Teacher professional development and classroom resources across the curriculum
Teacher professional development and classroom resources across the curriculum
Dr. Theodore Schurr is a molecular anthropologist at the University of Pennsylvania. For the past twenty years, he has used genetic tools to trace Native American origins. He has conducted field work in such locations as Siberia, Kamchatka and Alaska. He was interviewed at his lab on the University of Pennsylvania campus.
Q: Can you explain how molecular anthropology supports the study of what we would traditionally think of as history?
Schurr: We can think of DNA as being, to some extent, the greatest history book we have as humankind. It contains evidence of our deep origins, our links to other mammalian and primate species. It gives us evidence of our relationship to skeletal individuals, and it also tells us a lot about who we are as a modern species—in spite of some obvious physical differences that we show in our outward appearances.
Q: What is a molecular anthropologist?
Schurr: A molecular anthropologist is someone who employs the tools of human genetics to questions of human ancestry, migrations, and origins. So, rather than looking at skeletal remains or looking at archeological remains, we look at genetic remains of individuals to understand those aspects of human variation in history. My work focuses on the Americas and Siberia, primarily. After collecting ethnographic data and biological samples for DNA, we come back to our labs and analyze DNA samples to look at aspects of genetic variation.
Q: Are there examples where molecular anthropology has refuted some kind of past knowledge about history?
Schurr: Sometimes genetic evidence helps eliminate certain situations that are sort of ambiguous or historically muddy. One example is with the black Lemba of the Mozambique in Southern Africa. They have Semitic languages and some aspects of Semitic culture, but yet they are largely Bantu in terms of their phenotypic appearance. So the question is: Why would a Bantu population speak a Semitic language and practice religious rituals that in some ways reflect Semitic or Judaic traditions? When you study the DNA of those individuals—at least on the male side—you see that there are Y chromosome haplotypes that trace their way up to Yemen and up into the Middle East. These chromosomes show a very clear Semitic link to the Lemba populations in the south. In this respect, we can clarify certain mysteries about a people's history. In other instances, there are beliefs about origins which may not be scientifically based. One example might be the Mormon belief that Native Americans and Polynesians are actually lost tribes of Israel. We don't see any clear genetic evidence of Semitic origins for Native Americans and Polynesians. So, this is an instance where a religious belief may not exactly cohere with the genetic data that we obtain as molecular anthropologists.
Q: DNA differs from other forms of historical evidence in that we can't actually see it. How do you deal with this discrepancy in your work?
Schurr: It is true that you can't see DNA, at least not the same way you can read an alphabet or even evidence of disease on a bone. To some extent, you are working on faith that once you do certain biochemical protocols effectively, you're getting DNA. But the methods themselves are really the key to being able to read the text of the DNA: the mutations that show connections between people, or genealogical linkages. What we do is very much like historians who work in archives and libraries and such. We look in the archives of the genome to see what has accumulated there in terms of mutation. The process allows us to make the DNA visible in that sense.
Q: What are the big questions that you are trying to answer through your work?
Schurr: My work focuses on the peopling of the new world. The Clovis-first model has been a dominant paradigm in American archeology and anthropology for quite some time. The basic premise is that approximately 13,000 years ago, maybe a little bit longer, big-game-hunting populations coming into North America pushed through an interior ice corridor into the central part of North America. There are several reasons why the Clovis-first model is now being seriously rethought. The first is that archeological data suggest that there were pre-Clovis people in the Americas—before Clovis technologies spread across the Americas. The second is that the dates for those sites and the genetic lineage dates are around 15,000 to 18,000 years older than Clovis. The third point is that the interior route defined by the access point for the first American Clovis populations was probably closed at the time that the Clovis sites arose in the Americas. There has to be a different way for the first Americans to have come to the Americas as a consequence of these three points. The coastal migration hypothesis is a good possibility: The first Americans used coastal routes to reach other parts of the Americas. This migration seems more likely than the interior first Americans' route through the glacial ice corridor.
Q: How has your work supported this theory?
Schurr: We say somewhere between 15,000 to 18,000 years ago, genetically speaking, we can see visibility of human populations in the Americas. Archeologically speaking, the dates that people are finding for pre-Clovis people are in the vicinity of 14,500 to 16,500. These dates show the physical archeological visibility of human populations, so that is actually good support for this particular genetic idea. In terms of coastal migration routes, we're left with the archeological evidence that is available to us that's not under water. Since we don't know exactly where the prehistoric coastline used to be, we can't access those sites. But given what we do have, we think that this coastal route is probably fairly accurate. What we are trying to do now is look at current populations from Eastern Siberia—actually moving a little bit farther into the interior such as the Altai—to reconstruct the path that they might have taken to come into this area, and to determine if we find ancestral DNA in these Siberian groups. That DNA may show that they followed this kind of a coastal path into the Americas. That's part of the ongoing work that we are doing right now.
Q: What is your research process from field to lab?
Schurr: First of all, we contact Native American communities and ask if they want to be involved in this kind of research. We obtain their permission and also individual permission to participate in the work. The second step is to actually talk with them about their families, villages, and tribal histories to help us properly interpret genetic data. The third step is taking a sample that we can use for biological data, which is typically a blood sample but can also be a cheek scraping. Back at the lab, we extract the DNA from the samples: This process involves a certain set of biochemical steps where we basically get the DNA out of the cells. The second step that we typically use is called the "polymerase chain reaction," an enzymatic reaction that amplifies DNA into a million-fold copies from the original amount that we use in a reaction. This is absolutely crucial, because it gives us an enormous amount of DNA from which we can characterize sequence variations. The next step after the PCR is to check whether the amplification has worked, and so we will do a gel electrophoresis to see if the DNA is present. Then, the fourth step is to look for what are called "single nucleotide polymorphisms," or "SNPs," and these SNPs then tell us how each individual DNA strand varies from the others. The fifth step is what's called "DNA sequencing," where we are actually using an enzyme—a DNA polymerase—to read every single nucleotide in a stretch of DNA. It could be a mitochondrial DNA; it could be a Y chromosome; it could be some other part of the DNA: We are actually reading every single nucleotide base—or single alphabetic unit—in a stretch of DNA to figure out which of those have mutated, and that information gives us a much more fine-grained look at sequence variation in human populations.
Q: How have the communities you worked with responded to your findings?
Schurr: Most people understand that blood connects people. But genetic evidence may contradict certain kinds of ideas that people might have. There are a number of Native communities that are reticent to talk about genetics, because they may not be purely Native American from a genetic standpoint. This is where genetics gets controversial, because DNA tells us a lot about ancestry and who we are biologically. It doesn't say who we are in terms of our own self-identification or cultural identification. If we say we are Native American because we practice those rituals and so forth, it doesn't mean that we are not Native American because we have a European ancestor somewhere in our family genealogy—but that's where some of the controversy lies. All of our work is done with informed consent. We obtain both tribal and individual permission. So if a person doesn't want to know this information, that person does not have to participate in the project or sign up to be involved in the project. We make that informed consent explicitly clear, so we are not trying to tell anybody anything that they don't want to know.
Q: When looking at Native American DNA, how do you account for European and African genetic lineages that may be present?
Schurr: There are probably five founding primary lineages in Native Americans: They are called A, B, C, D, and X. X is unusual: It is only seen in North American populations, and that's still an enigmatic part about its ancestor history. It does seem to be associated with Algonquian speakers across North America. All five lineages have their roots in Asia, and that is true because we can see all of them widespread—except for the X group—across all the Americas. If you see genetic lineages aside from those five, and they look like types we know occur in Europe and Africa, they probably came from people of European and African decent in the last five hundred years. This hypothesis is also backed up by historical evidence, genealogical data from the tribes we are working with, and so forth. The tribes have some reckoning of their ancestry over the past number of generations, and so we can actually see very clearly when genetics meshes with these genealogical data.
Q: What is NAGPRA and how does it affect your work?
Schurr: NAGPRA is the Native American Graves and Repatriation Act. It's a piece of legislation designed to rectify the wrongs exacted upon the Native American populations in the past two hundred years—such as the taking of cultural artifacts or human bodies from graves from battlefields and so forth—in order to put them into museums in various collections. The law allows Native Americans to claim or repatriate them into their own communities, so that they can rejuvenate various cultural traditions and bring back sacred objects. This legislation has both positive and challenging influences on our work. It restricts the sorts of things we can do with human remains: The only way we can do work with human remains that are of identifiable Native American origins is with explicit agreement and permission of the Native American tribes who are claiming them. In some cases, this legislation is going to absolutely shut the door on any further work. But it also is forcing museums and archeologists and anthropologists like myself to keep talking to Native Americans much more explicitly about a whole number of issues. It will ultimately lead to each group gaining a better understanding of each other, and to hopefully promote more of a spirit of cooperation.
Q: Do you ever feel either uniquely privileged or weighted by responsibility because of the work that you do?
Schurr: The saying that "knowledge is power" is certainly true with regard to genetics. There are some unique responsibilities as a geneticist that you have to accept. You are going to get criticism from people who say that you are doing work that is racist; or that you're trying to exploit people for various purposes; or that the work you do has no particular social meaning. So, in some ways you have to have sort of a thick skin. On the other hand, you have to be very sensitive to the needs, beliefs, and concerns of the communities with whom you work. In that respect, who you are as a person emerges in the context of doing scientific work. It is easy to do scientific work without any thought about the consequences of what you do. You just work in a lab, you're isolated, all you have are your machines running and everything else, and that's all there is to it. You generate data, and you interpret it, and you don't think about the consequences in the outside world. Nowadays, that model simply isn't possible, whether it is because of NIH ethical provisions; whether it is because of the way you engage communities in this work; or because of the need to train your students properly so that they'll act ethically. And I feel very strongly committed to that process.
Q: As a molecular biologist, how to you view the concept of race?
Schurr: The early physical anthropologists used the notion of race to almost mean subspecies: the Africans were vastly different from whites, and whites different from Asians, and a whole variety of characteristics separated them all. Now we know through genetics that we are extremely similar biologically and genetically speaking, so this notion of race as subspecies has no meaning for modern humans. The differences are skin deep: They are just physical manifestations of local adaptive processes that we have undergone in the last 50,000 years as we have expanded across the globe. Anthropologically speaking, race is an important historical notion, and it's a social construct that helps to explain the variation that we see. But it has no biological meaning from a genetic or molecular anthropologist's standpoint.
Q: Obviously, issues about identity in the twenty-first century are complex, and it's a big issue to a lot of people. How is genetic evidence going to help us define our identity?
Schurr: Genetic evidence in itself is not simple. It's not going to tell us exactly that we're Catholic; it's not going to tell us that we're Irish; it's not going to tell us that we are Ethiopian. However, there are certain of these lineages or even sublineages which are much more common in certain parts of the world and suggest that our ancestors came from those places. And that's a piece of information that we will all use to figure out who we are and where we came from. But as it turns out, there are different parts of our genome that are inherited in different ways. Mitochondrial DNA comes from your mother. If you are a male, your Y chromosome comes from your father—all the other parts of your DNA come from both parents and their grandparents and their great-great grandparents and so forth. So actually, depending on what part of your DNA that you are looking at, you may actually have one biological ancestor in one part of the world and a different ancestor in another, so genetic reckoning of identity can be quite complex as well. We are complex culturally, linguistically, and biologically, and that's what genetic evidence shows us.