Webinar: From Foraging to Farming – How Our Skeletons Changed
Aired August 19, 2020
Briana Pobiner:
All right. Welcome, everyone. Welcome to the Smithsonian's HOT Topic: Human Origins Today program series. My name is Briana Pobiner. I'm a paleoanthropologist and educator at the Smithsonian's National Museum of Natural History. Welcome to the third so far in our online HOT Topic program series. For those of you who have registered today, we will be continuing this HOT Topic program series and you will get an email about our upcoming programs. This is a monthly series that's hosted with the Human Origins program at the Smithsonian's National Museum of Natural History.
One logistical note, this program is being closed captioned. You can navigate to the CC button if you want to turn the closed captions on or off. This will either be at the bottom of your screen or the top of your screen, probably next to the Q&A button. The second logistical note is that if you have questions for our speaker today, who I will introduce in a moment, please type those questions into the Q&A, during the program, which will be about a 30-minute presentation followed by question and answer. I will be answering any questions that I can in text form in the Q&A behind the scenes. Then for those questions that are still there at the end of Dr. Chirchir's presentation, I will come back on screen and I will be asking those questions to Dr. Chirchir and she will be answering verbally. Please, if you have any questions about the presentation, about the content, you can put those in the Q&A, which is those two speech bubbles.
Again, thank you everybody for attending our HOT Topic program, which is a monthly series that is organized by the Smithsonian's National Museum of Natural History. I'm very excited to introduce our speaker today. Dr. Habiba Chirchir is a biological anthropologist and an assistant professor at Marshall University in West Virginia. She's also a research associate with us in the Human Origins program at the National Museum of Natural History. Her research focuses on understanding the relationship between skeletal anatomy and behavior. Specifically, she studies the evolution of modern human skeletal anatomy and how we evolved anatomical features that distinguish us from our ancestors and our similarities in those features with other mammals with whom we share certain behavioral traits. She uses CT scanning technology and X-ray imaging to examine morphological traits of interest in the skeletons of humans and other primates, as well as the skeletons of felids, which are cats, and canids, which are dogs.
Habiba received her bachelor's degree from the University of Nairobi in Kenya, her master's degree from New York University and her Ph.D. from George Washington University. She then completed a post-doctoral fellowship with us in the Human Origins program at the National Museum of Natural History, prior to starting her current position at Marshall University. For me, it's a real special pleasure to welcome Habiba back to the museum today, so to speak, although none of us are actually at the museum. With that, Habiba will share her screen, she will start her presentation. I will turn my microphone in my video off. Thanks so much, Habiba, for being with us today.
Habiba Chirchir:
Thank you very much Briana for that introduction. I am sharing the screen right now. Let me know if it's appearing on your end.
Briana Pobiner:
Yep. You're all set. Thank you.
Habiba Chirchir:
All right. Well, thank you so much for the introduction. It's lovely to be back at the museum, so to speak, with you guys. It's been a while, but this is exciting. I'm very pleased to be here today to be sharing my work with everyone in attendance. Thank you all of you for joining in to listen to some of my work. Now, as Briana mentioned, and as you can see from the title of my presentation, I'm going to be talking about bones and how our skeletons have changed over time, especially in relation to our behaviors. In other words, if we are farming for instance, or if we are hunting and gathering, are our bones stronger or are they lighter? How have they changed as our subsistence strategies have changed? How are they different from those of our ancestors? How are they different from those of our closest living relatives?
To start off, I'll provide you with a little bit of what bones can tell us. They can tell us many things and I'm going to focus on what I'm particularly interested in, what my work focuses on. We can infer an individual's age from the skeleton by looking at the dentition, looking at how the long bones have fused in the ends. We can infer sex, especially if we have the pelvic bones. We can infer our estimate stature of an individual or a population by looking at measurements of the long bones. We can tell or identify pathologies. We can identify diets through isotopic analysis and so on.
Now, these last two points here that I have highlighted that we can infer physical activity by looking at the human skeleton. We can also of course look at the bones and see their evolutionary changes over a long time. Starting with a physical activity, what I mean is that we can look at how dense a bone is, the strength of that particular bone and tell whether one was traveling long distances. Someone walking every day for a long distance, making the thigh bone for example to be strong. An animal for example, was it climbing trees as a means of locomotion means of navigating its environment? Those are some of the things that we can infer in terms of activity. In terms of evolutionary change, we can look at for instance, how curved or how structured certain bones are to identify relationships between species or between populations. Throughout the talk today I'll be focusing on these two last points. What can bones tell us about physical activity and what can they tell us about evolutionary change.
Now, if you're wondering how we infer physical activity from bones in particular, I would like to just show you real quickly a nice illustration of how that change or how bones respond within a short time to activity. Prior to describing some of these images that I'm showing you down here, what we know by a whole century of research on bone morphology, or how bone changes, we know that bone increases in density as we exert it or if we put more stresses on, it increases in density. It also changes in its orientation in response to stress.
Now, I'd like to draw your attention to these images. What we are looking at is a section through the hip bone of a fetus, of a three-to-six-months-old, a six-to-12-months-old and a 24-to-36-months-old. The white material that you see inside these images is bone, these are boney struts. The black represents air spaces. These air spaces are where in living tissue in a living organism it would be having marrow.
Now, if we look at the fetus, you see a lot of white in there. There's no particular structure that we can identify. When we look at a three-to-six-month-old, there's more spacing. By 12 months you see more spacing and then you also see more bone in the lower portion and the upper part, if you can follow my cursor here, the pointer. Then by about 24 to 36 months what we see is that bone structure is running in that upward downward trajectory or what we refer to as superior-inferior pattern.
Now, what's interesting about this, is this is the age when children are starting to walk. As they put stress on their limbs or they put body weight on their hip bone, the bone is also orienting itself to resist those stresses. I love this picture because it's a beautiful illustration of how bone changes within a short duration of time.
Now, you might be wondering then what are the mechanics that allow this to take place. Without going too much into detail, because a lot of these things, of course, physiological activity of cells is often quite complicated. I'm showing you this schematic to briefly summarize what happens with bone. Basically, when we apply a load or a strain on our bones, such as when we are walking or when we are running, there are receptors in bone that will sense that strain and consequently they'll activate cells within bone to start laying down more bone as a way of resisting that stress. Alternatively, if we don't have any strain or we are not using our limbs for instance at all, then another type of cell is activated to eat away that bone. This is a continuous process that's taking place in our bodies depending on how much loading or strain we put on our skeletons. That's the brief summary of what happens, so the mechanics of how bone changes.
Now, keeping in mind the interests I was telling you about in terms of changes in bone or in the skeleton that are short term and changes that are long term. I also wanted to show you, excuse me, to show you what's going on in the fossil record because of course, those again are changes that are carrying in the long term. Probably many of you are familiar with this, especially if you've gone to the National Museum of Natural History, the Smithsonian museum where they have a beautiful exhibit of some of our early ancestors.
What we are looking at here is the human lineage from about 3 million years here on the left, all the way to our own species here on the right. What's fascinating is that at about 2 million years when we see the emergence of these species known as Homo erectus, this is when we see changes in anatomy that are similar to what we see in modern humans. We see a change in stature, we see taller individuals, we see narrower bodies or changes in body shape, changes in body mass, some of which persist to our own species. In my work I try to link or to understand if some of these changes, one of them being, and I'll talk about this, is low bone density in modern humans, whether that is something that we also see in some of our early ancestors.
Now, I've talked about the short time changes and I'm turning my attention to the long time changes. Now, to summarize some of the changes that we see in the long term, and of course some of them are also short term, we know that there are features that are uniquely human. Those features include things such as having a narrow pelvis, having long legs, having short toes, having large joints. All these is a suite of traits that we associate with our ability to walk upright. Now, more recently, some of my work and that of other colleagues, seem to suggest that we have, we as in Homo sapiens, have lightly built skeletons. That means we have low bone density. I'll be referring to lightly built, or having a gracile skeleton, as a way of expressing that low bone density that we see in modern humans. The question is, are these lightly built skeletons a result of low activity levels within our lifetimes or is this an evolutionary adaptation or even still an evolutionary mismatch? I'll get to these here when we get to some of the questions that I've been asking, more detailed questions.
Now, so far I have been describing this and maybe you are wondering why should we care about this? Why should we care about how bones change? For me, personally, of course I care about it because it's very exciting, it's very informative about our present, about our past. It's knowledge and we are always seeking knowledge, isn't it? But in addition to that, there's some applications. I'll tell you about some of those applications that some people might have an interest. What we know is that some bone diseases such as osteoporosis is very prevalent, especially in the Western world. In fact it's actually a public health concern and that's because it is a disease that's characterized by low bone mass and consequently increases fracture risk which may lead to morbidity and in some cases even mortality.
If we look at this graph here, what we are seeing is a plot of osteoporotic fractures, strokes, heart attacks, and breast cancer in the United States from about the years 2004, 2005, and 2006. What see is osteoporotic fractures are quite high in number compared to the other disease incidences. This is just highlighting that public health concern that I was mentioning. But we of course know that clinicians and other bone biologists are really interested in questions of what are the metabolic causes of low bone mass. What are the dietary causes on all of this. As well as they're interested in identifying ways to mitigate this loss. But what I'm doing in a way is trying to look at this concern from an evolutionary perspective to see if what happened in the past is what is resulting in the trouble that we have now in this disease that is a major concern of ours. Again, I'll come back to that at the end when I've wrapped up some of these questions that I'll be talking about.
To address some of these things that I've raised regarding how bone changes with physical activity in the short term and whether it's related to changes in the long term, the main question I ask is whether the gracile skeletons we observe are a consequence of low activity levels, or a kind of evolutionary adaptation or mismatch. To get to that, first of all, we have to establish whether the pattern of gracile skeletons is indeed a recent evolutionary event. Right now probably you are wondering, well, where do we begin to address this question? What are the methods we use? What parts of the skeleton will be we be looking at? I'll give you a brief representation of how we get to collecting our data to assess this.
Often, we use high resolution scanning, computed tomography scanning. What I'm showing here on the left is a micro CT scanner. This particular one is at the American Museum of Natural History. Basically, we take our specimen, or any particular bone of interest, we prepare it, put it into either in a container in a piece of foam to stabilize it and we put it into the machine. The machine uses X-rays to gather 3D pictures and assembles it such that we have an image to analyze. The other machine that we use is known as the pQCT scanner, quite similar in terms of using X-ray imaging. This picture actually was taken at the Smithsonian at the Natural History Museum perhaps eight years ago.
Now, when we have these images from these scanners, what we do is we take a region of interest in the bone in our image and then we quantify the number of white pixels that represent bone and then we divide that by the total number of pixels in a particular region. That's what we end up with as our bone density. That's what'll be really referring to throughout this talk. Here are some additional pictures showing some of the bones that we've scanned including this femur here of an early ancestor from East Africa.
As you can see, or maybe you may not be able to tell, but it's sitting inside a piece of foam. That piece of foam will stabilize it when the scanner starts rotating. Here is just an additional picture of me preparing some of these specimens in South Africa. Then down here in the bottom are pictures of some of the bones that we have that have been recently scanned. Those results I'll be showing you today. The one I'm pointing at on the far left is the skeletons from the Czech Republic. These are Homo sapiens from the upper paleolithic period, that's about 26,000 years. Then here we have some from Israel. These are also Homo sapiens from about a hundred thousand years ago.
Then we have the result, just to show you what a fossilized bone image would look like. This is the inside of one of these really fossilized bones. What you see is a lot of gray and white. This is the trouble of working with fossils is that you end up with an image that's not very distinctive in term terms of what is bone and what's not bone. It requires a lot of work in the lab to clean up these images so that we can tell what's bone, which is the darker material, versus the air matrix or air spaces which in this case are filled up with fossilized or minerals and soil. That's just a quick glimpse of what we deal with in terms of scanning, in terms of specimens.
Now, to get a full representation of the skeleton, so if you're going to really ask these questions, we have to sample all the bones that we can get or at least most of the bones that we can get. In the upper limb we've sampled the upper arm bones, the forearm bones of the hand itself. In the lower limb we've sampled the hip bone, which is the femur, the tibia, which is the leg bone and some toe bones. That's the representation of the data I'm going to show you today. Sometimes we've added, or in the past I've added vertebrae, but in the fossil record those are usually a bit harder to come about. The right bones to scan can be a little bit more challenging to identify.
To answer that first question about changes within our lifetime, so depending on our physical activity, what we did is we sampled modern humans with different subsistence strategies. When I say modern humans and referring to people that lived in the last 10,000 years. These are samples from the archaeological record, some of these samples actually housed at the Smithsonian, but also includes specimens from other museums too. We had farmers, we had hunter gatherers, included industrialized populations, and fisher foragers.
The presumption here is that if you are a farmer or someone that has lived in an urban, industrialized environment, you are relatively sedentary because you are either going to the farm and working in that farm and returning home or you are going to work in a factory, for instance, and a returning home. If you're a hunter gatherer or a fisher forager, you are of course traveling long distances to gather your food or to hunt for game or you're on boats, you're rowing to go and capture your kill, your fish, the big mammals and so on and so forth. There's more activity taking place. I refer to these two, the hunter gatherers and fisher foragers as active, while the farming and naturalized groups are more sedentary.
I'll show you few results here of this comparison. If we compare the hunter gatherers and foragers versus farmers and the industrialized populations we see that ... Let me orient you here on the graph, on the box plot. We see that the foragers actually have greater bone density than the farmers and the industrialized groups. These box plots, the bold line in the center represents the median. The long tails that we are seeing is the range of variation. When we pull this samples of the sedentary versus the foragers, we actually see quite a significant difference. This really affirms or supports our hypothesis or idea that if changes are taking place within our lifetimes and if you are more active the more density you have.
This is not just my work alone but also work of other colleagues that illustrated this very nicely in this image. If you look at these hip bone of a hunter gatherer compared to an agriculturalist, we see the white material which is bone, it's quite dense in here. There's a lot of it. The actual thickness is big. When we look at the agriculturalist's here, we see that there's more sparse and thinner bone. Again, farming that idea of change within our lifetimes. But then the other question is how does this translate to long term, large time scales or long time scales if you will.
To get to that, the long time scale, so evolutionary change, what we did is we took our humans, the ones I just showed you in the previous slide. These are the recent modern humans, sedentary ones. Then we have our active research humans and we compared them to those upper paleolithic humans from about 26,000 years ago from Europe. Then we compared them again with early modern humans from Israel from about a hundred thousand years ago. Compared them to Neanderthals from Europe from roughly 60,000 years ago. Then we have our sole early Homo, an individual from about 2 million years ago. I should just mention that early Homo is our genus but not our species. We think this is a Homo erectus. Neanderthals, of course, are not our species but same genus and closely related. Then we have the rest are all our species but occurring early in time.
The pattern that you note is that these two modern humans, ourselves, are quite low in density compared to the rest, regardless of species. This is really, really interesting because it confirms or affirms the idea that these gracile skeletons are a recent evolutionary event, and at the same time there's a correlation to activity. If you're more active, you are foraging, you have more density. If you are farming or you are industrial, you have low density.
This is great because it's just the beginning of a lot of more hypotheses to be tested, as I'll show you in the next few slides. In addition to that, perhaps you already saw this image from the announcement that went out for this talk. This is an illustration of some of the comparisons that we made, including chimpanzees, our close living relatives and some of the older fossils from South Africa in particular. When we compare them the chimpanzee, our human ancestor Australopithecus africanus, some of the early modern humans, and recent humans, we see a pattern in which, again, like I mentioned before, that recent modern humans are unique. I like to show this image because it illustrates this fact very nicely.
In particular, if you look at the bottom pictures, we see that ... These are sections through the hand bones. The hand bone of a human has very sparse bone, it's quite porous compared to that of a member of our own species that occurred a little bit earlier, which has more bone and of course, very distinctive from this early ancestor, as well as the chimpanzee. Again, reiterating that recent change in bone density. The thing that, of course, we note or the most important thing that coincides with this low bone density is the fact that in the last ... When we are seeing this change, this is a time period when we have a significant shift in behavior of modern humans. This is the time when we start domesticating crops, this is the time we start domesticating plants. This is a time when we start living in settlements and of course eventually living in city states and becoming the beginnings of these sedentary lifestyles that we lead now.
Returning to those questions that I started out with, are gracile skeletons a consequence of low activity levels or evolutionary adaptation? At the moment I would say it's likely both, because we see change depending on what you do in your lifetime and also we see change in the last 10,000 years. There must be something that's causing this shift that's not just change that we do within our lifetimes and that's the end. It's change that's actually affecting our genetic pattern. It's being passed on into populations. A better word is that it's a systemic change.
Then the second question or the sub-question, if you will, is whether the pattern of lightly built skeletons is a recent evolutionary event. All the data so far that we've gathered, that others have gathered, indicates that it is indeed a recent evolutionary event. Now, returning to applications of some of this work, I think looking at skeletal changes from an evolutionary perspective does not conflict or does not divert away from physiological research that's going on, on bone diseases. But it really does complement that work and it helps us understand a little bit why we are vulnerable to bone disease. Because in evolutionary terms, of course there are mismatches. There are features that are advantages and there are features that are disadvantages. There are features that are both advantages and disadvantages. As I tell my students in our evolution course that these are things that, they are trade offs that we see in our skeletons or in our morphology throughout human prehistory.
Now, some of this work has been highlighted a little bit in the last five years or so, showing that we have light skeletons due to less activity, that the agricultural innovations are what led to these light skeletons. I just want to say yes, I think this is the case, but at the same time it opens up windows to test other hypotheses. The systemic change, I believe, is probably more than just an agricultural, we become sedentary and then we have light bones. I do believe there's more to it, which of course opens up more lines of investigations that I continue to do.
In summary, through my work and work that I continue to do, we need to thoroughly document the changes or to answer these questions, especially relating to being sedentary and how that affects our bones. While we have data that has shown that, this is not the end of it, we still need document these anatomical changes consistently in the last 10,000 years from different geographical regions so that we can have a better insight into this shift. One of the exciting things that I'm working on that I think the work that I've just shown you opens up is to try and use other mammalian analogs to document changes similar to those seen in modern human dogs. In particular, I'm interested in dogs because I think they present an analog that would inform modern human anatomy.
I'll show you just a little bit of the preliminary work that I'm working on right now, which is comparing domestic dogs to wild canids. If you're wondering why domestic dogs and why canids, is that we know that these are species or these are organisms that were domesticated in the last at least 15,000 years. I guess we can have debates about when exactly that happened and people that study dogs obviously have a lot to say about that. But generally speaking, the last 15,000 years dogs were domesticated. We know their closest living relative is the gray wolf. How do those two compare? Does domestication have an effect on bond density? What we've done is compared the gray wolf to a variety of breeds of dogs, including the husky, the greyhound, the St. Bernard and the Eskimo dog.
This is the last graph I'm going to show, I promise you. Showing bone density in the wolf and the domestic dog. What we see is that overall when you look at the means as well as the median, statistically speaking, we see that the wolf has more bone density compared to the dog. You might say, well this is the median, this is the median and you have a large range here. But even with a large range, the domestic dog has lower bone density than the wolf. This is really interesting. Those four breeds we compared, all of them have lower bone density than the wolf. Keep in mind, we have the husky there, a dog bred for endurance. Keep in mind we have the Eskimo dog there, also a dog that's been used in endurance. Especially Eskimo dog was obtained or is a collection is from the American Museum of Natural History, a collection that was acquired from the 1900s, or thereabouts.
This is really, really fascinating and I'm really excited about this. I think it might be able to tell us something about our own so-called domestication if you'd like. Because there's been this lovely proposition or hypothesis that have been put out that modern humans underwent our own self-domestication in our own way. For example, settling and being cooperative and living in societies was an advantageous trait or an advantageous behavior, perhaps some of the byproduct of that behavior is having a gracile skeleton as has been shown in some other species of dogs of carnivores, if you will. If people have questions about this, I'll be happy to talk a little bit more about it afterwards. But I just wanted to touch on it a little because I think it's quite interesting.
To summarize, so far I've shown you that gracile skeletons seem to be a recent phenomenon through comparisons of human ancestors and recent modern humans, which are showing that we have light skeletons. These light skeletons seem to have occurred quite recently. These conclusions are implications for understanding evolutionary adaptations. Are they related to domestication? Are they related to our sedentary behaviors? How does it fit into the bone disease? Was it an advantage that led us to be more vulnerable to bone disease, and I'll give you an example such that if you have a lighter skeleton for instance, there's an advantage there in that you can move it more easily, you have less mass to move around. But on the other hand, perhaps you're pushing the extremes, evolutionarily, to the point that you're more vulnerable to disease or there's increased porosity so to speak. Then lastly that sedentism plays a role in the margins of light skeletons, it seems that it does play a role, but there might be alternative explanations such as what I was describing as a self-domestication hypothesis.
With that, I would like to conclude and end by thanking all of you for being in attendance today. I would like to thank the Human Origins program, particularly Dr. Briana Pobiner, for inviting me to participate today. Other folks at the Human Origins program, Dr. Rick Potts, Jenny Clark, people that I've worked with in the past, thank you very much for all you do and all of your support, and many other folks including Niamah for organizing this and curators from various museums and institutions that have allowed me access to specimens. Thank you.
Briana Pobiner:
Wonderful. Thank you, Habiba. That was fantastic. Thank you for giving us a tantalizing glimpse into what you're working on now regarding the self-domestication hypothesis. We have questions, we will get to as many as we can between now and 12:30 when the program ends. The first that I'll ask you is a basic methods question. This is from Mercedes. Is it necessary to handle the bones using gloves?
Habiba Chirchir:
It depends, I would say. It depends on what specimens you're dealing with. Modern human skeletons often at museums tend to be relatively well preserved, so you don't need to handle them with gloves. The fossils, it also depends on where they were found and their state of preservation. The ones I've had to handle so far, it's not necessary because they're highly fossilized. They're almost like rock, so it's not necessarily to use gloves, but I know in other areas where fossils have been found in caves, the bones might crumbly and they might be very delicate, so it might be necessary to use gloves.
Briana Pobiner:
Okay. Thank you. Here's a question from Heather. Bone density or structure changes in childhood, does it continue to change in adults?
Habiba Chirchir:
Yes, it does. It does, depending on many factors. Some of them I have not talked about, of course, dietary, hormonal, genetic factors. But the one that I've touched on is activity and it changes with how much activity you put on your skeleton. For instance, if you are an active child into your teenage years, you're an athlete for instance, your bones will be stronger, greater bone density. That density will actually persist into your adulthood even if you stop being very active. You see low prevalence of say, osteopenia or osteoporosis in people that were really active during their teenage years when they're growing. Yes, our bones do change throughout our lifetimes.
Briana Pobiner:
Excellent, thank you. And I'm going to ask a follow-up question because somebody asked about an athlete. This is a question from CJ Green. In the slide of the gracile skeletons being a more recent evolutionary event correlating with activity, where would an Olympic athlete fit?
Habiba Chirchir:
That's a really good question. I haven't done the studies of athletes, but colleagues have done it, not looking particularly at bone density, but at bone strength. And what they show, actually, it's a paper that was published, I think, in the Journal of Human Evolution, they showed that athletes were closer to the upper paleolithic humans that I showed. Yes, they do increase, but again, keep in mind our upper paleolithic humans, the samples that we have are quite small. We might look at two upper paleolithic humans and compare them with five athletes. I say they're quite similar, but I wouldn't say we have a full picture. Yeah, they tend to be quite strong. On the other hand, also it depends on which bones you're looking at. I think in that study what they looked at was, I think, they looked at people that were rowing, people that are using their upper limbs more. It seemed to show in their upper limbs that they were quite strong.
Briana Pobiner:
This is a nice follow-on question. This one and the next one I think I'll ask are sort of about predictions. Steven Rockaur asks, "Is the relative osteoporosis you see now reversible? If we were to live the sort of life of early human or Neanderthals, would our bone density respond appropriately?"
Habiba Chirchir:
That's a good question, but a hard question to answer. That's because of course we know our bones will change throughout our lifetimes depending on how much activity we exert. So, yes, in that case we would. But in terms of a long-term change to be like our ancestors, I do not know. That's a little bit the reversal of the evolutionary process. I couldn't say. I couldn't speak on it, but just within change within our individual people, within their lifetimes, yes, we can exercise a lot and build up our bone density. But in terms of population-wise, I couldn't say too much.
Briana Pobiner:
Okay. That's fair. Here's a really interesting question from Sophie QB. If a child grew up in a spaceship without gravity, would their bones not show that pattern at 36 months, but look more like a younger one?
Habiba Chirchir:
Probably. I would say yes. Without gravity, so the pattern of growth is ... your cells are not, the mechanoreceptors are not sensing the weight, the stress. So most likely problematic, diseased-type bone or skeleton, if you will.
That's really interesting actually.
Briana Pobiner:
Yeah.
Habiba Chirchir:
With all these discussions of space of ...
Briana Pobiner:
Exploration. That's true. Colonization, maybe.
Habiba Chirchir:
Colonization if you will.
Briana Pobiner:
Yeah. Here's a question from Suzanne Ubic who asks, "In industrialized societies, have comparisons been done between manual workers and heavy industry workers and people who don't rely on physical labor for their income?"
Habiba Chirchir:
Not that I know of. I think it would be really interesting to make this comparisons. The problem is actually using or collecting these data in living people, you see. You can use equipment that clinicians use, for example, a DEXA (dual X-ray absorptiometry) can't do that. But the people that often clinicians are more interested in diagnoses of individuals or maybe just fewer samples, but people that are more interested in a broad change of bigger patterns, at least not in the close in biological anthropology or paleoanthropology. Not that I know of. Sorry. Can't answer.
Briana Pobiner:
No, that's okay. Here are two questions that are kind of similar, one's from Christina. "Do you think changes in dietary intake when we relied on agricultural products, in place of foraged foods, might lead to reduced calcium or vitamin D intake, thereby contributing to reduced bone density?"
Habiba Chirchir:
Sorry.
Briana Pobiner:
Similar question. CJ Green asks, "What do you think the impact of eating or drinking dairy has had on this? Isn't it a modern human thing? Could it actually leach calcium from your bones and what about the impact of fluoride in our diets?"
Habiba Chirchir:
Well, I'll start with the first one, which was a bit more general. Yes, it has an effect. Diets have an effect on bone density as well as of course teeth. There's some work showing that as soon as we started using corn, we are domesticating all these grains, you see a change in .... there are more pathologies, in dentition pathologies, in our skeletons. So this really could be a contributing factor. But I would say this, the pattern that we are seeing seems to be consistent even among populations that were not engaging in agriculture or not farming. We have the foragers. The foragers have strong bones, but they still are not as high density as our ancestors. There's something there. I think diet plays a critical role, but I think there still are something else beyond just diet.
In terms of dairy, yes, together with including more grains in our diets, I think it would have an impact how much of a leaching they would have on calcium, I couldn't say. But overall, the change in diet has been documented to be to ... Using more diary and using more grains in our diet has been shown to increase pathologies in particular, to lead to an increase in pathologies.
Briana Pobiner:
Thank you. Here's a good question from Hannah Jacobson. "If you know this, how quickly can bone density be remodeled? For example, would our skeletons be different over a six-month period from the beginning of quarantine where maybe we had an active lifestyle, to now a less active lifestyle?"
Habiba Chirchir:
Well, so if you think about it, actually it does happen quite fast. If you think about if you break your arm or break your leg, any of your bones, it'll heal. That bone will heal over. We don't want that, but say you did not do anything about it, you did not see a doctor, that bone will heal over within a duration of a number of weeks, maybe four, six weeks, it'll have grown over where the break happened. Yes, it does remodel fast, but I couldn't speculate on what quarantine has done for us or to us, I should say.
The example of the bone break is also an extreme situation in which the body physiologically is trying to heal itself. There's a faster mechanism taking place compared to say, just walking from the living room to the kitchen and there's nothing wrong with your body. There's no compensation to heal it or to remodel it. I would say it does not in a long time. In that picture I showed you of the kid, well the child, at about two years, they're starting to show ... You see that change in orientation in the distribution of bone, in the orientation of bone. Yes, weeks to years obviously in that case.
Briana Pobiner:
Excellent. Thank you. Here's a question from Kimberly Tommy. "Did you look at a specific breed of domesticated dogs? And if you did, why that breed?"
Habiba Chirchir:
Yes, I did. I did look at specific breeds. I had a greyhounds, I had St. Bernards, I had Eskimo dogs, and then we had huskies. There's a reason for this and there's also, how do you say, availability of specimens. The huskies in particular, I was really interested in them, I mean the Eskimo dogs because of their endurance. Part of what I was trying to get at is whether you can look at differences between say, dogs that are bred for endurance versus dogs that are quite gracile, like the greyhound. That was part of the reason I was getting at.
But at the same time, it was also availability of the collections of the specimens at the museums. When you go to museums, it's hard to find known breeds of dogs. You just find Canis familiaris, that is dogs all together, but the specific breeds are usually hard to find. I was lucky enough that the Smithsonian has the greyhounds and a few other breeds. Then the American Museum of Natural History had the Eskimo dogs and St. Bernards and the Field Museum in Chicago had the huskies. Yes. Yeah. It's both. But availability as well as there were reasons that I was trying to get at.
Rather, in addition to what we are trying to do is also add in the dingoes. I think that would make it really interesting because if we think about dingoes, probably they're a bit more wild, so to speak. We have dingoes from the archaeological record from about 5,000 years ago, if you can believe it. That's pretty neat. Yeah, I hope I answered that question at least.
Briana Pobiner:
Yeah, thank you. Cecilia Thonad asks, "In addition to activity, what other factors that count for the bone changes or structures from primates to modern humans?" She asks, "Diet, heredity, age?"
Habiba Chirchir:
All the above. All the above, Yeah. Well, let me just go back and start with activity and then get to the others. For other primates compared to humans, of course, say for example monkeys. They're arboreal, they're climbing trees. You'll see patterns that are completely different from ours. In terms of diets, it's harder to say between primates and humans. But then again, like I was mentioning, in modern humans in the archaeological record, you see that there's influence of diet or rather certain diets resulting in some known pathologies. In terms of heredity, yes, you see that if you look at all primates that are compared — chimpanzees, orangutans, baboons, different types of monkeys — you see that generally while there're variations between species, they all tend to have high bone density. Of course, there's a heredity or phylogenetic signal there that might be going on. Did she mention a third one?
Briana Pobiner:
I think it was age and heredity and something else. Maybe diet.
Habiba Chirchir:
Yes. Age too. Yes, I did touch on age, yes. Age is important and that's why we try, as much as we can, when we are sampling modern humans to sample at least individuals of, if the age is known, 40 and below or 45 and below, because after that, you really just don't know what you're getting at, if the individuals who had osteopenia, the beginnings of osteoporosis. Yeah.
Briana Pobiner:
Thank you. I think you actually just answered the next question I was going to ask. This is from Sophie QB. "Are all the skeletons that you have scanned to compare the same age? If some are older than others, could that affect the comparison?" I think she means sort of biological age as opposed to geological age.
Habiba Chirchir:
Right. Right. Right. Yes. Absolutely. We try as much as we can. There are some of course from the archaeological record in which you couldn't tell the age, so that presents a challenge. But what we do or what I've done in the past is if I see that there's a bone that presents itself as, obviously just looks a bit more pathological or when you hold it it's a bit lighter, I exclude it from the analysis or from the scanning. So as much as possible to try and scan anything that's 45 and below. The Smithsonian has some wonderful collections there of known age, so that always helps when you have known age. Other museums too. But when it comes to the archaeological record, it's a little bit more trickier, but we try.
Briana Pobiner:
Great. Here's a question from Lisa Burbarian, and I apologize if I mispronounce your last name. "Dr. Chirchir, have you done anthropological research on the evolution of human bones in Kenya? If so, did you discover anything distinctive about the fossils in Kenya compared to elsewhere?"
Habiba Chirchir:
Yes. It's really preliminary. I'm very excited about this. Last year we were able to scan a couple of bones of human ancestors, of fossils from Northern Kenya. These are members of Homo erectus and what's called Paranthropus. Okay? My expectation was that well, Homo erectus will be more similar to us in having low bone density, but no, it has high bone density. If you like, I don't know Briana if we have time, I can show that graph a little bit. One more time. Do we have time?
Briana Pobiner:
Sure. Sure. After this we'll have time for probably one or two more questions.
Habiba Chirchir:
All right. Let me just share that screen and I hope it will help the person that asked the question. If we look at this graph, this early Homo, this is a Homo erectus, we think it's a Homo erectus. But either way it's identified as a Homo species and you see it has high bone density, it's a single specimen. Compare that to modern humans. It was really, really interesting because I thought it should be maybe a little bit closer to modern humans. Now, the other one that I just talked about, I'll stop sharing the screen now. The other one, the Paranthropus also had high bone density and that wasn't too surprising. Have I stopped sharing the screen, Briana?
Briana Pobiner:
Now, you have. Yeah.
Habiba Chirchir:
Okay. We were able to only scan those two because we only had permission to scan the two. It's a long process. We had to get permission to get the fossils and travel to South Africa to scan them and then return the fossils and then leave with the data. Now we are starting a new project to scan more of those fossils from Northern Kenya. This is really going to be something. I'm really looking forward to getting those results. To answer your question, yes we have, but only two and both of them show really high bone density.
Briana Pobiner:
Oh, interesting. Well, that's exciting research in progress. Okay. I have one last question, which is basically sort of questions from two people combined. This is another prediction question. Shannon Hathaway says, "I teach sixth grade social studies. We start the year learning about early humans. My students always ask what we would look like in the future, based off of how much we've evolved over time. I would love to hear your thoughts so that I can talk with them. Thank you." Christopher asked, "What will our bones look like in the near future?"
Habiba Chirchir:
I don't know if I have a straightforward answer for your students, because it's a bit of, I guess, a harder question to, especially if you're working with kids in which you want to break down some of these responses. But if you think about the evolutionary process, it's a continuous process and we really don't have a direction. We don't know what is advantageous or disadvantageous, what's a byproduct of a particular selection. It's really hard to say, but what I can say, generally speaking, is that we are changing. Most likely in years to come after we are out of this world, there will be creatures that are probably somewhat similar to us, maybe a bit different from us, because this process is continuing. I couldn't speculate on how we will look like, but of course the things we do may have an influence on whatever the next species that comes about or just the same species evolving into something else. So hard to say.
Briana Pobiner:
It is. No. I think those prediction questions, especially about the future are really difficult. Okay. I will ask one last question from Platinov. "Can you explain a bit more about the self-domestication hypothesis?"
Habiba Chirchir:
Okay, yes. This is really interesting and some very clever research has came about to this. Basically, what it postulates is that, as people, as human beings became more cooperative and started working together, cognitively cooperative, working together in communities or in social groups, the need for these large bodies and more strength is diminished. There was more corporation, and one of the byproducts of that selection for corporation was changes in our physiology and in our anatomy that was not expected. It wasn't part of the selection process. I'll give you an example of something where part of this came from.
There was this famous study that was done in Russia of foxes. Basically, what was done is that these researchers bred tame foxes in one line and aggressive foxes in one line. They were selecting for particular behavior, tameness or aggression. What they noticed, which they were not thinking about, was that there were changes in the physiology as well as in the morphology of these foxes. The aggressive foxes just tended to have, in terms of morphology, had slightly larger teeth, had slightly larger jaw lengths and skulls, while the tame ones tend to be more like dogs. They were very puppy-like, had curly tails, had floppy ears, droopy ears if you will, and so on.
The speculation or the hypothesis is suggesting that if the friendliness and cooperation affects neural crest cells, cells that occur during development, that also have an impact on our morphology. It's a really, really interesting idea. Perhaps that's what's happening to us because what we see, and if we have time, I have a slide I can share about this ... If we have a minute and if the person that asks the question is still on here. Can you see that?
Briana Pobiner:
Yep.
Habiba Chirchir:
Okay. What you see is that even in modern humans in the last 10,000 years, you see a change from these robust bodies to gracile bodies, in the face, in the thickness of the cranium, of the cranial bones. This is the origin or the ideas behind this human self-domestication hypotheses.
Briana Pobiner:
Cool. Thank you. We have run out of time. First of all, thank you for the wonderful presentation. I apologize to everybody whose questions I wasn't able to get to. Thank you to everyone in the audience for asking wonderful questions. As I mentioned in the beginning, so my name is Briana Pobiner and I'm a paleoanthropologist and educator at the Smithsonian National Museum of Natural History. This is a part of our monthly HOT Topic, which stands for Human Origins Today program series. Those of you who registered via email, you will be getting emails about our future HOT Topic programs, which we generally try to schedule on the third Wednesday of the month at 11:30 AM. Stay tuned for those.
I just want to thank Dr. Chirchir again for a really fascinating presentation, for being able to answer all these rapid-fire questions. Thanks to everyone in the audience. All right. Take care. Bye everyone.
Habiba Chirchir:
Thank you, everybody. Thank you, Briana.
Briana Pobiner:
Thank you.
