On the Human Condition
Volume XXVIII Number 2
Photo © Tyagan Miller
Model of Kennewick Man skull
Photo courtesy Friends of America's Past, www.friendsofpast.org
Letting Ancient Genes Speak
At first glance, Frederika Kaestle seems to have an identity crisis on her hands. She is an anthropologist, but she more often wears a head-to-toe "clean suit" inside a pressure-controlled lab than wields a shovel or scribbles notes in the field. She's an assistant professor in Indiana University Bloomington's Department of Anthropology, but she spends much of her time at the Indiana Institute for Molecular Biology on the opposite side of campus.
Kaestle calls herself a molecular anthropologist, but that's not as contradictory as it may sound. Her tools may be the newest molecular biology techniques, but her research interests are firmly rooted in anthropology's age-old questions about human life and culture.
Kaestle is an expert in ancient DNA (aDNA). It turns out that DNA--the genetic code that plants, animals, and humans carry in their cells--can survive for millennia. Kaestle says 100,000 years ago is "a reasonable cut-off point" for recovering viable aDNA. In her genetic anthropology laboratory, she and her students extract and sequence the ancient DNA of bones (and sometimes teeth) taken from locations around the world such as Machu Picchu, Iceland, Israel, and many sites in the Americas, from Alaska to Brazil. The lab's oldest samples are 12,000-year-old remains of Paleoindians, the earliest people of the Americas.
Who were the earliest people in the Americas? Where did they come from? How are those earliest peoples related to Native Americans alive today? These are hotly debated questions in anthropology and beyond, and after more than a decade of collaborative research, Kaestle and colleagues from the University of California believe they've arrived at some pretty clear answers.
In a series of studies, Kaestle and her collaborators have extracted ancient mitochondrial DNA (mtDNA) from approximately 20 North American Paleoindians and compared that ancient mtDNA to mitochondrial DNA from living peoples. Kaestle notes that ancient DNA studies often focus on mitochondrial DNA, which is found outside the cell nucleus, because mtDNA is passed from mother to child, making it an excellent indicator of lineage.
"If you look at modern Native Americans," she explains, "their mtDNA falls into one of five major matrilines [a line of descent from a female ancestor], which are known as A, B, C, D, and X. These matrilines are a subset of matrilines found in Mongolia and Western Asia. So our question was, what lineages would we see in the Paleoindians? What we found, mostly, was A, B, C, D, and X."
What this means, according to Kaestle, is that today's Native Americans are descendants of an ancient population that came from Asia.
A few decades ago, such an hypothesis was hardly controversial; it was generally assumed that the first peoples of North America were ancestors to living people today. But that assumption has been called into question by scientists studying morphology, or the form and structure of organisms. "If you look at the anatomy of these ancient peoples, their cranial form, tooth form, things like that, they just don't resemble living Native Americans very much," Kaestle says. "That has led to a lot of debate about whether there might have been an early population that did not survive, one that was different from and not ancestral to modern Native Americans."
In Kaestle's view, the genetic confirmation provided by aDNA research is hard to refute. She admits she and her colleagues don't yet have a good explanation for the lack of resemblance between ancient and modern-day Native Americans, but she says, "it's pretty clear from the evidence that there is continuity between ancient Paleoindians and modern Native Americans. The modern Native Americans are the descendants of the first people who got here 12,000 to 15,000 years ago. Otherwise, we wouldn't see the same lineages."
Futuristic Tools, Prehistoric Facts
Ancient DNA and molecular biology techniques "allow us to access data and information that is just not available in any other way," Kaestle says. "You can use similarities in material culture and language and anatomy to hypothesize about biological relationships between populations or villages or families, but ultimately, the only sure thing to use is biological markers such as DNA. DNA is a very good way of determining biological relationships."
And understanding biological relationships, Kaestle explains, leads to deeper insights into ancient cultural practices and social organization. "For instance," she says, "we may be testing an hypothesis that certain mound-building people started a new mound for each new matriline in the culture." If aDNA findings bear out the assumption that each mound contains human remains from a distinct matriline, then "that tells us something about how kinship was structured, about how that culture thought about families, and maybe even something about status," she continues. "The type of grave goods in a mound indicates status. Did different matrilines have different status? Or was status not associated with family?"
Ancient DNA from nonhuman sources such as animals also enhances researchers' understanding of ancient cultures. Kaestle explains that anthropologists have many questions about wildlife in prehistory, including where various animals existed, how they were utilized by ancient Native Americans, and how those uses may have changed after Europeans arrived with their animals. But when it comes to the bones of, say, ancient bison and cows, it can be hard to tell the difference. Ancient DNA tells scientists which is which. And knowing that, Kaestle says, "tells us what kind of game a population was hunting, which tells us what kind of knowledge the people had in order to be able to hunt that game, as well as how far they may have traveled to hunt."
Discoveries using aDNA shed light on burial practices, bison populations, and even prehistoric bacteria--DNA is especially useful for understanding ancient patterns of infectious disease, Kaestle says. Currently, she is exploring tuberculosis (TB), which can be detected genetically in human remains. Although severe TB leaves readily detectable lesions on bones, "that's only the minority of infections," Kaestle says. "If you want to understand how TB affected an entire population, you need to know what proportion of that population was infected, and aDNA gives us a much better picture of that."
It also offers a bigger picture of the infected population's culture. "We know today that TB is often much more problematic when you have a dense population under stress," Kaestle says. "Knowing that an ancient group suffered from it allows us to think further about the wider context of that group's living situation."
Like her work with Paleoindians, Kaestle's TB research, done in collaboration with IU Professor of Anthropology Della Cook, is clarifying a persistent debate regarding the emergence and spread of TB in North America. It's been confirmed that TB was present in ancient Native Americans before European contact, but Kaestle says her research team is "the first, I think, to identify which strain of TB these ancient people were infected with."
Based on preliminary analyses, Kaestle's team has concluded that the ancient North Americans in her study (the remains date back a few thousand years) carried a TB strain not seen today. "Our findings suggest that these populations were infected with a precursor of what infects humans today," she says, "and that, perhaps, the first populations brought it with them when they came from Asia."
Today, when more than 1.5 million people worldwide die every year from TB, including some 1,500 deaths every day in Africa, greater knowledge about the evolution of TB is clearly significant, says Kaestle. "This work increases our understanding of how evolution works between humans and disease, which has obvious implications for world health and our treatment of TB today."
Kennewick Man or Ancient One?
Given its capacity to prove--or disprove--relationships between ancestors and descendants as well as point to--or away from--cultural connections between the long-dead and the living, aDNA research can have significant ethical implications. As Kaestle and co-author Ann Horsburgh write in a 2002 Yearbook of Physical Anthropology article, "the results of aDNA studies may impact the social, political, and legal situation that living groups find themselves in and may contradict or offend beliefs about their ancestors and origins."
Kaestle underscores such ethical concerns throughout her writing, research, and teaching, a sensibility that stems in part from her own early experience with a very contentious study.
In July 1996, ancient human skeletal remains were found in the Columbia River near Kennewick, Wash., an area that is overseen by the U.S. Army Corps of Engineers. The remains, later determined to be those of a 9,000-year-old Native American, were immediately controversial. Local and government officials, Native Americans, and scientists all made claims on what should be done with the bones, which were dubbed Kennewick Man by anthropologists and the press but called Ancient One by Pacific Northwest Indian tribes.
Shortly after the remains were found, the local Benton County (Wash.) coroner requested analyses of them, which brought some of the remains to the University of California, Davis lab where Kaestle was a graduate student. She began doing aDNA analyses but the federal government quickly halted the tests. In response to tribes who claimed the Ancient One as an ancestor, the U.S. Army Corps of Engineers agreed to re-bury the remains without study. In October 1996, a small group of anthropologists quickly filed suit to block repatriation and keep the Kennewick remains available.
"In the process of the suit, the federal government was instructed by the judge to do more analyses of the Kennewick remains to figure out whether they could be culturally affiliated with a modern-day tribe," Kaestle recalls. By this time, in 2000, Kaestle was running her own aDNA lab at Yale University, and for a second time, she was asked to analyze the Kennewick Man.
"I said yes," she says, "but the two samples I received were heavily mineralized. They'd turned to stone, essentially. So after months of effort, we weren't able to recover any DNA at all."
Eventually, the scientists who filed suit won the right to study the remains, although the court cases continued until summer 2004, when the Indian tribes involved decided against appealing to the Supreme Court. Today, a team of researchers is examining the Kennewick remains, which are housed at the University of Washington's Burke Museum of Natural History and Culture, a "court-ordered neutral repository."
As Kaestle looks back on the Kennewick case today, she calls it "regrettable."
"To be honest, I wish I had not worked on Kennewick the second time around," she says. "It's not that I think the remains should have been repatriated; I would certainly be interested in any DNA results from the Kennewick Man. But in my work, I try to err on the side of respecting the wishes of living peoples, and in this case, the tribes did not want any work done.
"It's a tough case; I just wish a decision could have been reached that would have been happier for all involved."
Every case of aDNA work, whether it involves aboriginal peoples of the Americas, Australia, the Pacific Islands, or elsewhere, must be "a negotiated situation," Kaestle says. "As researchers, we must always consider, who are the stakeholders, what are their feelings, and what are our obligations to them? In my experience, open and honest communication among the various stakeholders--anthropologists and archaeologists, native peoples, the government--often results in an agreement for the study to proceed, with repatriation afterward."
Genes, Not Culture
That said, Kaestle hastens to add that "genes are not culture." In other words, proven genetic links between an ancestor and a descendant don't prove a cultural connection.
"I have a genetic link to a lot of people in the past, including my ancient Scots ancestors," Kaestle says, by way of example. "But do I know what those ancestors of 10,000 or 12,000 years ago would have wanted? I'm sure I don't believe the same things. People alive 10,000 years ago don't have a lot in common culturally with people alive today."
Although it is possible to culturally affiliate living Native Americans with more recent but still prehistoric peoples (around 500 to 600 years old), Kaestle says making such a connection to Paleoindians is too big a stretch. "Basically, 9,000 or 10,000 years is a lot of time for cultures to change. When you reach back that far, we're talking about the origins of agriculture. That's how old Paleoindians are.
"When it comes to how Native Americans have been and continue to be treated in this country, we have a lot to be regretful about," Kaestle acknowledges. "But there is a limit to what anthropologists can do to redress the problem."
Despite the ethical pitfalls of working with ancient remains, Kaestle is thoroughly enthusiastic about the future directions of aDNA research. As genetic technologies continue to advance--she cites DNA chips as an exciting development--she predicts that even more ancient DNA, perhaps 200,000 years old, will become readily accessible in the lab.
In the end, though, it makes little difference that her tools are the most modern instruments for mapping genes. "I study what anthropologists and archaeologists have always been interested in, kinship, populations, how people define themselves, and how all of these things have changed over time," Kaestle says. "DNA is just another tool to approach the same old questions."
Lauren J. Bryant is editor of Research & Creative Activity magazine.