Bernard Wood - On the Origin of Our Species: Darwin and Human Evolution

Transcription

1 On the Origin of Our Species: Darwin and Human Evolution February 9, 2009 Bernard Wood lecture presented as part of the Darwin Distinguished Lecture Series. These events are sponsored by Arizona State University, Office of the President, College of Liberal Arts and Sciences, School of Life Sciences, and the Center for Biology and Society. Transcript Mark Spencer, Research Associate with the Institute of Human Origins: [00:00] Welcome to "On the Origin of Our Species." This is an event that was inspired, as the title suggests, by the 200th anniversary of Charles Darwin's birth and the 150th anniversary of the publication of "On The Origin of Species." [00:00:16] In putting together this event, we thought that it would be a nice idea to go back and look at what the contribution of Charles Darwin really has been to the study of our own origins. [00:25] Of course, Darwin treated biology broadly and one of the important things that he did was bring humans into the study, into the fold of biology as a field of study. [00:36] We're going to begin today with a lecture by Dr. Bernard Wood, who is presently the university professor of Human Origins at the George Washington University, an adjunct senior scientist at the National Museum of Natural History, the Smithsonian Institution. [00:52] He is also director of the Center for the Advanced Study of Human Evolutionary History at George Washington University. Dr. Wood is a medically qualified paleoanthropologist who practiced as a surgeon before moving into full time academic life in [01:07] Today, he is going to talk to us about Darwin and human evolution. [01:11] [applause] Dr. Bernard Wood: [01:19] Thank you very much. There are several people in the audience who could probably have done a better job who are on the faculty here but they don't have a British accent. [01:27] [laughter] [01:28] So they were not deemed suitable to talk about Charles Darwin. I was thinking why has this man got a lot of hype and sure, some of it is deserved. Some of it is probably not. I think the world is realizing that a lot of people that we thought were substantial are actually turning out to be rather insubstantial, especially the people on Wall Street and the people who have earned very large sums of money running banks. It's nice to think about somebody who really was substantial. [01:59] And the more I read about him and the more I learn about this man, you realize that here's a man of considerable substance. That's the only thing we think about him but that's what somebody thought about me I would be mightily pleased. But I don't think they ever will but I think that is surely what we think about Darwin. [02:15] I want to cover a lot of ground so why don't I just get on? I want to put the acknowledgements up front because then I don't forget. I want to thank Peter Lucas, Lisa Darwin Distinguished Lecture Series page 1 - ASU School of Life Sciences Grass Roots Studio

2 Nouvelle, Paul Constantia, Matt Skinner and David Strait for the help for some of the things I am going to talk about in the talk. [02:31] This is a photograph of an oil painting of Charles Darwin which is in Christ College. It was painted seven years before he died. I think it's a rather nice picture. [02:39] So what we are celebrating is 200 years since his birth. He was born in Shrewsbury, which is not far from where I used to live, in this place called the Mount, which was the home of his father who was his primary care physician. The family lived there. It's now the offices of Shrewsbury Council. You can't really go in there. And if you do go in there, it's rather disappointing because it is filled with filing cabinets and linoleum on the floors. It's a great shame. [03:04] So he was born in Shrewsbury 200 years ago. What you will find in Shrewsbury that you wouldn't necessarily find in this country is that there is a Darwin shopping center. And there is actually on the shopping center all sorts of heretical stuff that I guess would not feature in the Midwest. [03:22] He then did all the things that you know about. He went to medical school and he didn't like it. He went to University of Cambridge and had a very good time. Then he went on the voyage on the Beagle and then he settled back in London. [03:33] Finally he moved to Down House here in Kent. The criteria he gave to his real estate agent was that he needed to have a house that had a reliable postal service. He needed the post delivered twice a day. Now you're lucky to get it once a day and of course that's of course a huge advance in civilization. [03:51] When he lived here there was a reliable postal service. The correspondence that he wrote one day, went to London the next day and then there was a reply the following day. This is Down House and it is looked after by English Heritage. If you ever have a chance to go, it's just a splendid museum. It's been restored much as it was when Darwin was there and here is Darwin with one of his children. Here is his study. [04:14] There is an old dog basket and a hip bath that he used to use when the ideas weren't really coming fast and furiously and he felt unwell and so he would have a bath in his study. [04:23] But it was here where he wrote the other thing that we're celebrating which is the 150th anniversary of the publication of what we call for short: "The Origin of Species." But it was only called that in the sixth edition. This was hardly a title for a best selling book: "On the Origin of Species by Means of Natural Selection, or, The Preservation of Favoured Races in the Struggle for Life." [04:44] Eventually by 1872, they just decided that they would call it "The Origin of Species." This was not what he intended to write. He intended to write what he called his "big book" which was to be called "Natural Selection," but once he got a whiff of the fact that after Alfred Russell Wallace was thinking about much the same thing, he was persuaded to write what he called an abstract of his big book. Darwin Distinguished Lecture Series page 2 - ASU School of Life Sciences Grass Roots Studio

3 [05:07] But the "Origin of Species" is a sort of abstract of what he was going to write, this large book, which he never got around to writing. The contributions of Darwin are really the idea of natural selection and he provided a lot of evidence. He was a great one for evidence. [05:22] He just piled it on. He just wrote to people. He got evidence, evidence, evidence, evidence, evidence. If you want to learn anything from Darwin, it's just keep finding evidence and you don't really give up. [05:35] So that was one thing. The other thing that he really did, which I think is in many ways overarching is this notion of common descent. From what Darwin really did was to change the idea of a Tree of Life from a metaphor into a reality. That was his major contribution. [05:53] I just love this. It was a page out of his notebook. I shouldn't say I love it. I'm becoming Americanized. [05:58] [laughter] [06:02] My daughter said, "Oh, are you going to give a talk about Darwin? He was a real cool dude." And I don't think that's something I would really bring up. [06:10] So this is his notebook and I just think it's marvellous. This diagram and there is the connectedness of life. That is, a simplified form of the Tree of Life. I think along with Bach's Mass in B-Minor and a lot of music that I like, I think it is one of the triumphs of western civilization. [06:29] So here is a Tree of Life and this is a tree on the outside of my office window. The last eight years I have put modern humans here rather than up there. But I guess I ought to move them up there now. [06:39] There are we. Here is a common ancestor of all living things. All the things that are alive today are on the surface of the tree. All the things that have ever lived are within the tree. So here are at the end of a twig out here. [06:52] The question I want to ask is whether modern humans still fit on the Tree of Life and who are our closest living relatives? This is a picture by Rembrandt who was a great guide but he got his anatomy wrong. The attachment to the forearm extensors are not right but nonetheless, this is Nickolas Tulp who was an anatomist in the low country. [07:11] He has the distinction of the first description of the chimpanzee. That was in It was in this book called "Observations of Medicine." They were mainly observations about medicine, but they also reported some dissections of some animals which were returned to Holland by the traders who were in the Dutch East Indies. And on their way back to Holland they must have stopped in West Africa. They must have picked up the animal that is represented in the frontis piece of the book here. [07:41] That animal we now know was the chimpanzee. Here is a little later description. It's called "On the anatomy of a pygmy," strange sort of creature. We know that is a chimpanzee because there is a skeleton of the animal which was illustrated in Tyson's book and that's in the Natural History Museum. Darwin Distinguished Lecture Series page 3 - ASU School of Life Sciences Grass Roots Studio

4 [07:58] In those days there was such a thing as plagiarism because here is the illustration right out of what was Nicholas Tulp book and I don't see any attribution. So at least there is a good model when I use images from the Internet. It's certainly not the first time that an image has been used without attribution. [08:13] There is the skeleton. The first recorded dissection of a chimpanzee was by a man called Traill and that was 1821 and then after that Richard Owen. He wrote up various dissections and I love this slide largely because it is a great shame that we don't have to dress up anymore when we lecture. And this is not exactly a recruiting photograph that you want to use. You should really become a palaeontologist and then you can look completely stark, staring mad. [08:43] [laughter] [08:45] But I want to assure you that Richard Owen used to look like that and that's just the ravages of old age, which are fast catching up on him. [08:51] By 1863 Thomas Henry Huxley in the series of lectures, which were written up in this book, these were lectures to the Workers Association. This was an attempt by the worthy Victorians to educate the working class. What the book is just a series of lectures that Huxley used to give. [09:10] In that book, he argues for a close relationship between modern humans and apes and especially African apes. Way back around the time of the publication of the "Origin of Species" there was already evidence that we and the African apes were really pretty similar. [09:27] But of course that made not the slightest bit of difference to how people thought about our relationship to the great apes. This is a diagram from a book by Sir Arthur Keith. And you can see this is Here are modern humans and they have a long independent history. And here are the... I think those are the gorillas, the chimpanzees and the orangutans. [09:48] They share a common ancestor and that common ancestor goes way back. And so there is no suggestion here in this diagram of a relatively recent shared ancestor between humans and the African apes, which was not shared by the other Great Apes. Note that the hypothetical common ancestor of modern humans the Great Apes went back to the Oligacy which we now know was a long, long time ago. [10:10] So now the situation is very different. The point I want to make is you know, what have we learned since the time that Darwin wrote, "The Origin of Species?" [10:21] We now know that the closest living relative of modern humans are the chimpanzees and bonobos. I'm sure nobody in this audience is discomforted by that but I'm jolly sure that the chimpanzees and bonobos are probably discomforted by that. [10:34] [laughter] [10:35] They are in a zoo along with the gorillas and the orangutans and think: "Well, why the hell, if we're their closest ancestor, aren't we waling round and instead of being fed bananas and being hosed down twice a day?" So that is the present situation. [10:49] There is a huge amount of evidence now for that relationship. This is a table which is taken from a paper by Brenda Bradley that was published in You just have to take my Darwin Distinguished Lecture Series page 4 - ASU School of Life Sciences Grass Roots Studio

5 word for it that this is five million years here. And these are the estimates based on various molecular biological investigations of the age of the hypothetical common ancestor of chimps, bonobos and modern humans. [11:12] You can see that there is a reasonable amount of agreement apart from the little disparity there for one reason or another. There is a reasonable amount of agreement that there was a recent common ancestor shared by modern humans, chimps and bonobos and it was between about five and seven million years ago. [11:28] Now, that's interesting because some of the fossil evidence which is actually claimed to belonged to the earliest members of the modern human triggered the Tree of Life are actually at the older end of that spread. So if the molecular biologists are right, then maybe some of these fossils can't be early hominids because they are simply too old, like me. [11:50] OK, so here are what we're interested in if we are paleoanthropologists what the topic of the lecture is about is about the green line here that's rather deceptively simple, simple green line here. Which runs from the hypothetical common ancestor of hominins and hominins is the name that we give to modern human twig of the Tree of Life. [0012:11] That's what we are interested in. If I'm sort of cornered at a cocktail party and they say: what do you do? I sort of stumble out that I am interested in these things. We share an ancestor with chimpanzees and bonobos and yes, you should take it from me that that normally gets rid of rather disagreeable people, if that's the first thing that you say. [12:29] So how do we make progress working out what the green line is like? You don't have to be a rocket scientist. In order to make progress you have to do one of a limited number of things. And I encourage the graduate students to put this on their wall because unless you are doing on of these things, then you are not doing the right thing. [12:49] So you are either finding more evidence which the people are trying to do with conspicuous success. So you either find more fossil evidence or these days you can also find molecular evidence. You can extract additional evidence form the existing fossil record. In other words, you can interrogate the fossils that you already have and squeeze a little more information out of them. Or you can devise new and improved analytical methods. If you are not doing any of those things, you are not doing your job. [13:19] I keep reminding myself and I keep reminding graduate students: You've got to be doing either this or this or this or this, otherwise you are wasting you time. But what I want to do is just to take you through the fossil evidence which has accrued since the publication of "The Origin of Species." [13:35] In the second edition "The Descent of Man" Darwin wrote "that there is a great break in the organic chain between man and his nearest allies which cannot be bridged over by any extinct or living species." That was perfectly accurate at the time. Then he went on to write, "no one should lay so much stress on this." In other words don't get your knickers in a twist about it. [13:56] For those regions which are the most likely to afford remains connecting man with some extinct ape-like creature have not as yet been searched by geologists. So just be thankful that they are being searched by the excellent faculty and Institute of Illinois University. Darwin Distinguished Lecture Series page 5 - ASU School of Life Sciences Grass Roots Studio

6 [14:13] And you should realize that the rich fossil record of one of the early hominids I'm going to talk about, Australopithecus afarensis, is largely due to the enterprise of the people from this university. [14:22] So in 1859, this is a strange diagram but there is a reason. Modern humans are up here and red means anatomically modern humans. So in 1859 if you read the literature the only thing that you would have known about was one of two fossils of modern humans. The first one to be written about was the red lady of Paviland which was discovered in 1827 in Wales. [14:46] But actually in 1859, we already had some fossil evidence of Neanderthals, although the evidence wasn't recognized as such and it wasn't published. So, I'm just going to add the Neanderthals here and I'm going to add another sort of category here that I'm going to call "pre-modern Homo". [15:04] These are the remains of the Neanderthals that we all know and love that were found in the Neander Valley in 1856, but in 1829 a child's cranium had been recovered from a cave in Belgium. [15:17] And then in 1848 an adult cranium had been recovered from a cave in Gibraltar. But although this was when it was recovered, the significance wasn't recognized until much later in 1860s and it was recognized by a man called Charles Bart. [15:33] I want to digress about Charles to convince you that Darwin wasn't the only professional person; well actually Darwin wasn't a professional person. He wasn't actually paid, he was independently wealthy and so he worked on his own. But Charles Bart was an interesting guy. [15:49] He was a surgeon and he was a surgeon in London in the naval hospital and when he retired from surgery in 1852 and then became interested in microscopy and he was the president of the Royal Microscopical Society. [16:05] In the late 1850s he was the president of the Royal College of Surgeons. And he went on to be the Treasurer of the Linnean Society and the president of the Geological Society. So here is a guy who you can justly call a polymath. The point I want to make is that this was the sort of person that Darwin was mixed up in. [16:27] Darwin was a fellow at the Geological Society. He would have known Bart and would have gone to meetings with him. So even though this is found is 1848 it wasn't recognized as such. Now what I've done here is that I've added the information that we now know about how old these things are. [16:42] And we didn't know that in 1859, so you can see modern humans we now know go back more than a couple of hundred thousands years ago. Neanderthals rather more than that. There's a bit of argument about the oldest Neanderthal but it's probably about three or four hundred thousand years ago. [17:01] So that was a situation in years later in 1909 we now know more: we know more from Europe, but more importantly by 1909 Eugene de Bois, a doctor from the low countries had gone out to and he had discovered the remains that we now call Homo erectis. [17:21] So the significance in the 50 years between 1859 and 1909 is that the evidence of human evolution had now extended out of the Europe. You then go another 50 years. You go to 1959, Darwin Distinguished Lecture Series page 6 - ASU School of Life Sciences Grass Roots Studio

7 this is a little bit before I went to university. We knew more about Neanderthal, not much more about Homo afarensis. Not much more about the origin of modern humans. [17:46] We knew rather more about the origin of Homo erectis because by this time the research, more research in Indonesia by Ralph von Koenigswald and the research in China had shown us much more about Homo erectis. [17:59] But more importantly we now move into African evidence. So in 1959 we knew about Australopithecus africanus thanks to the discoveries of Raymond Dart. We knew about Paranthropus robustus thanks to the work of Robert Brume and we just known about what was originally called the Jensanthropus boisei and I like to call it Paranthropus bosei. That had just been published. [18:28] So in 1959 we now have four of these rather broad categories of our ancestors and the evidence now extends into Africa. Now there's been inflation. There is a lot more evidence. There is bosei. There is robustus. There is africanus. There are more of these light brown things. Here we also have Afroensis. Here is Australopithecus africansis and for example a taxon here that I don't have time to talk about. [18:56] There are these green ones that everybody who finds them is absolutely convinced they are the earliest hominids but they can't all the earliest hominids. What I call those are either possible or probable early hominins. The fossil record now goes back to beyond seven million years and when I was a medical student, if somebody walked into the room and said, "I think I've found an early hominin and it's seven million years old" and you would have said they are barking. [19:22] Nobody was looking in regions that were that old. So what is missing from the diagram? OK, this is an interactive class. Good Lord. [19:31] [laughter] [19:33] What is missing? Well, here's clue. Somebody said lines are missing from the diagram. Absolutely. Absolutely. There are no lines in the diagram. There are no lines suggesting that something is ancestral to something else. Why are there no lines in the diagram? [19:51] Well, because there are not, at least as far as I'm concerned, there aren't many places in the hominid fossil record where you can be reasonably sure that something is ancestral to something else. [20:03] I think you can be probably reasonably sure that Ethiopogus is ancestral to bosei. You can probably, thanks to the work that the faculty here, that you can be reasonably sure that anamensis is ancestral afarensis. Probably the gastrosensis which are erectis and most of the world doesn't recognize the gasti... I thought I turned my phone off. [20:26] OK. Well, luckily she's not my wife. [laughter] [20:34] And the maybe Ardipithicus kadabba is ancestral to romidus. I should never be allowed to have a phone as complicated as this. I can't even turn it off. I did think I had turned it off. Darwin Distinguished Lecture Series page 7 - ASU School of Life Sciences Grass Roots Studio

8 [20:45] So those aren't the only example where I think, I'd be prepared to bet just a few dollars that these things were ancestral to something else. The reason that there aren't any lines is that I'm not sure that you can put lines. [20:57] Now, some of my colleagues are absolutely sure that you can put lines but I'm not really sure that you can. Now, if you don't like all this complication, you can roll these up into a smaller number of more inclusive categories. You can put all the green ones into either Ardipithicus romidus. You can put all the untidy African, kind of archaic ones into afarensis. [21:19] You still recognize africanus. You put all the megadonts after the fits into the senior taxon which will be Paranthropus robustus. Probably if you're this lumpy you wouldn't even recognize Homo habilis. [21:32] There are people in the world who think that you should use Homo sapiens for everything back to and including Homo erectis. I think they are barking mad but nevertheless there are people in the world who think that. And there are reasonable reasons I guess for thinking that. [21:48] If you want to rationalize in this way you can also rationalize them in that way and then human evolution becomes a much simpler story. Essentially you just start from a reasonably ape-like creature here and you grind your way up here. [22:03] There's a little aberration here and then you just come up to modern humans. I frankly don't think that human evolution is that simple. Why do I not think it is that simple? Well, it's not that simple for any other large African mammal and why the hell should it be more simple for us than for any other large African mammal? [22:21] So even just from an empirical Basian point of view just seems to be not very sensible to think of human evolution in this way. [22:29] What I want to do now is just to take one of these early hominids and one that I'm really sorry that Charles Darwin wasn't alive to see, because I think he would have really been interested in this. This is one of the Mentadent archaic hominids. [22:44] The reason I'm doing this and beginning to sound like Philip Tobias is because Philip Tobias love anniversaries and things like this. I realize half way through this talk that I'm sort of doomed to repeat that. [22:55] I want to talk about this taxon. The reason I want to talk about this taxon is that although we now know that first evidence was found in 1955, that was a molar tooth, most people think that the first evidence was found and written about in That makes it exactly half a century ago. [23:16] What was discovered Oldevai Gorge was this most extraordinary cranium here. These are creatures that I just love. I mean, I really like them. I like working on them. Most people ignore them because it's almost certain that they weren't ancestral to modern humans. And a lot of people don't like working on things that weren't ancestral to modern humans. [23:37] That suits me just fine, because that means that there aren't that many people interested in it. This is the cranium which was found at Olduvai Gorge and small pieces have been reconstructed by Mary Leaky. Darwin Distinguished Lecture Series page 8 - ASU School of Life Sciences Grass Roots Studio

9 [23:49] This is a mandible that was made to fit with the cranium. And as you will see in a moment was a very prescient reconstruction. These are creatures, the initial evidence was found at Olduvai and then a site not far away. Then the evidence expanded up to include some sites in southern Ethiopia. More recently probably there is evidence of the same creatures down from the site in Malawi. [24:13] There's this huge continent in Africa, the only place where we have evidence of this creature is East African river valley. Now does that mean that the East African river valley was the only place things were living? I suspect not, but that's where we find the fossils and you can only know what you know. And I'm going to stop otherwise I'm going to sound like Donald Rumsfeld. [24:32] [laughter] [24:33] So theses are very interesting creatures. Here is the palette. They had very, very small anterior teeth, very, very large molars and what we molarized pre-molars. What these creatures are doing is clearly trying to make the largest food processing area that they possibly can. [24:52] Here is the palate which is compared to a human palate. But if you just look at your little finger nail, as long as you haven't chewed it, your little finger nail is about the size of one of your mandibular molar teeth. That's just one of those things, the body is made that way. [25:07] The size of the molars of the creature up there are about the size of your thumbnail. So if you put your fingernail next to your thumbnail you will see just how megadent these creatures are and they probably weren't as large as that, even though they had these large jaws and large teeth, they probably weren't as large as modern humans. [25:26] Here is the mandible that is discovered and it's actually a very good plaster one that they made in 1951 was a very good guess. You can see here that the enamel of the teeth is virtually worn away. One of the things that is distinctive about these large molars and pre-molars is that they have thick enamel. But yet they were clearly eating something that was abrading that enamel because there is an example of how much enamel has been worn away. [25:56] This is a bit of a puzzle because the micro-wear which has been observed on these creatures actually doesn't look as if it was all that abrasive but frankly something must have been removing that enamel. So there must have been an abrasive diet. [26:11] We've also been working recently to try and work out whether there was another reason why you might thick enamel on large molars and this is work that was done largely by Peter Lupus and Brian Long. What they and to a smaller extent, me worked out was there is a biomechanical benefit from having thick enamel but only if you chew on large hard objects. [26:34] If you chew on small hard objects the enamel thickness actually is no benefit. But if you load your teeth by chewing on large, hard objects, then there is a benefit to having a thick enamel. So it may be that the thick enamel was enabling them to cope but not actually successfully with an abrasive diet. [26:51] It would also have allowed them to chew on large hard objects. The main things that they might have chewed on, one sort or another of a nut. These nuts are actually rather like the teeth. Darwin Distinguished Lecture Series page 9 - ASU School of Life Sciences Grass Roots Studio

10 The nuts have a hard outer coating and a soft inner coating and the teeth have a hard outer coating and a softer inner coating. [27:10] The battle is the break the nut before the tooth. As far as material science is concerned it's an interesting problem. The other thing about these creatures were that there were large ones that had these crests down the middle of the cranium and smaller ones that didn't. [27:24] When they were found initially this small one was thought to have been a different species than these, but I think we've now shown to a reasonable amount of satisfaction that this amount of morphological differentiation is probably compatible with quite a high level of sexual dimorphism. Nonetheless in the same species. [27:42] The similar level of sexual dimorphism probably a larger one has been very elegantly demonstrated in Australopithecus afarensis. One of the interesting things is that as the sample size has increased, which is along this axis, the parameters...here there are no parameters, you just have a single value, but here there are means values. [28:01] You see that eventually the mean values after shifting around a bit they actually establish a reasonable level that after a sample of about a dozen. This is another variable. The mean shifts around a bit and then after about there is a sample of just over a dozen. You see the mean after that. That doesn't really change very much. [28:20]So for those people who say, your sample isn't large enough. You can't really tell anything about these creatures, I think you can. Certainly empirically from these data you can say that once you have about a dozen, then even if you have 24 or 36, it doesn't actually change the parameters of the sample. This is very crude. [28:37] It will provide a lot else, the larger sample will tell you a lot more about variations in your metrical characters and so on that it probably won't help you in terms of very crude parameters about the creature. [28:50] So what is the relationship between these three metadont archaic hominids? There are a couple of hypotheses on the block. One is that their distinctive morphology and the morphology I'm going to be focusing on is actually nothing to do with the teeth but the morphology of the base of the cranium. [29:07] One of the things that these two share which they don't share with that, is that the underside of the cranium in those two taxons are not very different than the underside of the cranium in us. In other words the foramen magnum is quite near the middle of the cranium. The petrous bone instead of being oriented more towards front to back is orientated more towards the side. [29:28] So the axis of the petrous bone is gone from sort of a front to back axis more to a side to side axis. And that has happened in that creature and that creature but not in that creature. [29:41] So the question is was that morphology in those two creatures inherited from a shared common ancestor which is what, that is the case in that hypothesis. In which case this Paranthropus robustus would not be closely related to us Australopithecus africanus or is the situation this slide where the shared morphology was not inherited from a common ancestor. Darwin Distinguished Lecture Series page 10 - ASU School of Life Sciences Grass Roots Studio

11 [30:06] It actually appeared separately. It appeared separately in robustus and separately in boisei. Now this is a different hypothesis from that. This hypothesis is what we call Paranthropus monophyly, in other words these are all the same plane whereas this hypothesis is not Paranthropus monophyly. The distinctive morphology of the base would have had to involve more than once. [30:31] The more sort of complicated hypothesis. We ask ourselves, well is there any other way that you could choose between these two hypothesis? In other words if you could demonstrate that moving the foramen magnum and re-orientating the petrous temporal bones is such a difficult thing to do developmentally that it would be extremely unlikely that this would have occurred more than once in human evolution. [30:56] Then that would suggest that this hypothesis would be more likely than this one. So that question is really: how likely are evolutionary changes in apparently complex highly integrated systems? And what is the likelihood that similar changes in a morphological complex such as the cranial base could have occurred more than once in the hominin clay? [31:17] Here is the underside of the modern human cranium. Here is the underside of a gorilla or a chimpanzee cranium. Here is the underside of a mouse cranium. Here's the foramen magnum, way at the back of this wild mouse. Here's the foramen magnum in the chimp, further back. Here's the foramen magnum in us. It's further forward. [31:37] Now, it just happens that there is a knock out mouse. Here is the cranial base of the neonatal mouse. There is the foramen magnum at the back. This is the wild type. Here's the nose end and that is the back end. Here is this knock out mouse. The foramen magnum, instead of being right at the back and facing backwards has migrated forwards and faces more downward. [31:59] This discovery was entirely accidental. These mice are used by people who are interested in striated muscle tumors. They use them as a model of the striated muscle tumors in human children. But it just happens that not only do they have a high incidence of striated muscle tumors but they also have this reorganized cranial base. [32:19] It doesn't interfere with the mice very much. They seem to do fine. So the point about this is that you can have quite large reorganizations with a relatively simple genetic basis. I'm not claiming that the genes involved in this mouse are the genes involved in the difference between chimpanzees and modern humans, but I am claiming that it's not such a big deal as one would think it might be. [32:44] So instead of saying it must be a homology, the change in the cranial base could be a homoplasia. I'm not saying it is but I'm saying that at least it's possible. [32:54] So the other way of trying to work out whether there is clade of these megadents archaic hominins is to say, is the homology really a homology? One can investigate this by using imaging methods to extract more evidence from the existing fossil record. [33:11] This is work done by Matt Spinner. This is the outside of a tooth crown. Here is the enamel. It's been micro-ct and you have asked a computer to work out where the boundary of the enamel and the dentine is and you have just remove the enamel. Darwin Distinguished Lecture Series page 11 - ASU School of Life Sciences Grass Roots Studio

12 [33:28] This is a bit like a fruitcake with a thick layer of icing. You just remove the layer of icing and you're looking at the fruitcake which is underneath. And here is the surface of the dentine which would normally not be available unless you have an expensive machine which is able to take micro-cts. [33:44] Now the advantage of this is two-fold. One is we wanted to see whether morphology that looked the same on the outer surfaces of the enamel actually also looked the same on the surface of the dentine. [33:57] The other thing is that it allows you to increase the same size. Because here is a worn tooth with somebody who is interested in dental morphology would look at and say most of the dental morphology is gone. But actually if you micro-ct it, you still can see the morphology of the surface of the dentine. [34:17] By extracting more evidence from the existing fossil record by using imagine techniques you can do two things. One is you can increase the sample size. The fossils for which you can look at this sort of morphology. The other is you can see whether what looks the same on the surface of the enamel actually looks the same at the surface of the dentine. [34:37] When you do that here, this is something which is called the midtridonial crest, which is of interest to at least two people in the audience. This will be scored as having a midtridonial crest. That will be scored as having a midtridonial crest. But actually when you look at the dentine you realize that what underlies that crest is not the same morphology that underlies that crest. [35:02] You might be tempted to score these the same. They both have a midtridonial crest, but actually when you look at the morphology of the surface of the dentine you virtually strip the enamel off you can see that it's not the same. [35:15] We've looked at the protostylid and discovered that what's a protostylid in the southern African hominins is not the same as what's scored as a protostylid in the east African hominins. We're also looking at these other non-metrical traits. [35:28] Lastly, I want to show what you can do if you use new and improved analytical methods. An example I want to give you is 3D morphometrics. This is a method of capturing morphology which is much more sophisticated than the way I captured it for my Ph.D. I just measured the length and the breadth of things. [35:47] This is a method of capturing morphology which means that if this is the surface of the dentine, you can find the location of the tips of the cusps in three dimensions. You can find the location of each of these little markers here in three dimensions. So you can do this around the base of the crown and you can do it around the ridge on which the cusps are. [36:08] So you can imagine, are you going to bet money on this method or me with my callipers measuring how long they are and how wide they are? They answer is that this method is probably going to get more information. [36:18] Here is a cluster of the ridge lines and here is a cluster of the base lines. Here is the mean ridge lines, sort of sample of chimpanzees. And here is the mean base line. By Jove, you can Darwin Distinguished Lecture Series page 12 - ASU School of Life Sciences Grass Roots Studio

13 actually sort out the M1s of Paranthropus veris from the M1s of Paranthrodites trogloditis. The M2 is from the M1s of veris and so on. [36:39] So you can get much more discrimination using this method of capturing a lot of morphology that I was able to do when I just measured these teeth and I just measured their length and their breadth. [36:52] So what I have tried to do is to show you that we now know where modern humans fit in the Tree of Life. As much as we know anything in biology it's reasonably clear that we are more closely related to chimpanzees and bonobos than we are to gorillas or orangutans. [37:07] Most of us are convinced that the hominin twig of the Tree of Life had several extinct branches. Some of my colleagues think it's really very simple. Some think it is really very complex. I'm sort of somewhere in the middle, leaning towards the slightly more complex end. There's no doubt that we need to keep supporting the people in IHO to go and find more fossil evidence because we cannot reconstruct phylogeny with what we have. [37:32] And the reconstruction of phylogeny that we're doing at the moment is entirely based on the neck upwards. We have absolutely no idea of the creatures that I showed you Paranthropus boisei. We know really nothing about what it looks like from the neck downward. So we need these people to go back and to find more fossils. [37:51] But we can still extract more evidence from the fossil evidence that we have. So we need more fossils and we need to be better at trying to squeeze as much evidence out of the fossils that are recovered. [38:05] I want to thank you for your patience and hand you over to Mark. [38:08] [applause] [38:13] Announcer: This lecture is part of the Arizona State University Darwin Distinguished Lecture Series. It is sponsored by the ASU Office of the President, the College of Liberal Arts and Sciences, The School of Life Sciences, the Center for Biology and Society and is a production of Grassroots Studio. Darwin Distinguished Lecture Series page 13 - ASU School of Life Sciences Grass Roots Studio