Robyn Williams: Have you ever thought of taking your body back to the shop and asking for a refund? Or have you, as someone close to me has just done, spent a fortune on trying to get a bit of broken body fixed – her spine in the case. Or have you in other words wondered whether our bodies were designed by a failed engineering student and maintained by the Dodgy Brothers? This is The Science Show on what went wrong.

The first part of this special Science Show is on bodies and the second is on the scientific basis of art with Professor Ellen Dissanayake from the US. But now let’s go straight to Boston and the American Association for the Advancement of Science where legendary journalist Tim Radford is waiting to look at your parts.

Tim Radford: Welcome to a press conference on I suppose the nature of being human. This is the world of fallen arches, bad backs, impacted wisdom teeth, but I hope not lost voices. And our speakers today, there are four of them, and I'll introduce each one as he or she speaks. And we'll begin with Jeremy DeSilva who is an anthropologist at Boston University, and he's going to talk about starting off on the wrong foot.

Jeremy DeSilva: Thank you Tim. So this is probably not the greatest news to you guys here, but this isn't news. We've known for a long time, since Darwin's time, that humans have evolved and that humans are not perfect, because evolution doesn't produce perfection, evolution works with the raw material that it has from previous existing creatures, modifies it, tinkers with it, what I would call produces the biological equivalence of duct tape and paper clips at times. And if that organism survives in its particular environment, passes on those genes the next generation, off we go. And fortunately our ancestors did survive many of these (what we're going to hear about) scars of human evolution.

What I work with is foot anatomy, and this here is not what you would design from scratch. In fact there are many prosthetics now, one of which is in the news for reasons other than feet. The South African sprinter Oscar Pistorius and many others have this single blade-like structure for running in particular. It's a single element. The human foot is made of 26 individual bones. It's not something you would, again, design from scratch if you need a rigid, stiff structure.

So why do we have 26 bones in our feet? Well, our ape relatives do, our ape ancestors did, primates do, and you can go back into the mammalian lineages. Many of the problems that we have today are a result of this. We have high instances of sprained ankles, of collapsed arches, plantar fasciitis, probably everyone in this room has had foot pain at some point and we can thank our evolutionary history to that.

It's not just because we wear shoes, it's not just because we walk on sidewalks or that we are a bunch of couch potatoes, because we know from the fossil record, and this fossil record is improving by the year, it's amazing how many fossils are being discovered, but the fossil record is indicating to us that many of these foot problems that we have today go back into the past. There probably are some new ones; bunions for instance probably is highly related to shoe wearing. But we have evidence of ankle sprains, osteoarthritis, fractured ankles and so on and so forth, back to the origins of upright walking. So this is something that has been with us for a while.

And I guess I'll wrap up by saying that what I think is important about this is that evolution sometimes can be perceived as this dusty old science that's behind glass and you just look at skulls and bones, but it impacts us, it impacts us today and I think it's really important to recognise our evolutionary history in the context of understanding why we are the way we are today.

Tim: Thank you very much. Our next speaker is Karen Rosenberg. Karen Rosenberg is an anthropologist at the University of Delaware in Newark, and she is going to tell us about labouring humans.

Karen Rosenberg: Yes. So if you are looking for an example of something that was not an intelligent design, you don't have to look farther than to think about the crazy, tricky, complicated, uncomfortable way we have babies. So we know from a lot of evidence in the fossil record that some aspects of our biology that make childbirth such a tricky and difficult process go way, way back in our evolutionary history, possibly back to the beginnings of bipedalism. So the way that we are able to mitigate the dangers and risks that are associated with childbirth is because we are cultural animals, because we have someone there to help us when we are in labour, when we are giving birth to our babies, and that person is able to mitigate a lot of the risks that humans encounter.

I certainly don't want to seem like an apologist for the medical profession here in stressing the dangers and risks of childbirth. Caesarean sections in some countries are up to 50% of births, and I don't think that 50% of women would have died in childbirth had they not had Caesarean sections. But I do think that childbirth is a time when natural selection is acting in a very strong way on human biology and on human development. And again, the way that we are able to mitigate those risks is through midwives, obstetricians, attendants of any sort in the childbirth process, and I think that goes back quite far in our evolutionary history.

Tim: Thank you very much. Our next speaker is Bruce Latimer who is also an anthropologist and an anatomist at Case Western Reserve in Cleveland, Ohio.

Bruce Latimer: Thanks very much. I'm talking about the back. If you want a place that's really a problem, it's the back. In fact there was a recent survey that showed that maladies that people suffer worldwide, lower back pain was number six. That was the first of the musculoskeletal issues. That's serious. Meaning that everybody in this room, and I know some of you…I'm not going to ask for hands…but some of you already have had back problems.

Now, let's ask this question; why do we have this problem? Well, I'll show you. I'm going to borrow Jeremy's tibia here. We come from an animal whose back was horizontal, was parallel with the ground, and we did this…now you're asking for trouble! Imagine this, if I gave you 24 cups and saucers and each cup would be a vertebra, each saucer would be an intervertebral disc, and I ask you to stack them. If you were really careful and you had a ladder, you could stack them. And then I would give you a book, like a dictionary, and I'd say this is the head, put that on the top. Well, if you're really careful you could probably do it, otherwise there would be a lot of porcelain on the ground.

Okay, but then I do this; I want you to take those pieces and I want you to make curves in them. I could give you all the duct tape in the world and you couldn't possibly do it. Well, that is what has happened to us. Natural selection has taken that spine and in order to balance over our hips and our feet we had to put curves in it. And the minute you put those curves in it and you start to load that spine, what happens? Well, I'll tell you what happens, you start fracturing vertebrae. And we do fracture vertebrae. Humans are the only mammals that spontaneously fracture vertebrae.

How about a herniated disc? Anyone here had a herniated disc? I'm sure you have. And if you live long enough you will have a herniated disc. How about things like spondylolisthesis? That's a terrible slippage problem that we get because we are the only animals that suffer from this. So it's a consequence of standing upright. In order to stand upright you had to balance over this peculiar spine, we had to put these weird curves in it, and then we go out and do things that stress it to pieces.

So the spine is truly a place that…remember, the design specs on your body…and this used to be so much easier for me to say…the design specs on your body are about 45 or 50. If you take care of it your spine will get you through that, but after that you are on your own.

Tim: Thank you very much. Alan Mann, an anthropologist at Princeton, will wrap it up and tell us about wisdom teeth.

Alan Mann: I'm so sorry, having heard all of my colleagues, you are, I am sure, expecting me to tell you the final drop in the bucket about how we are about to fall apart, and I'm not going to disappoint you. I think one of the ideas about what we are saying is that evolution doesn't produce perfection. We are functional creatures. That's what evolution is all about. And for my study of wisdom teeth or third molars, that's exactly what is going on. But in fact it gives you another perspective on evolution.

For our understanding of why we have impacted third molars or wisdom teeth, we should not look at evolution operating on the teeth themselves, although it does, but the initiating factor was our dramatic increase in brain size over the course of human evolution. Our brains expanded more than triple from our ancestors, and as a result the architecture of the braincase changed, the context in which the facial skeleton fit with the cranial skeleton changed, and in this the face is now underneath the braincase, the dental arcade had to accommodate itself to this change and it shortened.

And so the third molar or wisdom tooth, the last tooth that erupts…and of course the reason for its name is that, as you all know who have children approaching the end of adolescents, when they reach that point and their third molars appear, also appears wisdom, and I know you all agree with me on that one.

So, what has happened? Well, a lot of people have had impacted third molars. Third molars produce a lot of chronic pain. Some thousands of years ago there was a random mutation. We're not yet sure exactly what that mutation was, it probably had some aspect within the Homeobox or Hox gene system. However, what happened was it suppressed the calcification of the third molar or wisdom teeth. So, many of you and many of your children have grown to adulthood without the appearance of third molars.

That particular mutation has increased in frequency so that in some populations more than 40% of people have one or more absent third molars. So you might ask the question; how did that develop? Because obviously if you have an impacted third molar, if you follow survival of the fittest, as Darwin did, then you're not going to fall over holding your mouth and dying in agony. Reproduction of the fittest is what it's all about. In other words, differential reproduction. And my scenario I think is quite realistic.

How would this work? Well, one evening a person who has had serious chronic pain with impacted third molars, perhaps a lower third molar impacting into the mandibular canal causing a lot of pain, the partner comes up and says, 'How about a bout of reproduction dear?' And the person says, 'Not tonight dear, my jaws are killing me.' That is in fact an evolutionary scenario, and because that would produce fewer offspring in those people, the frequency of this feature would increase over time. And so what we are dealing with is a scar of human evolution, perhaps not for us but for those people in the developing world whose impacted third molars can't be removed by dentists, it's still there.

Robyn Williams: Alan Mann from Princeton at the American Association of Science press conference in Boston. And so to questions chaired by Tim Radford.

Question: Seth Borenstein, AP. Alan, do you have statistics showing the change in rates of third molars over time?

Alan Mann: The population with the highest frequency of missing third molars are the Inuit of the Arctic of North America, they can go as high as 45%. The evidence in the past is very difficult because the data is not very clear, but we do have many skeletal populations where an appreciable percentage of the people seemingly do not have the appearance of third molars.

As far back as the Middle Pleistocene there are several mandibles from the East Asian fossil record which show an absence of third molars. So it has a pre-history. I would suspect that whatever Hox gene or Homeobox gene is responsible for this, it perhaps has appeared several times. We know that Hox genes, just single changes can produce a total lack or an almost total lack of the dentition associated with dramatic problems in the facial and cranial skeleton. It is also associated with the onset of early cancers.

I don't think the particular genetic change I'm talking about would have those kinds of serious implications, but something in that realm which we haven't isolated yet is probably responsible.

Question: And the society that has most third molars?

Alan Mann: Neanderthals, as far as we know, there is not a single instance of third molar agenesis.

Question: Dan Keller, freelance. If there is a gene or a SNP controlling a third molar development, does this imply that there are separate genes for all sorts of teeth, or is this unique, that only the third molar and the other ones are controlled by some overriding thing, or do all teeth have their own genes?

Alan Mann: There has been a lot of research on modality in the onset of dental calcification. And it seems as though there are fields separating the anterior from the posterior dentition. And when you look at some of the familial patterns where you have these SNPs that produce, for example, the loss of all anterior teeth or the loss of all posterior teeth. This seems to be working along that pattern. But again, if we can isolate the particular factor that is responsible for interrupting the calcification, whether it's part of the stream or it's some factor that we are not aware of at the moment, we don't know. So there is modality between the anterior and posterior dentition.

Question: Dave Tenenbaum from Why Files. Bruce Latimer, you made the wonderful stack of cups and saucers, but what if you tried to stack the cups and saucers horizontally to make our ancestor's spine? That wouldn't work too well either. Why was a spine so great for horizontal usage and so terrible for vertical usage?

Bruce Latimer: What you've done is to take a single curve and you've structured it so that you've got…it's supported in the front and supported in the back, and you have a curve and your gravity vector is perpendicular to your spine. So it's well adapted to controlling those forces. When you turn it upright, our problem is it was to balance over our hips and we had to create all of those curves. And that means suddenly you don't have a single curve any longer, you have these reversing curves, kind of a sigmoid curve to the spine, and that's where the problem arises, is that we are trying to control those forces within that spine and it's a very difficult thing to do.

And more than that even, it's not enough that we have done that but as you walk you throw your upper body 180 degrees out of sync with your lower body. We all know this. You throw your right arm forward, at the same time your left leg goes forward. So you are constantly twisting and torquing your spine. And ultimately what happens after the millions of cycles, you will go through the annulus fibrosus in the disc and that's when you herniate discs. So by bipedality doesn't just impose vertical forces on it that it wasn't really adapted for originally, but we also have a new function, that's the twisting and torquing function that other animals don't do.

Tim: Thank you very much. Robyn, and then one at the back.

Robyn Williams: Robyn Williams from ABC in Sydney. When I was a Neanderthal I don't remember having a bad back, and when I left Africa 50,000, 60,000 years ago I seemed to be quite mobile. Is it only modern life that essentially gives us this pain, or was there evidence of deterioration way back as well?

Bruce Latimer: You know, that's a great question, thank you. It's strange that when we do look at the fossil record we see problems in the back that go way back, as it were. For instance, the Lucy skeleton, it's 3.2 million years old from Ethiopian, a site called Hadar, and Lucy already has something called Scheuermann's kyphosis, we see it there. If you go to South Africa at a site called Sterkfontein, there's another spine of an Australopithecus, it also has Scheuermann's kyphosis.

So back problems, they are remote (I won't say it again!) and we can see, particularly this is an interesting one, that humans are the only mammals that suffer from scoliosis, that horrible lateral curvature in the spine. No other mammal suffers from that. Do you know that in the Homo erectus skeleton from West Turkana we see that. It's a 1.5 million-year-old skeleton, its number is WT15,000 for those of you who like that sort of thing, but we see the first recorded case of scoliosis. So back problems are probably some of the earliest problems that our ancestors suffered from.

Question: Steve Mirsky from Scientific American. There was a paper in the New England Journal back in the late '90s where they did MRIs of people who had never had back pain, and half of them had herniated discs. So is it not possible that a lot of the back pain that gets attributed to spinal issues are really other issues, muscular issues maybe?

Bruce Latimer: You know, it might well be. As I said, if you live long enough and you go through enough walking cycles, you have twisted that disc, an intervertebral disc, so many times that what happens is the annulus fibrosus, what holds in the jelly in the middle, the nucleus, that begins to delaminate, and you can see that histologically, in older people it's starting to delaminate, and then that allows that nucleus to worm its way through there. Now, that's a herniated disc.

You can herniate in other directions. If you herniate of course anteriorly you're probably fine, you go to the side, you're fine. But the problem is we normally herniate posteriorly, in the back, and that's where the nerve roots are. But you can have a serious herniated disc and not suffer from pain. If it's not pushing on that particular nerve track you may not even know you have it. But it's so common in humans that…just for fun, who here has herniated a disc? See? So you can have them and they can remain subclinical.

Question: I'm Ann Gibbons from Science magazine. I have a question, this is Scars of Human Evolution, and from what you've described we have a Miocene ape's body plan that has been retrofitted and redesigned, so they started first with an ape body plan for walking on all fours. Do apes have problems? Do they have back problems, do they have foot problems, do they have labour problems? Can you contrast in these different areas a little bit?

Jeremy DeSilva: I don't think there's good data on that. There is some evidence for fractures, healed fractures in the ape skeletal record, and apes certainly do have healed fractures from falling out of trees or things like that. There is one interesting fracture in the ankle, the distal fibula fracture that is exceptionally rare in apes. There was one study that looked at 200 ape skeletons and just found it once. There are 18 distal tibia in the human fossil record that show two instances of it already. So this is evidence of upright walking producing this real problem that the apes wouldn't have had to have dealt with.

But in terms of pathologies in ape skeletons, I think there is data that is lacking there, and would be a nice comparison at some point. But they also don't have even the anatomies that lead to some of the pathologies we have. For instance, you can't get collapsed arches if you don't have arches, and they don't have arches. So evolutionary innovation of ours to involve this arch can lead to problems which they wouldn't have even had to deal with.

Bruce Latimer: In terms of the back, if you contrast a chimpanzee or a gorilla spine to a human, you couldn't have, among mammals, a greater difference. And the major difference is this; the African apes have taken their spines and they have locked them into a poker spine. If you think about an ape's pelvis, imagine it if you will, it's a very tall iliac blade, and they have taken their lumbar spine, they've reduced the number of lumber elements down to three or four and they've put those big blades there and they've bridged it with ligaments. And it is an incredibly stiff spine. That's a climbing adaptation. In fact, you can't flex that spine.

Humans, on the other hand, because we walk upright we have to have a very, very mobile spine. And ours can twist and turn. As an example, we are the only mammal that can do a back bend. Think about it. If you don't believe me, go home and take your cat…no, don't, I'm going to get in trouble! It was a joke. So humans have an incredibly mobile spine, so it's the mobility that leads to the problems that we have.

Apes, it's funny, you do see problems but they are specific to the apes, one of which is they end up getting discal infections because they don't flex the spine and that way they have trouble pumping nutrient in and out of the disc and therefore they end up with discal infections. And you see that a lot, much more than humans. Humans, on the other hand, you see a lot more osteoarthritis and that sort of thing.

Karen Rosenberg: As far as childbirth is concerned, we don't know very much about birth in other primate species in the wild because we never see it, and the reason that we don't see it is that those animals, when the mother goes into labour they isolate themselves, they try to get away from potential predators, from conspecifics and from primatologists. So we don't have much opportunity to observe it, although obviously in the lab we do. For apes, the size of the baby is much smaller relative to the size of the mother. So even though apes have, for primates, relatively large brains, and even though they have broad shoulders, the overall body size is so small that they seem to give birth, from our perspective, quite easily.

Actually monkeys have a more difficult time because they have a tighter fit of the head in the birth canal because of the body size relationships between mothers and their infants. But it doesn't seem that childbirth is a time with nearly as much risk for any other primates as it is for humans.

Alan Mann: For the dentition, I'm afraid we are in a class all by ourselves, and for our problems with our third molars there are couple of primate species that are relatively short-faced, and that includes the gibbon, where we do know that there are instances of third molar agenesis. But for our close primate relatives, the African apes, I don't know of any instances of actual third molar agenesis. So this is limited to our lineage in this particular context.

Question: But is it bipedalism and larger body brain size?

Bruce Latimer: Well, certainly in the back it's walking upright. So we've had to modify and make quite dramatic differences and modifications. But we also do something else that other mammals don't do, and that is we carry things. We carry things in front of us. And we all know they tell you to bend your knees when you pick up something heavy, right? Well, why do they tell you that? They tell you that because if you bend your knees it means you have to pull whatever you are carrying closer to your spine and that reduces the lever about your spine.

The problem is one day you are going to be reaching in the trunk of your car to pick up some groceries and you're going to bend way over like this and pick that thing up…and imagine the lever you're creating. And that's when we end up with problems. So it's not enough that we had to make anatomical and structural differences, but our behaviour…we go through life carrying things.

Question: [name] freelance in Belgium and Australia. I have a question in two parts. The first one is if Lucy and her contemporaries already did have back problems, she must have said 'not tonight dear' an awful lot. So why did the back problems persist while our third molar is about to disappear? And it seems to me that if something works well we can thank evolution, and if it doesn't we can blame evolution, so what use is evolution as a way to talk about these things? In other words, the three of you, what kind of results are you presenting that really help us understand these things except to say that we change our posture, that causes some problems, end of story?

Tim: Thank you very much. Who wishes to be goaded?

Bruce Latimer: I'll take it. Number one, as Jeremy said, evolution tinkers with what it has. It can't create perfection. It only works with what is available. So your work, as he describes it, you use paperclips and duct tape to make these things work. So you can't invent a brand-new spine. If you could, it would be great, but you can't. So that's one of the problems.

Now, to get to this topic of why an evolutionary approach is important, I would say it's important because it gives you new insight into several of these conditions. Certainly in the postcranial skeleton in the neuromuscular area it tells you something about why we suffer from these things. Why do we have problems? Why is it chronic in humans? And I'll just say again that, remember, your body is designed to last you through your reproductive phase, which is probably 50. So natural selection will get you through that, unless you do silly things like play football and crash your heads into people and do those kind of things, well, then you're asking a little much of the system. But it will normally get you through your reproductive period. And after that, as I said, it's blind to natural selection, so it doesn't make that change.

Question: When it comes to, say, the coccyx, it's not so much a scar of human evolution as it is a vestigial element of it. Does it serve any purpose, and are there any problems associated with the human coccyx that might not be seen in our ape relatives?

Karen Rosenberg: Matt Cartmill?

Matt Cartmill: Yes, humans and apes don't really differ very much in their coccyx. All the hominoid primates have these vestigial tail vertebrae, and naturally there are usually fewer in some of the apes than there are in humans. But they still serve a function because the old tail muscles that used to be in charge of tucking the tail down between the legs, the sort of thing that happens when your dog is ashamed of himself, those muscles have become involved in doing some of the jobs that Karen was talking about of supporting the pelvic viscera from underneath in this new upright posture that we have to deal with. And when that doesn't work then we start getting things like prolapse and evagination of the pelvic viscera. So the coccyx and the tail muscles attached to it are still very functionally important, and they are at least as large in humans as they are in a chimpanzee, let's say.

Tim: Thank you very much.

Question: It's Steve Mirsky again from Scientific American. The info that we got says that the title for this session came from a 1951 Scientific American article, so I have a vested interest in finding out whether that article was…did the article influence you personally or was it influential in the field? How did you wind up citing that article?

Alan Mann: Wilton Krogman, who was the author of that 1951 article and a true pioneer in physical anthropology, a person who dedicated his scientific life to studying growth and development and was particularly interested in cleft palates, he was involved in looking at the kinds of things that came to be called the scars of human evolution. And Krogman was a particularly adept person at this. For example, another Scientific American article he wrote somewhat later was 'Sherlock Holmes as an Anthropologist'. And so he was involved in many ways in attempting to broaden the notions that anthropology had developed into the public sphere. And so the scars were a way for him to present the data in a well-publicised and well-known magazine to understand that, as we have all been talking about, evolution has been functional in ourselves yet we are suffering these problems and many of those problems are going to remain as part of our biology, although in the article Krogman felt that a lot of these would be solved in time either through biology or, as we are so adept at doing, through cultural intervention.

Karen Rosenberg: But I would just add that in some ways he kind of anticipated the much more recent field of evolutionary medicine, even though he didn't talk about it with the same vocabulary that people talk about it today, I think he was kind of anticipating it.

Question: Dan Keller, freelance. It seems the bone guys have problems because of gravity, but in terms of labour and delivery, are there better postures for promoting labour and promoting delivery, and what do other anthropoids do? It seems like this supine position is kind of unnatural.

Karen Rosenberg: Absolutely, and the position that doctors prefer us to have when we're in labour in the United States and a lot of other countries, lying on our back, is not very common around the world. If you look cross-culturally I think it's fewer than 20% of cultures have that as a typical posture. A much more common and more helpful posture is squatting and which actually opens up the outlet a little bit between the ischial tuberosities, makes a little more room, and that's something that is more typical of humans as a species. But in a medicalised world, doctors like to have women in a posture that is convenient to them, not necessarily one that is most advantageous for delivery.

Question: Hi, I'm Barbara Moran with Nova. And I had a couple of feet questions. One is why do humans have an arch, now that you mentioned it, and also can you give just one or two specific…how specific bones or feet structure relate to or cause certain problems?

Jeremy DeSilva: So, with the arch there are two hypotheses, one developed a lot by the guy to my right, that the arch is a shock absorber and it's got to take up a lot of the forces within the foot during walking to prevent those, to dampen those from coming up through the joints that can degenerate very easily in the absence of an arch. And some evidence for that was published recently showing that flat-footed individuals…this is part of the Framingham nurses study…flat-footed individuals have a much greater likelihood of having hip replacement later in life.

There is another hypothesis that is being developed relating to the arch being made of ligaments that have elastic properties to them, so there's a little bit of spring in them, and that these can be stretched and recoiled and put a kick in your step, particularly when you are running. And there's a lot of work being done by the running folks, like Dan Lieberman over at Harvard.

Robyn Williams: And Dan Lieberman was on The Science Show talking about running a few years back. That was Jeremy De Silver from Boston University and with him Karen Rosenberg from the University of Delaware, Bruce Latimer of Case Western and Alan Mann of Princeton and the press conference at the American Association for the Advancement of Science was chaired by Tim Radford. This is The Science Show on RN.