Domestication of Plants and Animals
There are a handful of times during human prehistory and history when major changes/transitions in the environment and socio-economic situation have led to problems with health, and it is therefore logical to concentrate on what happened to health at these transitions (a question-driven approach). These major times were the transition to agriculture from hunting and gathering, the development of urban centers, and the rise of industrialization. As people started to domesticate plants and animals, for example, in Neolithic Europe, population numbers began to rise and settled communities developed with permanent housing. In effect, to support an increased population, agriculture had to develop, and today it remains the mainstay of feeding the world. The risks to the health of these human populations practicing agriculture lay in increased population density, allowing infectious disease to be transmitted more readily, diseases of their animals being passed to them via contaminated meat and milk (e. g., tuberculosis), the accumulation of refuse and waste in their settlements attracting vermin and disease, the challenges of maintaining a clean water supply, and a decline in the variety of food available, with a reliance on cereal crops. Many studies of skeletons from this period of time around the world reveal an increase from the preceding period of hunting and gathering of iron-deficiency anemia, infectious diseases, stress markers in bones and teeth, trauma, and dental and joint disease. For example, in North America, there appears to be a consistent trend for an increase in caries of the teeth with the transition to maize agriculture (Figure 4). Maize is a highly cariogenic food containing high levels of sugar (sucrose) which are very readily metabolized by bacteria in the mouth. In addition to this sugar contribution to the diet, there was also a decline in wear on the teeth, which allowed food to accumulate between the cusps of the molars and premolars. In contrast, in Britain caries does not increase until the Roman period (first to fourth centuries AD) - 7.5% of total teeth - and the Late and post-Medieval periods - 5.6% and 11.2% of teeth - when imports of exotic sugary foodstuffs, and sugar, respectively led to
Figure 4 Dental caries in a premolar and molar tooth from a hunter-gatherer individual from North America.
These increases; in this case sugar in cereals was not the main cause. Furthermore, not all cereal crops have a high sugar content; in Thailand, where rice was (and is) the staple crop, there was a relatively low rate of caries found. Skeletal changes of anemia are also seen in higher frequencies in settled communities in the past. Again, North America provides abundant evidence and two main factors are probably at work. Maize is deficient in iron and contains substances that make iron hard to absorb from the gut; a diet reliant on maize may have predisposed people to anemia. The other factor may be related to increases in infection in agricultural communities due to a rise in population density and poor sanitation leading to parasitic infection of the gut, hemorrhage, and malabsorption of foodstuffs into the body, including iron. However, there are instances where high rates of caries and anemia are found in hunter-gatherers (Figure 5). In Australian prehistoric aboriginal populations, for example, the evidence for anemia is high in tropical/subtropical environments but low in desert
Figure 5 Cribra orbitalia (anemia) in an orbit of the skull: Late Medieval France.
Figure 6 Dental enamel hypoplasia from Late Medieval England (grooves of the teeth).
Communities, suggesting that the former environment may be predisposing people to parasitic infection and anemia. Multiple indicators of stress including dental enamel defects (poor nutrition) and infection also appear to commonly occur in agricultural communities in the past, for example, at Dickson Mounds, Illinois (AD 950-1300) in North America, which suggests that, in general terms, practicing agriculture was detrimental to health. The hunter-gatherer group at this site had 0.9 defects per individual; 1.18 defects were found in the mixed hunter-gatherer/agriculture group, and the fully agricultural group had 1.61 defects. Furthermore, reduced age at death has been noted in individuals whose skeletons reveal dental enamel defects (Figure 6). Another study, which examined health at the agricultural transition compared a hunter-gatherer (50 BC-AD 200) and agricultural (AD 1050-1250) group of skeletons from West-central Illinois. It was found, through analyzing the cross-sectional shape of the femur and humerus, that females had stronger bones in the agricultural group; it was suggested that they were instrumental in growing and processing of cereal crops.
Development of Urban Centers
As time went by social organization became more complex, more sophisticated artifacts and buildings appeared, and trade links became established. Urban centers developed, for example, in Late Medieval Europe, with their accompanying advantages and disadvantages. Large population increases led to people living in high densities, often crowded into inadequate housing with poor sanitation and drinking polluted water. Urban centers brought trade and new resources, and immigrants, attracted to the towns and cities for work and resources, but people also brought disease with them. Studies of human remains from urban contexts generally have revealed poor health compared to populations living in rural environments.
For example, a study of sinusitis in rural and urban Late Medieval English populations found a generally higher rate in urban inhabitants and the most severe sinusitis in the males of one particular urban site (Figure 7). There were 72% of individuals affected at one urban site (St. Helen-on-the-Walls, York), with 76% of males and 69% of females involved, while at one of the rural sites (Wharram Percy, Yorkshire) 51% were affected (44% of the males and 60% of the females). Although sinusitis can be caused by many factors, such as allergies, house dust, and smoke caused by burning fuels such as dung, wood and peat, by analyzing whether dental disease (a contributory factor for sinusitis) had led to sinusitis, it was found that it contributed very little to urban sinusitis compared with rural sites; this suggested
Figure 7 Pitting of bone on sinus floor (sinusitis) from Early Medieval England.
Figure 9 Nonspecific infection in a lower leg bone from North America (right bone in figure).
Figure 10 Damage to a foot due to leprosy from a Late medieval individual from Denmark (normal foot at bottom).
Figure 8 Healed fracture to the tibia and fibula (lower leg bones) from Late Medieval England.
That environmental pollution was the main factor causing this health problem in urban sites. Furthermore, it was known from documentary data that the males of the population at York were likely working in the many industries operating adjacent to the parish in which they lived. Lead poisoning may also occur as a result of pollution from certain industries, and in the Roman Empire the use of lead in water pipes, and lead vessels and utensils, predisposed to lead poisoning. Lead solders on tins of food also led to poisoning in victims of the nineteenth-century John Franklin expedition to the Canadian Arctic.
Another example of urban versus rural differences in health can be seen in England where stature in Early Medieval (rural) populations tends to be higher than in later and post-Medieval (urban) populations. As stature is a measure of health during the growing years, a poor deficient diet and a young life exposed to pathogens will predispose to shorter long bones and a reduced height compared to what would be expected. However, not all urban environments were necessarily more detrimental to health. A study of trauma (Figure 8) in rural and urban skeletal populations from Nubia found higher rates in the rural group, suggesting that cultivation and herding animals, and negotiating rough terrain, probably contributed to these high rates. Generally speaking, however, infectious diseases (Figure 9) such as tuberculosis (spread by droplet infection and through infected meat and milk), leprosy (Figure 10) (transmitted through droplet infection), and venereal syphilis (spread by sexual intercourse) were more prevalent in urban populations in the past purely because the conditions were right for their transmission. Venereal syphilis in Europe, for example, was very uncommon until the Late Medieval period, which reflects a time when urban living was more common, trade increased, and sexual promiscuity increased (Figure 11).
Figure 11 Destruction of the skull due to venereal syphilis from Late Medieval Scotland.
Low levels of hygiene and contaminated foodstuffs and water also contribute to a depressed immune system, making people more susceptible to contracting infectious disease.
Industrialization
In Europe the advent of industrialization in the early nineteenth century, where manufacturing industries became predominant, further increases in population density occurred, with a large part of the population eventually living in an urban environment. Housing could be very poor indeed with many families living in one room with inadequate ventilation, and diet could be deficient in certain constituents. Alongside industry came pollution of work places and the environment in general, and the population succumbed to diseases associated with their work. Analysis of human remains from this period has also shown poor health. A recent study of the skeletons of children from the eighteenth/nineteenth-century Christchurch, Spi-talfields site in London, England found that industrialization had a major impact on health although some indicators were not as common as expected, due to other factors. Infant and child mortality was higher than in a comparative Late Medieval urban site, growth was more retarded, and there was a high rate of vitamin C and D deficiencies (scurvy and rickets). However, rates of respiratory infection were low compared with the Late Medieval urban site, which was also borne out by a study of the adults from the same population. This may be because the population, being of a high social status, was protected from ‘polluted’ air outside their homes, but also lived in lower population densities, thus preventing respiratory infections from spreading. Clearly, though, industrialized societies would generally be more exposed to a poor living environment, especially their place of work. Rickets, for example, became much more common
Figure 12 Rickets in leg bones from Early Medieval England.
With industrialization because people worked long hours in factories, lived in poverty, and were exposed to smog in their environment. This prevented ultraviolet light reaching their skins, something necessary for the production of vitamin D in the skin and the subsequent absorption of calcium and phosphorus to make strong bones. While the earliest case of rickets so far reported is from South Africa and dated to 4820 ± 90 BC, and occasionally there are examples from the record of people living in rural environments with rickets, there are very few examples until the urban post-Medieval industrialized period (Figure 12).
World History
