Season 6 - Episode 621
Daniel Peppe, associate professor of geosciences, is part of an international team whose decade-long research project has shifted Africa’s prehistoric timeline by ten million years. Their revolutionary discoveries were featured in the journal Science and supported by National Science Foundation funding. In this Baylor Connections, Peppe takes listeners to eastern Africa, where multi-disciplinary collaboration yielded insights that have a major ripple effect throughout the scientific community.
Derek Smith:Hello and welcome to Baylor Connections, a conversation series with the people shaping our future. Each week we go in depth with Baylor leaders, professors, and more, discussing important topics in higher education, research and student life. I'm Derek Smith, and today we are talking about groundbreaking research in the geosciences and beyond. We're visiting with Dr. Daniel Peppe. Dr. Peppe serves as associate professor of geosciences at Baylor. His research focuses on understanding how environmental change drives evolutionary processes in plants and animals, with a specific focus on reconstructing ancient climates and ecosystems through time in North America and East Africa. As a researcher, Peppe has been part of an international team whose National Science Foundation funded work, has shifted Africa's prehistoric timeline by 10 million years through insights gleaned from the presence of warm seasoned grasses. The project was featured in the Journal Science and it's going to have a ripple effect that we get to discuss today. Dr. Peppe, thanks so much for your time and thanks for joining us on the program.
Daniel Peppe:Yeah, thanks for having me. I'm excited to get a chance to talk to you about the work.
Derek Smith:Great to visit with you on this. And I think the fun challenge of this is going to be really, there's a lot of layers to this, literally and figuratively, that we can break down here over the next 20 minutes or so. So I'm wondering, as we talk about some of these things, C4 grasses or warm season grasses, the early Miocene, shifts of 10 million years. I think a lot of us without a science background, not looking at a chart, we could get lost if we're not careful. So could I have you give us a little 101? Could you give us some vocabulary words that if we just have a basic understanding of them, they'll help unlock the conversation?
Daniel Peppe:Yeah, that's a really good question. And the topic is obviously really complicated and it's compounded by the fact that we're talking about something that happened millions of years ago, and most of us don't think about things millions of years ago. So when we talk about the Miocene, the Miocene was a time period in earth history that began about 25 million years ago and ended, I'm trying to remember exactly, about 6 million years ago, somewhere in that ballpark. And what we're talking about is this time period known as the early Miocene. And that time period is between about 15 and about 25 million years ago. And in particular, what we are talking about is this time in the early Miocene in eastern Africa, when early apes were evolving. And so this time period is really interesting from the standpoint of what's happening on the landscape, what the animals and what the plants are. So in the early Miocene, this is when early apes evolve. This is also the time period where we start to see the ancestors of the modern African ecosystem. And so things like ancestors of elephants for the first time, ancestors of rhinos, ancestors of hippos, all of those types of animals. The things when you think of, the African mammals, those, their ancestors are evolving and their first occurring in Africa during the early Miocene. So that's one piece is this ancient timeline. And then the other piece is actually talking about the ecosystems themselves. And so one piece of this is we talk about open and closed ecosystems. And the difference between them we could think about that is really has to do with the amount of space there is between the trees and if the branches and trees are interlocking or overlapping. So in closed systems, these would be forested environments. Generally the branches of the trees, they're connected or interlocking, the understory, so underneath the canopy is relatively dark. The places where there's light are places where there are breaks where maybe a tree is falling down and then you start to get maybe some grass or some other types of plants. And in contrast to that would be an open ecosystem. And for those of us in central Texas, we're familiar with these, whether we realize it or not, open ecosystems are essentially just systems where there's more open parts of a landscape than there are trees. And so in open environments you often have a lot of grass. And then there's open spaces between the trees. There may be places where trees are close together, but you have lots of distance. You often have distance between trees. So let's say something like maybe 10 to 40% of the landscape is trees and the rest is small shrubs and grasses. So that's the difference between open and closed. And there are obviously very different kinds of environments, different plants, different animals live in those different environments. And then the final piece is when we're talking about C4 grasses. And so what we mean when we're talking about C4 grass is we're talking about plants that do photosynthesis in a very particular type of way. There's two types of photosynthesis, what we call C3 photosynthesis and C4 photosynthesis. And I'm not going to go into all the details. If you took college biology, you probably had this and you probably forgot about it, and that's totally fine. The key takeaway is that plants that do C4 photosynthesis, what they're able to do is they can close their pores, they're called stomata. They can continue to do photosynthesis without negative implications for the plant. So what that means is that plants that do this kind of C4 photosynthesis, they're more successful in hot and dry environments, which is why we often refer to them as warm seasoned grasses. C3 plants, which make up most of the rest of the plants do C3 photosynthesis, and there are C3 grasses. What then happens to them is that they need to open their stomata more often in order to continue to do photosynthesis without having negative repercussions. And so they're favored in cooler and more tempered environments. And the thing for C4 plants, a lot of our agricultural crops are actually C4 plants. So things like corn, things like wheat, are C4 plants. And a really major question is when did C4 plants first evolve, because they have very specific adaptations, but they also have lots of characteristics. One of the things that many C4 plants have are things that are called phytoliths. They have these little silica bodies that grow in their cells, and they're actually really difficult to chew and eat. If you've ever you chewed on a corn leaf or something like that, you'll notice it's really hard. It's because it has these little silica bodies in it. And so if you're an animal and you eat those kinds of plants, you have to have special adaptations of your teeth in order to do that. And so there's a whole evolutionary implication of when C4 plants evolve and when they occur on the different continents is a big question because C4 photosynthesis evolves more than 20 times. And so that's the thing. And so to take us back to the study, those are the kind of underlying things to get us all on the same page. And then when we talk about C4 plants, the traditional thought prior to our research was that the first occurrence of C4 grasses, these warm grasses in Africa, was about 10 million years ago. And so the idea behind that was prior to that, in the early and middle Miocene, Eastern Africa and Equatorial Africa was mostly forested. And some people have even said that it was a continuous forest. So it was a continuous closed ecosystem. And the animals that were evolving, particularly the apes, were evolving in closed forests. And so their adaptations were a result of living in forested environments. And then starting around 10 million years ago, we start to see grasses and warm adaptive grasses for the first time on the landscape. Environments start to become more and more open. And eventually that gives rise to our ancestors who become bipedal. They walk on two legs and eventually you get the modern African ecosystem. And so that's the state of where things were prior to our work.
Derek Smith:Did you and other colleagues, did you go in with the hypothesis? Did you go in trying to prove that these warm season grasses were actually found well before that? Kind of take us back to the beginnings of this research process that led to that discovery?
Daniel Peppe:Yeah. So that's a great question. And so in a lot of ways, that's not at all what we expected. And so the basis of this study, and so this project that I've been working on for the last 10 years is one that sort of came out of work that I started actually back when I was a graduate student. And so in the mid two thousands, and I was working with my colleague Kieran McNulty, whose at the University of Minnesota, and actually at that time was a professor in anthropology at Baylor University. And so we were working on one site, this site on a place called Rusinga Island in early Miocene. And we were trying to reconstruct what the climate was like, what the environment was like. And at that site, there is a bunch of early apes. And so one of the questions that we were trying to understand is, what were the environments like when these apes were evolving and how did environment influence ape evolution? And so what we realized, and this really built out of an idea that Kieran had, is what we realized, is that we could answer a question for our location, Rusinga, but there was many other sites of a similar age across Kenya and Uganda, and they had different apes at those sites. And so one of the questions was, do they have different apes at these different sites because their environments and climates are different, or do they have different apes at the different sites because they're different ages? And so the same taxa are sort of evolving through time. And those were sort of our two alternative ideas. We went in with some prior knowledge. And so we knew that the idea that the early Miocene was a total forest, was not correct, but what we didn't know was how diverse landscapes were. And we thought it was possible that they were C4 plants because there is some evidence looking at the molecular analysis of the DNA of C4 plants. There's some ideas that they evolved even further back prior to the Miocene, but we didn't really know if we'd find them. We thought we might find them at a few sites, but we actually found them to be really widespread. And that was a real surprise. And so Kieran started building this idea with some of our other colleagues. And so, we have colleagues Laura MacLatchy and John Kingston at the University of Michigan, James Rossi, who's at Stony Brook University, Susie Cote, who's at the University of Calgary, who are all paleo anthropologists, and then we also had some geologists. So Dave Fox whose at the University of Minnesota, Sky Al Dana, who's at Berkeley, Steve Driese, who's recently retired faculty member from Baylor. And so we started building this consortium and we had other colleagues, there's almost too many to mention, and I'm going to forget people and I hate to do that, but Ellen Miller, who's at Wake Forest University, Sky Zandnigo, who was at Stony Brook, Bonnie Jacobs, who's at southern Methodist, this huge consortium of people of anthropologists and geologists and paleontologists. And we put together this grant proposal that was funded to essentially work at all the sites. And so I was the lead geologist. And so what we did was all of the geologists on our team, we visited all of the different sites, and then with our colleague Rahab Kinyanjui, who's a paleo-botanist from National Museums of Kenya, she visited all the sites with us and she collected samples. And so we collected the same types of samples at all the different sites so we could reconstruct climate and environment at all these sites. And then we were working hand in hand with our paleaonthropology colleagues who are collecting the fossil mammals and the fossil apes. So we could answer our question, what were environments like when early apes were evolving, and were they the same or were they different? And that's really the nexus of this project that we've been working on.
Derek Smith:Great explanation. Thank you. As we visit with Dr. Dan Peppe and Dr. Peppe, where are some of these locations? If we're looking at the map of Africa, where would we see these?
Daniel Peppe:Yeah, so in Eastern Africa, you have several countries. And so you have around Lake Victoria is where you can kind of look. And so Lake Victoria is this huge lake. It's the largest lake in Africa by surface area, and it's bordered by Uganda, Kenya, and Tanzania. And so we were working in a series of sites in Kenya and in Uganda, and so basically western and northern Kenya. And then just across the border into Uganda is where we have all these sites. So during this early Miocene time period, this is when the East African rift system was forming. And part of that system, you have these volcanoes that are being created, they're growing, they're creating topography, they're erupting. And so you have all of these early Miocene sites that are centered on more or less sort of a north, it goes from southwest to northeast transects starting in Lake Victoria, and then moving up almost all the way to the northern border of Kenya and the northern border of Uganda.
Derek Smith:This is Baylor Connections. We are visiting with Dr. Dan Peppe and Dr. Peppe, take us a little bit around the proverbial water cooler or a chat session, if we were to show up at a conference with you and other colleagues from geosciences. Shifting a timeline by 10 million years, sounds like a lot of years, and it is. Is that as many years in geoscience time as it sounds like to us, and as you're studying this, as you're going through this, what's the implications? How, what's the sense of, "Oh, we're finding something." What's that like for you all?
Daniel Peppe:Yeah, so it is really significant. And so just to give you a sense, right? So the previous research had documented C4 warm grasses 10 million years ago. There was one study that found some evidence for them 15 million years ago, and then what we found was sites as far back as 21 million years ago. So we went from this 10 million years to 21 million years ago. So we doubled the timescale in which you have grasses. This is a really significant change. And not only that, but that previous study that had found them at 15 million years ago was a single site. And so the idea was maybe this is just isolated and it's not representative. But we have nine separate site, sort of broad site complexes that we studied, and we found grasses and we found warm grasses at most of those sites. So what that means is that we have them commonly at many sites, and they're regionally abundant. They occurred across the landscape and they occurred through time. And this is a really important and big discovery. It was something that we were surprised to find, and I think that most people didn't expect, I would say the majority of people didn't expect that. And so this now means that we now have to start thinking about, when did we first have C4 grasses? 21 million years ago is the minimum time in which they first occur in Eastern Africa. So they likely occurred before then. So that's one piece of it. The second piece of it is, we find them pretty commonly across the landscape. So that means that they're locally abundant and that they occur across Kenya and across Uganda. So that's another really big and significant change. And the piece that's also really interesting about it is, that it appears that although they're on the landscape, the animals don't really seem to be eating those warm grasses until maybe about 10 million years ago. Although admittedly, there's not a lot of information between 15 and 10 million years. So we're missing a big piece of that puzzle. But what this tells us is that those plants are on the landscape. And so this maybe suggests that it took a while for animals to develop adaptations, to eat them. It also means that we have a much more heterogeneous landscape, meaning we have a mixture of environments occurring at the same time. And so that likely played a really important role in the evolution of these modern African mammals, like the evolution of ancestors of the modern African mammals. And so it really fundamentally changes how we think about environments in the early Miocene. What it means is that all these ideas about grasses being the driver of these changes, it means that that can't be the full explanation. It may still be the reason, but those plants and those environments occurred much earlier than people had thought. So this really means we have to really rethink some of these evolutionary hypotheses. And just as an example, so we had these two papers. And so one of the papers that I was the lead author on was focused on this first C4 grasses. The other paper that I was a co-author on, was led by Laura MacLatchy from the University of Michigan, was focused on a single site. And so the single site in Uganda called Moroto, which a little bit over 21 million years ago, at that site, we find abundant C4 grass, so abundant grass. We know that it was a wooded grassland, which means that it was only 10 to maybe 30, 10 to 30% trees. So that's a pretty open environment. And what's really remarkable about it is that is the site where we have the oldest evidence of an ape, where we have both parts of the skull as well as parts of the skeleton. And the adaptations from the skeleton indicate that it had a stable back and it had short limbs, which is similar to what we see in modern apes. And the idea was that those adaptations were for climbing and swinging between branches within forests, so these closed [inaudible] forests and then eating fruit on the edge of trees. And so what we know is that the environment where this ape lived and evolved, was not a forest, it was an open ecosystem. It was a wooded grassland. And so the other thing that's really interesting is the teeth, when we look at the size and shape and the structure of the teeth, those have characteristics to indicate it was a leaf eater. And so based on the occurrence of an open environment with C4 grass, we now are hypothesizing, our group's hypothesis is that those adaptations, that this ape, what's called morotopithecus had, were for climbing up and down trees and then moving between trees and these open places on the landscape and then climbing out to the edge of branches. And so this is a fundamental rethink of why or how apes got these characteristics. And so it's this kind of result. We'll need to be thinking about this now for lots of different animals, lots of different plants, all these environments in Africa. And so it's a real sort of fundamental change in how we're thinking about the evolution of open environments and the evolution of grasses in Eastern Africa.
Derek Smith:This is Baylor Connections. We are visiting with Dr. Dan Peppe, associate professor of geosciences at Baylor. And Dr. Peppe, what's the response from the scientific community being obviously science magazine? That's a prestigious journal in which to get published, that was important to them as they shared that. Just take us through what the response has been in terms of people. Were people's minds blown a little bit? Are they going back, looking at their old research and thinking, "Well shoot this paper's no longer valid?" What's that been like?
Daniel Peppe:It's been really fun. We've gotten a lot of good feedback from our colleagues. I suspect that what we will see is that I think that this will invigorate research. This in some ways is a very controversial idea. We're overturning long-held hypotheses. And so I think what this will mean is that people will start looking at this in detail. One of the things that's that's been really interesting is that there's a huge amount of information from about 10 million years ago to the present in Eastern Africa. And there's really not very much from 10 million years to about 25 million years. And so our data set significantly increases the number of sites and the amount of data from that window from 10 to 20 million years. And so I think the next piece really is to fill in even more of these gaps. And I think that's what we're going to see, and I'm really excited and really interested to see that as that comes out, as people continue to work at this. This is now kind of a new idea, and so people can test it. And that's going to be the best part is is testing it in other sites, trying to replicate our results, seeing what they find that's similar, seeing what they find that's different, and that's when we'll really be able to put together the whole story. And so it's an exciting time for me, and I think hopefully for others in my field to start working on this. And it's a new idea to start testing and to start studying more and more detail.
Derek Smith:Well, that's very exciting. We'll look forward to that, and appreciate you taking the time today to share with us and unpack this a little bit. Congratulations on the discovery, and we look forward to what's ahead. Thanks for sharing with us today.
Daniel Peppe:Yeah, thanks so much. Thanks for having me.
Derek Smith:Appreciate it. Dr. Daniel Peppe, associate professor of geosciences at Baylor, our guest today on Baylor Connections. I'm Derek Smith. A reminder you can hear this and other programs online, baylor.edu/connections, and you can subscribe on iTunes. Thanks for joining us here on Baylor Connections.