Paleopathology and Paleomedicine

11 May

Paleopathology and Paleomedicine

INTRODUCTION

One of our most appealing  and persistent  myths is that  of the Golden Age, a time before the discovery of good and evil, when death and dis- ease were unknown.  But, scientific evidence—meager, fragmentary, and tantalizing  though  it  often  is—proves  that  disease  is older  than  the human  race and was not uncommon among other species. Indeed, stud- ies of ancient fossil remains, skeletons in museum collections, animals in zoos, and  animals  in the wild demonstrate that  arthritis  is widespread among   a  variety   of  medium   and   large-sized   mammals,   including aardvarks,  anteaters,  bears,  and  gazelles.  Evidence  of  infection  has been found  in the bones of prehistoric  animals,  and in the soft tissues of  mummies.  Modern   diagnostic   imaging  techniques   have  revealed evidence of tumors in fossilized remains. For example, researchers performing  CT-scans of the brain  case of a 72-million-year-old  gorgo- saurus  discovered  a  brain  tumor  that  probably   impaired  its  balance and  mobility.  Other  abnormalities in  the  specimen  suggested  that  it had suffered fractures  of a thigh, lower leg, and shoulder.

Thus, understanding the pattern  of disease and injury that  afflicted our  earliest  ancestors  requires  the  perspective  of  the  paleopathologist. Sir Marc Armand Ruffer (1859–1917), one of the founders of paleopathol- ogy, defined  it as the science of the  diseases that  can be demonstrated in human  and animal remains of ancient times. Paleopathology provides information about  health,  disease,  death,  environment,   and  culture  in ancient populations.

In  order  to  explore  the  problem  of  disease  among  the  earliest humans,  we will need to survey some aspects of human  evolution,  both biological and cultural.  In Descent of Man and Selection in Relation to Sex (1871) Charles  Darwin  argued  that  human  beings, like every other species, evolved  from  previous  forms  of life by means  of natural se- lection. According  to Darwin,  all the available  evidence indicated  that

‘‘man is descended from a hairy,  tailed, quadruped, probably  arboreal

in  its  habits.’’  Despite  the  paucity  of  the  evidence  available  to  him, Darwin  suggested  that  the ancient  ancestor  of modern  human  beings was related  to  that  of the  gorilla  and  the  chimpanzee.  Moreover,  he predicted  that  the  first  humans  probably  evolved in Africa.  Evidence from the study of fossils, stratigraphy, and molecular  biology suggests that  the separation of the human  line from that  of the apes took  place in Africa about  five million to eight million years ago.

The fossilized remains of human ancestors provide valuable clues to

the past,  but  such fossils are very rare  and  usually  incomplete.  South African  anatomist Raymond Dart  made the first substantive  discovery of human ancestors in Africa in the 1920s when he identified the famous fossils known  as Australopithecus  africanus (South  African  Ape-man). The most  exciting subsequent  twentieth-century discoveries of ancient human ancestors are associated with the work of Louis and Mary Leakey and  that  of Donald  Johanson. Working  primarily  at  sites in Olduvai Gorge and Laetoli in Tanzania, Mary and Louis Leakey identified many hominid  fossils,  including  Australopithecus  boisei and  Homo  habilis. Johanson’s   most   important  discovery   was  the  unusually   complete skeleton  of  a  primitive  australopithecine (Australopithecus  afarensis), commonly  referred to as Lucy. New hominid remains discovered at the beginning  of  the  twenty-first  century  stimulated   further   controversy about the earliest hominid ancestors, as well as those of the chimpanzee.

Paleoanthropology is a  field in which  new discoveries  inevitably

result in the re-examination of previous findings and great debates rage over the identification  and classification  of tiny bits of bones and teeth. Further discoveries will no doubt  add  new insights into  the history  of human  evolution  and create new disputes among  paleoanthropologists. Scientists also acknowledge  that  pseudopaleopathologic conditions  can lead  to  misunderstanding  and  misinterpretation because  they  closely resemble disease lesions, but are primarily the result of postmortem pro- cesses. For example, because the primary chemical salts in bones are quite soluble in water, soil conditions that are conducive to leaching out calcium can cause changes in bones like those associated with osteoporosis. Despite all the ambiguities associated with ancient remains, many traumatic events and diseases can be revealed by the methods of paleopathology.

Insights from many different disciplines, including archeology, his- torical geography, morphology, comparative anatomy, taxonomy, genet- ics, and molecular  biology have enriched our understanding of human evolution. Changes in DNA, the archive of human genealogy, have been used to construct  tentative  family trees, lineages, and possible patterns of early migrations.  Some genes may reveal critical distinctions  between humans  and other primates,  such as the capacity for spoken language.

Anatomically  modern  humans  first  emerged  some 130,000 years

ago, but fully modern  humans,  capable of sophisticated activities, such as the  production of complex  tools,  works  of art,  and  long  distance

trade,  seem to appear  in the archaeological  record  about  50,000 years ago. However, the relationship between modern humans and extinct hominid  lines remains controversial.

The Paleolithic  Era,  or Old Stone Age, when the most important

steps  in  cultural   evolution   occurred,   coincides  with  the  geological epoch known  as the Pleistocene or Great  Ice Age, which ended about

10,000 years ago with the last retreat of the glaciers. Early humans were hunter-gatherers, that is, opportunistic omnivores who learned to make tools, build shelters, carry and share food,  and create uniquely human social  structures.  Although  Paleolithic  technology  is characterized by the manufacture of crude tools made of bone and  chipped  stones and the absence of pottery and metal objects, the people of this era produced the dramatic  cave paintings  at Lascaux,  France,  and  Altamira, Spain. Presumably,  they also produced  useful inventions  that  were fully bio- degradable  and,  therefore,  left no  traces  in the  fossil record.  Indeed, during  the 1960s feminist  scientists  challenged  prevailing  assumptions about  the  importance of hunting  as a source  of food  among  hunter- gatherers.  The  wild grains,  fruits,  nuts,  vegetables,  and  small animals gathered  by women probably  constituted the more reliable components of the  Paleolithic  diet.  Moreover,  because  women  were often  encum- bered  by  helpless  infants,  they  probably  invented  disposable  digging sticks and bags in which to carry and store food.

The transition to a new pattern of food production through farming

and animal husbandry is known as the Neolithic Revolution. Neolithic or New Stone Age peoples developed crafts, such as basket-making, pot- tery, spinning, and weaving. Although  no art work of this period seems as spectacular  as the  Paleolithic  cave paintings  in France  and  Spain, Neolithic people produced  interesting sculptures, figurines, and pottery.

While archeologists  and anthropologists were once obsessed with the when and where of the emergence of an agricultural way of life, they are  now  more  concerned  with  the  how and  why. Nineteenth-century anthropologists tended to classify human cultures into a series of ascending,  progressive  stages  marked  by the  types  of tools  manufac- tured and the means of food production. Since the 1960s new analytical techniques  have made it possible to test hypotheses  about  environmen- tal and climatic change and their probable  effect on the availability  of food sources. When the idea of progress is subjected to critical analysis rather  than  accepted  as inevitable,  the  causes  of the  Neolithic  trans- formation are not  as clear as previously  assumed.  Given the fact that hunter-gatherers may enjoy a better diet and more leisure than  agricul- turalists,  prehistoric  or modern,  the advantages  of a settled way of life are  obvious  only  to  those  who  are  already  happily  settled  and  well fed. The food  supply  available  to hunter-gatherers, while more  varied than the monotonous staples of the agriculturalist, might well be precarious  and uncertain.

Recent studies of the origins of agriculture suggest that it was almost universally adopted  between ten thousand and two thousand years ago, primarily in response to pressures generated by the growth of the human population. When comparing  the health of foragers and settled farmers, paleopathologists  generally  find  that  dependence  on  a  specific  crop resulted  in  populations  that   were  less  well  nourished   than   hunter- gatherers,  as indicated  by height, robustness,  dental conditions,  and so forth.  In  agricultural societies,  the  food  base  became  narrower   with dependence on a few or even a single crop. Thus, the food supply might have been adequate  and consistent  in terms of calories, but deficient in vitamins  and  minerals.  Domestication of animals,  however, seemed to improve the nutritional status of ancient populations. Although the total human  population apparently grew very slowly prior to the adoption of farming,  it increased quite rapidly  thereafter.  Prolonged  breast  feeding along with postpartum sexual prohibitions found among many nomadic societies may have maintained long intervals between births. Village life led to early weaning and shorter  birth intervals.

The revolutionary changes in physical and social environment associated  with the transition from the way of life experienced by small mobile bands  of hunter-gatherers to that  of sedentary,  relatively dense populations also allowed major shifts in patterns  of disease. Permanent dwellings, gardens,  and  fields provide  convenient  niches for parasites, insects, and rodents.  Stored  foods are likely to spoil, attract  pests, and become contaminated with rodent  excrement,  insects, bacteria,  molds, and  toxins. Agricultural  practices  increase the number  of calories that can be produced  per unit of land, but a diet that overemphasizes  grains and cereals may be deficient in proteins,  vitamins,  and minerals.

Lacking the mobility and diversity of resources enjoyed by hunters

and  gatherers,  sedentary  populations may be devastated  by crop  fail- ures, starvation, and malnutrition. Migrations and invasions  of neigh- boring  or  distant   settlements  triggered  by  local  famines  may  carry parasites  and pathogens  to new territories  and populations. Ironically, worrying  about  our  allegedly unnatural and  artificial  modern  diet has become so fashionable  that  people in the wealthiest nations  have toyed with  the  quixotic  idea  of  adopting   the  dietary  patterns   of  ancient humans  or even wild primates.  In reality, the food supply available  to prehistoric   peoples  was  more  likely  to  be  inadequate, monotonous, coarse, and unclean.

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.’’ Neverthe- less, prehistoric  peoples  gradually  learned  to  adapt  to  harsh  environ- ments, quite unlike the mythical  Garden  of Eden.  Eventually,  through cultural evolution, human beings changed their environment in unprece- dented 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 second-

ary 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 inten- tional  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 por- trait  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  paleo- lithic ailments  in terms  of congenital  abnormalities, injury,  infection, degenerative  conditions,  cancers,  deficiency diseases, and  that  all-too- large category,  diseases of unknown  etiology.

Nevertheless, by combining a variety of classical and newly emerg-

ing 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  con- ditions,  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 appro- priate  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 dis- tortions  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 mas- sacres,  may  provide  information about  a  large  group  of  individuals during  one moment  in time.

Despite the increasing sophistication and power of the new analyti-

cal techniques  employed in the service of paleopathology, many uncer- tainties  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, ampu- tations,  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 sur- vival 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  dis- ease. 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 pathologi- cal  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 diag- nostic  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 rick- ets, 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 particu- lar 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 mal- nutrition and  infectious  diseases—iron  deficiency  anemia  or  inflam- matory  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 dis- eases  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  dis- orders 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 devel- opment  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 manu- facture  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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