CARTA: The Upright Ape: Bipedalism and Human Origins - Running, Walking and Evolution

this ucsd-tv program is a presentation of university of california television for educational and non-commercial use only check out the new youtube original channel you see TV prime at youtube.com slash you see TV prime subscribe today to get new programs every week you for at least 50 years has been realized that uprightness or bipedality is really of all the characteristics that define humans and our immediate ancestors are hominins bipedality is really probably the most distinctive that is from the beginning and continuing into the present day it's standing and walking moving locomoting on to lower limbs which really sets us apart more than anything else really from the beginning from our closest relatives now of course the human family tree has expanded a lot in the last 50 years I think most people in the field would agree that bipedalism was a part of the normal locomotor repertoire from the beginning in fact by definition that almost has to be the case if you're a hominin bipedalism must be at least the part of your locomotor repertoire somewhere even down here there's evidence that some bipedality was practiced and I think we had also people in the field would agree and everybody else that by later Homo erectus and certainly Homo sapiens that we had exclusively bipedal behavior so those things are not really in question what is in question is what happened in between the two there's still lots of questions here that are up in the air so I hope you enjoy the talks I think there's really quite a variety here represented in terms of topics and in terms of approaches hopefully by the end of it we'll have if not a clearer view of how bipedality evolved at least a more complete or complex view our next speaker is Dan Lieberman from Harvard University and he'll be giving a talk entitled the evolution and relevance of human running it's important to remember that humans have several gates right we we've been talking a lot today about walking but also humans run and there's two ways of thinking about running there's an endurance running which is generally within anaerobic threshold so something can do repeatedly over long distances burning oxygen and then there's sort of a continuum but not completely up to sprinting which is basically running as fast as you can and that's of course anaerobic now most of what we've been talking about so far today has been walking and for very good reason walking is a very important gate and as we've been discussing that the evolution of walking was incredibly important early on in the in the evolution of hominids in fact it may be the defining feature what makes a hominid and sure there are debates about just Kahn what kind of walking these earlier earliest hominins did and to what extent these hominids engaged in walking and climbing but that's not in debate that walking was very important and there's a number of good reasons for that in terms of just bipedal posture it's important for feeding and as Chris ruff just mentioned we also know that humans when we walk actually spend about a quarter of the energy to move a kilo of our body mass a given meter than a chimpanzee walking either bipedal E or or Core quad repeatedly but when we became walkers we paid some prices right and the biggest price is that once we've got up on two legs we lost the ability to gallop so we became slow and we became unsteady so a typical chimpanzee can run actually twice as fast as the world's fastest human who st. Bolt and they're much more agile they're much less likely to fall over even while doing remarkable acrobatic maneuvers in trees so humans aren't so good at sprinting even so sprinting must have been very important in human evolution we saw in some earlier slides I couldn't find any pictures of australopiths being chased by by lions but this guy is certainly being chased by line you can imagine it's a big selected disadvantage and if any of you have been crazy enough to get drunk and run in the streets of Pamplona with those bulls you realize just how stupid it is to try to run even as fast as human being can run with an animal like that running behind you Bulls can run a lot faster than human beings and also they've got these nasty horns so you never catch me doing that but what we're really good at is endurance running right and by endurance running we generally have a kind of cutoff point but we consider it arbitrarily to be distances longer than five kilometers you're doing an under aerobic capacity and it's the kind of run you can do repeatedly day after day after day and today of course millions of people like to run marathons for almost a million people this year will run a marathon and they're not all crazy by the way they a lot of them actually love to do it over and over again and I think it reflects not just a desire to get fit and raise money for charity but also because we have some special human abilities and today I'd like to talk about how how how and why we have all those abilities and that it's not just about fast walking because running isn't very different from walking that there's evidence that running was selected for in human evolution that it played an important role in the evolution of the human body and also something we haven't really talked about too much today that's actually relevant to some important health issues that we face today as human beings so first I'd like to talk about how good we are at endurance running then I quickly like to talk about when and why it involved and finally briefly mentioned its relevance to human health so an important point to note is that even average human beings even Al Roker and these various celebrities and presidents are actually quite remarkable our abilities to run long distances and I want to give you a few examples of data criteria to judge just how good we are so a first criterion is distance how long can humans run long distances now if you look at social carnivores which are the major animals out there that tend to run long distances there's actually very few animals that like to do endurance running naturally so hyenas and hunting dogs and wolves typically run between about 10 and 15 kilometers a day if you look at the at the literature you can make horses and dogs run long distances there of course also remarkable quadrupeds and they're really long distances if you actually do horrible experiments people used to do this back in the 1930s they would put dogs on treadmills until the dogs died and you can make dogs run at a trot for about 100 kilometres horses can also go very long distances at a trot but actually they can go much shorter distances when they gallop and actually there's a lot of data which show that the maximum distance that most horses can run without certainty get injured is about 20 kilometers and that's actually in the range of what humans can do day-in day-out average daily sort of average runners people you know just to go out there just to keep fit will run between 5 and 15 kilometres a day of course there's lots of people who run 42 kilometres a million more than a million times a year and of course there are humans who are now really into ultra marathons as well so humans really in terms of distance match up there with some of the world's best running animals and of course we're not social carnivores at least from the carnivore and we're not ungulates we're primates and it's important to remember that primates actually hate to run chimpanzees will run about a hundred meters a day in fact they don't even like to walk that much typical chimpanzee will walk about two to three kilometres a day so we're we're really up there with the world's best cursors cursor is an animal that's selected for running and we're actually unusual we're remarkable compared to any other primate another important difference between humans and other animals of the context in which we run so most of the animals that are good at running long distances can't do it when it's really hot they tend to do it either at night at dawn or dusk or in the middle of the winter or in cold environments those are the kinds of conditions in which you generally find hyenas and hunting dogs running but humans are remarkably good at running in really hot conditions in fact there are people who actually pay their own money to go run marathons in Death Valley and the reason we can do that is that we we cool by sweating what you can you can dump about 581 kilocalories of heat per liter of sweat and actually about 80% of your sweat typically goes into into into evapotranspiration so humans are actually able to run in really hot conditions and keep and keep a thermo regulatory homeostasis and we're really remarkable in the context we're also pretty good in terms of speed so this is a graph of speed on the x-axis and meters per second and this is the human endurance range so people can run you know marathons basically up to about 6 meters a second and it's important to remember that if these are horses ponies and dogs this is a 65 kilo dog that again the endurance gait for these animals as a trot gallops are not endurance gates and so even average middle age professors like me can actually run easily above the trot gallop transition speed of a dog my body size I can actually run above the trot gap transition speed of a pony and I'm not that great a runner and there are lots of good runners I'm sure they're people in this room who can run above the trot gallop transition speed of a full-sized thoroughbred horse so humans are actually remarkable at law and read be able to run really long distances at speeds that make other animals gallop and I'll get back to why that's an important point later on Chris Roth also mentioned about costs that were very efficient in terms of walking we're actually not that bad in terms of running there's some old data from from from the backs 1970s where people said that humans were really costly running but actually that turned out to be based on one Italian guy and they started measuring some more Italian guys it turned out that we we actually fall right on the line so this is body mass against the cost of transport so joules per kilo per meter and as you can see as animals get bigger they get more efficient and humans are pretty much right along the vertebrate line we're up there with horses and and antelopes and running birds like that we're actually quite efficient at running and one of the cool things about human running is that once so walking is what's called a u-shaped cost of transport so as you walk you have an optimal speed which is more or less to turn by the length of your leg because you'll use your leg like a pendulum but as soon as you start running you use your leg like a spring it's called a mass spring gait and when we run we actually so good at using our legs of Springs that as we speed up the cost doesn't increase up until we start sprinting so actually there's almost a flat's very slightly u-shaped curve which means that if you run from here to LA at 3 meters a second or 4 meters or a second or 5 meters a second you actually spend the same amount of energy and the only other animal for which we know that's the case our Kangaroos so we're actually remarkable also in terms of our cost to transport and then finally this is what's something I take pride in is I'm getting older and older but we're really good at longevity this is the famous Johnny Kelly who ran the Boston Marathon for many years now he wanted when he was 26 year old he ran 214 but he actually stayed within 20% of his of his speed this is actually typical of most runners up until he was in his 50s his late 50s he was still running sub three-hour marathons and people can run marathons up until they're 100 years old this is a guy named I think his name is Mike Richards or something about Peter Richards from England who's now 100 years old and still running marathons and we're really good at running long distances late into life so I hope I've convinced you that we're really actually remarkable in our capabilities and every year they have these man versus horse races and they have them in Wales you know you can imagine a bunch of drunken Welshman and pint in a pub saying but you can't outrun a horse and so they started this race they've been having it every year and on most years the horses do win but on occasionally the humans actually do win especially in the in the warm years they also have these races in Arizona and by the way I should say that when the humans run against the horses the horses are required to have veterinary checkups every 20 kilometers not the humans they don't worry about the humans getting injured so we're I hope I've convinced you that we are remarkable at long distance running not only compared especially compared to other primates but also compared to some of the nature's best runners and so these capabilities then demand an explanation and so the questions they raise is why are we so good at this and also when did we become so good at this and unfortunately I only don't have enough time to talk about the when but the important point is that I think that we didn't evolve just only to walk in human evolution but running was added and the best guest that we have is that it occurred at some point and in some way over this very complex transition the other speakers have already talked about between Australopithecus and Homo and and and we as other speakers have emphasized and I totally agree this is a very complex transition it didn't happen like that there's a lot of variation one one can't really characterize yet really what happened over the course of this transition but we know that we went from smaller bodies to bigger bodies smaller brains to bigger brains smaller teeth to bigger teeth and there was also some shifts in locomotion how for example we lost some arboreal 'ti and crosses transition and the hypothesis that Dennis bramble and I have suggested is that when you look in the fossil record you start seeing lots of features in the skeleton of Homo erectus that look like their adaptations for running and again I don't have time to talk about that today but the way in which you assess these adaptations are looking looking for features that are relevant to the differences between walking and running so again as I said before in walking you use your leg like an inverted pendulum you basically plant your leg on the ground and then your body center of mass goes up and over that leg but in running you use your body like a spring you're set that's actually falls during the first half of stance and you're storing up lots of elastic energy as Springs and the tendons of your legs and the and and that helps push you up in the air so we can look for evidence for those mass-spring features another major difference between walking and running is that walking is much more stable than running and so runners are much more likely to fall over as you probably all know and so there's lots of interesting adaptations in the human body for stabilization so we start looking in the fossil record we see a lot more of these features in Homo erectus now does that mean that australopithecines couldn't run of course not I'm sure they could run does that mean that Homo erectus was as good as a modern human we don't know it's very hard to assess that but it looks like that there's some importance to that transition in terms of running and it kind of makes sense from an ecological perspective Bryan Richman referred to this as well but we know that over this time period there was major shifts in the environment of Africa we know that around 2.8 million years ago the ice sheets started forming right so that the the glacial era started and in Africa that was manifested by an increased drying out of the environment so we know that there was sort of basically more open habitats as this transition went on and of course that would have had major effects on the on the on the on the on how humans got their food right how they how they use the environment and so there seems to be sort of two coincident solutions to this kind of climate change so one group of critters which evolved around 2.6 million years ago are the robust australopithecines and these are creatures with really huge teeth and big chewing muscles and they look like they're adapted deep very mechanically demanding maybe fallback foods you know the less desirable foods and they probably walked around all day long chewing chewing chewing right but at the same time are more or less the same time we see the origins of the genus Homo and there's lots of features in the genus Homo which suggest that we switch to a more high-quality diet and a very different kind of die we have smaller teeth and etc and so that and and and and in fact it not just just shifts in diet but it's just an overall shift in behavior this is really the origins of hunting and gathering right we know that we have the beginning of stone tools and food processing which increases the amount of energy you can get per unit of food we know that there's a good chance as a more cooperation and food sharing we know that ranging patterns must have increased is lots of ways of trying to figure that but typical hunter-gatherers walk and will run between 9 and 15 kilometers a day it's a big shift from probably what happened earlier and we of course we have the incorporation of meat in the diet even have these early bones which have cut marks and they've been open and broken open for the marrow and we know that by 2 million years ago there are archaeological sites which have skeletons of animals that really look like those animals were hunted big large animals very complete skeletons so that raises the question that during the shift as humans start changing their diet including a corporative meat and changing their ranging patterns when they were getting meat how did they do it how did they hunt right what was the behavior necessary for humans to hunt now this is actually not so easy proposition if any of you go on Safari and you decide to get out of Jeep and you want to try to kill a wildebeest or a kudu you might actually have a challenging time and you'd probably want to use some weaponry but it turns out that most of the weapons the projectile technology that we think that humans would use actually weren't invented then the stone putting a stone point on the end of a spear was actually invented less than 300,000 years ago maybe 40,000 years ago I see selling right pretty there but it's it's certainly not 2 million years old right further out remember you can't just chase these critters your typical African ungulate can run about 20 meters a second can do so for about 4 minutes Hussain Bolt who's the fastest human alive can run ten point four meters a second and he can do that for about 10 seconds joins a little bit slower he can run for 20 seconds after 30 seconds he's all out there saying bolt will have no chance whatsoever capturing like a kudu or something like that so how do they do it well I gave you some of the clues earlier one is that humans are able to run again at speeds that make animals like the size of ponies have to trot that's very important and the other important point is that when animals gallop okay they can't pass so you cool I cool primarily by sweating we basically expert water all over our bodies we basically turn our bodies and the great big giant tongues right which we can lose a huge amount of of heat but when quadrupeds gallop a galloping gait is a kind of a tilting sort of seesaw motion and there's some elegant studies which show that as soon as it quadrupeds start to gallop their guts start to slosh like like giant piston engines into their diaphragm and so quadrupeds cannot pant and gallop at the same time if you don't believe me take your family dog for a run make the dog gallop but please don't do it for too long on a hot day you'll kill the dog so the combination of these two features the fact that we can run at speeds that make animals gallop and the fact that animals cannot stand well regulate properly when they're galloping gives us the possibility of doing something called persistence hunting and persistence hunting is occurs usually in the middle of the day when it's really hot and runners will pick an animal and usually they'll pick the biggest animal possible because just like humans bigger animals overheat faster for rules of scaling and what they'll do is they'll chase that animal they know to make the animal run at a gallop and the animal will will gallop away as body heat will go up and then I'll go hide in the bushes and try to cool down and the runner will then track it and then chase it again and so through a combination of walking and running tracking and chasing you can actually drive an animal here a kudu for example into a state of hyperthermia now it's important to note that the runner doesn't have to run the whole time right they're actually walking about 50% of the time but the ability to run at those speeds is very important very critical in this adaptation so here this guy can walk up to this kudu which is dying already and kill it without any real serious threat to his body so the important point about this kind of strategy for hunting is that it involves very little risk you don't have to get up close to the animal until the animal is already dying you don't need any serious technology right you don't need you don't need any major projectile technology of which course didn't exist for most of human evolution and it actually doesn't cost us very much a lot of people think that running is horribly costly behavior but actually if you were to walk 15 kilometers you spend about 650 calories if you want to run the same distance you basically just add the fries to the Big Mac which is about 650 calories and I believe that this kind of behavior help release a constraint on brain size that's after running that brain size gets bigger we don't see it very much anymore of course because people are now don't have to do this anymore because we've invented projectile technology if I have just a few more minutes I just want to mention why I think this is important for human health and that is because a lot of us today I mean look at you all right and I've been most of this day we've just been sitting all day long right this is a very abnormal behavior it used to be that if we were hunter-gatherers we'd have to walk or run about into 15 kilometers a day but now exercise is really something that only the wealthy can do it's something that that's become a privilege for those who have time and money and as we exercise less and change our diet more and more people are getting overweight so obesity levels have doubled in my lifetime and diabetes and cancer and other metabolic diseases have been increasing and so the point point is that we not only evolved at a very different diet but we also evolved to walk and run and as as evidence for just how important running is for our health there are many such studies but I just want to highlight one from Stanford's called the Stanford runner study they looked at more than 500 runners so just amateur runners members of runners clubs and then match them with 423 healthy controls so these were not overweight people they were not smokers they were not drinkers and they've been following them every year since 1984 and more than 20 years later the runners have a 20% lower chance of dying in a given year and there are death rates for most diseases are about half that of those of the sedentary controls but also they've been measuring disability and their disability scores are about 50% lower which translates into bodies that are about 14 years younger by those by that scale so the important point then is that not only walking but also running played a very important role in human evolution and and it's still important to us because it plays a major role in human health and I think the world would be a far better place if not only more of us walked a lot but also if lots of us ran a lot as well and hopefully more people will also start doing that barefoot but that's another lecture without that thank you very much our next talk is by Leslie Aiello she's of the venner grande foundation in Chicago and her talk is entitled bipedalism and the evolution of the genus Homo what I want to do is take you back to the mid 1960s and to this particular bone now this is a toe bone it's your big toe bone and what's very interesting about this is what you can tell about the fossils at about the capabilities of the fossils from very small bits of material now this is old of a hominid town and was found in 1961 by Louis and Mary Leakey at Olduvai and it comes from the upper part of bed one so it's slightly more recent 2 than 2 million years and what's interesting about this bone you can tell from this bone that whoever owned that bone had a bipedal form of locomotion that was very similar to our own now remember this is 1.9 1.8 million years ago and the the reason that you can tell this was pointed out by Michael day and John Napier two of the leading early formative comparative anatomist in the field of human bipedal locomotion and what they simply pointed out is that this toe bone had a little twist on it now I if you compare the lateral torsion on the tone bone and you have two human populations here you have chimpanzees and gorillas here you have old about hundred ten the homo bone right here within the human range of variation now what this tells you is that again whoever owned this bone was walking in a very similar fashion to ourselves we have the differences between the human and ape foot and we have the trend of the first transfer through the human foot where we hit on the heel roll over to the latter side of the foot roll under the ball of the foot and twist off with the big toe it's something very very different from what we see in the chimpanzees and again is a very important factor here you have the chimpanzee foot coming up with a mid tarsal break and then rolling over as the force rolls through the foot in the human foot the foot acts like a solid lever and this is because of the structure of course of the lateral side of the foot this old mohammed attends toe bone was published two years after Leakey tobias in napier and published Homo habilis and Homo habilis part part of the para type where was the Olduvai hominid foot and what was happening at that particular time our idea of human evolution was very very much different at the time that Mickey Tobias in Napier published como helpless we knew of the robust australopithecines from South Africa Australopithecus africanus from South Africa and Louis and Mary had just discovered paranthesis Boise hires in John's Obispo ACI the picture from the Illustrated London News when was first discovered they actually thought Xan jaqobis was on the straight-line to homo and of course this changed very rapidly as soon as the Homo habilis fossils were discovered but at this time if we move back to the late 1960s early 1970s our idea about what was going on in relation to human evolution and relation to the evolution of bipedal locomotion was very very different than what we have today no one's yet mentioned Rama cathetus when I was a student in the 1960s Rama Pythagoras was the first hominid dated about fourteen million years ago and even though there were no fossils in between it was a straight line from Rama Pythagoras all the way up to homo sapiens and what was interesting about it is they reconstructed this bipedal image of Rama Pittacus from that amount of fossils and I if you sort of follow the line of argument Rama pithy goes we're supposed to have a small canine tooth because it had a small canine tooth that couldn't protect itself so it would have had to view stone tools and if it used stone tools it would have had to walked upright to use those stone tools and so you know from that amount of fossils you get to that reconstruction but also note that the reconstruction has an opposable toe and that this comes from a work that goes way back into the 30s because before the 1960s there was very very little known about the post cranial skeleton of any of the fossil hominids and a lot of our ideas about the evolution of bipedalism came from comparative anatomy and the main theory was proposed by Dudley Morton in the mid 1930s and you went from a chimpanzee type very mobile foot to a groin but can weave into a fully modern human foot and what Louis Leakey was doing was desperately trying to position Homo habilis as the first member of our genus Homo you can see in this chart that even it's called Australopithecus habilis here and this came from a very well-known textbook at the time David pill beans ascent of man Louis Leakey was busily trying to convince us that these rather scrappy skull bones had a very large cranial capacity that the dentition was very much more human-like than you had in the australopithecines and Han bones had the manipulative ability that would be suitable for Tullius the older by hominid 8 foot was part of this and what he was stressing at that time was the very strong first metatarsal that would indicate that weight transfer as you were pushing off but also very robust lateral metatarsals and that you have the locking mechanism between the cuboid and your calcaneus here that would lock your foot into that lever that allowed you to push off in a very efficient locomotion now I if you do a analysis of some of the tarsal bones you find that the Olduvai hominid foot isn't fully modern and the reason for this is the morphology of the tailor's here and leading into the navicular on the medial side of the foot when Nate Napier and Davis were publishing this they actually commented on it but they emphasized this very human mobility of this foot because they were very interested in establishing Homo habilis as the earliest member of our genus and in later years Michael De who was my PhD advisor actually said that they probably overstressed the human conduct the human motion in this foot because of the fact that they were trying to establish this as homo now what I found quite interesting the fossils from the side of dominici Homo George Lucas or early Homo erectus dating about 1.7 to 1.8 million years the earliest hominids Out of Africa the foot bones that we have for the diminishing material aren't identical to modern human feet the this is worth it was recently published by Herman Panzer and the rest of the WEC team and here here you have the Dominici foot and again remember as you roll your weight around push off in your big toe that first met God metatarsals very robust in humans it has a very expanded head to at reflecting that force that you push off with chimpanzees have a very small head the sum of the australopithecines that we have for first mental tarsals for again relatively gray cell heads the Domini see fossils also have extremely grace' heads what really excited me about this paper was actually this diagram because here you have a modern foot and you have the line of force going along the first metatarsal the demin is a flood is reconstructed with the line of force going between the first metatarsal and the second metatarsal now there's a very interesting structural reason for this and this is the torsion in your tibia because in a modern Homo sapiens we have a lateral torsion in the tibia that automatically places our feet in and with an outward direction and what's fascinating about the Dominici material is the typical torsion is less so the foot doesn't point out as laterally as much as it does in humans and that this is more than likely responsible for the relative degree of Shaw gray cell first metatarsal in other words they're transmitting the force over the foot in a different fashion than we would now we don't understand why this is so but what it tells us is that something's going on here and even when you get into this early Homo erectus stage where you have assumingly a body form it's much more similar to ourselves than to the earlier australopithecines there's something very different going on in the mechanics of walking also we should notice here is the difference in the tailless earlier on today we were talking about variations in the form of the trakula and there is a very strong difference between Homo habilis and the diminishing material having a very much more modern shape of the tailless now we actually should have known this because Bernhard Wood who's sitting somewhere in the back in 1974 published a multivariate analysis showing that the older Vitalis is not similar to modern humans but it's actually much more similar to the only tailless we knew at that time that belonged to a robust australopithecine from South Africa now of course that things are very different now in terms of our ideas of human evolution in comparison to where they were 40 years ago some pointed out we now have 22 or 23 species depending how you count one of the interesting things also is the Rama Pittacus here is now no longer directly related to the hominid line ok what what I mentioned so far dominici early home erectus er 8 1 3 is a home ood type tailors coming from Kobe fora you have all the Y hominid 8 the Homo habilis and you have the robust australopithecine and depending how you classify them you lump all of these into Homo or as some of suggested the Olduvai hominid tailless is australia's robustus or a robust australopithecine it's been misclassified these all come in this very interesting time period of around one point eight to two million years ago now we have Australopithecus sediba with sediba you have this very interesting foot where again the tailless is quite human-like we've heard about the pelvis that's extremely human-like but also about the heel bone the calcaneus that's almost a clot and it's anatomy and you have a very mobile subtalar joint now something's different is going on here and what the question is is how many different forms of bipedalism do you have leading up to this period at two million years ago and also we in terms of evolution is sediba actually an ancestor of the home of mine or are they two parallel three parallel lines in terms of how many alternatives to ourselves do we have existing in this particular time period in terms of a fairly modern morphology of the foot we can take it back to about 2.3 million years with more material coming from the omo which is just north of kobe fora you have very modern tailless and very importantly you have a very modern calcaneus but if you move back from this things become very very sparse we referred about Australopithecus afarensis and having a number of different foot bones and the attempts of people to reconstruct this into a composite foot the only other recently complete foot we have is the little foot specimen number two at Stefan pan and I put a very long time spend in here because you've had dates anywhere from four million all the way up to about 2.2 million years for the little foot specimen we really don't have any idea where it goes but it's probably somewhere in this three two perhaps a little bit more recent time period what I was able to do with one of my PhD students will Harcourt Smith a few years ago is actually analyzed the little foot material and we use 3d morphometrics on it and what we're able to compare some of the tarsal bones with little foot to the head are composite material and to Olduvai home in a tent and when you look at the analysis the better analysis of these bones it's not too exciting they're all right there in the middle between the African Apes humans here are the orangutan but if you do a exact randomization or comparative analysis some very interesting results popped out of this the yellow histogram here is comparing every the intercept specific comparison so comparing every modern human to every modern human every chimpanzee at every mud every other chimpanzee it gives you what the inner specific range of variation is the blue is when you compare different species and the Olduvai foot is very similar to little foot so little food was fantastic fontaine its eye in deposit slightly older than Australopithecus africanus found its neck fond head if you compare all the biome and a date to the afarensis material or if you compare a little foot to the afarensis material they're so different from each other they couldn't have come based on the range of variation we know in living species from the same species and by inference the same local motor pattern so at least between these three feet that we have you know some degree of associated material with we seem to have at least two different patterns and possibly three different patterns now another very interesting thing with this is when little fit was first published it was published with the opposable toe which actually is a very similar almost identical diagram to Dudley Morton's middle evolutionary stage in the hypothetical evolution of the foot when we went and looked at the middle canario form the little furred St w57 one actually had no indication of a possibility in it but the Hat our specimen the Australopithecus afarensis did seem to have an indication of any of the this material that it did have a slider degree of oppose ability then you would find in the other foot specimens so if we call it come back to summarize this what we seem to have is the little foot specimen coming from somewhere in this region having a quite close correspondence with the older by foot the tailless has strong degrees of similarity the navicular and into the mid middle Canaria form the odd one out is the africanus composite foot so the question is is you know do we actually have two and possibly three different patterns of bipedalism coming up through this time period where we have so many species of hominids where we don't have associated skull adult material and where we actually don't know what the relationships between one and another are the other foot that we have of course is Ardipithecus and this is much older coming from about 4.4 million years ago and earlier today it's been pointed out that it has this very remarkable grasping foot when an arti Pittacus was published it was argued that this completely changed our interpretation of the evolution of the human line that no longer did we have a chimp like ancestor but chimps were specialized as well as the other African Apes and what the core Basel type of hominid would be would be Ardipithecus with this very strange Anatomy that's very big very robust grasping toe and of course this would overturn the old Dudley Morton idea of chimp like two more grow Lloyd to a more human type of foot now before you get too excited about this remember what happened to Grandma Pittacus that it was sort of exiled from being a hominid ancestor look at the evolutionary tree here this is the group of Howard fossils we've been talking about Australopithecus early homo this corresponds to this part of the evolutionary tree the older specimens here are over here and look at the range of other myosin apes and other fossils we have I mean it's a very crowded geography here here we have our deepest thickest do you know what or your Pethick is been bollocks the cow fought far this is in terms of the evolutionary distance from the hominids or your pet the goose was one of the most complete skeletons when I was a student in the 1960s it's a beautiful specimen and this is the reconstruction that was done of Oreo Pythias notice the bipedality notice the similarity with Ardipithecus in fact they could actually be sisters in terms of the weight way they're drawn here and what's very interesting about this is the the Oreo pathetic foot is extremely similar to the bar deepa thickest foot what what's going on if Ardipithecus is changing our idea about the evolution of locomotion was Oreo Pittacus a parallel evolutionary development we actually don't know and the this I think is one of the most important comparisons that has to be made in terms of informing our idea about the evolution of bipedalism is what is Oreo Pethick is doing there that seems to be so similar to this new and exciting specimen that's being called one of the representatives of the human law so in summary then there's a number of extremely important questions butts this difference between Rd and Oreo pivot us what's Australopithecus sediba telling us about the number and variety of bipedalism we have going on at this time and one of the things that I'm extremely interested in there just it disappeared was what's happening in post homo erectus and when did we actually get a post cranial skeleton bipedal locomotion that we would recognize as identical to ourselves now one question that we haven't addressed at all in this conference is why did bipedalism evolve in the first place you know why are we standing on two legs because it is a huge change in our Anatomy so please come up forward with some questions at the end thank you very much our next speaker is dr. Matt Cartman from Boston University and he will be talking about body fat and bipedality okay so parent parents mind your children here's my true vien man again we've seen in before human beings are different from other animals in a lot of ways as you've heard and the job of scientists like today's speakers is to figure out how we got that way the explanatory stories that we paleoanthropology times tend to tell set around the distinctive human traits that we're proud of okay unique features that seem to be connected with the standing of our species at the top of the world's food chains and dominance hierarchies and one such trait that we all like to talk and think about which is what this meeting is devoted to today is bipedality the complex of adaptations to two-footed posture and locomotion that make us upright and upstanding and let us stand on our own two feet when all the other metaphors of self-esteem associated with walking around on our hind legs waving our hands in the air other features that we associate with human dignity and status are our nimble hands that we use to make all sorts of things and of course our big brains and all their correlates including the ability to talk and reason in ways that are far beyond the capacity of even the brightest non-human animals but there are some other human peculiarities that we don't like to talk about so much for example we have uniquely smelly armpits full of scent glands nobody knows why and we have really weird hair that grows down to our tail bones keeps falling into our eyes adult males like Nietzsche here develop these these big puffs of face fur that cover our mouths and keep getting sucked in when we eat both sexes have protruding bags of fatty connective tissue something like a camel's hump sticking out in back behind our hip joints an adult female supplement these with another pair underlying the milk glands on the chest and humans are about the only land dwelling mammal of our size with no covering of fur over most of our bodies as you see in this photo here even when we hide the body parts that we're proud of our hands our heads and our our legs we can we can instantly identify these animals as human can't we by their protruding buttocks and above all by their sleek hairless slightly fatty shiny skin now this peculiarity of humans has been remarked upon by anatomist for decades though it may not be quite as familiar to all of us as would John's animates here and other terrestrial animals that have been made hairless by evolution or by selective breeding or by disease like the chimpanzee with the mange up there its animals startle us with their wrinkled appearance they they lack the thick layer of subcutaneous fat that keeps human skin taut and shiny many of them tend to store most of their fat around their intestines and kidneys as abdominal fat like the yellow stuff that you see here tucked into the folds and crevices of the mesentery x' in the human abdomen okay here are some figures on skin fat versus goat versus gut fat in goats in these animals most of the fat is abdominal fat indicated by the yellow bars here on various degrees of in addition and obesity and goats the subcutaneous fat indicated by the letter Q is a small percentage of the whole but in humans the vast majority of the body fat is subcutaneous and easy and the yellow bars down at the bottom the abdominal stuff these are tiny ok there's a similar big difference between humans and many other animals so human bar being the percentage of of cutaneous fat on the left there and then they all these other animals guinea pigs and sheep and musk oxen and so on but now to figure out what if anything this difference means we have to take differences in body size and diet into account because the animals involved in this comparison here are mainly herbivores leaf-eating animals have to have big guts indicated in yellow here on the deer where the leaves that they eat consent and ferment because animals can't digest cellulose so deer is kind of like a four-legged compost heap okay it it can't digest the cellulose in its diet until it's broken down into into shorter carbohydrates by its gut bacteria but people are different we eat foods that are higher in energy and easier to digest and we pre digest a lot of our food by cooking and fermenting and so on before we put it in our mouths so people have smaller guts as Leslie Aiello has famously demonstrated and therefore less space for gut fat so you might expect us to have less abdominal fat than animals like deer and goats the more appropriate comparison for humans might be carnivores like cats and dogs and bears here are some data comparing the masses of skin fat the line above with gut fat down below in carnivores and humans it turns out that there's a no and there's an allometric factor here the bigger carnivore gets the more the larger the percentage of its total fat that goes into subcutaneous fat so when we compare the ratio of skin fat to gut fat in humans and other animals we have to correct for body size and when we do that you can see that humans the red arrow here have a lot more skin fat and less gut fat than we would expect for carnivores in our size range you'd expect a carnivore of our size to have about twice as much skin fat as gut fat the difference between the dotted and solid lines there humans have 12 to 13 times as much because this is a log logarithmic scale okay so it shouldn't come as too much of a surprise then when you take the fur off carnivores even human sized carnivores also look saggy and wrinkled they don't have the kind of sleek shiny skin that we see in our own species so why do we have so much skin fat it may have something to do with them a regulation okay which Dan Lieberman talked about earlier we humans cool ourselves by sweating instead of padding the way most mammals do maybe we got rid of our fur so that sweat can evaporate from our naked skin when we get overheated it can evaporate faster maybe then if so then if we need the naked skin for evaporation maybe we need the fat as a substitute for the fur on those occasions when we need to run the thermal regulation the other way and stay warm maybe so there's a lot to be said for that story it's in most of the textbooks but there's two problems with it than annoy me okay the the first is that there are some animals that cool themselves by sweating and also have insulating fur like the galloping zebras that Dan Lieberman showed you earlier like this course second when humans go on a diet and the first pounds that get lost come from the skin fat if we need our skin fat to stay warm you might think we'd hold on to it as long as possible and there's a chicken and egg problem here which is really what what I'm concerned with which came first the fat the baldness or the sweating it would be more convincing if we could figure out a reason not related to thermoregulation why one of these factors could have been put into place earlier and provided a substrate for the evolution of the other two so what I want to suggest to you today is that our peculiarly fatty skin may be a byproduct of that upright posture that we're so proud of ok the weight of the organs and fat in the abdomen is supported by two in two ways first by direct attachment above the red arrows to the inside of the body cavity below by the pressure exerted on the abdominal contents by the contraction of the abdominal muscles surrounding them underneath the skin now in an animal that walks around on all fours the resulting intra-abdominal pressure produced by the contraction of these supporting muscles is pretty evenly distributed from one end of the abdomen to the other but in an animal with an erect trunk that pressure is concentrated at the tail end of the abdomen down here for the same reason that the pressure in a carton of juice is concentrated at the bottom because the weight at the bottom that has to be borne is much larger than the weight that has to be borne at the top so the result is an increased risk in the case of viscera here of hernia and prolapse what are those terms mean a hernia prolapsed is when an organ that opens to the outside falls out through its own opening this animal shows a human pelvis sliced down the middle where this has happened to the uterus which is also dragged part of the bladder and the rectum out with it as it descended from the front and then back this so-called fallen womb isn't an uncommon occurrence about 11% of all women in this country will suffer some symptoms of uterine prolapse at some point in their lives herniation is different the hernia occurs when there's some structure running through the muscles surrounding the abdominal cavity and that structure going through it like the esophagus going through the diaphragm here produces a weak spot at which a part of the gut bursts through under repeated intra-abdominal pressure from straining of coughing or whatever in a hiatal hernia like this the stomach and part of the small intestine wound up getting pulled up as a loop of gut into the inside of the chest cavity the most familiar sort of hernia course is inguinal hernia in both sexes the gonads develop up near the kidneys three months their intrauterine and then descend into the pelvis and in females they stop there in the pelvis sensibly enough but in male mammals they keep going and they wind up in a skin bag the scrotum down between the hind legs one of one of the poster child cases for unintelligent design and animal bodies and the descent of the male gonads and all of the plumbing connections they drag behind them the ducts and the vessels in the nerves these produce a big weakness in the abdominal wall muscles that's a prime target for hernias in humans not so common in quadrupeds in fact quite rare and very common in humans the result is any little hernia like this one okay we're a loop of small intestine has been pulled through the same canal with the test is followed in its descent and wound up as a gut loop down in the scrotum in humans 75% of all hernias and whole species are this type in males it's 97% of all hernias and about 25% of all men are going to get one I'm sorry they're much rare and quadrupedal mammals for the obvious reason the concentration of pressure at the lower end of the upright human trunk as you can imagine having a loop of gut like that going through that canal and getting stuck down there can be life-threatening now in general as you might expect prolapse and hernia are more common in obese people makes sense when you fight when you pile fat into the abdominal cavity intra-abdominal pressure goes up the abdomen inflates with fat so it's easier for the uterus to get pushed out or for the stomach to herniate up into the chest cavity next to the esophagus but here's the crucial fact the more obese a man comes a man becomes the less chances of getting the inguinal hernia okay very marked reduction with increasing obesity how come I suggest that it's because when humans at least humans of reproductive age pile on excess fat they added disproportionately to the skin and skin fat pushes inward not outward on the body wall adding skin fat doesn't help directly with uterine prolapse because there's no skin fat pushing upward on the opening of the vagina it doesn't help with hiatal hernia because there's no fat pushing downward on the top of the diaphragm but skin fat resists inguinal hernia like this and because skin fat gets added it higher rates than abdominal fat in humans obese men are in effect providing themselves of the trust that reinforces the body wall so it makes sense that a uniquely erect mammal should have uniquely fat skin to reduce intra-abdominal pressure and transfer it to the outside of the abdomens weak points and this is also true and females women also suffer from inguinal hernia and like men they're insulated from it by obesity okay but they have to deal with another really major factor that increases intra-abdominal pressure namely pregnancy given this uniquely female stress on the abdomen we might expect that female humans would if anything have an even higher ratio of skin fat to gut fat then males have to free up abdominal space and keep the abdominal pressure as low as possible during this inflationary period of pregnancy and in fact this is what we find the human pattern is even more pronounced in women than in men women have a significantly greater preponderance of skin fat over gut fat both in percentages shown here and in absolute mass here the female bars comparisons are the two on the left so to sum up in most other mammals about half the body fat is visceral but humans the vast majority is subcutaneous the red bars and this makes functional sense as a response to the increased stress on the lower abdomen resulting from upright posture now if all is is correct then the peculiar features of the human skin must have begun evolving along with bipedality back in early Australopithecus and the distinctive appearance of the human body may predate the advent of an active open country lifestyle of the kind that Dan Lieberman talked about in animals like these the earliest members of the genus Homo an inherited layer of insulating subcutaneous fat may in fact have been one of the things that made that new lifestyle possible thanks you

Channel: University of California Television (UCTV)

Views: 97,225

Keywords: Dan Lieberman, Leslie C. Aiello, Matt Cartmill, bipedalism, evolution, hominid

Id: YTv5KhUtbx0

Length: 58min 44sec (3524 seconds)

Published: Thu Mar 15 2012