Haagen Klaus studies the ancient and mysterious remains of societies along Peru’s northern coastal areas. A recent project has seen him racing against the clock in the modern-day town of Olmos to rescue skeletons from a looming construction project and the scathing rains of El Niño. Here, Klaus picks up his story beginning the morning after a torrential rainstorm.
The morning after torrential rains and an exploding transformer had made the hotel go dark, electricity was restored, and just after dawn I peered outside the hotel. The rains had temporarily ceased. But their aftermath left Olmos a muddy mess and drove daytime humidity to unpleasantly high levels. Walking across streets and even sidewalks involved slogging through a lot of mud. Yet the local townspeople were glad. For several months, Olmos had been in a severe drought, with crops endangered and livestock threatened. Over the next few weeks, the rains would come again after sundown, but their on-again, off-again nature lowered the danger of catastrophic flooding. Still, everyone paid close attention to any subtle changes in the weather that could indicate if more serious rains were just over the horizon.
In our makeshift Olmos laboratory, skeletal analysis continued with my students Jenna, Butch, and Ana, project crew chief Raul, and the ASE archaeologists. In my previous two blogs, I gave some very brief descriptions of what bioarchaeology involves and how we collect data. But when bioarchaeologists examine skeletons, what do we really look at? To help you understand our findings (which will be detailed in the upcoming final blog), this installment is going to be like Bioarchaeology 101 or, How can one “read” ancient bones and teeth?
Bioarchaeological science is most concerned with life and how people in the past lived. Only very rarely do ancient skeletons tells us about how people died. Most of the information we seek deals with demography, disease, diet, physical activity, trauma, and genetic relationships.
The Tales Skeletons Tell
Some of the most important and basic information from ancient bones involves demography—especially the age and sex composition of a group of skeletons. From the time we start to develop bones and teeth in utero, various aspects of our skeletons change rather predictably. Among children, a most likely age-at-death can be found from studying the different stages of tooth formation and eruption patterns, bone growth, and fusion of the growth plates at the ends of many bones. Among adults, we study a series of relatively predicable degenerative skeletal changes, especially the degeneration of stable joints in the pelvis. In terms of sex, the skeletons of boys and girls are virtually indistinguishable, and it’s only during and after adolescence that the skeletons of males and females become distinct, with size and shape variations developing in the pelvis and the skull.
Age and sex patterns in a sample of ancient skeletons can also tell if they’re representative of a once living population and not a random or skewed group of individuals. Demographers have worked out the most likely distribution of the ages-at-death in living populations, so we can compare our samples to see how similar they may be.Within the structures of ancient cemeteries (an example of which is seen here) are many potential reflections of demographic patterns, such as age-at-death, sex ratios, and birthrates. (Photo by Haagen Klaus)
Another very intriguing use of demography from skeletons involves estimating birthrates. It’s counterintuitive, but demographers have shown that with higher birthrates, more children are obviously born, but also, proportionally more children die and appear in cemeteries. It’s become well understood that patterns of subadult age groups in ancient cemeteries reveal nothing about childhood mortality but are instead reflections of female fertility. When birthrates decline, it’s often a symptom of the social and biological stresses surrounding mothers, the intertwined result of poor nutrition, chronic infection, and intense physical activity.
Revelations of a Common Condition
Bioarchaeologists spend a great deal of time reconstructing patterns of disease and the co-evolution of disease with humans—especially the behavioral and social factors that drive diseases in some settings but prevent it in others. Decades of research have been poured into the study of tuberculosis, treponemes (the family of bacteria that includes syphilis), fungal infections, and various types of cancer that can affect bone. The tibiae (shin bones) often display lesions called periostitis. There are dozens of potential causes for periostitis, and although the lesions don’t reveal precisely what infection caused them, their very presence can show if a group of people was generally undernourished, had stressed immune systems, or was living in unsanitary conditions.
Our Diets, Etched in Bone
Patterns of biological stress produced from the social, economic, and ecological settings we live in can show up in many metabolic and nutritional pathological conditions in the human skeleton. Bioarchaeologists look for signs of chronic childhood anemia that are produced by the expansion of the marrow spaces of the cranium. The resulting condition looks almost like coral, and its scars can remain on the bone for a lifetime. Other skeletal metabolic diseases, such as scurvy and rickets (chronic vitamin C and D deficiencies, respectively), are also important to diagnose and track.
Some of the most important markers of metabolic health are enamel defects, often in the form of pathological bands or grooves on a tooth crown, that can be produced in a child’s still forming teeth during an illness, fever, or other stressor.
Teeth are a wellspring of information about diet. Diet really represents the cornerstone of how people adapt, and the acquisition of food is the basis of every human economy. I often say to my students, “Give me the teeth of an ancient population, and I can reconstruct the economic history of a civilization.” This can actually be done because a wealth of scholarship in bioarchaeology and human biology has shown that the patterns of human oral biology and pathology—dental caries (or cavities, as your dentist calls them), tooth loss, abscesses, periodontal disease, and patterns of tooth wear—are closely linked to diet.
Even greater depth regarding diet can be gained from studying the isotopic composition of ancient bones. We really are what we eat, chemically speaking. The proportions of various stable isotopes in food, such as carbon and nitrogen, wind up in bone crystals and collagen and can help show if people consumed large proportions of maize, grassy cereals, fish, or land animals. Analysis of a small sample of a rib, a tooth crown, and even hair would reveal their chemical composition, which, along with studies of oral health, allow us to reconstruct what people ate—and the very foundations of ancient economies.
Who Got Physical … and Physically Violent?
The ways we use our bodies are also hallmarks of different kinds of adaptation among human groups. One way we can use bones to discover past physical activity is through the study of arthritis. Such degenerative changes can take the form of irregular bony spurs around joints, porous areas of bone death on a joint surface, or bone-on-bone grinding. Factors such as genetics and body mass may contribute to arthritis, but most research supports the fact that long-term patterns of excessive physical activity can outstrip the capacity of cartilage to repair itself. While patterns of arthritis don’t reveal a person’s specific activities, they do provide important insights into their long-term patterns of activity and intensity of labor.
Past injuries receive much scrutiny. Some patterns of broken bones are typical of accidents and can deepen our perspective on how hazardous physical activities were in the past. Others are more likely the result of violence between people, which produces unique patterns ranging from broken noses and cranial fractures to wounds inflicted by arrowheads, swords, maces, firearms, and other weapons. Mapping patterns of trauma on skeletons can reveal broader behavioral patterns and demonstrate how violence suffered may have been related to warfare, competition over resources, ritual violence, domestic violence, or violent sports, to name just a few examples.
Alternatively, the lack of violent injury among a group of skeletons can often have a lot to do with societies that were relatively peaceful and creatively sought to avoid conflict.
What Was Passed On?
The study of genetic relationships in the past, or biodistance, involves the attempt to calculate the genetic similarities or differences between individuals. Genetic patterns can reveal the biological, historical, and geographic origins of a people, as well as the many ways that behaviors and adaptations can bring about microevolutionary changes among human beings. On smaller scales within cemeteries, patterns of genetic variation and family structures can reflect details of social structure, migration, gene flow, and even marriage patterns.
Two principle windows exist on this universe of information. First, the mathematical study of morphometrics looks at size and shape differences that can reveal genetic relationships. For a long time, variations in the shape of the skull were studied, but the inherited size and shape of teeth are probably a far better outward expression of underlying genetic variation. Second, we can directly examine the structures of ancient genomes. During the 1990s, sequencing of ancient DNA became technologically feasible but could typically only look at a small section of our mitochondrial DNA. Today, a suite of new technologies collectively known as next-generation sequencing is able to reconstruct entire ancient mitochondrial and nuclear genomes. Biodistance research is part of an amazing scientific revolution involving the human genetic past.
Putting It All Together
All these diverse lines of biological evidence—demography, disease, diet, physical activity, trauma, and genetics—are intrinsically important. They speak to the lives, experiences, and histories of civilizations. At the same time, they humanize the lives of individual people who lived before us, making it impossible to look at a skeleton simply as an abstract biological artifact.
To close the circle further still, we can bring these many lines of biological information back into archaeology—into the contexts in which we found them to begin with. From there, skeletons can reveal the various chapters of our history, showing the deep connections between history, ecology, adaptation, human biology, evolution, social identities, how we perceive and respond to disease, and other aspects of cognition. These are among the deepest questions surrounding the human condition.
Indeed, bioarchaeology’s immediate focus might rest with identifying pathological lesions in ancient bones—and giving voice to those long silenced by time. These are, in fact, among our essential goals, but to me, a larger purpose remains. Bioarchaeological science tells us quite fundamentally where we come from and explains who we are today—and where we may be going. When looking at tens of thousands of years of bioarchaeological data from across the world and among diverse cultures, certain repetitive patterns of biological outcomes, human-ecology relationships, and socioeconomics emerge within the cyclical rise and fall of societies. Bioarchaeology provides lessons regarding possible future paths for humanity, at least in the near term.
Wanted: Home for Scientists
Back in Olmos, Jenna, Butch, Ana, Raul, and I worked intensely, analyzing skeleton after skeleton, day after day. One day, coming home to our hotel, drama awaited. The manager came out to meet Raul and me and told us, a bit embarrassed but in no uncertain terms, that we had to leave. Our bags were about to be tossed into the hallway. He had forgotten to check the schedule, and a visiting soccer club was coming in less than 24 hours to play the hometown team. And we were in “their” reserved rooms. Just like that, all science came to a stop. We were in trouble. In Olmos, finding a place to stay is a lot easier said than done. Especially with all the construction workers in town, hotels are booked to capacity weeks in advance. The scramble was on for a new place to live just as the home stretch of the research was on the horizon.
Stay tuned: In the final blog posts, I’ll tell you how the field season indeed wrapped up, and I’ll share the unexpected conclusions reached about these people’s lives and ancient Peru’s famous Middle Sicán culture.