Ghosts and Hybrids: How ancient DNA and new fossils are changing human origins

I want to talk about the problems that are really engaging me right now in the things that stick in my craw the things that I started wondering about and to do this I want to talk about the work that we're doing in South Africa uncovering new fossils I'm going to give you some of the wonderful resources that we've been able to put together to share this stuff with the support of National Geographic the University of Wisconsin and some other sources we have been able to document our work in South Africa from the very beginning on video audio and I can in certain cases allow people to tell their own stories so I'm going to start by talking about our discoveries and where we're going with fieldwork I want to talk then about some of the ways that our discoveries and other discoveries in ancient DNA in the DNA of modern people in the fossil record more broadly than our work are changing our view of human origins and I want to present some of the things that are puzzle meat about this the big problems that I think are facing us now some of the ways that I think might be promising to tackle this by those those big questions and then where we're going next so that's in a nutshell where I'm going this is all the work of many many people and I'm privileged to be able to share some of their words with you directly but I also want to point out that we're working with the team of more than 150 scientists on all aspects of the work that we do and feel and then all of the discoveries that have happened in other areas of paleoanthropology that all that I'll talk about are the work of many many people and I've got notes on the slides and stuff about whose work this is but I want you all to know that we are in a field right now that is going a revolution and you're gonna see the evidence of that revolution and it's the work of all of us together so first I want to tell I want to show you Steve Tucker Steve is one of the cavers who discover in our fossils in the rising star cave in 2013 and he's going to describe to you the first time that he and Rick hunter his friends saw these fossils in the cave kevin has always been great having you want to answer that question of what's around the next corner that's like always the question in one tonight it's mostly fueled by curiosity but as you get into caving more and more the scientific side of it comes into it you want to know how did these places form what happened here millions of years ago what happened you have billions of years ago basically it creates a fascination with us whole environment in my wildest dreams I would never have thought that caving would take me to what's happening here you can almost call this a bit of an accident so my caving buddy and me Erick we were out exploring this cave on a Friday night we'd gone into a very remote section of the cave part that I'd never been in before and in that sectional we stumbled upon fossils yeah at first we didn't exactly know what fossils yet we started looking around a bit more and so we found a mandible and that was when we knew this was probably hominid that was very eager of the gut excited about it and since this discovery it's crazy what's happening yet so that was filmed in 2013 and these guys in September of 2013 so fundamentally five years ago we're in this cave they were working with Pedro Bosch off and my friend Lee Berger lead is a national team traffic exploring residents he's also a profit University of Witwatersrand he is famous for a number of fossil discoveries in South Africa this cave was totally unexpected and when I saw the video that you just saw and when I saw photographs that came out of this cave I was blown away right because you're looking at an open cave system very difficult to get into you see that squeeze I'm going to show you more about this squeeze that they're doing in just a minute but yes but there they are right and it was clear to us from the photographs that this was some sort of non modern human some sort of human relative we didn't know what it was we didn't know what we were gonna find there but you could see the bones right we had every expectation that there was going to be part of the skeleton and yet it was in a very difficult and challenging place the rising star painted this underneath this hillside it was at the time disused horse farm and and the cave was used by cavers it was well known to them because it was a place that had lots of nooks and crannies and squeezes and it was somewhere that you could get into this kind of interesting stuff without spending a whole day underground so they used it for training new people our cavers that we've worked with now extensively since then the entire cave and society of South Africa do not get it excited by this kind of cave right this is actually just kid stuff for them they get excited by caves called Armageddon that you know you have to camp underground to explore you know over multi days right so so the people were not going into these caves with with an idea that they're gonna find new fossils and that's despite the fact that we're working in the Cradle of Humankind area just south side of Johannesburg where many known fossil sites have been investigated for now more than 80 years so we know there are fossils around but people had an idea of what kind of sites had fossils in them and this was not their search pattern at all so this was a surprise and yet there we were now the problem of the caves I'm sure you hear a cross-section of it they're a part of it there are more than kilometres of underground passages in the rising star cave system and the one that's critical to us is this lean in to this area where the bones were found the dinna letty chamber this is a laser scan of the entire cave system we now have this in 3d and it's registered against light our scanning of the surface so we have an exact orientation with the surface detail and I want to point out that there are a couple of places that are hard to get to in this cave one of them is known as the Superman scroll and the reason why is that it's about ten and a half inches in height and in order to get through you have to shoulder through it horizontally but in one stage the rocks are such that people who are larger like me have to one arm forward and one arm back right so it's like Superman this one is a seven and a half inch passage that is a twelfth meter vertical climb we call it the chute and this was the real constraint I don't fit in this Lee doesn't fit in this no no archeologists that we work with fit in this in order to investigate what these bones could be and to figure out this site we had to recruit a special group of people and so Lee went on Facebook and said I need help please send this message up to as many people as possible we need people with archeological experience who have caving or climbing experience the catch is this the person must be skinny and small they must not be claustrophobic and they have to be available next month fifty-seven people applied for this and and Lee was able to select a team of all archaeology PhD students from the u.s. from Canada from Australia and and this became our underground expedition they were supported by a series of volunteers mostly from the caving Society but some people from MIT's University public we had 60 people on site to support this team underground for a month in November of 2013 and including me right I gotta tell you I like showing you guys this slide to let you know that I do go away the caves but the fact is I'm useless you know it's like I say right this is a team enterprise and I have certain abilities that are really useful for this this whole exercise but going into skinny places underground it's not a ton but I will say right we have a second fossil site in the cave the Lacetti chamber I'll show you the fossils in a minute um but the Lacetti chamber is a little bit easier to get to that I still can't make it and Lee went there once and on his way back out he was stuck in the squeeze and and the squeeze is not a crazy crazy squeeze but when I saw him go through it going down I was like well I guess I'm stuck here right I can't fit through that and when he came back up he didn't fit and so it was literally 45 minutes of getting him through the squeeze that squeeze has become known as the burger box so serious we do you know we unfortunately in the time that we've been working there not had any serious safety events I'm going to show you the chute this is Rick and Megan burger actually in the chute I'm going to show you what this is like for our team coming up so once you're gonna see you to start out with is and I'm gonna turn down the program volume actually mute the program what you're seeing here is Beckett Pisciotta who is coming up the lower part of the chute and marina Elliot has got my Steadicam she's about to hand this camera over to Becca and you're gonna see a camera switch Becca's squeezing into this little crack that actually marina when she saw this video said what is where is that I don't even know where that is because the different team members who are different heights fit in different in this passage so here is marina now taking the next section of this and you get a real picture of the physicality of this the athleticism that all the team has to be able to do this I want to tell you that everything that we do in this chamber all the equipment that we use all people who access this have to be able to make this climb and as you can see it's a free climb safety harnesses actually impede the team if they're going up and down they're safer without a harness on and so everything that is in the chamber eventually has to come back up that includes lighting wireless routers computers and fossils and so this place takes our team members who are incredibly skilled underground this is Ellen foyer regal is taking of it the top part of the shoe takes our team a half an hour to traverse through the cave into the dental Eddy chamber to work and a half an hour to come back out so it is really really a difficult place to work we've likened this to uh we call them underground astronauts and the reason for that is they're only communications when they're in the chamber are virtual you know we're able to talk with them on telephones actually but there's not any ability there it's like a spacewalk you know you really are in a remote place that you can't get help immediately if you need it ok so a month that underground our team working above ground conserve the fossils as we went and over the course of that first 21 days underground and a second field season of more limited scope 13 days we recovered more than 1500 fossil specimens of what we really quickly discovered was a previously unknown species we named it Homo Naledi I want to tell you a bit about millennium give me an introduction we've recovered every bone in the skeleton at least you know in in partial form we've recovered bones from a minimum of in the initial phase 15 individuals today I can increase that we have at least 20 individuals in the Duma let each chamber they represent each body part and most of them multiple multiple times so we have a very good record of the anatomy of the species I'll show you some salient features of it first lots and lots of cranial remains and this is true of most of Archaea of paleontological sites we find lots of skulls and teeth and skulls and teeth are very important I'll talk about why they're important in a bit but with miletti the biggest most obvious thing is that their skulls are very small compared to our skulls they have brains about 450 to around 600 cubic centimeters and the very biggest individual we have that is about a third the size of your brains so we're looking at a very small brained common this is Jonker cheese reconstruction of what the levy would have looked like when it was alive and I think this is you know I I love his work I think this is as good as an artist can do obviously some aspects of this are more speculative but they're still based on some sort of scientific point of view you know skin pigmentation for instance we don't have any bony knowledge of this and so we use what we know about the modern human distribution of skipping the brains of eye I'll talk more about brain anatomy in a bit but but we do know quite a lot about the brain anatomy externally of Naledi we have the remains of at least now 20 individuals I will tell you that we have individuals of all ages represented in this sample this is a very old adult you can see here the wear on the teeth has gone down to the roots on the first molar so we're looking at somebody near the end of their lifespan we have here's a toddler age individual about a two year old if they age in human terms I'll tell you we don't know precisely how fast they developed how fast they aged chimpanzees develop much faster than human children do and so we don't know exactly where the lady lies but their canine eruption is late just gives me their canine a Russian is early it's late at chimpanzees and so there's a hint that maybe this is a more human-like pattern their teeth are around the same size as your teeth their incisors in the front are a bit smaller their promoters are about the same size as yours their first molar is just a hair bigger than your first molar depending on how big yours is some of you are big too and so this would be maybe your size the second molar and then the third molars the wisdom teeth are not in this individual are bigger bigger and that's very different from you your third molars if you have them how many guys have third molars wisdom teeth yeah they're smaller than your second course if your third molar is bigger than your second molar we want to see it's not impossible right that's rare your second molar is smaller than your first of all for the leg is the opposite and that's a primitive pattern that's something that we see in early hominids like Australopithecus like Lucy we don't see it in living people their promoters have a very primitive morphology as well you don't see especially this third premolar you know see that Anatomy in a living people it's in fact quite unique we don't see it in Lucy either their third molars are large and and highly asymmetrical this is very symmetrical too we can look at the rest of the skeleton though and that's actually quite rare skeletons in the fossil record we've got an incredible PV we've got a lot of evidence about human origins from fossils a lot of that is however biased towards skulls and teeth and we have post cranial bones of many species and we have some partial skeletons some really really cool but what we don't have for most species other than modern humans and Neanderthals is a representation of the skeleton of one or multiple individuals that lets us correlate parts with each other and so this becomes a really important sample I want to talk about some of those parts this is in the site as it was unearthed a hand you can see tear the metacarpals the carpals of the wrist you see here finger bones these are the middle phalanges the intermediate ones that are curled over like this is a hand in a death pose in articulation in sight and this is that hand here's the palm here's the back of the hand I want to show you a couple of things the finger bones the distal ones have really broad fingertips that's like us chimpanzees have super narrow fingertips as does Lucy as does any kind of early comedy big thumbs stout thumbs wrist bones that are configured like ours but I want to show you the finger bones are really curved and that's not like us at all our finger bones are a flat and curvature is something that occurs during development as the growth plates are activated on a curb substrate a curvature can emerge and that's what we're looking after we're looking at Ansari used to grasp onto curved things the thumb also I want to point out has got this the AUSA there's a couple osteolysis in the room who really no thumb bones and I want to show you the base of this is really small and at the end of this the distal end is really large and there are these huge ridges on it for the for the musculature of the hand and you look at that and say wow that's really impressive right that must be some strange thing about this individual and this is the fossil site where I can show you seven and I can show you that then they all have the same kind of morphology we're really looking at a population that has some odd things in it that we haven't seen before in the fossil record feet are human my students at the rock work who's now an anatomy professor at the North the Arkansas college of osteopathic medicine he came to study of the feet and he was looking at these foot bones and after a few days of studying the hundred and seven foot bones right he says why did you bring me here and I said in me this is amazing yeah he says these feet are completely unremarkable and I said you're kidding me thank you he says these could have walked into my dad's breakfast now is that was a podiatrist and I got to tell you exactly knows everything there is to know about feet right I think this oh right and so what I hear him saying this I'm sort of concerned you know because I think these are cool but I don't know if he like he does I had to pull them over to the next table where they're working on the skull and I said that skull walk in here dad's practice because we're looking at something that has human-like morphology very human morphology in his lower limb and has a very primitive skull and that's really weird lots of feet from the site if we look at what Nalini looks like as a figure right this is again john gerdes painting of this I want to show you this is Homo erectus this is a skeleton that we know called the narrow Academy boy or the Turkana boy this is Lucy as a reconstruction right and I don't go too much into the hair and that sort of thing I just want to show you Lucy's got these big shoulders she's short she's small body mass she's got short legs Turkana boy has a very human frame you know his proportions are fundamentally human-like even though his skull is in exactly hours the look is this weird combination shoulders that are sort of canted upwards very musculature mus muscular but not super long arms legs that are proportioned very much like ours a very small skull right this is a strange mixture of characters that we haven't seen before and so we're faced with a problem how do we explain this how do we explain the presence of many many individuals of this species a chamber with no other animal bones other than six bones from an owl is weird well almost immediately as we were working underground in our first phase our cavers brought to us a piece of news there is another place in the case where there are bones our chamber the dim Eleni chamber this is an overhead view of the cave system the dim Eleni chamber is here in yellow our surface entrance is here in blue this is where I sort of hang out and this pink area is called the Lacetti chamber the Lacetti chamber sorry little study chamber produced a partial skeleton which was identical Minnis morphology to the first chamber skeletal material this is an individual we nicked into nail which means gift Institute you miletti means star it's a suit so we have an individual there along with a couple of pieces of other individuals the showing that Naledi is in this cave system and using some significant parts of it I'll give you one other piece of information we didn't initially know how old Naledi was after three years of dating methodologies giving samples to multiple independent laboratories the line so that they didn't know what they were looking at right and they didn't know that two different labs had the same sample we derived an age estimate for the dim Eleni chamber fossils they are between two hundred thirty six thousand and three hundred thirty five thousand years old these fossils if you know anything about human evolution we know Lucy is three and a half million years old our evolutionary history seven million years and these very early small brained creatures come from the early phases of evolutionary history never have we found a fossil younger and then 2 million years in Africa that has morphology like we're seeing it on this fossil species lived at the same time that modern humans were originating in Africa all right so that's a big story what I want to do is probe I was really privileged to lead the description of mayo and and these photos won one of the top ten science images of the year last year so it was really really pleased about this oh let me talk broadly about human evolution this picture the famous market progress is not how it happened this was from time-life series of 1964 and it's a wonderful piece of art it's really iconic people are repeated to begin and again Google you know for instance you see this everywhere and we all know this is not how evolution happened and yet the image is burned in our minds I want to talk about what we thought about human evolution 15 years ago okay and there's a diversity of opinions and I'm gonna represent a bit of that diversity but I want you to know I'm scary of typing a bit but I want to focus on some issues that really represent new information all right so here's a picture of Britain size over time like this is time 3 million years ago 2 million years ago 1 million years ago today bring size 400 600 800 cubic centimeters you can see that there's an early phase of our evolution which we call Australopithecus that is small brains and there's a later phase that we call Homo that represents brain size increase and it has been somewhat this is a log scale right so it's it's actually curvilinear and it's accelerates a bit as you get toward the present that's 15 years ago 15 years ago we knew that the march of progress image was wrong right we if you read human evolution 15 years ago they're talking about how bushy our evolutionists but I've drawn a couple of of pictures from that era just to let you know when they're talking about bushy they were talking mostly about this middle part of the tree this part that represents the last australopithecines including robust australopithecines and the peroneus members are dentists coma and as you get toward the present they realized that there are multiple populations here but they tended to draw sort of straight lines between them you know like something about our early evolution was really specie owes diverse and our later evolution became a bit more focused like there was a trend and that trend was manifested maybe differently in different regions that the trend was real there was a lot of disagreement about what happened to certain kinds of archaic humans this is a Neanderthal skull this is from la pharisee de France this is a crow man yawn you know why I call him the crow ganyan because he's from cro-magnon and also in France right this is about thirty thousand years old this Neanderthal about fifteen thousand years old this skull is an early skull from China this is from Dijon China and it's about sixty five thousand years old all right so we're looking at here two skulls are about the same age maybe maybe this one a little younger and this one after the Neanderthals there was a lot of disagreement about what role Neanderthals might have had in our origins the idea that modern people throughout the world had an African origin was especially noticed and became a big subject in the 1980s so this wasn't new information 15 years ago but there was a debate about the role of growth of an African population did they replace all of the Neanderthals and other kinds of early people or was there some kind of interaction between them do people have Neanderthal genetics today there's a lot of disagreement about that 15 years ago I would say we all knew that Africa was the focus of our evolution and that African populations had spread the question was whether there was any the nation of Neanderthals another thing right so that was 15 years ago I would say however that everyone in the world who is an anthropologist thought that if anybody has Neanderthal DNA it's going to be these people who were Europeans after all and not these people who were Chinese and certainly not Africans right so so the idea was that there was a regional contribution possibly but but there might have been a complete replacement of the Neanderthals that's 15 years ago now this opinion was not Universal 15 years ago but it's representative of an opinion that was respectable 15 years ago all right Stephen Jay Gould very famous biologist writing in about 2001 so this is before his death there's been no biological change in humans of forty or fifty thousand years everything we call culture and civilization we've built with the same body and brain all right now some of you in the room we're evolutionary biologists here like how did that be possible right we all evolved we've all let me just say 15 years ago I was publishing on recent human evolution and I was a really facing an uphill battle and this was a really respectable opinion that what's different about people today is cultural there's nothing about us that has changed in any massive way that's biological and another thing this is not 20 years old but it was a respectable opinion also 15 years ago Eric Lander most genes have only a handful of common variants in their coding regions with the vast majority of a Leal's being exceedingly rare that's that's true right that's the I will expect from a variation in Amos this limited diversity reflects the fact that modern humans are descended from a relatively small population that underwent exponential expansion and evolutionary recent time this is also true this spectrum of frequencies of alleles comes from our demographic growth tantalizing examples suggest that common variants may hold the secret to many disease susceptibilities this was known as the common disease common variant the idea that when you look at traits in different populations common variants that are common human populations will account for a substantial degree of the explanation for why the trade is heritable this went behind the funding of the human genome project right this was why we spent so much to sequence a genome because we're going to find out what causes disease 15 years ago these are biological sort of ideas about humans and their evolution okay now let me run through what's happened in 15 yrs first we have ancient DNA sequences from ancient mutants we now know what the contribution of Neanderthals was to human populations right here Neanderthals they branch off for modern humans some time in the distant past this is a Middle Pleistocene an age maybe five hundred thousand six hundred thousand years ago and there's a contribution of Neanderthals both to the early evolution of humans and there's another chart human populations in different parts of the world Neanderthals and from an early branch of modern humans into some Neanderthals and from some other Neanderthals into other later people in addition to that there's another branch a branch that we've discovered in a place in Siberia called Denis of a cave and this branch represents a very early branching of this archaic human Eurasian lineage so different that researchers have decided that this isn't just a Neanderthal that it represents a very deep population they've called it Denis events that population also contributed some of its genetic material to living people but living people primarily in Sahul that's Papua New Guinea or they're getting broadly right area as well and Aboriginal Australians and a tiny fraction of their DNA to people in East Asia so there's multiple contributions from archaic humans from their genetics into living people all right so that's that we now have settled that we know what the contribution was we have found hybrids just a few weeks ago this nature cover right represents an individual from Denis of a cave who has part Neanderthal and Denis of it if you say well maybe that's just a mixture right that's a very much a mixture because this individual every chromosome position where he has one Denis event variant he has a cheese he says she has another chromosome position that's a a natal period so in other words every time you've got one that's like in the under table one looks like a nice event that's an f1 hybrid so we've found the hybrids of ancient people it's not just that they hybridize with us and integrate their genes into us which they did but also we found actual individuals who represent the direct mixture of them this is not so weird first I want to show you a couple of charts that that show that humans are not so weird for instance these are chimpanzees and bonobos you have these multiple subspecies of chimpanzees today Eastern Central Western chimpanzees and bonobos they also have exchanges in their prehistory ok what's weird about humans is not today's is not the fact that we have these genetic exchanges with past people what's weird about us is that the past people aren't here and so today we're really uniquely uniformed here's an elephant phylogeny we're a lot more like the elephant case today you've got mammoths Colombian mammoths woolly mammoths you've got an American Mastodon here the master Don doesn't mix with these others it's quite distantly related they suffer in like 20 million years ago but the elephant by La Janine was started about five million years ago and separate African elephants Tesla Sedona Africana today from mammoths and pelvis Maximus that's Indian elephants and all of these paleo boxy Don's they've all mix with each other over five million years of mixing so now and the elephant phylogeny is a bit like ours in that there's only a handful of these representatives left right the the mammoths are gone Indian elephants and the two African elephants are all of their name so Wow yeah there's nothing unusual about our evolutionary history and the extent of mixture populations what's unusual is that humans today are the only ones left this was not a new idea right this is a model from Jeff wall in his lab in 2009 right so I I don't want to say it's ancient DNA that made this happen we have signs from living people's DNA of diversity that was difficult to explain from just one very fast growing population and it's in part that that's given rise to the next big thing but the mixture that remains is fairly consistent and a low absolute proportion of everybody's total ancestry so this is Neanderthal no this is Denis of and genetic genetics throughout the world and you see here it's is high in Australia New Guinea very low in East Asia and pretty much the Ural everywhere else Neanderthals have a consistently low fraction that ranges up to about 3% and is never higher than that in living people okay I'll just skip this and go straight to now I showed you this one before and you might have noticed potential unknown hominid once you have ancient genomes and you know that ancient genomes contributed to living people's genomes you start looking at that closely and you start to realize wait a minute that looks like a pattern I know what ancient genome looks like when it mixes in with the living few verses genome and once you know what pattern to look for you can look for it without the ancient genome you can say let's look for the footprints of ancient mixture in living people's DNA we have found those footprints not only living people but also in ancient genomes this potential unknown hominin is the first of the ghost populations that's been identified it diverged from everybody else that we have ancient genes and living genes from sometime around a million years ago way before ander Tolls a Denyce events branched from each other and contributed a fraction of the ancestry of the Denyce events so this denisa van genome which I've already told you is strange is doubly strange because it's got some input from somebody mysterious we don't know here's that Denis of a finger finding things that we didn't know where there has been a common feature of my field in the last 15 years I want to give you some examples denisa best bigs in the genome that has identified this ancient population came from this bone Wow that's not much an archaeologist would not made anything out of this yeah this is the sort of bone that goes into cabinet of curiosities oh yeah we've got a hominid phalanx want to see what can I learn from this nothing it's an immature you've got a growth plate line on here that's all you can learn from it until genetics came along and it was like oh yeah there's a whole genome here it's something we've never seen before Wow you know that's a magazine but it doesn't take genetics to do that this individual this may be the earliest modern human that's ever been discovered outside of Africa this maxilla comes from a place called miss Leah cave it's around 180 thousand years old and it's in Israel its way older than our we have never found modern humans outside of Africa that rule Wow this skeleton this is from a cave called in Guam it is on the island of Flores it has a very small skull it has strange-looking bones it has a small stature it has very primitive feet and wrists it looks really different from modern humans it lived there until sixty thousand years ago on an island that it had to get to by crossing two deepwater straits that was discovered in 2003 let's live chosen 15 years arbitrarily because the splendas things start to show up but one already right here we go here's something we discovered we had no and no reason to answer you guys could look at Flores and say Florence is an island weird things happen on Islands here's something strange you know that we can integrate that easily into our view of human evolution strange things on islands that's not--that's not people strange things in the middle of Africa are a big deal this is a continent on which our species was originating and that was home to large brained human relatives throughout the last two million years and here 250,000 years ago we found something very different that's weird and let me just note a couple of things I've shown you this one before I just want to say this guy come handy on 15 years ago all anthropologists would agree that this was in an early representative of today's European population that this was an ancestor of today's Europeans it is an ancestor but this individuals population the early Upper Paleolithic population of Europe represents less than 10% of today's European ancestry this is almost a ghost population we know that in part because we have other individuals this one from OWASA in Romania this individual is 10 percent Neanderthal nobody today has anything like that there was a mixture that happened in Europe that three days today's European population the today's Europeans mostly derived from somewhere else that's 8 months of course we mostly derived from Africa regardless but not only that we also mostly derived from somewhere not Europe within the last few thousand years and when you look at the DNA of these ancient Europeans you start to see here's the DNA distribution of populations today in Eurasia you see this range of variation when you look at early European farmers that 6000 years ago in Europe they cluster with a population this population is start India farmers from Northern Europe where today they should be up here with Sardinia and those early cro-magnon type hunter-gatherers they don't look like anybody living now so that when we reconstruct these relationships this is a program called tree mix that gives rise to this formation of a tree with dotted lines that represent mixture an ancestry between groups we reconstruct these ancient populations that we don't have representatives of these are ghosts we don't know who they are and that seems to be a recurrent feature of our field in the last 15 years we find things that we didn't know existed before and we now can predict that things existed that we haven't out ok yeah okay so our evolutionary history I like this analogy a lot was like a braided stream during the last million years or more we have had very deeply diverged populations that sometimes encountered each other and sometimes mixed with each other it doesn't look very much like today's human population but it does look a lot like the populations that we see of other kinds of large mammals with large geographic ranges there's something really weird about us but it's a different analogy than we're used to thinking of now I want to talk about a couple of genetic things that bother me I'm going back to this chart one thing that's true is that these people that were ancient people that don't look like living people you may ask why are they different from us and one reason is that natural selection has been affecting all of us natural selection doesn't affect very many teams in the genome-wide comparison but it affects some genes a lot and those changes have been really noticeable this is frequencies in ancient population samples of the allele that today less people digest milk this is lactase persistence and you see in the most ancient samples it is zero ancient people living today in Germany in Norway in places that today people digest milk quite easily because the frequency of this is is very high eight thousand years ago they didn't have it this is new and it increased over time this is a model of how natural selection should increase an allele over time increase over time in the way the selection increases elders look that we were selected there's lots of evidence of selection recently this is some of my work from 2007 and we looked at variants that looked like they could be selected and we said wow this is very strange if you projected this back to see what should be fixed in our evolution it would be a very very large number we should have evolved super fast and we didn't evolve super fast it just looks like we're evolving recently kind of fast and that's interesting but more to the point when we look at most traits most traits are not traits like lactase where one gene makes a big difference most traits are polygenic traits their traits that many many genes make a difference and in the last five years especially even in the last one or two years has become possible to look across many many many genes and make a score that's called a polygenic score predicting what something is phenotype should be based on the heritability that's spread across hundreds or even in some cases thousands of gene loci and when you do that this is stature this is how tall your genes predict you should be and how tall your genes are so these are populations of humans and you can see that there's a good agreement of this and that agreement constitutes a client there's a client these are West Asian populations North Asians East Asia and South Central Asian populations there's a client over space that corresponds to a client of polygenic height that's selection that selection on height of these populations now these polygenic situations we're just now getting a brick line right when I introduced at the beginning Eric Lander the common disease common variant the idea that common genes will explain a lot common genes do explain a lot but you have to look at lots and lots and lots of common genes to explain and looking across lots and lots of genes every trait that's a disease related trait and disease I'm pointing at because people study disease a lot not because they're unique has these lots and lots of aliens that that can relate to it these are called complex traits it's imposed to a simple trade some diseases are simple traits like hemophilia is simple in the sense that one gene change can cause it it can be complex in the sense that most of those are rare and there's lots of rare ones today when we look at irritability across traits like that we think about it in terms of models and one common model today is called the Omni genic model I want to point to this because the insight and this is attributable Jonathan rich art and and his students the inside of this is that even if most genetic changes are caught are really due to changes in a small network of genes that that really really are functionally connected to a trait that network of genes is Co expressed in different kinds of cells with other genes and that Co expression actually influences how the core genes are expressed in the gene in itself so as a consequence heritability becomes smeared over lots of lots and lots of genes that's a really core insight about the way that human genetics is influencing our traits and the reason why I bring it up it's an insight from human genetics that I'm bringing in the reason I bring it up is because of this problem remember I said the Neanderthals everybody agreed they contributed this population if they contributed to anybody and everybody agreed that they wouldn't have contributed to this population the Chinese population Chinese people today have more Neanderthal ancestry than European people today this to me is a deep problem because every anthropologist five years ago well eight years ago would have said the Neanderthals if they contribute to anybody contributed to Europeans y/o European shares some features with the in Turtles there's some features that they share people who argued against that would say those features are shared by convergence or parallelism they're not a meaningful in terms of genetic interchange they're just because they live in the same place today we appreciate that Neanderthals lived not only in Europe like France but also a most of Central Asia they were broad in their population distribution and today Chinese people have more Neanderthal than Europeans that suggests why do I think this is a deep problem that suggests that until eight years ago when we had genetic information from these guys my entire field was barking up the wrong tree and that's a problem right because the only way that we have to study every other fossil is by looking at what they look like let me show you hoping the levee here's its brain size this is brain size this is no lady here's Homo floresiensis right at the Hobbit here's some australopithecines here's how will habilis bigger than the lady rudolfensis erectus bigger than a lady if I put a lady in Florence on this same chart that I showed you a bit ago about brain size you see brain size gradually increases wait a minute what a snail here there are these things we were missing and yet when we study and our work earlier this year came out in PNAS when we study the morphology of miletti brains externally they look very human-like in the aspects we can see if they look like homo brains even though they're smaller than any other homo brains okay you look at millennium you say this looks like it should be like these primitive things and not these more progressively more human-like things right it really does and that's also true of the skeleton here's traits and you can see that Naledi often resembles these primitive early hominid species and rarely but occasionally resembles modern humans and not those other species if we do a cladogram of this and say where does no letty fit looking with some of you will get into the details of this and I don't want to go deep it but if you want to say I'd have to cladograms to show you done with the best methods of two different types this is a Bayesian tree and the other one is the maximum parsimony tree and they put in Eleni in totally different places when I look at the fossil record I want to know how species are related to each other I'm going to use their morphology this is what I got and I've just shown you the genetics shows that what we thought about the fossils we know the most about the intervals was wrong and now I'm showing you that these other fossils that we've recently found the morphology puts them in totally different places it's weird it's wrong it's disturbing our tree was bushy and what's interesting about this is not per se the bushiness we've known that a long time what's interesting is that these question marks are really intractable question marks we don't have evidence today that tells us with any authority how these species are related to each other so I'll return to the evolution of our human ancestors in Africa and I'll tell you we have some fossils of early modern humans they're highly diverse they seem to variable to be one very tight population they're diverse and some of the population structure that genetics shows us exist today in Africa between koi some people in particular and other Africans dates to more than 300 thousand years ago in terms of population structure so that early modern human population was diverse it was already divided into multiple populations at the time that Naledi lived and the letti lived among our diversifying species and signatures within African populations show that there were conquered oceans in Africa from groups as different from each other as Neanderthals and Denisovans are from us there were ghosts populations in Africa we've got fossils from almost the Holocene this is 17,000 years old this is from uol era in Nigeria that have a really not very current human looking to ask to them they might represent these ghost populations or something like Homo Naledi might represent this ghost population we know not oh this is no lady next to one of the earliest modern human skulls this is from southern Ethiopia these two could have lived at the same time these tools from cata pan are 500,000 years old from South Africa and more broadly the tools across Africa found in this time frame when the lady lived or what we call Middle Stone Age tools they're advanced tools the tools that we think go on with modern humans how did this happen the answer to this question is I don't know how it happened we're going back into cave to find out we're still digging we're trying to uncover evidence that would relate cultural evidence and letting we've gone back into the dim Eleni chamber we're excavating now more areas we're uncovering more bones we found bones in unexpected places and our team underground is just doing amazing things they're back in the field this month I want to show you another creepy video and this is just a hint all right here's our team in the back sections the Fisher's that lead off of the dinna letty chamber where we found bone remains of Homo Naledi this is Steve Tucker you saw him at the beginning he's about to take off his helmet here because his head doesn't fit with his helmet on I don't know the answers to these big questions in my mind I they puzzle me they really bother me I know that the way that we're going to find the answers is with more fieldwork with more exploration finding other caves like this and we have recovered in the rising star cave this year a skeleton of an infant that we have in a plaster jacket in the laboratory that has a complete dentition that has all of the information skeletally that we're going to dissect virtually nobody will touch it so the hard work of the field goes on I think we're going to find the answers to some of these things but these are big questions they deserve us to think about the past in a new way to try to understand how to bring to bear all the evidence that we have from different sources and that's what we're doing with our large team and that's the way that I think the field is going to change okay I've gone a little over and I just want to be respectful of everyone if you have to leave if you have to please don't think you're offending me but I'm also willing to stick around for a little bit and answer questions if you have them so please feel free and with that I'll just say thank you again so much for your attention for coming [Applause]

Channel: MSU Research

Views: 10,085

Rating: 4.742857 out of 5

Keywords: Human Origins, Ancient DNA, NATGEO, National Geographic

Id: C_8KnN7tpoU

Length: 57min 20sec (3440 seconds)

Published: Wed Dec 26 2018