Paleopathology Methods And Problems

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Because direct evidence of disease among ancient human beings is very limited, we will have to seek out a variety of indirect approaches in order to reach at least a tentative understanding of the prehistoric world. For example, studies of our closest relatives, the great apes and monkeys, have shown that living in a state of nature does not mean freedom from disease. Wild primates suffer from many disorders, including arthritis, malaria, hernias, parasitic worms, and impacted teeth. Our ancestors, the first ''naked apes,'' presumably experienced disorders and diseases similar to those found among modern primates during a lifespan that was truly ''nasty, brutish, and short.'' Nevertheless, prehistoric peoples gradually learned to adapt to harsh environments, quite unlike the mythical Garden of Eden. Eventually, through cultural evolution, human beings changed their environment in unprecedented ways, even as they adapted to its demands. By the domestication of animals, the mastery of agricultural practices, and the creation of densely populated settlements, human beings also generated new patterns of disease.

Paleopathologists must use a combination of primary and secondary evidence in order to draw inferences about prehistoric patterns of disease. Primary evidence includes bodies, bones, teeth, ashes, and charred or dried remains of bodies found at sites of accidental or intentional human burials. Secondary sources include the art, artifacts, and burial goods of preliterate peoples, and ancient documents that describe or suggest the existence of pathological conditions. The materials for such studies are very fragmentary, and the over-representation of the hard parts of bodies—bones and teeth—undoubtedly distorts our portrait of the past.

Indeed the possibility of arriving at an unequivocal diagnosis through the study of ancient remains is so small that some scholars insist that the names of modern diseases should never be conferred on ancient materials. Other experts have systematically cataloged paleolithic ailments in terms of congenital abnormalities, injury, infection, degenerative conditions, cancers, deficiency diseases, and that all-toolarge category, diseases of unknown etiology.

Nevertheless, by combining a variety of classical and newly emerging techniques, scientists can use these fragmentary materials to gain new insights into the patterns of ancient lives. The study of human remains from archaeological contexts may also be referred to as bio-archaeology, a field that encompasses physical anthropology and archaeology.

Funerary customs, burial procedures, and environmental conditions, such as heat, humidity, soil composition, can determine the state of preservation of human remains. Cremation, in particular, could create severe warping and fragmentation of the remains. Bodies might be buried in the ground shortly after death, covered with a mound of rocks (cairn burial), or placed on a scaffold and exposed to the elements. Both nomadic and settled people might place a body in some type of scaffold as a temporary measure if the death occurred when the ground was frozen. Later, the skeletal remains could be interred with appropriate ceremonies. In some cemeteries the dead might be added to old graves, causing the commingling of bones. Added confusion arises from ritual mutilation of the body, the admixture of grave goods and gifts, which may include body parts of animals or grieving relatives, and distortions due to natural or artificial mummification. Burrowing animals and looters might also disturb burial sites and change the distribution of bones. Catastrophes, such as floods, earthquakes, landslides, and massacres, may provide information about a large group of individuals during one moment in time.

Despite the increasing sophistication and power of the new analytical techniques employed in the service of paleopathology, many uncertainties remain, and all results must still be interpreted with caution. Since the last decades of the twentieth century, scientists have exploited new methods, such as DNA amplification and sequencing, the analysis of stable isotopes of carbon and nitrogen, and scanning electron microscopy in order to ask questions about the health, lifestyle, and culture of ancient peoples. Scanning electron microscopy has been used to examine patterns of tooth wear and enamel defects caused by stress and growth disruption, and the effect of workload on the structure of limb bones. Where possible, chemical investigations of trace elements extracted from ancient bones and hair can provide insights into ancient dietary patterns and quality of life. Lead, arsenic, mercury, cadmium, copper, and strontium are among the elements that can be identified in hair.

The analysis of stable isotopes of carbon and nitrogen provides insights into bone chemistry and diet, because the ratios of the stable isotopes of carbon and nitrogen found in human and animal remains reflect their ratios in the foods consumed. Thus, the relative importance of plant and animal foods in the diet of prehistoric populations can be estimated. Differences in ratios found in human bones for different time periods may reveal changes in diet. For example, scientists determined the relative amounts of carbon 13 and nitrogen 15 in the bones of human beings living in various parts of Europe more than twenty thousand years ago. These studies suggested a diet that was high in fish, shellfish, and waterfowl. Analyses of the isotopes in the bones of Neanderthals, in contrast, suggested that their dietary proteins came largely from the flesh of larger prey animals.

Today, and presumably in the past, most infections involved soft tissue rather than bones, but bones and teeth are the primary source of paleopathological information. Scientists can subject skeletal remains to X-rays, CT (computer tomographic) imaging, chemical analysis, and so forth. The bones may reveal evidence about an individual's history of health and disease, age and cause of death.

Specific injuries identifiable in ancient remains included fractures, dislocations, sprains, torn ligaments, degenerative joint disease, amputations, penetrating wounds, bone spurs, calcified blood clots, nasal septal deformities, and so forth. Projectile weapons, such as spears and arrows, have been found in fossilized vertebrae, sternum, scapula, humerus, and skulls. But projectile tips embedded in bone are rare, either because healers extracted them, or, most likely, the projectile point that caused a fatal injury lodged in soft tissues. In some cases long-term survival occurred after penetrating wounds, as indicated by projectile parts that were incorporated into the injured bone and retained as inert foreign objects.

In favorable cases, the type of injury and the length of time that elapsed between the traumatic event and death can be estimated. Bones usually heal at relatively predictable rates. Survival and healing suggest some form of treatment, support, and care during convalescence. Some skeletons exhibit fractures that resulted in deformities that must have caused difficulty in walking, chronic pain, and degenerative joint disease. The fact of survival suggests the availability of effective assistance during convalescence and after recovery. During healing, bone is usually replaced by bone. Sometimes, however, healing is faulty; complications include osteomyelitis, delayed or nonunion, angular deformities, bone spurs in adjacent soft tissues, calcified blood clots, growth retardation, aseptic necrosis, pseudoarthrosis (fibrous tissue is substituted for bone), and degenerative joint disease (traumatic arthritis).

Bone is a dynamic living tissue constantly being modified in response to the stimulus of growth, and to physiological and pathological stresses. Many factors, such as age, sex, nutrition, hormones, heredity, and illness, affect the bones. Heavy labor or vigorous exercise can result in increases in bone mass. Degenerative processes change the size, shape, and configuration of the skeleton and its individual bones. The skeleton can be modified by inflammation of the joints (arthritis) and by decreases in bone density (osteoporosis).

Bones respond to changes in their environment, especially the mechanical environment created by body weight and muscle forces. The morphology of a bone, therefore, records the mechanical forces exerted on it during life. Usually, paleopathologists are interested in bones that display obvious pathology, but normal bones can provide evidence of body size, behavior, degree of sexual dimorphism, activities, workloads, and posture. Bones may, therefore, testify that an individual habitually performed heavy lifting, pushing, pulling, carrying, standing, stooping, walking, running, or squatting. For example, a peculiarity of the ankle joint, known as a squatting facet, is found in people who spend much of their times in a squatting position. Thus, the absence of squatting facets distinguishes those who sat in chairs from those who did not.

Most diseases do not leave specific signs in the skeleton, but tuberculosis, yaws, syphilis, and some fungal infections may leave diagnostic clues. Twentieth century studies suggest that the skeleton is affected in about one to two percent of tuberculosis patients. The kinds of bone lesions caused by syphilis are generally different from those caused by tuberculosis. Congenital syphilis may produce the so-called Hutchinson's incisor defect. Leprosy often results in damage to the bones of the face, fingers, and toes. Because hormones regulate the growth and development of all parts of the body, a malfunction of the endocrine glands may leave signs in the bones. Some peculiarities in ancient skeletal remains have been attributed to abnormalities of the pituitary and thyroid glands. However, because of recent changes in patterns of disease, physicians, unlike paleopathologists, rarely see the results of historically significant severe, untreated infectious diseases. Various cancers may be identifiable in skeletal remains. Although primary bone cancers are probably rare, many other cancers may spread to the bone. Some relatively uncommon conditions, such as osteomyelitis and various benign tumors of the bone and cartilage, have been of particular interest to paleopathologists because they are easily recognized.

Various forms of malnutrition, such as rickets, scurvy, and anemia, may cause abnormalities in the structure of the bone (porotic hyperos-tosis). Rickets was rare during Neolithic times, but became increasingly common as towns and cities grew. Osteomalacia, an adult form of rickets, can cause collapse of the bones of the pelvis, making childbirth a death sentence for mother and fetus. The presence of calcified blood clots in many skeletons might reflect the prevalence of scurvy in a particular population. Given heavy or chronic exposure, some soil elements, such as arsenic, bismuth, lead, mercury, and selenium, can cause toxic effects that leave their mark on the bones. Porotic hyperostosis is a pathological condition characterized by porous, sieve-like lesions that are found in ancient human skulls. These lesions may be caused by malnutrition and infectious diseases—iron deficiency anemia or inflammatory processes, bleeding associated with scurvy, or certain diseases (rickets, tumors). Generally, it is difficult to determine the specific cause of such defects. Moreover, postmortem damage can simulate these conditions.

Although tooth decay and cavities are often thought of as the results of a modern diet, studies of contemporary primitives and research on ancient skeletons disprove this assumption. Dental problems and diseases found in human remains include dental attrition due to diet, temporomandibular joint derangement, plaque, caries, abscesses, tooth crown fractures, tooth loss, and so forth. Analysis of dental microwear patterns by scanning electron microscopy and microwear measurements began in the 1980s. Microscopic pits, scratches on tooth surfaces, and surface attrition reveal patterns of wear caused by abrasive particles in food. Abrasive wear could lead to infection and tooth loss. Dental disorders were often worse in women, because of the effects of pregnancy and lactation, and the use of teeth and jaws as tools.

In general, the condition of bones and teeth provides a history of health and disease, diet and nutritional deficiencies, a record of severe stresses or workload during life, and an approximate age at death. Bone fractures provide a record of trauma, which might be followed by infection or by healing. Before the final closure of the epiphyses, the growing bones are vulnerable to trauma, infections, and growth disorders. Stresses severe enough to disrupt growth during childhood result in transverse lines, usually called Harris lines or growth arrest lines, which are visible in radiographs of the long bones of the body. Because Harris lines suggest severe but temporary disturbance of growth, a population suffering from chronic malnutrition has fewer transverse lines than one exposed to periodic or seasonal starvation. Starvation, severe malnutrition, and severe infection may also leave characteristic signs in the teeth, microdefects in dental enamel known as pathological striae of Retzius, enamel hypoplasias, or Wilson bands. Severe episodes of infant diarrheas, for example, can disrupt the development of teeth and bones. Scanning electron micrography makes it possible to observe disruptions in the pattern of these lines, but there is still considerable uncertainty about the meaning of pathological striae of Retzius.

Archaeological chemistry, the analysis of inorganic and organic materials, has been used in the discovery, dating, interpretation, and authentication of ancient remains. This approach provides many ways of reconstructing ancient human cultures from bits of stone tools, ceramics, textiles, paints, and so forth. By combining microscopy with chemical analysis, scientists can recover information about the manufacture and use of ancient artifacts because such objects carry with them a ''memory'' of how they were manipulated in the past. Perhaps the most familiar aspect of archaeological chemistry is the carbon-14 method for dating ancient remains. Carbon-14 dating is especially valuable for studying materials from the last ten thousand years, the period during which the most profound changes in cultural evolution occurred.

Multidisciplinary groups of scientists have combined their expertise in archaeology, chemistry, geophysics, imaging technology, and remote sensing as a means of guiding nondestructive investigations of sensitive archeological sites. As the techniques of molecular biology are adapted to the questions posed by paleopathologists, new kinds of information can be teased out of the surviving traces of proteins and nucleic acids found in some ancient materials. Improvements in instrumentation allow archaeologists to analyze even smaller quantities of biological materials. For example, by using mass spectrometry and lipid bio-markers chemists can distinguish between human and other animal remains.

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Responses

  • Costantino
    What are the problems with the paleopathology method?
    8 years ago
  • Minna
    Do any infectious diseases leave active traces in a grave site?
    10 months ago
  • awet
    What types of disease did we find from paleopathology?
    4 months ago

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