Seminar by Professor Chris Stringer: Some current issues in the later stages of human evolution.

yep um and then we can get very nice okay let's try and share the screen so can you see that okay yep that's good good okay fine well um thank you for the invitation to come and talk to you so yes some current issues in the later stages of human evolution and i'm chris stringer from the natural history museum in london so doesn't seem to want to advance but let's keep trying it so today there's undoubtedly only one human species around homo sapiens also known as modern humans and although we come in many different sizes and shapes and colors there's no doubt that we are one species we're completely interfertile and we share many features um morphological features genetic features and in the skeleton too and we can see on the right hand side there a modern human skeleton from our exhibition in the natural history museum in london and when we look at our skeleton we can see that we've got a number of derived features compared with some of the other humans that i'll be talking about so for example in our skeleton we've got a high narrow rib cage indicating smaller lungs relatively a narrow less flared pelvis we've got smaller joint surfaces on the bones we've got a lighter build to the whole skeleton and when we come to our head to our skull again a number of distinctive features we've got a globular brain case high and rounded particularly expanded in the upper parietal region there's a weak brow ridge or no brow ridge at the front of the brain case we've got distinctive ear bone shapes we've got a narrow base to the skull we've got a flat mid face we've got relatively small front teeth and we've got a developed chin on the lower jaw so these are all features which we can look for in fossils to try and map the evolution of homo sapiens in the past and when we go back in the past there's a lot of diversity so these bars here different colored bars represent different lineages of humans most of them i would regard as different species of humans that were around on the earth in the last 1 million years so when we come into the last few hundred thousand years you can see in the green there on the top left we've got homo sapiens we've got the neanderthals in yellow people called the denisovans in the middle of the diagram there so i'm going to concentrate on these ones in particular in my talk and even 70 000 years ago which is like yesterday geologically speaking there were still at least five kinds of humans around on the earth so we homo sapiens have been evolving in africa the neanderthals have been evolving in europe and asia over in eastern asia there are these people called the denisovans and down in southeast asia on the islands of south east asia we had two dwarf species of human on flores in indonesia homo floresiensis nicknamed the hobbit for its small size and in the philippines species we've only learned about in the last couple of years homoluzensis so there was all that diversity even 70 000 years ago so we're going to look at four things if there's time one is the situation in africa our origins there and our dispersals from there going to look at data in europe and asia about the neanderthals and our interactions with them i'm going to look at the disciplines in eastern asia and finally this big question which we really can't yet answer satisfactory what happened to all those other kinds of humans why are we the only ones left so first of all let's look at africa and our origins there and so here's a very simple representation of the evolution of the neanderthal and homo sapiens lineages so on the left there we've got a representation of the neanderthal lineage evolving over several hundred thousand years um and that evolution took place in europe and asia and we've got a late neanderthal there from france la feresie and lower down one from spain from the cemetery which is over 400 000 years old and which seems to represent an early member of the neanderthal lineage and then on the right hand side we've got the representation of the evolution of homo sapiens which started as far as we know in africa so we've got a a recent fossil homo sapiens at the top there about 30 000 years old from france from crow manuel and lower down one from morocco from gibraltar about 300 000 years old so geneticists estimate that we had a common ancestor maybe five or six hundred thousand years ago between us and the neanderthals and who that ancestor was where it lived is uncertain we don't know even the continental origin of our ancestor with the neanderthals it could have been europe it could have been asia it could have been africa and until recently there was a view that uh the evolution of modern humans in africa was a fairly straightforward a linear gradual process with gradual change over the last half a million years or so from something more primitive such as this species homo hyderabagensis on the left through intermediate forms to later homo sapiens within the last 100 000 years so a simple unilinear model and often an assumption that it occurred in one region of africa often east africa was the favored area for the evolution of homo sapiens and in the last few years we've had some nice fossils which may represent early members of the homo sapiens are images turning up from morocco in fact this site of jebe morocco has been known for more than 50 years and fossils from it started to appear in the 1960s but it's only recently that they've been studied in great detail new finds have been made and the site has been well dated and we now know that this form of possibly ancestral homo sapiens is about 300 000 years old so there are beautiful stone tools associated with these fossils we can see some on the right hand side there and on the bottom left we've got a composite skull from jebulite hood and it's got some modern human features in the teeth in the shape of the face for example but the shape of the brain case is still long and low and that's a primitive feature it doesn't yet seem to have evolved the high and rounded brain case that we find in later on our sapiens we find that brain case in a fossil that's over two hundred thousand years old from omo kibish in ethiopia so this has recently been redated um as it says here by dating the proximal deposits of an eruption we obtain a new minimum age for the omaha fossils of 200 about 233 000 years so this team of scientists led by people in cambridge dated a volcanic layer overlying the ammo kibby skeleton uh and dated it to over 200 000 years so this skeleton as far as i'm concerned is a homo sapiens it's a modern form of homo sapiens it's got a high and rounded brain case got a chin on the lower jaw relatively small brow ridge and the skeleton also shows modern human features but if we look at the pattern throughout africa from from 300 000 years down to about 100 000 years it's actually very difficult to make a clear gradual pattern of change from a more primitive to a more modern appearance the fossils shown different mixtures of features even from single sites they show different mixtures of what we can call primitive and modern features so it looks like there's a complex pattern of origin for homo sapiens and i've been part of a group who've developed the idea that the evolution of homo sapiens wasn't occurring in just one region of africa this is a quote from eleanor sherry who led one of our papers humans did not stem from a single ancestral population in one region of africa as is often claimed instead our african ancestors were diverse in former culture and scattered across the continent so on the bottom right there you can see a representation of this idea that this is a pan-african origin different lineages going through time in different areas at times connecting with each other at times going their separate ways some of these lineages going extinct and what we call modern humans coalescing in a sense from these different morphologies in the last 100 000 years or so and it's even more complicated than that because not only is there diversity when we look at the homo sapiens fossils across africa but it seems that there were other species coexisting with us and we have to remember that even now our fossil record only comes from possibly 10 of the whole area of africa um so there's a lot still to learn about the african pattern so for example this fossil from cabway in zambia broken hill that's often known as i call this homo hyder against this or homo rhodesians it's a distinct species of primitive species some people and i've for a number of years thought is to see this as the ancient ancestor of homo sapiens in africa but we now know this fossil is about three hundred thousand years old so it's about the same age as that moroccan fossil from jebel yogurt that we talked about earlier and yet it's much less like homo sapiens so as it says here in this paper of nature from a couple of years ago the age estimate raises further questions about the mode of evolution of homo sapiens in africa and whether homo hyde against its or rudisiensis was a direct ancestor of our species so this pattern here is in question and particularly the shape of the face seems to make it much less likely that this ancient species hydroborgensis or rodisiensis is the ancestor for homo sapiens and we've got an additional species down in southern africa a much more primitive species which again we've only learned about in the last eight years or so a homo naledi so found in uh deep in a cave system near johannesburg uh as it says homogenous overall body plan his shoulders hips and torso heart back to much earlier ancestors while its lower body shows more human adaptations the skull and seeds show a mixture of traits so this species has a very small brain more or less an ape-sized brain and yet it was still around in southern africa about 300 000 years ago and we don't know when it went extinct so there we are the pattern now seems to be that around 300 000 years ago we had homo sapiens evolving in parts of northern africa we had hydro bergensis or rodisiensis in zambia and down in southern africa we had hormone led so this diversity which we really wouldn't have guessed 10 years ago and of course our dna data comes in here it's extremely important and regressively we don't have ancient dna from the african continent really ancient dna obviously with the warmer conditions in africa it's much less conducive to dna preservation than in regions like europe or parts of asia but what geneticists estimate is that looking at the diversity of humans today outside of africa that diversity derives from an expansion out of africa probably starting around 60 000 years ago so this is from the paper i was a co-author with with anders bergstrom and colleagues and we argued that as it said the genetic ancestry outside of africa is consistent with deriving from a major worldwide dispersal less than 60 000 years ago but that dispersal was going to bring the homo sapiens people coming out of africa into the territories of the neanderthals who were already there in europe and asia and it may be a bit more complicated even than that 60 000 dispersal so there is evidence that there were earlier if you like attempts at colonizing asia and europe by homo sapiens one for example known from greece from epidemic we've got what seems to be the back of a homo sapiens skull shown there on the top left there this looks like the back of a high and rounded skull so it looks like a homo sapiens and yet we can date it at more than 200 000 years old so there may have been some earlier you could call them foul disperses of homo sapiens out of africa which never established the species outside of africa until later on and similarly signs of early homo sapiens fossils in china and in sumatra and the presence of humans apparently in northern australia more than sixty five thousand years ago now they would have needed boats to get to australia and what we have in levels at this site of najib in northern australia is a lot of use of pigments and complex technology which we assume is the work of homo sapiens and yet this site is dated apparently at about 65 000 years ago not everyone agrees some people think the site has been wrongly dated and it's probably only about 45 000 years ago which would make it consistent with this sixty thousand year dispersal of homo sapiens but if the patterns correct that uh there was an early wave out of africa more than a hundred thousand years ago which eventually reached australia and there was a main wave about 60 000 years ago which is the one that is represented in modern genetic diversity outside of africa we have to assume that that main wave which started after sixty thousand years ago over printed and removed any trace of any earlier waves of homostat sapiens that still survived okay so now let's look at the pattern in europe and asia and their interactions with the neanderthals and the neanderthals are really the most famous ancient fossil people they're called neanderthals because this skeleton on the bottom left was found in the neander valley in germany in 1856 neander valley neanderthal and although the first finds were from europe we now know that neanderthals extended across asia they're in western asia they're in uzbekistan they're in siberia they may even have been in china at times and they've undergone a tremendous change in image in the last 20 years i would say in particular so at the top right there we can see a representation of the neanderthals in 1909 and at that time there were none of the early primitive fossils that we know about from africa and so the neanderthals were pushed into this position of being sort of missing link in human evolution depicted here as being very ape-like hairy bent knees grasping big toes and so on um clearly that's wrong the neanderthals were fully human their brains were as large as ours sometimes larger than the modern average they walked upright as well as we do um and a representation from today from the recent period is shown there on the bottom right this is a neonatal as shown in our human evolution exhibition in london um done by the canis brothers a very human representation of a neanderthal there but nevertheless the neanderthals are distinct from us although they're fully human i think they represent a different kind of human i argue with different species of human so we mentioned the shape of the rib cage and the pelvis well the neanderthals have a much bigger rib cage much broader much deeper they've got much wider pelvis so their internal organs probably were larger than ours their lungs may have been 20 percent larger than ours they have a more robust skeleton overall and the difference is even extend into the skull and you can see here some of the distinctive neanderthal features some of these are primitive features the longer lower skull the strong brow ridge they inherited from their ancestors and the weak chin development but they have distinctive features which mark off the neanderthal image such as the projecting middle of the face distinct shapes of the inner ear bones and a little depression in the back of the skull called the suprainiac fossa so those again are features we can look for in fossils to map the evolution of the neanderthal lineage so modern humans then evolved in africa came out of africa on this main dispersal about 60 000 years ago and we can see on the uh the top right there some signs of intermixture between the neanderthals and us which we can map through dna so that expansion coming out of africa these are all early early sapience fossils for which we've got genomic data so this brings us on to that question of interbreeding we've been arguing about it for a long time uh the fossil on the bottom right there um from portugal was argued to be a hybrid of a neonatal and a modern human um in fact it's only about 26 000 years old and now it looks very unlikely to be any kind of hybrid unfortunately we don't have its dna to test the view that it's got uh an unusual amount of neanderthal dna in it and i was aware that of course closely related mammal species can often hybridize we've got an example on the top left there the brown bear and polar bear can hybridize and have fertile offspring jackals and wolves can do that many species of baboon can do that so i was aware neanderthals and homo sapiens could have hybridized potentially but until recently i thought it was unlikely that it happened i didn't think it would be normal behavior and it happened maybe 40 or 50 000 years ago so we wouldn't find evidence of it today in modern human genomes and i was wrong about that and this paper in science from 2010 began to show that so as it says here close encounters of the prehistoric kind the long-awaited sequence of the neanderthal genome suggests that modern humans and neanderthals interbred tens of thousands of years ago perhaps in the middle east in fact we now say more widely in that in europe as well as a result most people i would say pretty well everyone living outside of africa has inherited a small but significant amount of dna from these extinct humans so i've had my genome tested and yes i like most people in europe and asia and australia and the americas have about two percent neanderthal dna in my genome so here are some of the sites which recently have been featuring in studies of the interactions of the last neanderthals and the modern humans who came into europe after about 50 000 years ago and here's one example this jawbone from o.r.c in romania it's about 40 000 years old and it's got a nice chin on the front so it looks like a homo sapiens but the teeth have some unusual features and so it was thought that it might have mixed ancestry well sure enough the genome of this human from romania has been tested and as it says here this individual has three this individual has um about close to 10 percent of neanderthal dna in the genome and so it looks like this individual's knee avatar ancestor was introduced in the previous four to six generations um so evidence here even near the end of their time we think the neanderthals went physically extinct around 40 000 years ago and yet this individual shows signs of neanderthal into breeding within the previous few generations and if you want more on this there's a nice review paper by you and colleagues this is a diagram from it's quite a complicated diagram a lot in this but you can see there on the left the divergence i'm gonna have to turn my phone off yes so we can see on the left there the uh divergence of the neanderthal and judicial lineage and we can see there in the center sorry on the right hand side we can see african recent human genomes diverging off and in the center there we've got the genomes of populations in asia and europe homo sapiens genomes some of them seem to be dead ends they don't contribute to present-day populations and others are diverging through and giving rise to populations today in east asia in europe and siberia and that neanderthal dna having got into our genomes mainly in the period it seems between about 40 and 55 000 years ago it could have been as high as 10 percent in some of these populations but selection then removes that neanderthal dna pretty quickly so as we map the levels of dna in early homo sapiens populations in europe and asia we can see that the neanderthal dna is declining so you can see on the left hand side the oasi individual the dna is at the level of about nine or ten percent but other homo sapiens fossils have lower levels of four to five percent and then it declines through to the levels of about two percent that we find today so this brings up the tricky question of species and are the neanderthals really a distinct species well i would say morphologically they are um even though there's interbreeding so this is a piece i wrote on the natural history museum website and as i say down here in my view if neodytals and homo sapiens remain separate long enough to evolve such distinctive skull shapes pelvises and ear bones they can be regarded as different species into breeding or not humans are great classifiers and we do like to keep things orderly but we should not be surprised when the natural world past and present does not match up to our neat and simple schemes and some of that neanderthal dna genomes today is still active so here's a paper one of many actually which tries to map the activity of some of that dna and you can see here at the bottom there the suggestion that type one balding menopause age susceptibility to sunburn lung capacity bone density whether you're a morning or an evening person your white blood cell count there are bits of neanderthal dna which be can be correlated with slight differences between different members of modern humans so some of this dna does seem to be active today in our genomes so let's move on now to the denisovans people who we now know live in east asia for a long period of time so we only learned about these people in the last 10 years or so russian archaeologists have been digging a cave called denisova cave in in southern siberia in the altai region for about 50 years and they'd found some fragmentary human fossils they were too fragmentary to say what kind of human they were but remarkably these fossils have fantastic dna preservation and so the whole genome of an individual was recovered from a tiny fingerbone fossil and the preservation of this fingerbone fossil was comparable to the quality of genome you could get from a modern human bone so fantastic preservation and this revealed a kind of human that was not neanderthal not not modern human but a separate kind of human that became known as the denisovans and mapping their occupation of denisova cave we can see on the bottom right there a section of one of the chambers of denisova cave and it's mapping the presence of denisovans in parts of the cave layers from about 45 000 years down to over 150 000 years ago and neanderthals were also there at some of the same times and they overlapped and there's even what's thought to be a first generation hybrid between a neanderthal and a denisovan this this girl has been nicknamed denny so here are some of the remains from genital gave in fact this is these are the best preserved most complete remains as you can see they're very fragmentary the ones at the top have denisovan genomes in them and there's even a part of a skull now over geneticism denisovan denisoven13 and the ones at the bottom have neanderthal genomes so very fragmentary material but remarkable dna preservation in them and this individual denny denisiver 11 as i say it's it's a it's a girl who had a neanderthal mother and a denisovan father so phenomenal data from this site of denisova cave and not only that it's not just the fossils that are producing dna now because work in the last couple of years has shown that even the sediments in the cave contain dna not only of the animals that were living in the cave but also the humans so here's an example of nuclear mitochondrial dna recovered from cave sediments of neanderthals in sites in asia and europe and it's been applied to genital cave with remarkable results so we can see here a mapping of the sections of the sediments in of dunisla cave so over 700 sediment samples have been obtained from this cave 94 of them contain mammalian ancient dna and remarkably 24 pretty well a quarter of them contain traces of hominin adna so these humans bits of dna may represent bones that have disintegrated uh they may represent even an individual that relieve themselves in the cave a woman that gave birth in the cave all of these could have led to the traces and survival of dna in these cave sediments so this is remarkable data which will revolutionize our view of human evolution going forward where there is dna preservation enclave sediments we don't even need the fossils anymore to map the presence of ancient humans and moving beyond uh the genome itself there's also work going on on proteomics the preservation of fossil proteins and these seem to have a better survivability often than the dna and so the study of fossil proteins is going to be big in the future also of human evolution and one example has already been published which shows how important this could be this jawbone was found in a cave in the tibetan plateau of china from a site called by shia cave and that cave has denisovan dna in its cave sediments and it's also apparently produced this jaw bone i say apparently because the jawbone was actually in the possession of of monks in this region so it was an excavated systematically but it's reported as coming from by sheer cave so this is a very robust jawbone there's no chin on the front it's got very large mobile teeth so in its robusticity and its big teeth it already looked like it resembled the denisovans who have very big molar teeth and a bit of proteomic material has been recovered a bit of fossil protein material and that maps on more closely to the denisovan genetic sequence than the sequence of neanderthals or homo sapiens so it this is probably a denisovan jawbone from the tibetan plateau of china and it's over 150 000 years old and there are other fossils in china that might be denisovans um you know there's one from india as well from namada uh there's a number from china that could be genecides and this also includes this wonderful skull which i was involved in studying earlier this year earlier last year now so the so-called dragon man from harbin in northeastern china so this is beautifully reserved fossil and one of the big questions is could this be a denisovan and that's something we can't answer at the moment we don't have dna or proteomics from this fossil but that's something we're looking at for the future to try and recover either dna or proteomic material from this wonderful fossil but it's dated again at over 150 000 years so we don't know whether there will be a good organic preservation and we also know that the denisovans probably extended a long way south of siberia because remarkably once the genomes of tunisians have been mapped it was found that populations particularly in ireland southeast asia and australia australasia had traces of denisovan dna in their genomes and it's as high as four percent in some of the genomes in populations in australasia and the philippines now it's not thought the ancestors of these people in australasia ever went anywhere near siberia so the assumption is that the modern human dispersal about sixty thousand years ago went through western asia and there was interbreeding with neanderthals there then populations moved through southern asia and moved down through south east asia and it seems to be down there that they mix with denisovan-like people um probably in the last 50 000 years or so so populations in australia and new guinea for example have both neanderthal dna from a slightly earlier phase of interbreeding and then added on to it denisovan dna so these denisovans not only were up in siberia but apparently they were down in southeast asia too and where exactly they were we don't know because we don't have any fossils that we can say are dunicimans from this region we know that homo floresiensis was living on flores and that doesn't look anything like a denisovan we know homo luzinensis was up in the philippines that doesn't look anything like a geneticide we've got the much more primitive species homo erectus still around on the island of java so some of us guess that these southern denisovans were probably living in regions like sumatra and borneo and sulawesi and indeed there are stone tools on sulawesi for example that are more than 150 000 years old and perhaps they were made by some of these southern dissidents so the neanderthals had a range which we know ranges east-west across asia the dunicipans by contrast probably had a much wider distribution north south from the very cold areas up in siberia and northeast china down to uh to regions like in sumatra and borneo and sulawesi so finally then this big question of why we're the only humans on earth what happened to the other people who were still around 70 000 years ago so here we've got that representation again of these humans that were around about 70 000 years ago as far as we know by 30 000 years ago all of these others had disappeared physically although of course in the case of the neanderthals and the genesis bits of their dna lives on in us today and here are some of the ideas of what happened to those other humans so uh various ideas and i've got these from the popular literature so on the top left there homo sapiens were to blame for neanderthal extinction because they were better hunters and out-competed them for food a computer model shows uh bottom left there climate change likely ice the neonatal is out of existence i mean the problem with that is if it was climate change that was hitting the last neanderthals it also would have been hitting the homo sapiens who were living alongside them top right there one of the recent ideas end of the neanderthals linked to a flip of the earth's magnetic poles a study suggests events 42 000 years ago combined with a fall in solar activity was potentially cataclysmic researchers say this was a significant event in terms of solar activity and uh a change of the earth's magnetic pole positions but i don't think it could be linked with the disappearance of the neanderthals and again it would have affected everything on earth not just the last neodytals on the bottom right there homo sapiens developed a new ecological niche that separated it from other hominins a new study argues that the greatest defining feature of our species is not symbolism or dramatic cognitive change but rather its unique ecological position as a global generalist specialist so we're able to spread widely and then through our culture and behavior we're able to specialize without having evolutionary adaptations our culture enables us to become a specialist in different environments such as deserts and rainforests and in the center there and quite a nice idea humans are our evolutionary success to friendship cooperation was the key to our long-term survival we cooperated more we had less aggression within groups than maybe these other humans such as the neanderthals had so i think overall i think our behaviour was probably the main factor in our success maybe we networked and accumulated knowledge better we learned to extract resources more intensively from the environment than other humans did and above all we found ways of improving the survival of our children and the old as our numbers grew and we spread ever wider perhaps we absorb some of the other species out of existence so i'll stop there and i hope we've got a bit of time for questions and i will try and answer your questions thank you thank you very much that was really interesting um it was really nice to hear about the more recent research in the yes um so we do have some questions um and i guess i'll just read them out if anyone wants to ask yeah let's try something yeah um good so um first one is i was wondering how how it is that people in the american continent evolved to have similar features and gene constitution of people coming from eurasia and africa right yeah well we think that uh the populations of the americas came over from uh southeast from eastern asia so at times of low sea level the sea level at times dropped by over 100 meters globally so as the ice caps grew as they often did in the ice ages water was sucked up if you like from the oceans fresh water was taken out of the oceans into these huge ice caps that built up so the sea level fell and there was a land connection between eastern asia and and alaska and it's thought the population traveled across that land bridge some of them may have even hopped across the islands to the south of that land bridge and this happened on present dating at least 20 000 years ago so the populations in the americas today genetically and physically relate to populations that you that were formerly in eastern asia i don't know if that that's enough to answer your question obviously once they're in the americas they've had 10 or 15 000 years of evolution within the americas with the movement of some populations as well such as the inuit they came across in a later wave from asia um what gaps in homo sapiens evolution and dispersion do you think have the most potential to affect academia i.e anything that would alter our understanding of geographic cultural changes anything that would affect our did you say that last bit again understanding of geographic or cultural changes right yes well obviously you know we have a very poor understanding of the genetics that affect cognition for example so obviously everyone wants to know whether neonatals could think like us and that's been a huge debate for many years so 20 years ago i and many of us would have argued that the neanderthals were qualified cognitively inferior to homo sapiens when you looked at their culture what they produced it seemed to lack diversity it seemed to lack the working of certain materials such as ivory and bone and antler which were all around but seemed to be hardly worked by the neanderthals it seemed to lack symbolic expression whereas with modern humans we find these fantastic cave paintings in france and spain and now borneo and sumatra and the advertisers were thought not to be doing that and so on and some people argue that neanderthal's an active and complex language and this this held the back um we now know that the gap is closed so we've found a lot more data about neanderthals we know that they behaved in more complex ways they were producing symbolic objects they were producing jewellery for example made of animal teeth they were marking bones with geometric patterns they were marking the floor of a cave in gibraltar as what's called a hashtag which seems to have been put there by neanderthals uh more than 40 000 years ago there's even evidence that they were marking cave walls so the neanderthals were behaving in more complex ways they were working bone and antler and ivory a bit less than we do i think there's still a gap that the neanderthals were not producing representational art i don't think there's any good evidence of a statuette or a painting of an animal done by neanderthals so there are some gaps but i think meantimes probably have language so yes i think if we can find ways to get to neanderthal cognition and some people are growing bits of brain tissue and they're genetic content to mimic the dna of a neanderthal so we can start to see how neanderthal brains were growing compared with ours and compared with chimpanzees so i think that will be an interesting way forward um and i think we you know we have a lot to learn about neanderthal diversity at the end of their time they seem to have been very low in numbers and diversity even doing in breeding we've got evidence of very closely related individuals that are apparently breeding with each other so the neanderthals potentially were a threatened species even even before homo sapiens appeared alongside them um but we know very little about earlier neandertal diversity and i think that's one of the things that cave sediments will help us with to really map neanderthal diversity across their whole range um if if you only recover partial fossils example the back of the skull what methods might you use to infer the rest of the fossil in order to draw conclusions does computational modelling or prediction play a large role in this yeah that's a very good question and that's one of the things about the epididyma fossil it is only the back of the skull but it matches very closely another early homo sapiens fossil from israel that's a bit younger in that age um but you're right and and what we know is from the african pattern is that a skull can look modern in one part of the skull and it can be much more primitive in another part so we do have to be cautious about that epidemic individual but i didn't get a chance to mention that there is interesting evidence of an earlier genetic interchange between neanderthals and homo sapiens so it looks like um when you look at the genome neanderthal modern human divergence is estimated to be as i mentioned maybe five or six hundred thousand years ago but when you look at the y chromosome and mitochondrial dna the divergence seems to be much younger maybe only half the age so there's a suggestion that there was an earlier exchange of dna from homo sapiens into neanderthals which replace their original mitochondria and white chromosomes with a pattern derived from homo sapiens in africa maybe about 300 000 years ago so that epitome of fossil could represent a homo sapiens individual that might have been part of this population interbreeding with the neanderthals at that time but i agree it's it's incomplete and it's much better to obviously work with more complete fossils for a more reliable picture if you like yeah um we have quite a few more questions that's all right um due to modern world internationalism i.e different populations from across the world into reading would you say humans will have a lot less diversity in several hundred thousand years yeah that's a good question um yeah it's argued that a lot of diversity i mean some of the populations who have been distinct for a long period of time for example island populations are now mixing of course with wider gene pools so their individual diversity which has evolved over maybe thousands of years in a sense is being diluted and perhaps lost and the same thing's going on with language diversity of course the number of languages in the world is shrinking as many populations disappear or dwindle or take up the language of a much larger body of people so yeah that diversity you could see is perhaps decreasing and i think in predicting the future it is very difficult i'm often asked you know what's evolution going to produce in the future and the fact is because evolution doesn't have a forward look it's about what works now so i think it's very difficult to look forward and i think something like climate change is going to be a much more significant factor in the diversity in maybe even 10 000 years it will depend who gets through this period of severe climate change that we're going to be faced with in the immediate future how well preserved are the dna from these ancient humans does dna degradation influence or discussions around breeding between our species and neon dogs yeah so yes i mean you know the first dna recovery was 1997 tiny bit of mitochondrial dna and now we've got whole genomes some of them to very high quality so i mentioned the denisova genome um from that tiny finger bone uh sventipalm at the time he said he was astonished because it was as good as genome recovery that he could get from a recent human bone even though that bone is probably close to a hundred thousand years old so we think tunisia cave because of that cold environment has been excellent for dna preservation and we've now got composite neater genomes that have um you know very good coverage so the number of genomes is going up and the number of early homo sapiens genomes is going up but of course we lack genomes from some of the other parts of the world the warmer parts of the world and that's probably always going to be a problem and maybe proteomics will come in and help us in some of those areas but i think the evidence of the interbreeding is very strong there was still just a minority of people who still challenge that there was interbreeding and the geneticists have misinterpreted the data but it does seem to be well founded and the interbreeding as you mentioned the the evidence is that for example our immune systems outside of africa oh quite a lot it seems to the immune systems of neanderthals the hla system for example seems to be closely linked with neanderthal hla systems so it's very likely that we evolved in africa we had no natural immunity to the diseases outside of africa the neanderthals had evolved those defenses having lived outside of africa for hundreds of thousands of years so by interbreeding with the neanderthals we got a quick fix to our immune system and picked up some of their immune defenses that was good news then the downside is today there also seems to be a link between the presence of neanderthal dna and certain autoimmune diseases so it may be that in some people that neanderthal dna is in a sense over sensitize their immune systems um so things like crohn's disease and biliary cirrhosis seem to be linked with the presence of bits of neanderthal dna what techniques are used to take fossils and why do they lead to large discrepancies in the age um that was my question i i meant specifically um there was one also which you mentioned which was dated to 65 000 years ago i think and i think you said that some groups thought it was from 45 000 years ago yeah so why the yeah so um yes i mean that's a whole whole talk in itself the dating method so the one that most people know about is radiocarbon dating so radiocarbon is produced in the atmosphere all the time and we take it up in our bodies naturally when we die we stop accumulating radiocarbon and the radiocarbon we've got disappears about half of it disappears about every five just over five thousand years the amount of radio cotton we got halves so if you have an ancient bone if you can measure the amount of radiocarbon in it you can work out how long it's been you know how long since that individual died by the amount of radiocarbon left and the problem is because it harms about every five thousand years so by the time you're back at 40 000 years there's only a tiny bit of radiocarbon left to measure and so that's where errors can come in and we have other methods of dating so luminescence dating can be used on sediments mapping really how long it is since that sediment was exposed to sunlight and that was the method that was used for that australian site where i said that it had been dated to about 65 000 years one level at the site other people actually cite radiocarbon dates that suggest it's younger so there is dispute there um in the case of the fossils from china and epidemic where you've got dating at least 150 000 years they're using a method called uranium series dating so uranium isotopes decay through time and you can use that decay a bit like radiocarbon dating to measure how long it is that that sediment or that fossil has been in the ground and i mentioned on the kibbish volcanics rocks can be dated very accurately by potassium argon dating and argon argon dating this method has been used to date rocks on the moon um and it can be used on earth from you know four thousand million years ago down to the recent past so when you've got volcanic rocks you can actually measure very accurately the decay that's gone on in those rocks since they solidify it or since an eruption happened thank you um are there genes that define whether we are morning or evening people well there are and i'm not an expert on this but yes there are apparently and of course these are genome-wide association studies so you've got to be a bit careful um obviously you you look for the prevalence of certain conditions let's say depression or schizophrenia and then you look for bits of dna whose presence seems to correlate with people having that particular condition and often it's only a maybe a one or two percent extra probability of having that condition and when you do that yes there are some genes which seem to map with personality traits such as being a morning or an evening person and as that diagram suggested and you can obviously refer back to that paper um there are some bits of neandertal dna that seem to actually favor someone being a morning person other bits of favor than being an evening person how is behavior and the accumulation of knowledge influenced by genes yeah that's a very good question um it's obviously not a direct link so this is mainly cultural transmission and so it's you know there are some people who modeled the retention and growth of knowledge in human populations and the idea is that if you're going to store knowledge you you need a certain core number of people to accumulate and hold that knowledge so small groups are that are threatened with extinction or some individuals in that group are threatened with risky activities let's say hunting behavior those individuals if they store important knowledge if they die that knowledge has gone from the group so the idea is that larger groups and more network groups are more likely to hold and build up knowledge and so that seems to be a process that was important for us that our groups potentially were larger than the neanderthals they were networking more widely across the landscape and so we were able to accumulate and build our knowledge better so that's not a genetic process it's a process of cultural exchange and cultural um evolution through time we have a couple of questions from ethan you wanted to ask them hi chris um great talk i just like to ask you uh three questions um so i was wondering why migrations occurred in waves instead of like a gradual continuous diffusion of people out of yeah i think that in some cases there have been waves and we can see that when we when we met let's say the last 10 000 years in britain we have had if you like waves of movements of populations into britain with farming with the second phase of farming with the arrival of of metal working and so on so there certainly have been ways when you can map it in that great fine detail and of course for the neanderthals and early homo sapiens we don't have that kind of resolution and i think what we see even in europe now is between 40 and 50 000 years ago and there's even more evidence coming out next month what we do see is that there were waves of homo sapiens coming into europe it wasn't just one wave so we used to think it was one wave at forty thousand we now can see that there was um a wave probably more than fifty thousand years ago that ultimately disappeared it seems then another wave about 45 000 years ago that too seems to have pretty well largely disappeared and then a wave at around 40 000 which is the one that really started to form the basis of the populations that we find in europe later on so i think you're right that this idea of a single wave of a small group of people uh in some cases is wrong on on islands it may be more accurate there are some islands which have been populated by just really one ancestral group of people but when we have more data we sometimes find there was an earlier group that that was supplanted so yeah it's it's a more complex story so i hope that at least partly answers that question what's your second one oh and um my next question is um so you maintain that neanderthals is a different species of homo than humans but um so one of the early earliest definitions of the species that i've studied in school at least is that species a different species cannot interbreed and have fertile offspring so how do you um account for that that's a very good question yeah so i was taught at school the biological species concept species are reproductively isolated and that is that is one species definition um it can be useful um but i think it's one or some i wrote a review paper recently there are at least 35 different species definitions the biological species concept is one of them but the more we learn about the genomes of mammals or birds today for example the more we realize the biological species concept doesn't apply in many cases on one estimate 20 percent of closely related bird species um most baboon species hybridized now you can say well they're not different species but then you're extending the morphology uh beyond any reasonable level for a biologist to say what is a species so yeah it's it's a it's a judgment um species concepts are humanly created as i said in the comment there nature doesn't recognize these these simple concepts that we create so yeah there are people who say neanderthals and us are both homo sapiens and i can see why they say that i disagree with it because if you if you believe that then you're you're multiplying the diversity of homo sapiens by two or three times compared with diversity today so for example there are no living humans that have a pelvis like in the abdomen um there are no living humans as far as we know that have ear inner ear bones or middle ear bones that are shaped like in the avatar so you're going to extend immediately extend the diversity of homo sapiens well beyond what we find today and what we find in a group of fossils that we know from dna are closely related to us yeah and the third question yeah yeah well i was i'm amazed at how many definitions of a biological species there are yeah there's a good literature on this if you if you google it yeah yeah but yeah um moving on so my last question so i've read the book by robin dunbar on human evolution the pelican brief introduction and uh he seems to use a lot of uh for sociality i wonder how contentious that is for for measuring sociality of uh later hominids yeah yeah that is very controversial there are some people who've really attacked it recently so you know the idea of dunbar's number that's become famous that he argued that uh you know the the brain obviously is mapping social groups and social social uh connections and our brain in in his view we were we were um our brain allowed us to map a larger number of of relatives in our social group than say neanderthals and as you go back in time the group sizes of these earlier humans would have been smaller and smaller and as i've said that would have implications for example for the amount of cultural knowledge they can store um so yeah dunbar makes a point about that and i was on a paper with him that argued that um and i don't know whether i believe it myself now it's been attacked by a number of people but what what he and uh and his colleague uh eleanor pearson argued was that neanderthals had bigger orbits this meant that their visual systems were larger automatically and this meant that the visual centers in their brains must have been larger and by implication since the brain is a finite size a larger occipital cortex cortex and visual system automatically means smaller parts for the rest of the brain so you know yes i think robin's really an interesting stimulating guy you should get him along to give a talk next yeah thank you so much and a great really good thought that was really interesting yeah um we still have a couple of more questions is that all right with you yeah let's try a couple more yeah um what are the modern anthropological implications of the interbreeding of homo sapiens and neanderthals why is it important to or why are we interested in examining this right yes so well the interbreeding is is medically important certainly so there are people looking now at what this dna is doing in our bodies so um there have been papers written that argue that some population susceptibilities to covid are related to the presence of bits of neanderthal dna and equally protection from covid is related to particular bits of neonital dna so so it may help to explain differences around the world for example african populations have a much lower level of neanderthal dna so so it's important it can be important medically and of course we've already gone over this species question you know the connection between us and neanderthals was a real physical connection and with denisovans too so there was interbreeding um and there's interest in in how this interbreeding happened because if it happened through peaceful partner exchange for example then these groups which i would call different species were recognizing each other as similar they're exchanging partners in a peaceful way now the other extreme there's a view that what happened was as happens in some hunter-gatherer groups and in some chimpanzee groups is that there were bands of modern human males and they ran out of partners and so they went and raided in the additive group and stole their females and forcibly incorporated them into their groups now that's a very different picture of how the interbreeding happens so um you know people are interested in this and geneticists tell me that as we build up data it will be possible at least in the future to map how the neonatal dna arrived in modern human populations was it mainly through males was it mainly through females or was it through maybe equal numbers which might suggest more of an exchange of partners so i think it's an interesting topic and it certainly does have medical importance anatomically yes people are arguing that there are even bits of our anatomy even bits of our brain which um do map onto differences of dna between the antares among humans yeah um and the last question how would scientists measure how far back her tool dates because the raw materials to form the tools will clearly be older than the tool right yes yeah that's a good point so of course um if you were dating a tool made out of lava if you date the lava you're dating when that eruption happened and not when the human actually knocked off the flakes from it to make at all so yeah we can date those tools generally speaking only by their associated material so a tool is lying in a particular layer you can date that layer by a bone which you date let's say with radiocarbon or there's a layer of stalagmite which you can date by uranium series or you can date the sediments themselves using luminescence dating so these methods you know can be applied in sites so the tools themselves are difficult to date um directly yes you date them by association and of course that's true for most fossils as well we can directly date fossils by radiocarbon but that only goes back maybe 40 or 50 000 years if we're lucky you can date them by uranium serious dating if they're covered in a crust for example but in many cases the fossils are only dated by the sediments they're in of course if you have the dna that also can be used to calibrate the age of the fossil for example mitochondrial dna through something called branch shortening you can actually estimate the age of a fossil independent of any other data and well okay i'll stop the recording

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Published: Sat Jan 22 2022