by Cherie Winner | © Washington State University
When archaeologist Bill Lipe returned from a dig in Utah’s redrock canyon country in 1972, he brought with him several bags of treasure. It wasn’t something most people would recognize as valuable; no fine pottery or knapped flints or bone whistles.
Lipe brought back trash.
He and his colleague R.G. Matson had spent the better part of a week excavating a midden, a garbage heap that had been used by different cultural groups from the early years AD well into late Pueblo times, in the 1200s. He thought it time well-spent; trash is one of the best sources of information about any culture, ancient or modern. Just think of what your own trash says about you and your household.
The midden lay in a natural rock shelter. Nearby stood a rectangular enclosure made by closely-spaced sticks a few feet long, stuck into the ground. Based on its size and the number of ancient turkey droppings on the ground, archaeologists think the Pueblo people who made the enclosure kept turkeys in it. Whether they did or not, the pen is so distinctive that the site was named for it: Turkey Pen Ruin.
What caught Lipe’s attention was that turkeys had clearly lived at the site long before Pueblo times. Deep in the midden, in layers laid down by Basketmaker II people between 100 BC and 500 AD, he and Matson found hundreds and hundreds of dried turkey poops.
It seemed unlikely that the poops, or coprolites, could have come from wild turkeys that happened to forage at the site. But it was almost as unlikely that they came from domesticated birds. The Basketmakers were early agriculturists who tended fields of maize and squash and stored their surplus corn in pits and bins made of stone slabs. Keeping modest flocks of turkeys might have fit their lifestyle just fine. But where would the turkeys have come from? Turkeys were originally domesticated by pre-Aztec people from wild turkeys in central Mexico, before 200 BC. Had domesticated turkeys been brought north from Mexico, as maize and squash had been? Or had the Basketmakers domesticated turkeys themselves, from the wild “Merriam’s” turkeys that roamed the Four Corners region?
Lipe and Matson knew the poops could hold the answer. Their field crew dug out a tower of trash, a stack 50 centimeters square and a meter and a half deep, and Lipe lugged it to the Museum of Northern Arizona, where he was assistant director. A few years later, when he joined the WSU faculty, he brought the midden material with him.
“It doesn’t sound like much, but that’s really a lot of dirt. It weighs a lot,” he says. He tried to analyze DNA from the Turkey Pen poops with the help of WSU molecular biologist Gary Thorgaard, who uses DNA analysis to trace the relationships of modern-day trout, but techniques for extracting DNA from such old specimens weren’t well-developed at the time.
“Ancient DNA is really tricky,” says Lipe. “The potential for contamination is so high, because the DNA is usually degraded.”
So the bulk of the midden material sat in storage until 2007, when Brian Kemp joined the faculty. The enthusiastic, fast-talking Kemp specializes in extracting and analyzing DNA from ancient materials—bones, teeth, mummified poops. Using “new tools to study old problems,” he had worked on questions such as the origins of American tribal groups and the migration of early peoples southward along the Pacific coast.
“He has so much energy. He’s a lot of fun to work with,” says Lipe.
Kemp is all for investigating ancient trash heaps. For him, the conventionally pretty kinds of archaeological finds don’t hold a candle to well-preserved poops. In some ways coprolites are even better than bones as a source of information about ancient people or animals. In addition to providing the DNA of the individual that produced them, they also tell us what that individual had eaten.
“They’re a perfect repository,” says Kemp of preserved poops. “These things are a perfect source for studying ancient population genetics.”
But Kemp had never worked with non-human DNA before, and when Lipe suggested the turkey poops might be worth a look, he hesitated. He and Cara Monroe, his lab manager, fiancé, and fellow archaeologist, ran some samples to see whether the work was feasible.
“I didn’t know anything about turkeys. And I have to say, I wasn’t particularly interested in it—until it worked,” says Kemp. “But once it worked, and it worked well, it was like, ohh, this could be big.”
Kemp’s lab is broken into separate rooms, one for handling ancient samples and the other for handling present-day material. He’s a pretty free-wheeling guy, but he insists that everyone in the lab obey one rule: Never, ever go from the Modern room to the Ancient room. If you have work to do in both, do the Ancient first. If you must do something in the Modern room first, when you’re done there, go home, shower, and change clothes before heading into the Ancient room.
The worry is that cells (and their DNA) from modern-day organisms might contaminate the ancient samples. The lab’s strict procedures do a good job of reducing contamination, but “foreign” DNA still sneaks through at times—which isn’t all that surprising, when you think about it. The samples have been in a trash dump for more than a thousand years; how could they not be contaminated?
Midden material is loaded with human hair, and Kemp’s grad student BreAnne Nott has found tiny bat hairs in the turkey poops (not because the turkeys were eating bats, she hastens to explain, but because the poops came from a site under a rocky overhang that probably sheltered bats). Contamination by mouse DNA is common, probably because mice had the run of the midden for generations. “When you open up the bags of midden from the Turkey Pen ruin site, it smells like mouse urine,” says Kemp. “It’s overwhelming, like you don’t even want to be in the room, it so much smells like mouse urine.”
In one corner of the Ancient lab, a tall metal cabinet holds cardboard boxes and brown envelopes bulging with zip-lock bags containing specimens: feathers and bones from various species, as well as coprolites— human, dog, undetermined, and, of course, turkey. Most of the turkey poops are 2-3 inches long and a bit bigger around than a standard yellow pencil. They’re brownish-gray, dry and crumbly, but amazingly intact considering they were produced by birds that lived more than 1,500 years ago. That they are still recognizable is a testament to the preservative power of a dry climate and the sheltered location in which they were left.
To get DNA from a turkey dropping, Kemp cuts across it and scoops a small sample out of its interior. He says cells from the intestinal lining continually slough off and join the soon-to-be fecal matter, ending up all throughout the poop, not just on the surface. In fact, he purposely avoids sampling the surface of the poops, as those are the areas most likely to be contaminated by things like mouse urine.
He puts each small sample into a plastic test tube and adds a chemical solution, bringing it back to life, in a sense. “These things soak up so much liquid. They get totally black and really gross-looking,” says Kemp, who adds that a successful retrieval is obvious to everyone in the room. “It smells like being on a farm. Once you rehydrate them, they are very distinctly bird crap.”
After extracting whatever DNA they can get from the samples, Kemp and undergraduate student Scott Wyatt hone in on sequences that come from mitochondria, the energy-generating structures within cells. For studies like this one, mitochondrial DNA (mtDNA) has two big advantages over DNA found in the nucleus. First, each cell has only one set of nuclear DNA but about a thousand sets of the mitochondrial DNA, which makes the mtDNA easier to find. Second, mitochondria are inherited only from the mother; they are among the goodies stored in every egg prior to fertilization. By examining an individual’s mtDNA, Kemp can learn what genetic lineage (or matriline) the individual’s mother belonged to, which enables him to construct a moms-only family tree. Making a tree using nuclear DNA would be much harder, because with rare exceptions, any particular sequence could have come from either the mother or the father.
Kemp and Wyatt look for three short stretches of DNA that accumulate mutations at a rate that allows the researchers to trace relationships over a span of several hundred to several thousand years. If the same sequences from two strains have few differences, the strains split from each other fairly recently. The more differences they have, the further back the strains diverged and the more distantly they are related.
Kemp compared DNA from Turkey Pen poops with the same sequences from six modern-day subspecies of wild turkeys, which had been established a few years ago by a researcher at Northern Arizona University. That would tell him how closely related the Turkey Pen birds were to those subspecies. He also wanted to compare them with DNA from the Mexican turkey that had given rise to the Aztec bird, the one already known to be domesticated. That comparison posed a special problem: The Mexican subspecies has been extinct for decades.
“We needed something that would baseline what we were looking for,” recalls Monroe. “I just immediately thought, ‘oh, the Smithsonian should have something.’” Sure enough, the zoology section of the Smithsonian had specimens of the Mexican bird that had been collected around 1900. She and Kemp wrote a proposal asking for small samples from the birds, and were rewarded with a package of barely visible bits of toe-pad tissue. “It was a tiny amount,” says Monroe. “It was like a fleck.” Kemp’s team was able to extract useable DNA from eight of the 12 samples, enough to give them the baseline data they needed.
While Kemp and Wyatt went after the DNA, graduate student BreAnne Nott looked for pollen grains within each turkey poop, for clues about what plants the turkeys had eaten. Her results are still preliminary, but so far Nott has found pollen of juniper, willow, and wildflowers—plants that turkeys (wild or domestic) might pick up while foraging near the Turkey Pen site. She’s also found substantial amounts of maize pollen. Maize means people, says Nott, and while wild turkeys could have picked up maize pollen by foraging in or near the fields, the amounts of it that Nott is finding—in one poop, 70 percent of the pollen grains were from maize—argues against casual acquisition.
To Kemp, the conclusion is clear. The turkeys weren’t just eating. They were being fed. They were domesticated.
Even more convincing evidence of domestication came from the DNA analysis. Among the dozens of Turkey Pen turkey poops Kemp and Wyatt have evaluated so far, only two maternal lineages appeared. Populations of wild turkeys in the area around Turkey Pen have at least 17 maternal lineages; if the midden poops had been made by wild birds wandering through the site, or if the people were simply catching wild turkeys and holding them in camp until slaughter, several more matrilines would be represented in the poops.
Not only that, but the most abundant Turkey Pen lineage is also the predominant matriline found in turkey bones from 36 additional archaeological sites around the southwest. Camilla Speller and her colleagues from Simon Fraser University identified it at sites spanning thousands of square miles and more than a thousand years of occupation.
There’s no question the Turkey Pen birds were domesticated, says Lipe. “The people were controlling their breeding. That’s the definition of domestication.
“This is what [the Basketmakers are] focusing on. They and their descendents are conserving, for more than a thousand years, one particular variety.”
The DNA results also presented a new puzzle. When Kemp compared the dominant Turkey Pen matriline to the lineages found in the six wild subspecies, he got a shock. That matriline is rarely seen in the wild subspecies found in the region—and it did not occur at all in the wild Mexican turkeys that gave rise to the Aztecs’ domesticated variety.
If the Basketmaker birds were not derived from local populations of wild turkeys or from Mexican birds, where did they come from?
Kemp’s family trees showed the unexpected link: Basketmaker turkeys were close relatives of turkeys native to eastern North America and the Gulf Coast of Texas and northeastern Mexico.
“It’s a total surprise to everybody,” says Lipe. The finding has big implications for our understanding of early Native American cultures. It means turkeys were domesticated at least two separate times: once, before 200 BC, by pre-Aztecs in central Mexico; and once by people yet undetermined, probably at about the same time, somewhere to the east or southeast of Turkey Pen Ruin. Exactly where, and by whom, remains to be discovered. Turkey remains from that period in the central and eastern United States haven’t been studied as fully as those from southwestern sites, but that is beginning to change. Kemp recently started collaborating with a colleague who found turkey bones in an early Moundbuilder site in Alabama, to find out what lineage those turkeys belonged to.
What excites Lipe the most is that the DNA results confirm what the historical accounts suggested. Like tomatoes and tobacco, turkeys were a gift from the New World to the Old. When the Spanish came to the New World in the early 1500s, Europe had no turkeys of its own, wild or domestic, but the Aztecs in Mexico already had flocks of turkeys numbering in the hundreds of birds. The Spaniards took some of those birds back to Europe, where they thrived as barnyard fowl. They became favorites of bird fanciers, who bred an array of showy, distinctive strains from the basic Aztec stock. Within a couple hundred years they’d become such a symbol of holiday abundance that Charles Dickens had Scrooge prove his new-found humanity by buying the Cratchit family the huge turkey hanging in the butcher-shop window. And when the Pilgrims and other immigrants started their new lives in America, they brought turkeys with them—turkeys descended from birds that originated in Mexico.
Kemp’s lab even analyzed DNA from present-day supermarket turkeys, and found that they are quite different from North American wild turkeys, but they differ from the Mexican wild turkey by just one mutation. In other words, the turkey on your table this Thanksgiving is descended from birds tended by Aztecs.
As for why the turkeys were domesticated, Kemp has a hunch about that too, and it does not involve a Basketmaker version of Thanksgiving. He thinks the birds were initially kept and bred for their feathers, only later becoming a major food source.
Turkey feathers, like maize pollen, played an important role in southwestern rituals and ceremonies. The Basketmakers also used them to make sturdy, warm blankets that warded off the chill of high-desert winters. Feathers were split down the quill and each half was then twisted with yucca fibers to make strong cord with the feathery parts fanning out around it. Woven into a blanket, such cordage gave the cloth heft, fuzz, and insulating power.
While fragments of turkey feather blankets and cordage have been found at Basketmaker II sites elsewhere in the region, turkey meat doesn’t seem to have been a hot commodity among southwestern peoples until the 1200s. In later Pueblo times, a large proportion of the faunal remains in a site are turkeys, says Kemp. “They’re eating turkeys all the time.”
If Kemp and his colleagues are right about Basketmakers keeping turkeys for their feathers, they’re still left with the dual mystery of what they did with the meat and why the midden contains so few turkey bones. Monroe says the people almost certainly killed the birds to get the feathers, rather than waiting until the feathers dropped off naturally. By the time feathers are molted, they are beat-up and ragged and not good candidates for use in either rituals or blankets. A crop of fresh, strong feathers would require killing the bird.
So what happened to the bones?
Even Lipe, who has explored hundreds of sites in his decades as a field archaeologist, is puzzled about the lack of turkey bones in the midden. Then again, he says, a bird leaves just one set of bones during its lifetime, but thousands of droppings. In a climate that preserves poops almost as well as it does bones, which are we more likely to find 1,500 years later?
Monroe thinks the Basketmakers’s other domesticated species, their dogs, could be the answer. If the Basketmakers fed the turkey carcasses to their dogs, the bones would have been crunched into small bits that could be all but impossible to identify now. But the midden material does include dog poops, which probably retain the DNA of whatever the dogs ate. Monroe adds analysis of dog poops to the ever-growing list of Turkey Pen projects for the lab to consider.
Those bags of trash Lipe brought out of the midden 37 years ago are providing a magnificent harvest.
“There’s decades of research there,” says Kemp. “With the genetic tools that we have—and the garbage is such a rich resource of information—there are so many ideas that you could address with just this bag of garbage.”
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