The First Animals: When, Where and How?

tonight is a debate about first animals associated with our exhibition of that name and it echoes in a way an event that happened that many of you will know about in 1860 when this museum opened on the 30th of June 1860 and the University of Oxford responded to the publication of On the Origin of Species by arranging a debate in a meeting of the British Association for the Advancement of science to debate the newly proposed theory of the evolution by natural selection and that debate of course was between the Bishop of Oxford Samuel Wilberforce and it was supposed to be with Charles Darwin but he was having one of his periodic illnesses so he sent along his young acolyte thomas henry huxley and that debate between Huxley and Wilberforce has become known as the great debate and a few years ago when we reopened after closing the the museum to repair the roof we decided we wanted to take it back to me in a place of debate and we've done that every year since 2015 at dressing a variety of topics often associated with the exhibition so our smart drugs cheating what are the ethics of having your personal genome analysed and so tonight we couldn't come to two first animals an exhibition that I should say has just been extended to September so if we think of an animal-based ecosystem or an ecosystem in which there are lots of animals we maybe conjure up an impression like this a highly bio diverse coral reef with a range of different groups of animals present but we take it for granted that that's been the same for much of our history and it's not true it's a very recent phenomenon in Earth history it's only for the past half a billion years or so out of 4.5 billion that we've had an censored ecosystems within the oceans or later on land and that's what we're going to debate tonight it's a question that was familiar to Charles Darwin who when he published on the Origin of Species had a problem with the sudden appearance of fossils in the rock record and he said that there's another in allied difficulty which is much graver i allude to the manner in which numbers of species of the same group suddenly appear in the lowest known fossiliferous crews that is by his interpretation there must already have been some evolution by the time the first fossils appear now obviously we know much more about an event that's become known as the Cambrian explosion and that's what we're going to debate tonight and we're going to address questions such as what does that Cambrian explosion represent what's the evidence for the the first animals and excepting that there is a Cambrian explosion well what's the trigger if there is a single trigger for that was it geological was an ecological genomic or geochemical or a combination of all of those so we've got four very distinguished speakers tonight to introduce the topic with with short five-minute presentations and then we'll we'll get down to the debate itself and I'll introduce them in turn just before their presentations the first up is Alison Daly who's a paleo biologist she is the epitome of an internationally mobile modern scientist BSC and MSC in a mother country of Canada PhD in in Uppsala in Sweden then went to the nhm in London then worked here in the department of zoology and in the museum and is now associate professor in the University of Lausanne in Switzerland she's a specialist in in arthropod evolution particularly a group I'm sure that will hear something about the anomaly carrots and also in aspects of paleo ecology so welcome Alison [Applause] right here we go good evening everyone thanks very much for coming to this debate and before I start I just want to say thank you to the OEM NH for organizing this event which i think is really something that's not happening too often in academia today and it's a really lovely original event to have this sort of debate so thank you especially to Vanessa and Paul for the invitation so yeah as Paul said I'm Alison Daly I'm from the University of Lausanne in Switzerland where I'm studying essentially the Cambrian explosion from the perspective of the fossil record so if it works here we have an animation if we were to go snorkeling or scuba diving about 520 million years ago the seafloor might look something like this this is an animation produced by flash bubble in Australia showing the sort of diversity of animal life that we see already over 500 million years ago some of these aspects look very familiar to us there's some sponges and things that look like algae and so on in the background that look a bit familiar to us but also some bizarre creatures such as the animals swimming through the middle of the screen there opa binya with five eyes and a big trunk at the front of its head some crawling very heavily armored mollusk like creatures various swimming arthropods that we'll see in a moment and the research I'm doing in my lab is studying how these bizarre and wonderful creatures can help us unravel the steps of evolution that led to the phyla or the large groupings of animals that we see today and we can really have a stepwise view of anatomical evolution by looking at these fossils we can also learn about their ecology so people in my lab we're studying some of these major these large predators especially arthropods so we're looking at how their components to the ecosystems they're actually quite abundant and numerous and well preserved here we have a selection of fossils of very early arthropods or stem lineage arthropods where we're trying to look at various features of their Anatomy their appendages their eyes we see similarities to modern arthropods but also very different body construction so we're trying to piece these together and work out the path of evolution that led to modern-day crustaceans or insects myriapods this group of creepy crawlies and sometimes delicious creatures we see today a question that occupies me in my lab is thinking about the timing of the Cambrian explosion so not so much the causes but what is this event actually look like and I think that's something we we probably will end up debating a bit this evening because depending on how you see the Cambrian explosion you're trying to explain a different event depending on how you see it so you could if these cones are sort of increasing animal diversity with time down the side very simply expressed this is the Precambrian in the Cambrian you could see the Cambrian explosion as an entirely Cambrian event with the origination and the diversification of animals taking place from about 540 million years onwards or you could think of it as having a deep pre-cambrian root that means that maybe animals originated a bit earlier than the Cambrian and then either diversified very rapidly but we don't see this necessarily in the fossil record or had an origination with not much diversification with the major cone of diversification happening in the Cambrian so from the arthropod point of view in my lab we've been reviewing this recently so this is a bit of a scary diagram but I'll walk you through it essentially we have four types of fossils trace fossils so tracks and trails body fossils preserve like the beautiful fossils I showed you before different sort of a 3d preserved micro fossils again preserving bodies and various other types of micro fossils in green we have a series of localities that essentially show us arthropod fossils for sure and in the blue we have localities with similar styles of preservation but no arthropods are present and we can see that the fossil record is telling us fairly clearly that there are no arthropods in the Precambrian rock record and abundant arthropods appearing in the Cambrian so first you see evidence of their trackways then you start to see evidence of crown group arthropods trilobites a very common fossil and then you start to see their their stem lineage preserved here in in Burgess Shale type fossils in this interval of time we actually have several forms of fossils that we can use to investigate the Cambrian explosion more widely and we can compare this to the Ediacaran rock record so BST preservation which is essentially flattened animals in fine grain rocks in the Cambrian we see a huge diversity of animals similar preservation in the Ediacaran here shows essentially algae and no evidence of you are a viewer through pods or in most cases animals in my opinion anyway in phosphoric micro fossils another form of preservation we see beautiful arthropods preserved in the Cambrian and incomparable modes of preservation no arthropods we can see some beautiful fossil records that tell us about this interval this transition from Ediacaran tube to Cambrian so here in purple is the Ediacaran the Precambrian Cambrian and pink this is showing diversity and disparity of trace fossils so tracks and trails with a massive increase again generally confined to the Cambrian with not much going on in these sources in the Precambrian and then we have a huge beautiful rock record right through this transition of a variety of taxa and groups of animals I'm sure what organisms I should say I'm sure we'll hear about throughout the course of the evening so famous Ediacaran biota and the Precambrian all sorts of small Shelley fossils so micro fossils that actually span the interval and indeed trace fossils as well so we have a nice rock record here traces micro fossils some bizarre Ediacaran biota macro fossils in the Precambrian before we even get up to these famous sites such as the Burgess Shale chang-jung biota which all appear at 518 or younger so this interval of time the start of the Cambrian is really really important for understanding this event and ultimately from my point of view I would put a big red X through these two models here just to sum up as best I can in five minutes personally I don't think there's a deep Precambrian route or diversification of animals starting very deep in the Ediacaran I think it's a largely Cambrian event from the point of view of the fossil record and particularly you arthropods which I'm working on and the causes of this event of course are the subject of this debate but you'll notice I've barely mentioned it so I guess as we go throughout the course of the evening we'll talk about this event but certainly talking about an event that's confined to the Cambrian rather than one that has a deep Precambrian root we're actually explaining two different things if we have these two different points of view so I think it's a point of the debate for the evening to look at these two models and talk about the timing and how that links to the causes and the many changes we're going to hear about I think from the other speakers going on at this interval of time so thank you [Applause] thanks Alison for setting up the debate very nicely our next speaker is Professor Phil Donahue who's a scientist who really straddles the boundary between paleo biology and the biological sciences and his research covers a very wide variety of groups he started off in a truly obscure part of the animal kingdom working on a group of micro fossils called Kona Don's a passion that we happen to share their necks tending that research into looking at early vertebrates and the origin of vertebrates fossil embryos molecular clocks the origins and major groups etc he is currently at the University of breast Bristol where he's professor of Perea biology he's won awards and medals in abundance and is a fellow of the Royal Society [Applause] so all used to be my boss and he's saying such nice things about me it's unbelievable so thank you Paul and thank you for never Nessa for all the amazing organization tonight and for the invitation despite you know people having knowledge of my track record and everything else and I'm also this evening to go and look at the exhibit which many of you will have seen already if you haven't make sure you do look at it tonight or later in the week it's an amazing display I've never seen this archive fossil archive of early animal evolution from all around the world all in one place before so it really is a treat even if you stare puzzlingly at some of the serious past hit force I was trying to work out what's actually a fossil that at all your honor to believe me right okay so so we're here discussing where all this came from where animal diversity came from these are all the animal body plans the fundamental body plans and they're defined almost on the basis of ignorance on the basis it's very difficult to resolve homologous or similar features of the anatomy between an annelids say and a private worm right so these are the the fundamental unit of of if you like animal design which emerged sometime deep in in Earth history and what I want to address is the question as Allison did as to when that happened so the answer to that should be really really simple right so we look in the fossil record there all these wonderful sites of exceptional fossil preservation and we can trace the origin of those body plans the origins of those phyla in the fossil record at least as far back for the majority of them to the middle Cambrian or the early cambrian so - around 5:15 - about 535 million years before present right so surely that's when they evolved so what I want to argue is that that's not the case and oh and by definition when you find the oldest fossil what it tells you only is that that's when that evolutionary lineage that's the minimum age for the origin of that by definition it must have evolved and the reason why is that when lineages evolved when they say when one phylum splits from its sibling phylum from a common ancestor that that's a phenomenon that happens within population genetics in terms of what we see in the fossil record we can't see that at all we can only see evidence of one phylum splitting off from its ancestor that it's shared with its sibling phylum when one of those descendant lineages has evolved some sort of feature in its anatomy that distinguishes it from its sibling lineage and indeed from its ancestor as well and not only that that feature which evolves to distinguish it from its sibling and his ancestor has to be a feature which is fossilized Abel and so there's always going to be a time lag between when that Eva when that evolutionary divergence event occurs when Feiler split from each other successively through time and when we see evidence of it in the fossil record and constraining the interval of time between the origin of these lineages and when they appear in the fossil record is really really hard ok we can get some clues as to where the the fossil record is a close or a less close approximation of the true timescale of animal evolutionary history by plotting on these blue bars the known fossil record of these lineages ok so here's a time scale geological time that extends back to the early neoproterozoic and these times these numbers at the bottom are millions of years before present at the tips we have all of the animal phyla all of those fundamental body plans and the black lines represent the the family animal Tree of Life if you like and we can see that some of these lineages like brachiopods and bryozoans are more closely related to each other they share an or an ancestor to the exclusion of other lineages right so the important thing about this diagram is it tells us which lineages are sibling lineages which ones off from each other at at the same time what we should expect since they split from each other at the same time we should expect their fossil records to be equal but some of them that's conspicuously not the case if we look at nematodes I'm a matter most which are kind of obscure but very diverse and abundant worms we can see that although they must have diverged from each other at the same time their sister lineages one has a fossil record that's 200 million years older than the other even though we know they must be of the same age and indeed if we compare the the nematode plus the Nevada morph lineage to its sibling lineages lineage which is all of the arthropods and their relatives again we see that there is a gap there that must be at least 150 million years in duration so there's some intrinsic evidence that the fossil record is not a perfect archive of evolutionary history another aspect is that if we consider not just the filer themselves but the ancestral lineages from which these phyla diverge from each other deep down to the origin of animals themselves while there are some fossils which we could attribute to some of these branches lower down in the tree there are no fossils to populate any of these other branches there is some systematic bias which has led to an absence of fossils to occupy these branches and I would posit it's because the by their very nature they were they were not fossilize about so what is the extent of a gap between the fossil record of animals and the true timescale of the origin of their lineages it's a really really hard problem many of us in the room who have worked on this disagree quite fundamentally and we all have very good data supporting our different views okay but they are essentially the same data that we're all trying to reconcile so some people have it that all of the by latarian animals so all of those that have primitively at least a plane of mirror image symmetry running down through the mid axis of their body in terms of their body plans which is almost all of animals many people believe that their emergence is confined to the Cambria and that the more primitive lineages like cnidarians corals sponges may have emerged late in the Ediacaran just before the Cambrian perhaps at about five seventy five sixty million years before present other people posit that actually these lineages may extend hundreds of millions of years before the Cambrian and others suggest that there may be some sort of in-between right but all of these you know that there is data to support all of these alternative views so how can we try to reconcile them so the way that I and others have tried to reconcile them is using a methodology called the molecular clock which combines is an integrative method that tries to constrain what we can understand about the genetic differences between living lineages - geological time using fossil evidence so it integrates all of the evidence and tries to come up with a holistic time scale for evolutionary history and it's based on just a small number of very simple assumptions which are like all assumptions which are simple our beguiling self so it's based on if you compare the same genes in different species you'll observe that there are differences in those gene sequences and they are a consequence of mutations right and if you count up the numbers of differences in those gene sequences by between different evolutionary lineages the number of differences that you see are a reflection of how long it's been since those lineages last shared a common ancestor if there's very few they shared a common ancestor relatively recently if there's loads loads then they must have a very deep ancestry they must have separated long ago if you can work out when at least one of those pairs of lineages separated from each other you can take those that numerical estimate of the genetic difference between the natures and convert it to an a rate a molecular rate of evolution and once you have that you can do some work you estimate the time of divergence between other pairs of lineages yet by extrapolation you use that mutation rate to establish an overall time scale for all of the the beasties that you consider this is the result of a molecular clock study that we've done and it's it is biological evolution scale to geological time which is a prerequisite I think to trying to reconcile different competing views on what caused for instance the emergence of animals and the way you should read it is not the position of where these branching events occur but in terms of these these blue bars which are the uncertainties in terms of the estimates okay so for some of these that uncertainty is very very large there and hundreds of millions of years in extent but for some of them they're really really short they're very very precise okay and generally what this diagram shows is that there is good agreement between the fossil record and molecular clock estimates what it suggests that for the filer themselves at the very least that the that the phyla emerged sometime within the late early after and the early cambrian interval which suggests only a short mismatch with the fossil record but it suggests for the the deeper ancestors for which I've suggested there is no fossil record it suggests that that they diverged deeper within the Ediacaran or even within the cryogenian and so you're by latarian ancestor the ancestor of all bilaterally symmetrical animals would have emerged sometime between the middle cryogenian and the the middle Ediacaran so between about 650 and maybe about 570 something like that so overall what it's suggesting is that the Cambrian explosion of animal diversity was perhaps not Cambrian and perhaps not an explosion [Applause] good well we have the basis for debate from the first two talks let's see where we go from here our next speaker is Professor Peter Holland who's the Lineker professor of zoology in the department of zoology fellow of Merton College X head of the department of zoology he's best known for his work on evolutionary developmental biology particularly the role of homeobox genes in animal evolution and you'll see part of the exhibition discusses that that aspects of first animals he's a recipient of many academic awards and again a fellow of the Royal Society and a very distinguished speaker in the field so Peter well I'm not going to talk very much about timing which the other two speakers have talked about I want to talk a little bit about more about potential mechanisms although I might get carried away and mentioned timings we'll see how it see how it goes so I first want to introduce you to the idea of genes and embryos and the sorts of ways in which animal embryos have similarities and differences from each other and what makes animals can breo's rather special and what are the genes that build those animal embryos if you look at this picture here it sort of says something rather obvious which is if we work from the right hand side moving across we have animal diversity over here think about animal body plans how animals are put together and of course how the animal is put together is built by the embryo where the cells that have to divide they have to build a shape and those cells have to build particular structures what's telling the cells to do that it's the genes that they have in their body so genes build embryos embryos build animals look at some of those genes well the genes that building the bodies of animals are really special there's really there's a huge number of these different genes and they do a lot of really interesting things so the example I put on the left hand side there are cells signaling to other cells cause animals are multicellular organisms and the way they pattern their bodies is they have specialized molecules which they send to other cells those self receive them they interpret those signals what do they do with those signals well all sorts of different things but one thing that's really key is that cells need to know where they are in the embryo okay think of it like a sort of postcode where that cell needs to know where it is couldn't then you can turn into the right things and a couple of different examples I put up here there's a famous set of genes called Hox genes which tell cells where they are along the body from the head to the tail primarily in structures like the nervous system and many it or the internal parts of the body there's a less now less well-known group of genes called parahawks genes which do something similar in the gut and there's another group of genes called NK genes which pattern parts of the muscles and the meezerman telling them whether it's a heart muscle loss or of different sorts of muscle those are really actually interesting sorts of genes they're arranged in interesting ways in the in the genome many of them arranged in clusters along chromosomes and I thought I'd illustrate that I'm gonna turn myself into an embryo now here's one I prepared earlier so if you wanted to try to understand how things work imagine imma imagine I'm an embryo and I will move forward and move this like I hope you can still hear me if I was an embryo then the signals are telling himself in the body where where they are and then in response to those signals different cells are going to switch on different sorts of genes for instance this gene here in blue is a gene called Hawk Swan and that's going to be expressed from here backwards ox to from there backwards Hawks 3 etc they're expressed in different regions and the cells can read off what they've got switched on in them and by that they can work out where they are and do the right things it's not sure what I'm going to do with this be so so what's that got to do with evolution well I think there's sort of questions we need to address are these are these ones here we want to look at how those genes originated and when they originate is in terms of animal evolution so how did they originate we know a lot about how genes evolved we know that genes new genes can come from old genes by gene duplication we know that genes can fuse and create new genes we know that non-coding genes and non-coding DNA which doesn't code for a gene can gradually change and become a gene so there are all sorts of mechanisms which are well understood but to work out when those special animal genes arose we have to compare between species and I just wanted that many people have tried to do this and I just want to very quickly show one set of data that my colleague Jordi perhaps and I put together a few years ago where we took a whole bunch of complete genome sequences from across the animal kingdom and we computationally extracted all the putative genes from those sequences and compared everything with everything and then you can work out which animals have got what and this tells you when genes arose and the sorts of things we learned from this this is a tree that I just want you to look at those zoom in on a couple of things what one thing that we discovered is right at the base of the animal kingdom if you like one what we would call the stem lineage of the animal kingdom that the branch leading to all animals modern more than a thousand new genes originated on that branch these are genes that didn't exist before and they include in that lots of genes of which being used to patent embryos but also and I don't think we should forget this there's also more than 1,500 new genes that originated on another branch which is the branch leading to the byla terior the by Lettieri over that group with the with the mirror image plane of symmetry left hand side right hand side front and back top and bottom these are animals which explore the world in three dimensions 99% the diversity of animal life today lots of new genes arose and they include many of those genes that I've just talked about which are involved in patterning the embryo so how does this relate to the Cambrian explosion what I've tried to show you um is relates to the genes themselves but if we think about what was happening in the Cambrian what it really looks like in the fossil record if the a 2d world became a 3d world by a 2d world I mean a world dominated by maps like fauna and algal mats and other other living forms which were living on the surface of structures but once we get into the Cambrian we could see mixing of sediments we can see burrowing we can see also many more evidence of more activity bulldozing through the sediments and what we see in the fossilized forms of the Cambrian are animals that could burrow mix of sediments crawl swim chase their prey we're really talking about those animals which explore the world in three dimensions we're talking about those animals which have had these new genes genes which tell cells where they are new genes which build bodies with a front and a back and a left and a right and a top and a bottom and what I try to argue is that once this way of building a body of beings pieced together these new genes have been used and their new regulatory principles have been put together to build a body of this type rather like ours or a worm or a snail there's something with the front and the back and the left and the right this just opened up so many new possibilities for ways of life around the animal kingdom it's really striking that all the by latarian animals on the planet today use those same sorts of genes to do this so my argument is that once those genes originated life set off in an explosion in many of those different lineages as animals diversified and use this toolkit of genes to build their bodies in lots of different ways okay thank you [Applause] thanks very much Peter exits with prop now we're going to take a different tack now and our next speaker is Professor Roderick abhi who's the newly appointed chair of geology in the department's of Earth Sciences as she was previously in the department there is the professor of biogeochemistry sheera PhD at Cambridge postdocs in Harvard and her research looks at the intersection of biological and chemical processes particularly in relation to natural systems and particularly in relation to phytoplankton in in oceans she's interested in in biological innovation over the course of Earth history and hence her interests in the Cambrian explosion whatever that might be and she's co-authored a book called the evolutions destiny the co evolving kept the chemistry of the environment and life rose [Applause] okay thank you very much it's a huge pleasure to be here part of this debate and I'm afraid I took it as a sort of competition actually I was oh I apologize I've been rather bombastic with my my preparation because I I want to convince you that that chemistry is the source of this explosion after all chemistry is is really what life is we're just chemistry in some kind of organized way so I'll apologize to my fellow speakers have been a bit more subtle with their persuasive argument and I guess I wanted to to make the point about evolution perhaps in the history that whenever evolution occurs and whenever there is perhaps a radiation and we think of the fact that the winner perhaps in this evolutionary arms race changes at that time that we need to consider that in the context of the environment and perhaps in the context of the chemistry of the environment so here we've got a rather buff chap who's being told that really he's he's not going to win in this world of video gaming tournaments because he really just doesn't have the genes so this is trying to make this argument that competition depends on what game you're in and and that that game can change as the environment changes so there will be changing winners to the survival of the fittest I just wanted to mention this sort of to physiologies I'm afraid I'm not very biological in the animal sense I think more about single cells and plankton but to me the Cambrian explosion is very much about ends it's about multicellularity mineralization and and so I was trying to think well in terms of chemistry what are we actually what are what are we what are the drivers for becoming multicellular what are the drivers for becoming mineralized those the two sort of obvious components that contribute to this explosion in the geological record and there too some bits of chemistry this is this is now just looking perhaps an environmental change let's say through this Cambrian explosion and some of the more obvious markers of the changes and complexity as we trek through this time period between 680 and 520 million years we've heard arguments for fossils of evidencing change exactly at this Cambrian explosion we've heard the genes perhaps putting the roots of this somewhat further back we have biomarkers suggestive of sponges some of the earliest animals in the fossil record around here although they're their origin has been questioned in papers last year and then we have this evolution towards these mineralizing organisms as we go into the Cambrian and a really nice marker of the environment is the the Delta c-13 of carbonate so this is just an isotopic marker really of the burial rates of limestone versus organic carbon and that actually can tell us something about the environment and what the pointer to make from this is that actually during this period of time where we have these apparent changes in complexity we seem to have an incredibly dynamic environment we've got these big oscillations in this isotopic marker of the environment and we can sort of argue about how to interpret these but it's clear that it's a very dynamic environment this is it's sort of globally reflective of ocean chemistry and often this is interpretation interpreted in the sense of the degree of oxygenation of the ocean ie how much oxygen is dissolved in the ocean and how is it distributed and this is one interpretation of the oxygenation of the ocean through that time these ooe events are when we have we think full oxygenation these periodic and perhaps braddock oxygenation event but at other times I guess it's very much worth noting that particularly as we come into this Cambrian explosion we think the deep ocean still remains anoxic has very small amounts of oxygen dissolved in it at that time and that can a fairly hostile place for animals that perhaps have high metabolic requirements for energetic lifestyles so it could be that this change in oxygenation you see these black mid-depth deep oceans transitioning to becoming better oxygenated as we go through this time scale and you might imagine that that could have some impact on the life that can live there and indeed this is just a little schematic to show you through a modern oxygen minimum zone there are still parts of the ocean today which are not fully oxygenated and indeed if you look at this sort of diversity realm as we go into the oxygen minimum zone you can see you tend to decrease the diversity of the animals that are able to live in these very low oxygenated environments interestingly we also see mineralization correlating with this diversity in the sense that we tend to have organisms that can be mineralized in these more oxic sones both above and beneath the oxygen minimum zone but as we go into these oxygen minimum zone we tend to find non skeletal benthos living there so there seems to be at least in the modern day a real link between this degree of oxygenation and both diversity and this potential for mineralization and we can argue about the potential links here is this relate to predation predation itself as a mode of life requires high amounts of oxygen to be energetically trying to capture animals and so there is some arguments that this low oxygen is is is exclusive of predators and perhaps that contributes to the - this lack of mineralization in the oxygen minimum zone if you don't need skeletons if you don't need defense against predation so my point in this slide is we have a highly dynamic oxygenation of that water column during this time with overall a trend towards increasing oxygenation there are also hints of other changes in the sea water chemistry this is now just a plot I'm afraid of a horrible different isotope system the strontium isotopic a composition of the ocean and it's I just want to show this it's a proxy really for the relative inputs of ions coming in from continents into the oceans versus ions that are being leached out of ocean basalts at hydrothermal vents and the higher you go on this graph the greater the input of ions from continental weathering and related to that then is the saturation state of the ocean if we pour more ions into the ocean from the continents we actually increase the saturation state with respect to calcium carbon and so there is some suggestion that this is actually an increasing saturation State as we come into this period of increasing diversification and indeed we perhaps perhaps have the highest saturation States as we see shelled fossils emerging and that might make sense that we've got the ingredients for mineralization there so we sort of I'm trying to show you that there are indeed seawater chemistry changes and oxygen changes that are accompanying this change in diversity and one might argue at least changing the context for animals that were perhaps living there and giving different winners the chance to win but I also want to come on to a slightly more nuanced chemical driver that could be at play in the background here and this links to very simple chemical equilibria we can actually make predictions for some of these trace elements which are rather key for life and how they've changed their ability through availability through time this is a model that is trying to show predicted change in chemistry and here I'll just focus this is the sort of period that we're talking about the 600 to 500 million years ago or so and you can see stark changes in are chemically predicted elements in the ocean so things like iron this is we know this fairly well iron drops out through this period in banded iron formations it becomes insoluble in an oxy koushin as we increase the amount of oxygen iron oxidizes to these oxy hydroxides and drops out of the ocean and becomes a vanish Leeloo in terms of its availability in the ocean by contrast if we look at single copper these are two elements of which are almost vanishingly available in the very ancient ocean they're locked up in insoluble sulfides and continents if anything gets into the ocean it is scavenged away into these these sulfides and these elements are totally unseen by life really until about this time of the Cambrian explosion when they're oxidized the sulfides become oxidized and those copper and zinc ions have become available in the ocean so this is a chemical prediction for a change but what's curious is that actually we can look into the proteomes of different organisms and I'm afraid I'm going to show you plankton here I will show you some animals in in the next slide but if we look from the cyanobacteria and I'll point out why this is key in a minute going into eukaryotic phytoplankton so cyanobacteria very simple cells coming on to the eukaryotes these these multi compartment cells so now we're just going to the single-cell level but we can look at their genomes and we can predict from their genomes looking at the metal binding proteins what their metal requirements are as we go from cyanobacteria to eukaryotic algae and we see changes in the chemistry very much more required in these eukaryotic algae than they are in cyanobacteria we see a decrease in the requirement for iron we see an increase in things like molybdenum a decrease in Cobalt and these are all the chemical changes that we would predict from an oxygenation around about this time being reflected in the metal requirements in the proteome of these organisms what's intriguing is going into the fossil record that we see a change in dominance indeed from these bacteria to these eukaryotic algae as we go across this key period of evolutionary change the bacteria dominate this is looking at biomarkers of their existence so the bacteria with these chemical signals of low oxygen in the environment and as we increase the oxygenation change the metal availability these eukaryotes start to take over so it's clear that there is a chemical change impacting the metal requirements of the life and the metal requirements of those life are then giving them a competitive advantage in this newly oxygenated environment where they're making use of metals that are newly available and we can even see this in the in the genomes of more complex life so just to show this increased use of copper and zinc this is looking here at the proteome and the number of copper enzymes from this proteome and you can see you go from archaea bacteria going up to much more complicated organisms you massively increase the use of copper these ec1 proteins which are which are copper proteins and we see this same trend in the zinc proteins if you go to the very simple organisms archaea bacteria suddenly you get to the eukaryotes and they have a much higher proportion of their proteome dedicated to their to the use of zinc so there are sort of arguments that actually chemistry held back evolution copper and zinc are both necessary for becoming multicellular they are used in messaging systems that Peter has talked about intracellular messaging systems rely on copper and zinc enzymes they're also involved in extracellular matrices allowing cells to bind together to cut and then to expand and so this is this is potential that this chemistry is driving the plankton but it's also driving evolutionary innovation such that you require these metals to become multicellular and more complex whoops and just a final link to sort of link this plankton evolution in addition to the animal evolution that as you go to these larger cells that eukaryotic algal cells they sink more effectively through the water column and are a much better food source for animals living the seafloor and essentially transfer more of that sunlit energy down in food form to animals living on the benthos so there's a higher transfer of energy from the the across the trophic levels and that could potentially also afford these animals the opportunity to become complex to start to move and to start to mineralize to have the extra energy that they can invest in in forming a skeleton so in the end it comes down to chemistry and plankton and I'll leave it there thank you so we've heard four very contrasting views and I'll just start off with a couple of questions and then we'll open it out to the audience so I think Phil you were the most diagnostic in as to whether the Cambrian explosion was was a real event and then we heard three very different views of it so I'd like to start off with a simple question is the Cambrian explosion real and if so what does it represent film so so for me it's really hard right because because I found long fossils as much as anybody else does and and I'm kind of incredulous of the fact that I work on a fossil deposit at the moment that's that within three million years of the base of the Cambrian and it's already got mollusks and it's got various groups of pan arthropods in there as well as cnidarians and other lineages and and it seems to me incredulous that they that you can fit all of animal evolution into that three million years right but then you go into the the Precambrian and there are various fossils that go back to about five seventy-five eighty which many people believe a representative of the earliest branches of animal evolutionary history but the rock record the the fossil record is silent about what goes on in between and and to me it's almost a paradigm that we have to or a philosophy that it all has to be fit into the Cambrian I don't really see why that has to be the case you know to me the fossil record begs that there is a prehistory but but being a fossil fondly I do worry about the fact that I don't find any animal fossils in the in the Ediacaran or at least early pilot Aryans and indeed I've spent the last fifteen years basically going from one fossil group to another proving that there are no violet Aryans or animals in the Ediacaran so it's hard okay so I think Roz and Peter you offered two very different views of a real event in essence and and I suppose the question is is can your respective views be reconciled can the chemistry be reconciled with with the genomics if I can if I can start then roschin yeah respond to my suggestion I think they might be completely reconciled because I think a lot of what we were hearing about with the chemistry particularly with zinc and copper might be real drivers of eukaryotic life and multicellularity and maybe the very early stages of animal evolution where as I was really focusing on new genes and new genetic pathways in which were building the by latarian animals so it's a little bit a step a little bit later and to my mind we see the really big and conserved genetic organizing principles applied to the bilaterians when perhaps the chemical changes might affect a slightly earlier stage but I'll wonder what you think about that I mean I think the the the true challenge for us is is knowing the point at which the metals change currently the the an independent record of when copper and zinc change their availability is not forthcoming at the moment actually we don't have a well dated record of that particular seawater chemical change and I think that the the the best evidence in a way almost comes from these proteomes and and and seeing the the differences between the bacteria and the UK and if we can have faith in the biomarker evidence for that changing dominance between the signers and the eukaryotes then I think you're right that the metal changes are somewhat earlier and and you're Hox genes can very validly and occur later on could I make a suggestion which is if if there's evidence in the proteomes of how many metal binding proteins there are in different groups over the past few years many many more genomes have been assembled it should be possible for somebody else to go back try to go and start analyzing that at a finest game scale of detail to see whether we see dramatic changes is in metal binding proteins as we move through the animals that could be the first research grant to come out of a music excellent Ally I think your your view is is you're quite diametrically opposed to fill rules in terms of quite a literal reading of the rock record how would you take that view that then there must be a fuse or at least how do you explain Phil's point about the you know the the rapid or the the appearance at the base of the Cambrian of a multiplicity of groups that must have a missing fossil record so I would say to that that there is still a fairly immense amount of time we're dealing with here did animals evolve exactly at the base of the Cambrian at 5:41 it could go back say as far as maybe 550 and what we see looking at the trace fossils and small shellye fossils we see it an increase in complexity that's taking place in the say bottom 20 million years of the Cambrian so if it's from 550 till the time we see complex ecosystems already in the first burgess shale type i owe to the chunjang at 518 we're still talking about you know 30 million years of time it's it's a lot of time for evolution to take place indeed I don't think that animals could evolve you know at 680 million years and then we don't see phyla until the Cambrian so they'll show the cooler clucks that suggests the phyla all appear in the Cambrian which I think we do we sort of agree with and everything you said about the rock record when you when you started is is simply true we have amazing preservation windows in the IDI Akron and we don't see convincing evidence of animals everywhere it's not a lack of rocks and it's not a lack of fossils molecular clocks inspired us us being the broader us of paleontology and geology as a community to really search in Ediacaran rocks and and look for any evidence of animal life and time and time again we're seeing the windows were open animals aren't being preserved so if early animals that hadn't yet evolved into phyla that we can recognize today were around even if they were small or soft bodied or huge and mineralized all those windows are open and we just don't see them in the rock record so I wouldn't say that we have to read the rock record completely literally of course there's going to be ghost lineages where somethin evolves we're not going to get the very first individual of a new species preserved in the rock record but I just don't see the need to go so far back even before the Ediacaran a hundred and fifty million years to go that far back Jim okay I want to open the floor to questions and a few took my sleeve in case you go mysteriously quiet just one caveat firstly we're recording so please wait for a roving mic to come to you but also please bear in mind when you're asking the questions I'm very conscious that this is a very diverse audience of people with all sorts of different backgrounds from people who live and breathe the Cambrian explosion from 9:00 in the morning till 9:00 the following morning through to people who have a passing interest so please I ask the questions using non technical terminology thanks very much first question I was wondering if you guys could talk a bit more about the cryo stain evidence for for potentially four early sponges I know there was that's so there's just some biomarkers from like during the snowball earth period before before the Cambrian before the Ediacaran that suggests that sponges might have been around at that time but then recently there's been debate on that because I think Rhys Aryans were found to produce the right kind of molecules but they might not produce them in the right ratios or something I was just curious about you folks as informed opinions on this like do you think the cryo stains are good evidence for early sponges or you think it's rise Aryans or you think it's just something else entirely right that's a whole bunch of technical terminology let me couch it in more general terms in in the past few years has there have been various publications that suggests that the the remains of the breakdown compounds of biological tissues have been found in in deep time they're down below the base of the Cambrian and some people have suggested that these might represent sponges of the people who have said that that's not feasible what you have suggested that they were initially proposed to be 100% a sponge biomarker and nothing else could make them and this new discovery that the rise Aryans make them certainly throw you some question mark a bit over the biomarker record I guess and it's it it is a question mark and we have to rethink quite what those biomarkers are showing us we have to know which organisms could make a fair amount yes I mean it's it it's it's a tall order right when you're looking at biomarkers trying to really that that we it's one of the real challenges of organic geochemistry that you can go into the sediments you can separate separate out molecules you can look at the diversity of those molecules but the big it's challenge for that field is making the link back to organisms and we see the same thing when we're looking at algal assemblages of biomarkers that you know they're almost never 100% a single organism and and and the challenge is spanning the diversity of all forms of life to see what could anything else have made it good for your view of I think what Roz says is absolutely right I mean exclusivity is very hard to demonstrate we need to find a biomarker that nothing else can make except an animal or a sponge in this case and there's other problems working in deep time these came from drill cores so there could have been contamination at any stage we need to work out the dating of these sediments as well to have the the age be believable and I think the recent study last year that suggests well they're not exclusive just sponges was fairly demonstrative of the fact that it can't be seen as a smoking gun as surefire evidence that sponges were existing claimed for other groups as well yes yeah so it's just one one character right it's not like anybody found a sponge it's just one feature that we know that particular molecule is is that is a breakdown product of organic molecules and there are different pathways to achieving it and different lineages are able to - or their products can go through that same pathway so it's an extremely ambiguous record I don't think we can say that we don't we can dismiss it altogether there is still a nonzero probability that it it is indicative of sponges but it's very close to zero you know I'll leave it right back hi and I was wondering from my memory of the Cambrian explosion and other fossils station to the era what was particularly special about it was the fossilization of soft bodied squishy not hard shelled animals surely you can say that the explosion or lack of explosion is due to just lack of sights with this perfect preservation of soft bodies squishy things disappear so how do you incorporate an account for soft bodies animals not being preserved or not necessarily seeing them in the fossil record can you extrapolate any kind of inference from that of what could be there or not there so does the exceptional preservation of soft tissues inform our understanding of the Cambrian explosion how does it inform it in terms of presence or absence yeah so I think maybe contrary to what people might just assume is that preservation of fossils and soft tissues in particular is actually better as you go deeper in time than it is say today or in more recent times so in the Precambrian and the Cambrian we see huge numbers of many different styles of preservation soft tissues preserved either as flattened carbon-rich films or in three dimensions in phosphate in silica various different modes and we don't see most of these types of preservation occurring very often in the rock records say after the end of the Ordovician so as you go more recently you actually have a worse fossil record of soft tissues maybe that's sort of contrary to what you might think and there are various reasons for this we have certainly changes in in ocean chemistry and changes in terrestrial environments all sorts of global changes going on but also if animals are confined to the evolution if they're evolutionist gentlemen confined to the cambrian it could be the evolution of animals themselves that are closing this window of preservation by that I mean as Peter talked about we suddenly go from a 2d world to a 3d world animals are moving in the sediment they're burrowing down they're mixing up that sediment they're swimming in the water column prior to that we had essentially in the Ediacaran nothing living in 3d nothing mixing up that sediment it was mat ground preservation so animals themselves and their evolution and their ability to move in 3d could be partly what closed the preservation window but preservation in the Precambrian is excellent all the windows where we see animals in the Cambrian are open in the Precambrian in the Ediacaran and earlier and no animals so I think from my point of view reading the rock record and thinking about soft tissue preservation it really is is an extremely strong evidence for being able to read the rock record close to literally and confining the Cambrian explosion to a real event that took place in the Cambrian so you squishy animals yeah so you're right you know they have these amazing sites of fossil preservation of squishy organisms in the Cambrian but they're not really squishy you know there are most of them have cuticle right and it's the cuticle itself that is preserved and you know if you do decay experiments you take a cuticular eyes animal like a shrimp or something and stick it in a bucket and watch it rot and I've done that kind of thing sorry you end up with the cuticle left behind these things you know they are although they're soft tissue they can quite commonly be fossilized and obviously Ali's perfectly right you go back into the Precambrian and there are sites that have the same style of preservation in the in the Precambrian there's a site in China that I've worked on where you have Tina force preserved the the most you know you wouldn't expect Tina Falls it's just bags of water yeah and yet they're preserved so why is it in those deposits we don't find all the baile Tyrians that I'm telling you should be there based on the molecular clocks and I think the reason why is because I'm not expecting to find mollusks I'm not expecting to find arthropods I'm expecting to find you know early representatives of the viola Tyria right and those aren't gonna look like anything like the living phyla except for maybe one lineage people have tried to infer the nature of the ancestral violence Tyrion and is invariably reconstructed as a flatworm like organism people have done rotting experiments on flatworms and there's nothing left at the end of it right there is no fossil record or flat ones nothing nothing at all and people have even looked to see well okay you know they move around in sediment is there a potential for their movement their ecology to be preserved in the fossil record and the answer is no yeah they don't even leave traces of their movement through the the substrate so our expectations that people have independently come up with for the nature of deep ancestors within complex animals are effectively met we don't find them in the fossil record and we don't see traces of them either Peter how does they the exceptionally preserved fossil record integrate with your view does it does it add to the picture and going to Phil's point how do we recognize very primitive members of the phylum we can make statements about what we expect the early members of fact of a phylum will have or or indeed a larger clade because we can compare between the living descendants and work out what they have in common and extrapolate back to the base so if we think about I mean I've been stressing the violet area this the majority of the animals to the left and the right sides of the body and which explore the world in three dimensions so that's excluding things like jellyfish and sponges etc and those biomaterials if we compare across what modern baile Tyrians we can infer that the first baile Tyrian most likely had some sort of central nervous system a brain or central condensation of nerves at the front end some sort of sensor opens at the front end a mouth and anus and muscle blocks we can infer that pretty likely that the common ancestor of all the living descendants had that I don't know anything else about it because all we can do is extrapolate back from those characteristics so what I would anticipate it was a pretty mobile animal able to mix sediments in the way that the way that both this Ally spoke about her and I spoke about so that would be my inference but I couldn't draw a picture of it the question asked ROS about this concentration of it cases of exceptional preservation of fossils around the Cambrian does that tie into your thinking about ocean chemistry what I think it does in a in a very simplistic sense you know if you think going deeper into time you're going to have well coming on to this question I suppose if are you likely to preserve soft bodied organisms as you go through the Cambrian explosion and my from a pure and simplistic geochemical approach I would suggest that actually your preservation potential is going to decrease as you go through the Cambrian explosion certainly if you're changing the oxygenation levels you're changing your potential for respiration of that organic carbon that's being generated by animals so the lower the oxygen you have the higher the the preservation potential because your lower the respiration rates of that organic matter so I guess it's just reiterating what Allison is is suggesting that she's saying the preservation windows are open through the Ediacaran and into the Cambrian and and if anything as you have lower oxygen further back in time you're likely to have better preservation so thanks very much let's take another question exorcising Vanessa so I was I was wondering cuz we've certainly heard from both Peter and Rosalind about the mechanism for the origin and so it's wondering what Alison and Phil what your thoughts are on what mechanism regardless of whether an animal's emerged at the beginning of the Cambrian or deep in the Ediacaran or the cryogenian what do you two think the mechanism was for that process so in terms of chemistry timing becomes really important and so if you know the the model that Roz and others have presented in the past is critical right are the biological events that that we are saying are the consequence of geochemical changes do they occur at the same time or after those geochemical events right so it's a testable hypothesis and at the moment I would I think most people who are formulating those hypotheses are taking a very literal view of the fossil record you know much more literal than the very enlightened view that Ali's been presenting and and I think you know they I think it's necessary to take a more biological more phylogenetic approach to test and refine those hypotheses of causality are they testing the origin of animals or are they testing the origin of bilaterians for instance but in terms of of of what what made animals animals what was the trigger and my I generally don't do why questions and history is just one damn thing after another you say that is a 24 year old postdoc I mean I think you're getting back to the question we showed right at the start of this event these these four factors and what was the trigger I don't know and I don't know if we can ever say I mean certainly we needed genetic sort of toolkit developmental tool kit to build animals we needed a permissive environment so ocean geochemistry of course will have played a role we see a period of change you know the start of the Cambrian we see water levels rising this is following a massive erosional event which would have brought lots of ions in into the ocean so certainly we also need there to be a permissive environment which indeed was their big shelves with an ocean rich in in ions and chemistry we need to build life certainly wants animals originated they start interacting with each other an ecology can also be a driver at least for the radiation and not the origination but exactly why it happened when it did and what was the trigger I think is is not always the right question to ask you need to sort of frame it in in something that you you can answer so not just what caused the Cambrian explosion but you know where do we see it on the continents how did diversification happen then maybe you want to go to the rock record to answer that if you want to talk about what could cause anatomical features to evolve you could look then at the more developmental side you could think about rates of evolution and again you might want to go to different sources of data it's such a complex interaction of all these things and kind of what Phil said at the end is it happened when it happened because that's when it happened and that's how eeveelution took place and so asking why it happened when it did it's just I don't know why maybe we never will but it just it did happen when it did and thank goodness it did right Ross has a raised eyebrow next to me it is it's a challenging event to understand I guess I did have a and I think there is it there is also a challenge that as scientists we try and justify our particular approaches so if we're a geochemist then our role is often reconstructing environmental geochemistry and if happen to see a change at the same time there of course it's a driver and and but I would almost disagree with with Phil I'm not even sure that timing can tell us everything but in in the sense that I'm not geological record and our various tools to interrogate the evolution through the geological people can ever resolve timing to the point of really saying what's a for sir and a driver and what's a responder my suspicion is there are enormous positive feedbacks that need one little fluctuation to set them off and you then go through this sort of ecosystem responses geochemical changes and I think my suspicion is you just need almost a chaotic stochastic perturbation to set the event often in motion I don't think I have a lot to add really I mean I'll you know I in my talk I really was stressing genetic changes yeah the met genetic changes are only going to give the potential yeah for all those feedbacks that we've just heard about the ecological feedbacks etc in the correct environments to be there so they do have to work together there's a question I'm itching to ask but we'll take one more from the floor anybody man in the green shirt so we've heard of the amazing different kinds of evidence that have been used to try and understand this time interval and what's been going on so I wanted to ask each of you a what piece of evidence would you like your keenest PhD student to knock on your door with that would really elucidate some of the gaps in our understanding of what what this is what's been going up you've not gone first yet Peter oh goodness me I think the problem and I'll focus on my research area entirely which is what we know about what these genes do is based on our studies of particular species which we then extrapolate we actually need more information or on testing functions of those genes in lots of different organisms then we can work out how much these genes are changing their functions over time and whether the sorts of things I'm talking about which is as a set as a toolkit which does this job and if less you have this genes you can't build a got or you can't build a nervous system we need to write we can actually check we can test that by doing comparative work in lots of different species but it's going to take a long time to do that I'm gonna my answer will be something that we will probably never be able to see but I would love to have Burgess Shale type biota discovered at like you know five thirty or something because we have a gap from the start of the Cambrian until it switches 541 to 518 which is our first time we see a full animal community which is the changing biota and these animals are all preserved as as flattened films we see beautiful preservation of organ system eyes guts nervous system all the external features absolutely amazing preservation of full animal communities at 518 so I'd love for a PhD student to say hey I was doing some field work and I found a new BST at 5:30 and then we see what animals are in there of course it's probably well never say never but it seems like very unlikely to happen because rocks of that type generally in that time period are are not found but people are finding new bsts all the time people are finding new burgess shale type localities all around the world last year there was a fantastic new one found in china the ching Jiang biota different from the Chang Jiang biota with with a different sort of mode of preservation so people are out there exploring looking for these new localities all the time and that would be like my dream moment to see to see that happen but I don't know if it ever will unfortunately so Duncan you were my keenness PhD student but I guess it's too late now so the thing I want is either a genome of either Chania or Sonya or Kimber Ella one of those just take your pick yeah I think mines mine similarly impossible I want a little I woulda an air bubble of Precambrian cambrian atmosphere to figure out what the oxygen levels were and I'd quite like a little test tube of Precambrian camera and see water see what it is I mean this is this this the world of indirect proxies where we try and read these things from signals and they always the the proxies of merge people think they're wonderful and then they say no they're not and these incredible confidence in these proxies and it would just be fabulous if we could figure out a way of actually having an atmospheric gas record that can we can take us beyond our ice cores or ice cores are fantastic for the last last million years but if we could find somewhere where there was old air and somewhere where there was old seawater that would just be phenomenal the latter has been claimed I know I mean whether you believe water bubbles in salty well yes I mean yeah exactly there are inclusions in hey lights minerals which people interpret to be paleo sea water chemistry but it's you're looking at own evaporite minerals that's presumably formed in an enclosed Basin and so all sorts of questions are raised about that but yeah that's what that's what I'd really like there's an elephant shaped question in this room that hasn't come from the audience so I'll ask it so one of the key differences between Phil's hypothesis and your view of the company explosion alley is is that molecular clocks tell us something about the origin indeed time of of the of animal groups so where's your point of difference with filling in terms of believing molecular clocks and and what they're telling is so I think molecular clocks have when they are well constrained and we have to remember molecular clocks are constrained with fossils so they sort of are using fossils to give minimum and maximum dates so first of all they are not completely independent of the fossil record and depending on which evidence you believe of the interpretation of fossils if you use an animal calibration point in the Cambrian versus in the Ediacaran it can affect the dates you're going to get inferred from your molecular clock so there it's not really independent but certainly when it's well constrained and I've worked with molecular clock workers and published a paper related to the arthropod evolution on this when as well constrained in the sort of upper parts of the trees classes orders etc when you can have a definite maximum a minimum you have a very nice rock record because things are fairly easily to recognize it seems to work very well or at least it gives consistent answers with the rock record to rest realization for examples what we were focused on it gave sort of approximately the same ages for terrestrial ization for many other pod lineages going very very deep in the roots of say Metazoa violet area we just don't have animal fossils that are not yet identifiable to a phyla to calibrate the base of the clock and there's been simulation studies by Graham Budd and others who suggested that also when you have new animals evolving or organisms in general that this happens very rapidly and is very abundant so that this could be giving a sort of artifact problem where molecular clocks are overestimating divergence dates particularly in basal nodes comes to fill in a moment but pieces do you have a view and genetics I suppose I can add something to that just a point of clarity really I mean I talked a lot about genes but the sorts of genes that I work on and worked on for more than 25 years these genes that pattern the embryo not the same sorts of genes that Phil is using to build those clocks okay and the sorts of genes that I work on are the least clock like genes you could ever believe clock like things you defy you if you had a clock like that you'd throw it away because they're there those sorts of genes I work on that they're mutation rates change that diverging all over the place they're shooting that's changing a staying still and then they're changing for a few million years they go all over the place so the sorts of genes I work on don't behave like clocks there having said that I just want to be clear that the sort of change that that are used to build those molecular clocks do behave in a pretty clock like way so although personally as a molecular biologist I have a little bit of nervousness about molecular clocks because I've seen so many genes behave in a non clock like way I also accept that the people who do build the clocks do it in a very very careful way so you know we like not just going to throw them away they do them in a very very careful way if you read their papers including Phil's papers extremely careful and you know we are left with a bit of a dilemma because the fossil record just doesn't quite look like the timings in those clocks to my mind is the refrigerator I don't know I'm not gonna answer that question I can answer that and further when you asked me at the beginning so yeah too bad so so I leave pointed out right then the molecular clock isn't independent from the fossil record right and that's it I said that at the beginning it is an integrative method for taking all of the data all of the pertinent data we have these two independent records of evolutionary history right which is the genes in the cells in our body and the cells of all other animals bodies as well they record all of evolutionary history back down to the last Universal common ancestor of all of life and beyond and then we have the fossil record as well right and the clocks bring all that together now molecular clocks they can only explore possible ages know when they're estimating the age of a clade they can only consider ages that that lie within the constraints that you put in at the beginning and those constraints are based on both the fossil record and the geological record as well and phylogenetic evidence it's a it's a whole big hot mess that's all integrated together right and some of those as are these pointed out are very very uncertain right and that expressed that just shows the fact that the fossil record is very uncertain and and the constraints that we place on many of these nodes are very loose because in Ali's view the fossil record is a close approximation of the true antiquity of evolutionary lineages but there are other people who actually think that animals evolved more than 600 million years ago you know based on Rawls showed them images of fossils that look like the embryos of animals I don't believe that they're the embryos of animals but I have to consider that there is a nonzero probability that they're right yeah and so the the evolutionary model and the molecular sequence data do their work trying to constrain the true time of origin within those constraints I can not tomorrow because the analyses take too long but next week certainly I could give you a time scale that fits exactly what Ali thinks right but what we do what we try to do is to take the most conservative interpretation of the fossil record possible and leave the evolutionary models and the molecular sequence data to do their work I am uncomfortable with the relationship between the fossil record and what molecular clocks tell us but that's science isn't it you know we can deal with two incompatible bits of data and that prompts me to do new research and I tend to Ross in the moment but if we just put the the mentor meter screen up whilst Ross comments could you could you we've got to wait a clock so if you wouldn't mind voting again would be quite interested but what comes out across well I just I wanted to ask Peter about comment too regarding the molecular clocks but when you have your innovation of over a thousand genes on those particular branches is that such an exceptional innovation of genetic diversity that it could actually raise questions about the conservative estimates of molecular clock rates through that time scale it well there's two parts that one it's an exceptional number of additional genes to arise on a particular internode because most of the other branches are about 300 not 1,500 so something jumped it doesn't mean things happen more quickly though because there's sort of we you know we don't know the length intervals of each of those no so we're not saying the genes necessarily arose more quickly in that time we're just saying actually there are a lot of new things there for an animal and there's a lot of new things there for a biomaterial how does it affect clocks I'm not sure we should equate the two because the genes which are being used to build the clocks and not those genes okay and I'm conscious that we we've run out of time sadly but I've certainly enjoyed this evening Darwin was mightily puzzled by the appearance of fossils at the base of the Cambrian and in some ways not much has changed since he wrote on the Origin of Species as we've heard tonight we that we understand a lot more but it as ever in science it's opened a huge range of additional questions so I'm sure we could have another of these debates and in ten fifty hundred years and there would still be big questions but very many thanks to all of the panel for very lucid presentations and and answers to questions and many thanks to all of you for coming if you've not seen the exhibition then please do all those squidgy fossils are on display until September thanks very much you [Applause] you

Channel: Oxford University Museum of Natural History

Views: 11,067

Rating: 4.8371038 out of 5

Keywords: animals, evolution, palaeontology, paleontology, science, Cambrian explosion, evolutionary biology, fossils, genetics, geography, ecosystems

Id: XrHrjTDn-tY

Length: 87min 54sec (5274 seconds)

Published: Tue Mar 03 2020