The Ancients - The Oldest Human Footprints in North America

Episode Date: September 30, 2021

This week our understanding of when humans first inhabited the North American continent has been turned on its head … by a set of c.22,000 year old footprints. In this episode, hear how footprints can form crucial evidence for populations of prehistoric people and animals, and how now extinct famous megafauna such as mammoths and giant sloths once interacted with early humans. To reveal all about this ground breaking new discovery, Tristan was joined by Bournemouth University's Dr Sally Reynolds.Sally's Twitter - @SallyR_ISLHETristan's Instagram / Twitter - @ancientstristan

Hi, I'm Tristan Hughes, and if you would like The Ancients ad-free, get early access and bonus episodes, sign up to History Hit. With a History Hit subscription, you can also watch hundreds of hours of original documentaries, including my recent documentary all about Petra and the Nabataeans, and enjoy a new release every week. Sign up now by visiting historyhit.com slash subscribe. by visiting historyhit.com slash subscribe. It's The Ancients on History Hit. I'm Tristan Hughes, your host.

And in today's podcast, while it's breaking news in the ancient history world, you don't want to miss this one because you might have noticed in the news over the past couple of days, over the past week, this groundbreaking new discovery that has been seizing headlines across the globe. And this is the discovery and dating of the oldest known human footprints from North America. To explain all about this new discovery and why it's so

significant and what these footprints can tell us about these early humans in North America, I was delighted to get on the show at short notice Dr Sally Reynolds from the University of Bournemouth. Sally is a mammalian paleontologist. She is part of the team that has been working at this site in North America. She is part of the team that has made this discovery. It was brilliant to chat to her. And without further ado, here's Sally to chat to her. And without further ado, here's Sally to explain all about this new discovery. Sally, thank you so much for taking the time to come on the podcast today. Thank you, Tristan. I'm really happy to be here.

Now, this is a story that has been seizing headlines across the world the past couple of days. And as if I'd say it's radically reshaping, it's shining so much more light on what we know about these earliest humans and when they possibly reached North America. Yes, absolutely. This is quite a game-changing set of findings that we have published. Not because older sites have not been recorded previously, but simply that the dating for this particular site is an order of magnitude better than the dating that some of the other sites have been able to deliver. The other thing is, of course, is the nature of the evidence that we've presented,

which is footprint evidence. Now, in another typical site where you have stones, it's possible that the stones can move within the sediment, so they could sort of migrate down under the action of gravity, and like they're in an older level than their true age. Footprints are so fragile that they can't actually do that. They don't have the ability to move. If a footprint is disturbed or the sediment is disturbed, it's destroyed.

to move. If a footprint is disturbed or the sediment is disturbed, it's destroyed. And that means that we are very sure that these very delicate footprints between these two seed layers have not been moved or disturbed in any way. That's brilliant. And we'll get into more about those footprints later on. But I must ask, how often is it that we can discover amongst, let's say, the archaeological material that survives in prehistory, how often is it that we find footprints as a source? Well, the truth is, is that there must have been more footprint sites out there which were perhaps not recognised for what they were while they were being excavated, and they may have been destroyed. So it's important to realise that although a lot of

footprint evidence has been published recently, it is a reflection of the fact that excavators and archaeologists are becoming a lot more sensitive to the different kinds of evidence that they may have recorded at their sites. In terms of how much footprint evidence we should expect, Matthew Bennett is always keen to relate the anecdote that there are only 200 odd bones in the human body, but that we have the potential to leave hundreds of thousands of footprints in our lifetimes. So we would expect lots and lots of footprint evidence, but it's detecting it and excavating it carefully in order to preserve this very delicate evidence. That is what is changing and that is what we're starting to see in the literature now. So just to set the scene for us about where we're talking with this new discovery in North America,

where are we talking that you and your team have been excavating? So it's in the Tularosa Basin, which is close to the little town of Almagardo. And it is where, believe it or not, the Manhattan Project was conducted. So that is the testing of the nuclear bomb in the Second World War. So that's its actual claim to fame. There is an airbase, a military base, which abuts the White Sands National Park. And so, for example, last year's trackway, the double trackway that we published, people were saying, where does the trackway go? Well, we, the double trackway that we published, people were saying, where does the trackway go? Well, we uncovered the double trackway and it actually leads right into the military base,

which of course we're not allowed to go into. So it's very clear to us that we are sharing this part of the landscape now with the military who are very good about giving us permission to be there. But they are testing live ordnance around the sites. So some days you can't go out into the field because the airbase is doing work. So it's quite an unusual place, an otherworldly sort of place, an alien, strange sort of landscape with a fascinating history. And in prehistory, do we have any idea what this landscape would have looked like, let's say, in the Pleistocene age?

One of the key questions that me and the team are wanting to ask is what sort of lives did these people lead? And obviously, in order to understand what lives they led, we have to be able to fill in the pictures of the landscape, what it looked like, how dry it was, did they have enough water to drink? What plants were they eating? What animals were living there? So those are the sorts of questions that I find really interesting. The landscape would have looked a lot like it does today. So the same white gypsum sands would have been a little bit wetter. There's a paleo lake, which is now obviously dried up, called Paleo Lake Otero. That would have had water in it. We're not sure if it was a wetland, sort of marshy, swampy kind of landscape, or if there was a big body of water,

or if it perhaps changed through time, so it went through wet phases and drier phases. We have water on the landscape though, and that's really the important thing to remember, because within this drier basin, water on the landscape would have provided a huge attractor for humans and prey animals. So the humans would have wanted to be in this dry landscape, close to the only source of water, so that they had access to the animals who'd be coming to drink, but also including water for their own resources. We can only go three days without water, and then we die.

So people forget, especially in wet England, where there is no shortage of water, that many of these early sites are in extremely dry areas and that water was a key limiting factor. But it also presented an opportunity for you to be able to control or at least plan for the movement of animals, which then could help you in your own hunting activities. And so if this area was therefore this draw, this magnet for life all this time evidence that we've been presenting and all of the evidence that we've been looking for, we're looking for the full suite. I'd love to find some fossils, etc., etc. But the site, the preservation is unique. So we have the preservation of these beautiful footprints.

We would have the preservation of stone tools, obviously, because stone is infinitely preservable. But we've lacked finding bone evidence. We haven't found any teeth yet. So we just continue to look and hope that maybe in some of the different sediments of the site, there might be slightly different preservation profiles and that we may have a chance of discovering something more than these amazing footprints, which are amazing. And you're a mammalian paleontologist, I believe. And it's not just human footprints, is it? Well, that's it, you see. This is where it becomes amazing. Because we have a record of

Colombian mammoth footprints, we have a record of giant ground sloth footprints, dire wolves, extinct camelids. So we have the entire ecosystem represented including animals that we think the humans were directly targeting as their prey animals such as the giant sloth which we published in 2018 and so the idea is that we have this evidence of the behavior between the species which is something that if you found a dead sloth skeleton lying next to a dead human skeleton, yes, it's exciting, but it doesn't tell you anything about their movements or their behavior in life. And so the idea that we have an opportunity to explore, for example, in the Double Trackway last year, this idea of this young adult, possibly the mum, carrying this little toddler across this plier on this urgent journey going at top speed

but traveling alone on a landscape where there were sloths and mammoths and not feeling enough fear to round up a small group to go with them and I think that's really interesting because it shows sort of a calculation of the risk, risk benefit, I need to get to where I'm going really fast, I'm going to take that risk of traveling solo across this landscape. And I think that tells us a lot about the humans and their position in the ecosystem. Because when the sloth sense the human tracks, the sloth backs away immediately, suggesting that the sloth is like, oh, I know these, I know the species, I'm staying away from them. That enables us to realise who's the predator and who's the prey, and how humans are conducting themselves on the landscape, which I think is fantastic. I mean, that is absolutely remarkable. We will get into this new discovery in a bit. But I do love this work you've been doing previously

on these tracks, which I love how much information you can possibly gain from seeing connections between human tracks and giant sloth tracks and trying to figure out the connections between the two species some more than 20,000 years ago. I know. And it's important in the context of one of the enduring questions around this time, which is what was the role of humans in the eventual extinction of the megafauna? And this site has also given us a new perspective on that because previously the thought was humans arrived at various places around the world and very soon after that the megafauna started becoming extinct. Well the White Sands findings then stretches out that time period where humans and megafauna were

living on the same site. And it's possible that humans were living sustainably within this community as predators. I'm not saying they weren't hunting these animals, but perhaps there were fewer numbers of the humans. And so as they were hunting these large animals, initially the impact was not as great. People forget that we understand a lot about the ecology of large animals by looking at differences between elephants and mice for example and we know that elephants are long-lived, slow maturing, very long gestation periods, slow growth and long lifespans and mice obviously are quite the reverse. So we know that these very large megafauna, even though we can't study them directly, are likely to follow a similar pattern. Slow growing, slow producing, long-lived, not having

many litters of babies. And so every animal that you killed, or two or three animals, would actually have made a disproportionately high impact on the population. So it would have taken a long time for these individuals to regenerate within the population numbers. And it wouldn't have taken much for humans then to start slowly over-harvesting, harvesting the animals and killing them off slightly quicker than they could reproduce naturally. And then that would have had knock-on effects, which could then help us explain the eventual extinction of these animals. that would have had knock-on effects, which could then help us explain the eventual extinction of these animals. Wow. It is so interesting, all of that.

And there's other big questions which we will get to as the podcast continues, as we now focus in on the discovery itself. And let's talk about the human footprints in particular. First off, basic question, but how many, so far, how many sets of human footprints, of human, prehistoric human tracks have we discovered from this site? I've actually lost count because every time we go out there we find more prints we've been experimenting with other ways of detecting the prints so we've been looking at the influence of ground penetrating radar that's with our colleague Tommy Urban and we can actually then pass over the surface and be able to detect the footprints below at depth, which is incredible if you think about it.

We are able to then go, oh, look, there's a mammoth down there. And potentially it gives us an opportunity to have a greater scope of the landscape because this is a landscape of kilometers in extent. And it's all potentially covered with footprints. And these non-invasive techniques, these are absolutely key, therefore, because you mentioned earlier how some footprint sites in the past, you know, have been destroyed by accident through excavation, excavation being destruction. I mean, is this a great example of how science is helping us now find more and more of these sites? Absolutely. And it's important to realise that even though the footprint evidence is very old, we are constantly trying new techniques. Can we use this? Does this

work? How does it work? How well does it work? And so we are exploring ways in which we can sample and prospect over a larger area that we may then better target specific sites which look interesting because obviously excavation is as you say destruction but it's also it's an investment in time and energy and on this very large landscape where you have many choices that you can make you want to be sure that you're targeting the most interesting sites in terms of different kinds of behavior that are being manifest but i literally thousands of prints hundreds of thousands of prints must be out there. And we have excavated hundreds of them. And there's no end in sight.

That's amazing and really exciting for the future. And these footprints, which have been discovered so far, are they also, at least some of them, rich in anatomical detail, shall we say? Well, certainly we can see clearly that they are human footprints. We can see clearly that they are unshod. Habitually unshod individuals have very widespread toes, which is something that you can see very clearly in these particular prints. I'm interested, and I'm working here in Florence with a colleague

who's also interested in footprint evidence, that's Dr Matteo Belvedere, and we were discussing, well, where are the shoes? There must be some of these individuals must be shod. So we're cooking up this experimental project where we'll have students invent sort of various kinds of primitive footwear and then walk on a landscape and see what sort of very subtle traces you might get if you were wearing very thin leather nothing fixed or rigid on your feet so the anatomical detail that we can see is clearly that of barefoot human beings the anatomical detail is such that we can use the length of the foot to compare to growth curves of other humans ordinary humans you and me

and children's feet, which we've been collecting for years, you know, so you'll say, oh, well, at this centimeter size, this child is normally between this age and that age in months, you can actually read off on your little growth chart. And you can say, well, if your footprint is this big, then it means your human individual is about that age. And this is why we've been able to say with such certainty that we're looking at perhaps adolescents and some children together with some adults on this landscape, is because for our species at least, we have a tremendous amount of growth curve data which relates to stature, height, weight, and variations between the different population groups,

because that tends to vary as well. Whether you're in your running era, Pilates era, or yoga era, dive into Peloton workouts that work with you. From meditating at your kid's game to mastering a strength program, they've got everything you need to keep knocking down your goals. No pressure to be who you're not, just workouts and classes to strengthen who you are. So no matter your era, make it your best with Peloton. Find your push. Find your power. Peloton. Visit Peloton at onepeloton.ca. Is that quite surprising, the amount of footprints that you've been finding, which are of adolescents, of younger humans rather than adults

if you think of standing at the school gates you think of parents standing at the school gates the mums are standing there and they're not moving very much but the children are running rings around the parents and playing and playing catch and everything so we do see that adults leave less footprints than adolescents and children, who are typically more active and so leave more footprint traces as part of their daily activities. So it's not that we're arguing that there are more adolescents, simply that there are more adolescent prints. It's not a disproportionate number of adolescents within the community,

but it's a high number of adolescent prints. Right, right. They're just running around more. And possibly they were. You know, it seems very clear to me that they felt very comfortable on this landscape and this is quite a tranquil scene of them just having fun together. And that's nice to have this sort of feeling

of not a dramatic scene. It's not a hunting scene. It's not a desperate struggle for survival. It's a very calm and tranquil scene out of prehistory. All right. So out of all of these footprints that you and your team have discovered, in regards to this new discovery, which footprints in particular are we talking about? Well, these are the footprints that were discovered in January 2019. There was a footprint trail that led into a bluff and so we were able to excavate the footprint trail out at depth which is very

interesting because most of the footprint evidence we have at the site is very close to the surface. So in this trench excavation of which you can see some photos that have been published along with the media stuff, we show that we were able to dig quite a deep trench we were able to put these footprints in profile with a seed layer at the top and a seed layer at the bottom now seeds they don't sound very exciting but they are if you're on a landscape where you don't have very much bone preservation because seeds being organic matter actually have the capacity to be used for radiocarbon dating. So when we saw the seeds, we got very excited because we thought, ha ha, this is

something that we can use. So to be clear, we haven't dated the footprints themselves because there's nothing in a footprint that can be dated. But we have to date the associated material and infer the date for the footprints. So what we have is a seed layer at the top and a seed layer at the bottom, which then give us these bracketing ages, 21,000 and 23,000, which then encapsulates the footprints, which is then the date of the footprints. Could you quickly actually explain to us what radiocarbon dating is and what that process entailed to date those seeds?

Absolutely. So first of all, you have to sample the carbon. Radiocarbon is a technique that works by the decay of a particular isotope in the carbon, which means when an organism dies and is buried, it stops taking up one kind of carbon. and so we're able to use the decay or the changing proportions in the two different kinds of carbon isotopes to be able to infer a date. It only works until all of the carbon isotope has been decayed, which is normally about 50,000 years. So for anything older than that, we have to use the same radioisotope differences, but for slightly different elements which have longer half-lives, like the uraniums, for example. And so, with all of this dating in place and being able to date the footprints to when we believe they were there,

what were the next steps following that, Sally? Well, it's tempting to say, let's go and get more older footprints. Let's go and see what the oldest footprints are on the landscape. And that may well come in time, but we've got some other sites that we're really interested in exploring. And we've got some very interesting trace evidence of perhaps early kinds of technology on the landscape, of which I can't say too much. But we're really keen in exploring these different sites and capturing this range of behaviour. And so why is this dating, having established a date for these footprints, why is it so significant, these conclusions in our knowledge of humans arriving in North America? We thought initially that humans could only arrive in North America after the ice sheets melted around 16,500. This clearly shows that humans were in North America long before that, which means we could have older sites probably going back as old as 28, 29, 30,000 years. It means that we fundamentally misjudged the timing of the earliest human

expansion into North America. And importantly, it means that some of the other older sites that were previously proposed are actually quite likely. And if that's the case, if it adds credence to these other sites, and it's during this Ice Age time, it also begs the question, what routes could these early people, these first people to arrive in North America, what routes could they have taken to reach North America at that time? At the moment, there are three prevailing views about the routes. There's the migration through the ice-free corridor, obviously, which is the inland route. Then there's the migration by the coastal route, which is often called the kelp highway. And then there is this third idea of open seafaring. Now we don't have much evidence for the

open seafaring route, but of course we can't discount any of these possibilities. And potentially it's important to remember that there might not only have been one route, there might have been multiple routes, and these multiple routes might have been used at different times. So it's tempting to look for one single answer, but it's important to remember that there might actually be more than one answer. Fair enough. So coming from different roots. And if they were there at this time, and you've also mentioned the footprints of the other animals that were there, and you said, of course, a key interest for you was this connection between these early humans and certain megafauna at this time. If there were humans living in North America thousands of years before when we previously

thought that humans came to North America, what might this also tell us about this association between these early humans in North America and the extinction of certain remarkable, iconic megafauna such as the mammoth. It's important to remember that this sort of breaks this narrative that we had of humans dispersed all over the world and animals started disappearing shortly after because here this extends the temporal window

where we have the overlap of humans and the megafauna. And I think that that's critical because it shows that the early human populations were probably harvesting these animals sustainably, partly due to the fact that they had very low population numbers. So it adds a bit of nuance to some of what we think we used to know about the human interaction with the megafauna and ultimately what caused the extinction of the megafauna.

And this is just helping sort of sharpen up some of those ideas by showing that humans and megafauna did actually coexist for longer than we thought. And if they did coexist for longer, you mentioned extinction. So can I keep on that a little longer? Because what do we think ultimately does happen to these early humans if they were in America some 22, 23,000 years ago? We have tantalizing clues, but until we're able to find bony evidence of these early Paleo-Indians at sites like White Sands, it won't be possible to do a full DNA profile. So it's not necessarily something that we have a lot of evidence for to be able to say what is the genetic ancestry of these people who were living at White Sands relative to the modern Native

American populations and relative to the rest of the populations in the Americas however in time it may definitely be a possibility to be able to build up a profile for which we'd obviously need more evidence and White sands might not be the best place to look for that evidence because we don't have this good bone preservation that you would expect or you would hope for if you wanted to do paleogenetic studies. However, these are questions that I think will shortly be answered. They may show, as you would expect, that early migrations into an area are not always successful and are not always long-lived. So we might expect that the people who lived at White Sands did not survive long enough to

contribute their gene pool to the people in the region today, but actually died out. And it would just be interesting to have that evidence and to be able to talk about the complexity of how certain groups on the landscape may survive, other groups might become locally extinct, and what that means in building up the pattern of genetic diversity on a landscape. And you mentioned as we were chatting not too long ago about how this new discovery might suggest that certain other sites that were potentially older than first thought are older. What sites are we talking about that we're now thinking could date to this earlier period than previously thought humans came

to North America? This Chiquite cave in Mexico is something that was published in the last few years. The cave has been dated to 30,000 years based on the kind of stone tools that are in the cave. has been dated to 30,000 years based on the kind of stone tools that are in the cave and this is something that people have really been very excited about but also very skeptical about and so there again some of the problems are that the inferences are that it's very old but you really need to build the case very well for the dating and people said it's too old it's not possible it's not possible that it's 30,000. It just can't be. So now, of course, now that we've presented this evidence, it means that people can go back and look at some of these older sites with a slightly less sceptical eye. And that other sites might then be discovered. People might start working in these areas and build up a fuller picture, perhaps, of life in Mexico and in New Mexico older than 23,000. And Sally also this

new discovery at White Sands for you in particular why is this discovery so valuable so special? I'm learning about the ecology of extinct fauna so for example we've never had an opportunity to observe a giant ground sloth family but we could potentially find ground sloth tracks which may show us a bit more about the ecology of these species. So although I'm aware that in a few months time there may well be an older site that's proposed it's the nature of things to continually push back these boundaries that for me the value of working at White Sands is to have this window into the past and to compile this unparalleled archive of behaviour both of these extinct megafauna and

the humans on this landscape and that's the real value of the site to me. Seeing those connections between animals and humans like several thousand years ago. Absolutely and this again is evidence we couldn't just get from the bony record alone. So in this way, technology is really helping us understand these people's lives, both the powerful moments where they're stalking large fauna, potentially trying to hunt them and kill them, to other more playful elements where you've got children playing in puddles left by mammoth prints, for example. And so we've got this whole range of human experience that is encapsulated in the footprint evidence.

And that is just a phenomenal archive to be able to work on. It's phenomenal. Amazing stories. This is such an exciting new discovery, not least because the discovery itself, but because of all of these new, exciting questions, all of these new, exciting roads that people like yourself and your huge team can go down in the future to try and learn more about these early people in North America. Well, I'm very excited to be a part of the work. We can't really believe how lucky we are. We feel immensely privileged that we've had an opportunity to develop the site and to be able to bring these interesting stories to the public so we do we feel extremely grateful and very keen to get out and to

continue the field work next year. Well Sally I won't keep you any longer as you've got lots of very important work to do on this and more and it all goes for me just to say Sally thank you so much for taking the time to come on the podcast today. Thank you.