Photograph by Chris Mueller Archaeology isn't always pretty. Just ask Karl Reinhard, the world's foremost expert in ancient feces analysis. Sifting through the dung heaps of history may not be the most glamorous work, but it provides important insights into long-lost details of daily life—most notably, the state of health in different cultures and in different settings. In order to reconstruct the health of ancient diets and environments, Reinhard looks at everything from pollen grains to bone chemistry. An archaeologist and paleopathologist at the University of Nebraska at Lincoln, he spoke with Discover reporter Jocelyn Selim about his scatological work.
What can be learned by studying prehistoric feces? Most obviously, if you know what people were excreting, you can get a pretty good idea of what they were eating. If you find thorny-headed worms, you know they were eating insects. If you see roundworms, you know there was meat. It's all part of establishing the relationships between human behavior and environment and the diseases they had. We didn't end up with all the diseases we have around now by chance. They evolved with us, and we want to know how that happened.
So how does that coevolution happen? Diseases change with the environment; there are a couple of historical milestones that illustrate when that relationship is especially evident. One is the move towards urbanization. The Anasazi, a Pueblo group in the American Southwest, began forming villages in caves about 10,000 years ago. When they did, the level of pinworm infection hit about 100 percent. Then when networks of villages appeared along rivers, all of a sudden there were fecal-borne parasites, whipworms, roundworms, and hookworms. The minor parasites of hunter-gatherers, which came mostly from eating insects incidentally, were replaced with nastier diseases when people started living in close quarters and letting their feces build up in one place.
What is the worst disease linked to urbanization? There is a particularly bad one called Chagas' disease, which is still around today, mostly in South America. It's caused by a single-celled protozoan that can get in and disrupt the nerves of the intestinal tract so that a person stops eliminating. We see mummies with masses the size of soccer balls in their guts, which would have ruptured, releasing a massive amount of bacteria into the system. It takes weeks, and it's a horrible way to go. We didn't have that parasite until we started building adobe houses, which that little bug loves.
So we created our own monsters when we decided to live more closely together? There's more to the story—the other historical milestone. Probably the main way new diseases appear has been through the domestication of animals. That allowed host jumping, in which a bug that infects some kind of animal switches over to us. I think there are only five or six parasites that we can say with certainty were parasites of humans before Homo sapiens emerged as a distinctive species. Parasites, bacterial and viral diseases—you name it, we got them from animals. AIDS was certainly endemic to nonhuman primates. Flu pandemics have been blamed on pigs and birds. And, of course, West Nile virus.
So are you really researching the prehistory of West Nile virus and other such emerging diseases? I'm examining the path of ecology of ancient times to look at specific periods of time and specific parasites and to see what human behaviors created an environment that allowed parasites to jump hosts. Maybe the West Nile thing happened before. This research helps us figure out how and why we get new diseases. We're getting at the point technologically where we can find evidence of DNA mutations associated with the host-jumping phenomenon. These tools may one day protect us from future epidemics.
Has your work changed any ideas about the spread of disease? Twenty years ago, when I started this project, nobody believed we would find parasites in the Americas. In fact, Native Americans had already accumulated quite a spectrum of parasitic diseases before the Europeans arrived. Take the Incas. We're looking at no less than three species of lice, not to mention different varieties of fleas, tapeworms, hookworms, the works. The Incas did seem to have fewer bacterial and viral diseases than Europeans did. But urbanization and agriculture brought these diseases to the Americas as well.
How do we defeat parasites in an increasingly urban world? I've been working with archaeologists at Hartkin Archaeological Associates in Albany, New York, looking at how social changes affected parasites. During the 1700s, parasitism was unavoidable: In some of the latrines, there were 300,000 parasite eggs per milliliter—about a fifth of a teaspoon. In the 1800s, the number of parasites dropped to tens of thousands of parasite eggs per milliliter. Now, it doesn't seem to be a problem. Proper sanitation can work wonders in reducing the risk of epidemics.
Mostly it seems like disease has brought only suffering. Has it had any positive effects? My hypothesis is that these parasites created us the same way we created them. For example, parasites produced an intense evolutionary pressure on emerging humans. Those with better brain capabilities and more memory could better associate behaviors, avoiding places and using certain medicinal plants, say, to keep from getting sick. So maybe we have worms to thank for our big brains.