Rewriting Modern Human Origins | Shara Bailey

thank you for being here and thank you to Leakey foundation for inviting me to come today to talk to you about my research you know I always heard that in Texas everything is big but wow you guys weren't kidding this is the biggest screen I think I've ever seen so yeah so I'm here today to talk about new fossils that were found in North Africa and how it's changing the way we view modern human origins I'm going to structure the talk so that I talk first about the discovery and second about the diagnosis and then finally about our interpretation of these fossils so first the discovery the year is 1961 we're in the middle of a Cold War Jonathan adea's president Roger Maris hits the sixtieth his 61st home run beating Babe Ruth's previous record and Barack Obama is born in Hawaii and elsewhere in the world the pan that the pan-african Games are going on in Morocco and that's where this story takes place so in 1961 some a fossil skull was accidentally found by miners who were excavating beright which is something that's used in the drilling process and this skull eventually found its way into the hands of some scientists and they went back and in subsequent years they discovered additional fossils in 1962 the original fossil skull you can see here was published in 1963 a second skull was found and in 1969 a juvenile a child's jaw was described jebel irhoud is a hilly area about 400 kilometres about six mile drive from rabat and although these first these original fossils brought a lot of attention to the area they were quickly overshadowed by fossil finds in South Africa and in East Africa specifically the Nutcracker man here the Leakey's mary and louis leakey here on the left in the upper right hand corner these defines from Schwartz Cron's and in the lower right hand corner Don Johanson and Tim white discoveries of Lucy these fossils of course were much older than the fossils that were found in Morocco now the fossils that were found in Morocco were associated with middle Paleolithic tools and the fauna suggested that they were somewhere between a hundred and thirty thousand and seven hundred thousand years old but you can imagine that finds in East and South Africa dating in the millions of years would overshadow that and people quickly kind of forgot about it for a while but one young scholar john jacob lamb a graduate student at the time in the 1980s went back and studied the fossils and he visited the site and he knew that one of the key things that had to be discovered about this site was an accurate date that date would allow us to put these fossils into a larger perspective and would help elucidate modern human origins jean-jacques hublin became the director of the Max Planck Institute in Leipzig in 2003 and I joined his group in 2004 and it was in 2004 with the backing of the Max Planck Institute and in collaboration with colleagues in Morocco Abdullah had been a sir who's from in SAP in Morocco the two of these men collaborated and were able to reopen the site this is jean-jacques you'd land on the left and Abdullah had been the sir on the right and here's a site in 2004 and one of the key things that they wanted to do when they revisited the site in 2004 was as I mentioned well of course look for new fossils but primarily they were interested in figuring out the date and so and they had to figure out a better strategy Rafi trying to figure out where the original fossils were found these this slide here represents some old maps of the site and you can imagine that you know little arrows pointing here and here you know the fossils well they're about here isn't quite quite as nice as we would like right and so they needed to go back and really take a good look at the site with using modern technology so here is Daniel Richter my colleague from the Max Planck Institute in 2004 he's drilling into the rock to put in dosimeter so that they can measure the background radiation which allows us to do dating techniques like electron spin resonance and thermo luminescence if you know what the accumulation rate is of the electrons then you can calculate an annual accumulation and then you can work back and figure out how old things are in the bottom right here is Shannon McFerrin who is a Max Planck archaeologist working with abdulahad benicar together so this is a site in 2007 and 2004 when they went back and put the dissemblers and they did find a couple additional fossils a worn tooth here or broken molar there but they didn't hit fossil pay dirt if you will until 2007 and this coincidentally is the same year that some very interesting news was published by Max von colleague Tanja Smith here featured on the upper right hand corner regarding the age of the child specimen one of the original ones found in 1969 and also providing us evidence on the speed at which this individual grew fast their growth was so by doing very sophisticated sophisticated techniques as you can see here they were they use synchrotron x-rays to look inside the jaw and to create 3d models or 3d representations of the teeth that were inside the draw jaw they were able to section teeth and they were able to figure out the age the exact age in days of this specimen and then knowing the exact age of this specimen they could then look at the eruption tooth eruption pattern and the and to see what teeth had erupted and compare that to what we see in let's say Neanderthals and they and Tonya Smith and colleagues figured out that this individual grew slow and slow growth is one of the hallmarks of being a modern human we have a very extended adolescent period juvenile period before we reach maturity and we're very unusual compared to great apes in that aspect and so this suggested that this modern human pattern of tooth growth was present in this individual for from jebel ear hoot and I'm going to come back to that later the other news from this was also by looking at the broken tooth enamel they were able to date this this specimen directly and they came up with a date of about a hundred and sixty thousand years so this made it then one of the oldest modern humans in Africa now I kept getting back to that fossil pay dirt that I said this happened in 2007 and it it was the result of very careful excavations that uncovered a skull and a lot of other material representing other parts of the skeleton so here is where the new fossils were found I'm going to show you a number of slides of the excavation here if you look very carefully you can see bits and pieces of the skull here coming out of the ground is a maxilla it is a better picture here of the teeth this is a lower jaw that was found but in the end the material was very very fragmentary and there's only so far you can go in the field and so they covered it in plaster and they dug out a big section of the rock in which it was encased and they were able to take it back to the lab in Rabat in order to study it more carefully and very slowly so here's Abdullah head internal jack with that cast after it's been taken out of the ground and all in total now coming out of this site as of 2007 we have 22 human fossils with a minimum number of individuals of five so there's at least five individuals here in 2007 we had the cranium mandible teeth humerus this is the upper arm bone lower leg bone the femur some lumbar vertebrae your lower back and even since then more material has been found ribs fibula maxilla cervical vertebrae and more teeth so so it's quite quite a find indeed and what this image is showing you here on the left is the the virtual reconstruction we were able to do using these very sophisticated techniques using micro CT and and even though there was a very broken up skull you can see here using these techniques you can virtually take pieces apart and put them back together mirror image the parts that you're missing and basically get a very nice and very accurate representation of the material so this is the virtual reality lab at the Max Planck Institute this is our Portland scanner that's used to do surface scans the micro CT scanner is much bigger it's in a different room the micro CT allows you to actually look at bone structure and an tooth structure and here here's an image of the jaw your hoot 11:00 and so as ice mentioned these fossils were taken out of the ground and brought to Rabat but by this time I had I left Leipzig in 2006 and moved to New York City to become a professor at New York University and so I did not I back to robot I didn't - look at these fossils I didn't have to because of this great technology and because they were able to build 3d models like this they sent me the files virtually and in fact it's it's almost better to do it this way because I can zoom in using software and look very closely at the morphology of the teeth and and even the underlying morphology underneath the tooth enamel which you never would be able to do just with your with your bare eyes and here is I'm going to load up an image of this skull I'm hoping it's going to it worked earlier so just give me a second though it's a big big big file so here's a 3d reconstruction of the skull now with this technology you can virtually remove the skull on one side if you want as I'm doing here and then you can have the computer algorithm fill it in and you get a very accurate representation of the brain and you can get an accurate estimate of the brain volume and the technique also allows us to look as I mentioned look underneath the tooth enamel this is a tooth here with the enamel enamel is the white part you see when you smile and for example on this tooth this this right down here looks like there might be an extra cusp there but once you take the enamel off and look at the underlying dentin surface it's very clear that that cost does not exist and so this technology again allows us to get a much more accurate picture of not only the the skull but also of the dental morphology so that brings us to the diagnosis so I studied at Arizona State University and my original work was on the dental morphology of modern humans of recent humans and when I talk about dental morphology or when I use the word dental morphology what I mean are the bumps and grooves that you see on the teeth work by Christy Turner and other people who at Christy Turner was at Arizona State University who's my mentor but other people as work by other people as well as long showed that there are different dental patterns in different people around the world so for example in in people who have European ancestry tend to have a high frequency of this cusp ear called the care bellies cusp it it's on your upper molar which is your chewing teeth on the tongue side so if you ran your tongue along it you would feel it if you had a big one people with their ancestry in sub-saharan Africa have a higher frequency of this cusp ear outlined by this triangle this is a cusp seven people who have their ancestry in Northeast Asia tend to have ridges on the tongue side of their incisors these teeth you see when we smile they also sometimes have ridges on the outside or on the lip surface of their incisors to go together with other traits as well what's really cool is that the dental morphology of Native Americans links them very well with Northeast Asians and so even before we were able to collect DNA from specimens the dental morphology was telling us that Native Americans have their origin in Northeast Asia and the the DNA has subsequently supported that all right they also have shoveling these lingual surfaces sorry these ridges on the tongue surface of the teeth some of them have double shoveling and other features going on and there's a pattern also in Australia of dental morphology nobody has articulated it yet still needs to be done but they have all sorts of interesting things going on but basically if you look at the bumps and grooves that are present on modern humans you can find these sames bumps and grooves and things on fossil humans as well and so after I've completed my master's thesis I decided to go on and complete my PhD by applying these methods to fossil hominids and specifically I was interested in looking at the question of modern human origins whether we have a single origin in Africa spread out around the world and replaced other people or whether modern humans evolved in multiple places around the world at about the same time because back in the mid 90s that was the question to answer the Out of Africa I pathi sis was hadn't been proven like it has today with the genetic information and so I moved on and I looked at Neanderthal teeth and to see if there was continuity between Neanderthals who live in Europe and parts of West lived in Europe and parts of West Asia and Europeans there isn't but before I get to that if you would just bear with me for a couple minutes while I walk you through Neanderthal teeth Neanderthal teeth 101 so just some basics of what differentiates Neanderthals from modern humans and this is going to become important when we're talking about diagnosis and diagnosing these fossils these recent fossils so for one thing the inner tall incisors these teeth again that we see when we smile are very curved they have tend to have big bumps or tubercles on the tongue side and they have that shovel shaping that ridges on the tongue side as well and this occurs together so all the and earth all incisors have all three of these characteristics now sometimes modern humans have some of these characteristics north east asians have these linked these tongue ridges on the tongue surface but they don't have all three of them in combination so this is a this is actually a homo sapiens it's about twenty five thousand years old from the Upper Paleolithic that's got some little bit of ridging but doesn't have the curvature and it doesn't have the tubercles the upper molar again you're chewing tooth is very distinctive in the inner tall's it has a very skewed shape which I've endeavored to to quantify by drawing lines between the cusps and making an occlusal polygon you can see right here which is a different shape than the one you see in modern humans in modern humans it's very wide down here and Indian Turtles it's very narrow down here and also the area itself is relatively smaller in Neanderthals when you compare it to the area of the tooth which indicates that the cusp tips are oriented more internally on the lower teeth the the lower second premolar your dentist calls at your bicuspid is very unusual in the inner tools it there's a big ridge here connecting the cheek the the cusps on the cheek side with the cusps on the tongue side there's multiple tubercles it's very asymmetrical and rather than being round here's one in Homo sapiens you can see it's missing that Ridge and in fact if I put two little dots here you kind of have a smiling face looking at you right and that's a very distinctly modern human characteristic that you don't see outside of modern humans on the lower molars there's this Ridge here we call middle Trigon eighth crest that's present in all Neanderthal lower molars whether you're looking at the wisdom tooth the second or the first molar and in modern humans it's a very very low frequency so that's just some of the characteristics there's more but you get the idea I think that we can definitely tell the difference between the an turtles and modern humans and these differences are so distinctive that if you gave me a single tooth one of these teeth I could tell you based on a single tooth whether you're looking at a Neanderthal or homo sapiens okay they're very very diagnostic so what do we see when we look at the jebel or who'd material are there very clearly modern even though they do have some they don't have they don't have the smiley face you know but they don't have this Ridge here that we saw in Neanderthals either and they're not as asymmetrical the premolar isn't is asymmetrical and the lower molar lacks this crest as I showed you in the previous slide and the upper molars are not skewed the way Neanderthal molars are now that tells us they're not Neanderthals but it doesn't necessarily tell us they're absolutely homo sapien so we went another step with the teeth and looked at the underlying dentin surface this was work done by my colleague Matt Skinner and we looked at the shape of the tooth and just I tried to take most of the graph I did take most of the graphs out but this is the one you I would have to look at so so these are upper molar shapes and these are Neanderthals and you can see it has a very skewed shape these are modern humans that are much more square these are guys that are in between these are archaic Homo sapiens or Homo erectus or some early modern humans are fallen here and jebel irhoud they're all the way over here okay so they're not even close they're not even with these other archaic groups they're very very very modern looking and the same can't we can say the same thing of the lower molar shape as well based on the underlying surface the surface underlying the tooth enamel so you'll have to trust me on that because I took that graph out everybody likes faces right so everybody likes skulls so I'll tell you a little bit about the skulls as well even though this wasn't my work specifically but what's interesting about the Jebel Haroun material is the face is very very modern-looking now they did a number of reconstructions that's what all these stars represent because you know when you're looking when you're using virtual reconstruction x' they can you can move things around they could change around a little bit so they did multiple reconstructions and every time you can see these reconstructions of the face and we're talking about this part of the skull here fall well within recent not just modern humans but recent modern humans so they're very very modern looking Neanderthals are out here here's Middle Pleistocene homo all right they all have primitive faces that kind of jut forward so this is a flat face it doesn't have it that the face is oriented along the coronal line so this way rather than having a face that's rather fold pulled forward like you see in the in Turtles and this is interesting because it contrasts with the shape of this of the skull and the neurocranium or the brain which in jebel your hood is rather primitive looking okay so here's modern humans here's Homo erectus here are some Neanderthals and jebel or hoot the two skulls that we have are falling somewhere in between okay so there they're not falling with anything in particular but they're somewhere in between all three of these so that that suggests and you can tell by the shape of it too this is actually very high forehead but it's a little bit elongated and it's primitive in that respect and their brow ridges on one of the skulls are rather large as well so there's primitive aspects to the skull as well but the face is very very modern so that brings us to our interpretation so before the reading of the jebel food material we had modern humans from a number of sites in Africa dating to somewhere between a hundred and sixty thousand years and a hundred ninety thousand years or close to two hundred thousand years but they were all from East Africa and there were some there's one skull down in South Africa people it's a partial skull people weren't paying so much attention to it but now it's now people are paying attention to it because we know that modern humans are older than we thought they were the original dates on the jebel irhoud material were based on faunal remains animal remains they did some analyses on animal teeth using electron spin resonance and they came up with dates between 90,000 and 190,000 it's a big range and but as I mentioned this juvenile this child's jaw was dated directly using similar methods we're actually using uranium methods and yes our electron spin resonance and that date came in between 140 and 176 but the new dates for this pushed that back by another hundred thousand years at least and this was this was really the big news this was when the John Jacques called me up and told me this I literally had to pick my jaw up off my desk because I knew it was modern you know it was not that wasn't surprising to me but I had no idea that it would be this old and you might be asking well how come if you dated that kid's jaw directly and you got a date a hundred and sixty thousand hundred and seventy thousand why is this date any more accurate and good for you for thinking that the answer is is that well the date that was made on that juvenile jaw was based on accumulation rate of where they thought it was found right and that's why these new finds in 2007 are so important because they knew exactly where they were found as you saw that old map it wasn't all that great we try our best but now with with with this new fine found in situ they could get a much more accurate estimate of the background radiation and the accumulation rate and therefore this dating is very very secure so pushes it back by a hundred thousand years and that was really big news but then again why why was it such big news right because we know that Neanderthals and modern humans share a common ancestor around seven hundred thousand years ago so they've been on different evolutionary trajectories for seven hundred thousand years and we know that there are Neanderthal ancestors in Spain a site called Sima de los huesos that dates to about four hundred thousand years ago and they are very clearly Neanderthal ancestors they have Neanderthal face like stuff going on and their teeth all these are all upper molars these are very very Neanderthal like so if we can find pre Neanderthals or you know going back to four hundred thousand years why wouldn't we find Fremont modern Homo sapiens right the ancestors of modern how much they'd be ins dating back three hundred thousand years in fact I would predict that we will find additional fossils that push that back even farther in the future and now that this barrier has been broken now there's a lot of places we can look and I think we're more open to finding those things so it's pretty phenomenal and also the big deal is that that was found in North Africa so before this we thought of modern human origins as being a single event out of Africa that's been shown very well by the fossil evidence and by the DNA now for for many years but it was thought that this origin came from East Africa right in one spot here spreading out maybe sixty five thousand years ago spreading out and getting to Australia by at least sixty five thousand years it's like they were running let's go to Australia and and then a subsequent Exodus a little bit later going out to Asia and another one eventually to Europe so there were a number of dispersals but our models all show them coming out of East Africa and now we have to reconsider that we have to consider that in fact this is a pan-african origin so there is no Garden of Eden or if there is if you want to use that that Garden of Eden Eden is all of Africa so there were populations around between 200 and 300 thousand years ago that were interbreeding with one another and through this gradual process you get modern humans and and then those humans of course spread out and they they when they meet Neanderthals and then when they meet up with Denis Evans the Denis Evans our recently named group I don't have a picture of their heads because we don't know what they look like we have a DNA they've been they've been identified through DNA from a teeny tiny bit of a pinky bone and about three teeth and they have DNA that differentiates them from Neanderthals and modern humans but they probably split split off from the inner tall's so they're closer to read Neanderthals and modern humans but we know that when the modern humans left they made it with the disease events and they made it with Neanderthals because everybody in this room has between two and four percent of Neanderthal DNA in them but we out but they eventually replace them obviously because modern humans the only ones here but the other cool thing is and this is something I was also involved with this summer is the we got finally got dates on these new species this new species from South Africa called homo Naledi and that date is 235,000 so what that means is that during this time that we about homo sapiens was you know Eve we we were evolving in Africa in different parts of Africa there was a completely different species that actually looked very very different from us more different from us than the an Turtles they were existing at the same time we don't know if there was any interaction between modern humans and Homo Naledi because there's no DNA that's been extracted I've Homo Naledi yet but we're still keeping our fingers crossed that we might find something and figure that out so that's another really interesting enigma so as I mentioned we have to think about modern human origins now as a pan-african event we've got jebel ear who to 300,000 years give or take 30,000 years there's material from alii spring in kenya that's older than 200,000 years and then there's material from flores pad in south africa that's dated to around 260 so we have the fossils that suggest that this process is going on and what's interesting or I let me back up one second this map is showing that but in this time period around 300,000 years ago there was no barrier between North Africa East Africa and South Africa so there was no Sahara Desert that was a green area okay so there this would have allowed for the intermixing and the movement of populations all around Africa and when people move and encounter each other they intermix that's just what we do so the other interesting thing is that the oldest Middle Stone Age material the MSA in Africa comes from these multiple sites here all dating to about this same time period and that at one time we thought these were Homo heidelbergensis or archaic Homo sapiens making these and now we know that this is this is probably the the artifacts left by by our species by homo sapiens and what's interesting is when we showed you that reconstruction of the Jebel yahood brain and when we look at the brain it is rather primitive it's rather small for Homo sapiens and perhaps that's not a coincidence that we find these middle Stone Age artifacts associated with these earliest homo sapiens as well and we don't really see big changes in the artifacts until later on so there might have been something that's related to brain reorganization or relative brain size that leads to innovations in technology that we see for example around 80,000 years ago things like ochre here that's been etched from blombo's in South Africa shells that have been perforated and worn either on clothing or as some kind of personal ornament pendant or something like that also dating to around eighty thousand years ago nice blades and these still bay points that are hallmarks are different from the middle Stone Age material that you see those shell those shell beads were found in other places as well including Morocco North Africa to publications here dating them to around eighty two thousand years ago so obviously there's connection between groups and they're sharing ideas as well as sharing genes in this modernization process and outside of Africa we also get shell beads similar shell beads but humans are using still these are middle Paleolithic type tools and this is a little bit older one hundred hundred to one hundred and thirty five thousand years so you've got some bits and pieces of modern behavior including these shell beads and also the people here in Israel at sites coughs and school which are about the same age between ninety and a hundred thousand years ago some of them were burying their dead so you have Inklings of modern behavior but not the entire package and it's not until later that you really see indications of this modern behavior would suggest then that modern behavior and modern faces or modern skulls I should say the complete modern morphological package don't go hand in hand so just to summarize we see a mosaic pattern of evolution in homo sapiens the face becomes modern before the brain size does and that before the brain shape head shape does we also are putting the pushing this date back to three hundred thousand years which makes it a hundred thousand years older than we thought before and the material coming from North Africa suggests that our origins is a pan-african event rather than occurring in one place only so I just want to acknowledge that this is a very much a collaborative project I was just one of many many people who were looking at the fossils and the tools and the fauna remains thank you for your attention [Music] [Applause] you

Channel: The Leakey Foundation

Views: 460,486

Keywords: human evolution, NYU, Shara Bailey, Homo sapiens, Jebel Irhoud, science, lecture

Id: USMY3SvqEws

Length: 33min 44sec (2024 seconds)

Published: Mon Nov 29 2021