go to me too and it is actually also means because of the politics of these situations that yeah I said nobody can agree about where life actually started on earth or what conditions so I'm giving you my partial view NASA like this partial view because that's the one to fly rockets to Enceladus and they need a reason why they would want to do that you know reason that they can give I suppose rather than we just like flying rockets and that's there may be life on Enceladus but that means that these reasons these these ideas on the origin of life talking about serpentinization and hydrogen and these particular reactions is appealing at the moment to NASA I hope that means they might fund me but you probably not anyway so that's that's within our own that's within our own solar system if we go further afield there's been a real a real drive to discover exoplanets planets circulating sorry orbiting distant stars and you know have been projections now that there should be something in the order of tens of billions of earth-like wet rocky planets in in the Milky Way alone so if that's true all of these earth like wet rocky planets should be producing the same kind of vents water is basically ubiquitous olivine is is we can detect olivine and interstellar dust it's again it's very very common so most rocky planets would have a certain amount of a fair amount of olivine in them and co2 again is common as a as a gas an atmospheric gas it's certainly in our own solar system so you could imagine that these same conditions would apply really on a very very wide scale and so life starting elsewhere may be constrained by the same reasons it may also require proton gradients across membranes to get going because the reaction between hydrogen and co2 is difficult and this is a probably probabilistically simple way of doing it so if you were to find say a thousand life forms in the universe you know would it be carbon-based or not probably it would mostly be carbon-based because carbon is ubiquitous it's extremely good at the kind of complex chemistry that needs to be done and it comes in a convenient Lego brick sio2 so you can build large complex molecules by adding on one brick at a time if you start with silicon you're starting with silicon oxide sand then you know don't try and build with sand you want to build with Lego so and carbon dioxide is a Lego brick and so if you were to find a thousand different life-forms I would wager a bet that it's going to be carbon-based let's say 995 times out of a thousand and something wild and funky perhaps the rest of the times but carbon is so common so good at what it does and so convenient in the forms in which it comes that it would be very surprising if it wasn't carbon-based but then we've already run into this constraint how do you make carbon dioxide react with co2 I would say we're likely to find bacteria many places throughout the universe but what about more complex things in bacteria I don't know how many people in this room would get very excited if there were bacteria discovered on Mars most scientists probably would get pretty excited about that I don't I really honestly show of hands just out of curiosity how many people here would be excited to find bacteria on another planet pretty much all of you great would we find anything more complex than bacteria we need to look back though and I've established what I'm suggesting is a set of constraints that cells anywhere are going to be based on reacting hydrogen with co2 and to do it they're going to need proton gradients across membranes and bacteria have remained constrained and haven't changed for four billion years in their morphology neither have archaea so could it be that they are constrained by the way that they generate their energy well I think that's probably the case and it really is John Maynard Smith was one of the great evolutionary biologists of the 20th century and he was UCL for a period where I am so I'm I think a lot of it's a great it's a great place you see Alan in at least in one sense in the sense of some of the greatest thinkers and biologists of the 20th century worked there for a while they all left and went to Cambridge or somewhere after a bit but for a while they were all there at UCL and I think a lot of us walk around these corridors and think oh TV s Haldane used to walk down here I better do something good today so Maynard Smith was one of the great evolutionary biologists of the 20th century and he liked calling things that shouldn't happen an evolutionary scandal you scandalized by sex sex really shouldn't happen why wouldn't people not just make clones of themselves instead and he spent a lot of his career trying to work out why sex does happen and why most things that make clones of themselves just fall extinct after a period and I'd like to think he never actually said that the eukaryotes were where an evolutionary scandal but I think he would have seen it in those terms the problem is that all complex life is composed of this one cell type this eukaryotic cell and we know I mean the fact that we all obviously share a common ancestor because the plants and the animals if you look at their cells under a microscope they're almost indistinguishable in the sense that they all have a nucleus they all have lots of membrane systems called the endoplasmic reticulum for example all lysosomes they all have mitochondria they you know you could write page after page in a textbook of things that plants and animals having common at the level of cells but funky have the same things in common as well and so does an amoeba or [Music] single-celled algae and so on it's a shockingly long list and it's quite baffling as to why that would be the case so traits like sex as well you know a lot so lots of amoeba in fact pretty much all of them are sexual it turns out for a long time we assumed they weren't because you never really caught two of them together but but but now we know their genomes it's funnily enough it's the genomes that give insight into these things we can see that all the genes that are required for meiosis which is to say that the recombination part of sex in the cell division we find them all in amiibo we find them all in very ancient looking cells and and there's plenty of evidence again from the genomes that they've been recombining genes and changing the structure of the genome continuously so we know that their sexual even if we've never caught them at it so this is the scandal then all eukaryotic cells cells share this long list of traits bacteria and archaea just don't do it they don't do sex for example they they pass genes around a bit they do some recombination but they don't fuse cells together line up whole genomes cross across genes and then separate up and you know they just don't do that so the scandal if all of these traits and there's hundreds and hundreds of them evolved by natural selection step by step and there's no reason to imagine that that didn't happen and each of these small steps offered some kind of an advantage and then again there's no reason to assume that that's not true then why is it that none of them evolved in the bacteria or the Archaea for the same reasons they really ought to but they don't so you could think of eyes as a nice example lots of creationists say what use is half an eye but you know evolutions full of things that most people would say was half an eye and it's exactly as natural selection will predict there are at least 60 or 70 separate origins of morphologically complex eyes that's not quite true as I'm putting it because a lot of them in in animals share a common ancestor on some kind of a worm that had a light-sensitive spot but it's partly true in the sense that the octopus eye for example was over here somewhere and human I have arrived with a camera I essentially independently it's convergent evolution they started from a light-sensitive spot and independently they ended up with a camera type there are one or two regulatory genes in common but they independently recruited all the rest of the genes but then there are think this is this is you'd leaner & algorri it's got a nice spot it's got this the same proteins light-sensitive proteins or adoptions in that high spot that we have in our own eyes this is even more amazing this is a camera type eye which you can see the lens you can see the retina you can see a cornea that's in a single cell that's a single protist eukaryotic protist the retina is composed of chloroplasts just reused for a different purpose the lens I'm not sure what the lens is made of but the cornea is made of mitochondria again they've just been cobbled together and used for a different purpose but it's a camera eye inside a single cell so my point is this is what natural selection will predict that there should be multiple different types of eye in different environments different ecological contexts different types of eye with different functioning oh and we don't see the evolutionary intermediates but we see ecologically all the different types and so we would expect to see something similar in bacteria we would expect to see some bacteria that have something that's a bit like a nucleus or some that do something a bit like sex or that it can do phagocytosis go around and Eng golf cells and eat them you know it's these are all valuable traits for us so why don't the bacteria do it it's not like the I there's a there's a big difference there in what we see around us so it really boils down to this question that I raised earlier on what was happening down this branch of the Tree of Life that wasn't happening over here and it's not to do with information because these guys trawl through all the information and still didn't come up with the answer and I want to make the point that it's not at the level of large plants and animals the the real difference the real void is at the level of single cells so this is a bog-standard alga the kind of thing you find in any pond in London or anywhere else you Gleaner and over here is a relatively complex bacterium is actually even got a little compartment inside it which some people have said is a bit like a nucleus it's not really the reason you can't see it well as it's roughly to scale and so you don't need to know what most of these things are in here too this is a lot bigger and more complicated so these are the mitochondria this is actually a chloroplast you can see the nucleus there but it's just you know it's on a different scale the level of complexity in a single cell has gone up by orders of magnitude compared to a relatively complex bacterium not in the biochemistry but in this morphological complexity and it's kind of interesting that if you were to compare two different eukaryotic cells they look rather similar so so this is Paramecium which is a single celled protists and this is a pancreatic a cenar cell a human one again they're roughly to the same scale and you know most people would look at them and say well they're kind of similar in terms of the amount of complexity going on in them they're not a world apart but this is a single celled protists and this is part of a multicellular organism and it's out of curiosity anyone got any idea how many genes by genes I mean protein coding genes Paramecium house any thoughts exactly twice the amount of humans 40,000 genes now maybe we do lots of additional regulation or maybe we're just not very much more complicated than the Paramecium but the point is in by most objective measures of complexity there is not a great world of difference between these two types of cell in terms of the number of genes in terms of the amount of morphological complexity in terms of the basically the hardwiring of it the real difference is between bacteria and single-celled eukaryotes rather than between single-celled eukaryotes and and large multicellular organisms so I'm going to have to rather than exploring all the possible options I'm going to tell you what I think the answer is otherwise we don't have we could be here all the rest of the week here's a group of cells that are pretty simple as eukaryotes go this is Giardia Giardia causes explosive diarrhea that anybody who's been walking in the mountains in America and may have had jadi or poisoning I never had it but I used to when I used to go walking in the mountains in places like that I used to be terrified though when I drank from the mountain streams I would get it but it doesn't have any mitochondria and people thought he didn't do sex either until quite recently when it turns out it is sexual and it turns out that he does have mitochondria too just not as we know them it has organelles which derive from mitochondria called Mitas domes to see the typical of science as well it took 25 years of probably about least 15 research groups around the world not just with Giardia but with with these others as well micros barodia trichomonas entamoeba mono circle monoi tease these are cells that don't have mitochondria and for a long time they were thought to be a kind of an evolutionary intermediate a living fossil from very early in eukaryotic evolution that were given insight into how complex cells evolved well it turns out they're not they're all derived they all had more contra the far more complex ancestors in the past and they kind of evolved down in complexity to become more like bacteria and so they all have mitochondria and it took 25 years of these research groups around the world to to mail that the reason it was done in part is because half of them are parasites and so there are medical interest and as soon as things become a medical interest then people are going to fund you if if people went to the funders and said these are really interesting living fossils that might give us an insight into the early evolution of complexity they're not unfortunately if you say it causes explosive diarrhea where's the checkbook so so that's what they said they said it causes explosive diarrhea and they they had 20 years of funding and they spent it very wisely on the early evolution of complexity and we now know that these are actually not living fossils but highly derived and the one thing that we can take away from it is they all have mitochondria in the past and that's important it's important in part because my Kandra as I said at the beginning were bacteria once and this was made famous by Lynn Margulis Margolis I should say she died of a stroke a couple of years ago I only met her once and I admired her enormous T but but but she had a knack of disagreeing with everybody about everything including me yes well that man is good she was married to Carl Sagan and they they divorced after a while they do after before she wrote her famous paper in 1967 they'd already divorced I'd loved to have heard their breakfast conversations between those two but anyway she was the person who really nailed the idea that mitochondria were bacteria once she nailed the idea that chloroplasts derived from bacteria as well and she also argued for a long time that there were lots of other symbiosis for example with spirochetes bacteria giving rise to the cytoskeleton and the flagella and so on nobody agrees with her about that and she was she was you know she was very strong-willed and disagreed with most people about most things but she was bang on for these central ideas on the origin of the eukaryotic cell and the amount of I suppose we call it hate mail now that she got if you read the literature from after her paper in 1967 through into the early 70s people did not like these ideas at all and they wrote really unpleasant diatribes in the literature you can understand why she became very hardened to abuse and eventually basically believed everybody else was wrong apart from her she was asked once why why is she does he enjoy being so controversial and her answer was I don't think I'm controversial I think I right I'm not even thought to use the word think so so that's Lynn Margulis and she nails that the mitochondria derived from bacteria and we still can't really agree about exactly which kind of bacteria were they but probably something like rhoda back to that where we're seeing there so something acquired these bacteria that went on to be the mitochondria and again there's been no agreement about what kind of a cell that was until quite recently and this is this is a place called Loki's castle which is just off the coast of Norway and and a Swedish group had been trawling around in the mud so underneath there - and sequencing everything that they found in those mutts so we've never even now seen what these cells actually looked like this is what's called metagenomic reconstruction so you sequence everything you try and piece together genomes by effectively matching the ends up and eventually you you put together the genome with these cells there's a certain amount of debate about whether there's contamination in there but it looks broadly true and the thing which is really surprising about it is eukaryotes are here this is another tree and right next to them all these so we started out with a Loki our keyattr they were discovered at Loki's castle and and since then various others have been found and they've kept going with this Norse theme so now we've got all the Norse gods down there we've got the Odin are keyattr and the Thor are keyattr and Heimdall are keyattr and so on but the thing which is really playing is that eukaryotes are branching right in the middle of those groups so whatever the host cell was that acquired mitochondria it was something pretty similar to this and the irony is we don't know what this looks like you don't know what kind of a cell it was some people say it was a primitive paga site that kind of tried to eat things other people including me say oh no it wasn't it was an autotroph II it used hydrogen gas I don't think we can really be very sure yet what kind of a cell it was but it was probably basically a fairly simple cell and so this is a this is another tree which I think is beautiful this is from one of the most I think brilliant biologists operating today a guy called Bill Martin he also has a knack of of winding people up and this tree goes back to 1998 and it's remarkable for several reasons one of them is that it's now more right than it was then so in 1998 when he put this forward I think most people must have thought he was bonkers look down here we have two separate origins from a hydrothermal vent these are the bacteria and the Archaea I haven't really gone into the details of that when I first heard him say that in 2002 I thought he was completely bonkers I now think he was he was absolutely right I haven't really had time to go into why they would so they share a common ancestor but down inside the vents the other thing which is really clear on here is he has a kind of genomic merger going on so genes from the archaea and genes from the bacteria are fusing together here to form the eukaryotes and this is a singular endosymbiosis this one is the chloroplasts so this is not really the same as lynn margulis now who had lots of these things going on in all kinds of different cell lines this was a singular event that gave rise to eukaryotic cells and later on the acquisition of chloroplasts gave rise to plants but it didn't change anything really about the big structure of eukaryotic evolution plants are the same type of cells that we have except with chloroplasts added in and a vacuole but you know they're basically the same so bill has this singular origin of complex life now a lot of people really hate this idea and I think it's in part because we don't really like the idea of freak accidents in sciences I kind of almost puts itself beyond science you can't study statistically an accident the singularity as they but you can't think about it in a very productive way if this was the origin of the eukaryotic cell it started something like this this is the only example that we know of of bacteria living inside another bacterial cell so there's plenty of bacteria living inside our own type of cell eukaryotic cells but it's really rare for bacteria to be inside another bacterial cell this is not a phagocyte it didn't end golf the cell to get in there it's got a cell wall around it it's actually a sign of back to him and you can see there's the photosynthetic membranes here so we don't know what they're doing there this actually is an old discovery this is from nineteen 20 mine when they were still called blue-green algae in those days and blue-green algae really refers to eukaryotes so everybody ignored that paper for 20 years until it turned out they were actually bacteria with bacteria inside and so this speaks more about the the whole sweep of evolution why would that make a difference well the cells that are living inside they are bacteria they ourselves they've got their own agenda they want to grow they want to divide they want to there was a lovely quote from from Jack mano who said that the dream of every cell is to become two cells and and so that's what these guys are dreaming about in here they're thinking how am I going to double and the way that they do it if you imagine a population of bacteria and they're all growing frantically and the speed at which they grow depends on the speed at which they can copy their genome or as much as anything else and so the smaller the genome was the faster they can grow and cells that you know if they've if there's something about the environment that means they don't need this gene now it's not useful and they lose it they delete it then they can probably go a little bit faster because their genome is just a little bit smaller and over a couple of days bacteria their growth rate does depend on that kind of factor but then the environment changes again and and and whatever it was that that gene did you need it again now and so they pick it up what bacteria do is they pick up genes by what's called lateral gene transfer it's like passing loose change around they acquire it again and before you know it you're back where you were but if you have got a same population bacteria living inside another cell they do the same thing they throw away genes that they don't need imagine that those genes are for making a cell wall and you're living inside another cell and you know you don't need a cell wall for protection inside another cell or for prevent yourself exploding with the with the difference in pressure between the outside and inside so you lose those genes you grow a little bit faster you've come to dominate the popular but so long as the cell doesn't die that you're living in you'll be all right you never need those jeans again and so there's a tendency for bacterial parasites to lose genes and to become simpler I'm not just not just bacterial parasites we see the same thing with Giardia and so on and a very nice example is is rickettsia which a few years ago people thought were was very closely related to mitochondria it's probably not so closely related but it's still a beautiful example it was the cause of that wiped out the armies of Napoleon and his retreat from Moscow and it's it's spread by these ticks and it's the bacterium here it is invading a large eukaryotic cell I think it's actually a kidney cell and the one thing about it which stands out is it's not a tiny genome it's around about one Megabass genome and that's true for all of these things I'm not just and waving here this is the the range of genome sizes of free living bacteria it goes up to around about 12 mega bases now this guy T Ryan Gregory did a lot of work on genome sizes and down at this other end these are they the parasites and the endosymbiotic and obligate symbiosis they're pretty much down at less than one mega base of DNA so just for comparison sake we have 3,000 mega bases of DNA the largest bacterial genome is 12 mega bases of DNA and some large algae like you'd leena you know up to a hundred thousand mega bases of DNA so we have you know quite constrained genomes in comparison with some single cell the largest one is there's a thing called amoeba W which I it was miscounted it was originally six hundred and seventy thousand mega bases it's come down to a hundred and fifty thousand last count but still you know it's it's very very substantially bigger than our own genome but what happens with these bacteria that live in other cells they lose genes they become simpler they whittle away and that's what ended up with the mitochondria all these mitochondria that we have in millions of billions of copies they all have genomes of their own and they're passed on down the maternal line from mother to daughter and mother to son but you know my kids don't have my mitochondria they have my wife's mitochondria it's a very strange arrangement that I'm going to now what it means is that if you want to be bigger more complex and spend more energy it's not just a case of having a larger surface area you've got a whole unit here that unit has some genes which in some way control respiration it's got their protein building factories the ribosomes you say it's a unit and if you want to expand you just make more units you have more mitochondria but it's not just that you're increasing the surface area you've got genomes with each one and that allows you to expand up on a massive scale and the person who's I think done more on this I again going back to the early 1990s John Allen has been arguing that they require genes to control respiration and you know still I would say the majority of the field is not persuaded that he's correct he is correct I'm sure of that but you know it takes an awful long time in science so sometimes the simplest idea is to catch on most people just don't really care very much I'm afraid but it's through it's the difference that they can to become a very large cell you just scale up mitochondria so this is a giant bacterium and there are a few around and these little white dots here are the copies of the complete genome so the giant bacteria that do exist it seems that they also need genes to control respiration and this this is the edge of the cell and this is the plasma membrane where respiration is taking place and they have as many as 200,000 copies of the complete genome and each genome is a normal sized bacterial genome with three mega bases of DNA in it and this is a eukaryotic cell the blue is the nucleus where to dis the main gene Depot and all these little the the green spots here are the mitochondrial DNA so there are hundreds or thousands of copies of mitochondrial DNA so the difference between these two cells is not that this cell has an awful lot more DNA than that cell they actually have a similar amount it's that in that case it's got a kind of genomic symmetry there's thousands of copies of the same genome exactly the same genome whereas here we've got one massive nuclear genome which is supported energetically by this kind of end point thousands of mitochondrial genomes which have whittled down and become smaller and smaller and more and more streamlined so all the mitochondria are effectively it gives us multi bacterial power without the bacterial overheads and that's what's allows all those overheads can go into supporting a massive nucleus with full of genes it's at least it's the raw material for natural selection to operate on and so we have a kind of genomic asymmetry and to me that's the real difference between bacteria and large complex cells it's we've got two genomes there isn't such a thing as the human genome there are human genomes the mitochondrial genome and the nuclear genome this is the last slide why then is complex life so rare why did it only happen once on earth and would it only happen rarely elsewhere in the universe there's a double there's a double bottleneck here one of them we have to get a bacterium into another bacterial type cell to break down this issue with with membranes and scaling so you've got to have cells within cells to be able to scale up but those cells have their own agenda you have what's called conflict levels of selection conflict that the bacteria inside want to grow fast and perhaps make their host cell fuse with other cells or whatever they want to do the host cell itself wants to keep them under control and bleed off the energy but they don't want them replicating at any old speed chances of it going wrong is really high and maybe this is why we don't see any surviving intermediates maybe they all dies because it was a pretty dodgy situation for a long period of time or even a short period of time it's just that this is a long evolutionary distance and regardless of whether what I'm telling you is right or not this long evolutionary distance there are no evolutionary intermediates that have ever been found and so all of this complexity in this type of cell and I would like to leave you with this thought we have no idea yet at least the difference between ideas and serious scientific knowledge where we can say that there have been experiments done and and real data how any of this complexity of eukaryotic cells arose and if we want to understand medicine and what goes wrong in our own bodies and we don't understand the why these parts arose in the first place what were the evolutionary driving forces that made them evolve how can we really understand ourselves and medicine and if this starts out with mitochondria in a very simple cell with none of that complexity the nice thing from my point of view is that perhaps all of this complexity arose and the reason we share such similar cells with with plants and with algae is not that we were all adapting to different external environments but we all were adapting to the same internal environment the problem of having cells living inside us and it's that that drove all of this complexity and once it became a stable system then eukaryotes could spread out and take you over the rest of the world and with that I'd like to say thank you very much this work has been done by many people and it's great fun having a lab with so many bright young people coming through it it's an inspiration for me thank you very much you

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Keywords: gresham, gresham talk, gresham lecture, lecture, gresham college, gresham college lecture, gresham college talk, free video, free education, education, public lecture, Event, free event, free public lecture, free lecture, bio-chemistry, Chemistry, Biology, Evolution, Science, energy, Life, ucl, University College London, Earth, Animals, Plants, fungi, bacteria, tree of life, archaea, eukaryotes, Carl Woese, Jacques Monod, Steven Jay Gould, Christian de Duve, Simon Conway-Morris

Id: oXeozqH5auQ

Length: 67min 40sec (4060 seconds)

Published: Wed Feb 14 2018