Demography is the statistical study of human population which seeks to explain variations in population size, structure and dynamics by considering the population of a given area or chronological period as a single object for quantitative analysis (Chamberlain 2006). Changes in the number of individuals in a population through time will depend on a balance between birth and death, as well as movements of people into and out of the population.
Detailed demographic analysis of the Bronze Age population in Scotland has yet to be attempted although several aspects have been addressed, mainly as part of individual excavation reports. The lack of dedicated demographic research into this period is due to a number of complex challenges. Not least amongst these is the fact that there is still little idea of population numbers or structure. This is because much of the evidence derives from excavated assemblages of human remains which show remarkable bias in terms of age and sex as a result of selective burial practises, as well as incomplete preservation (Bradley 2007; Chamberlain 2000, 206).
Attempts to estimate the population size of Scotland in the Bronze Age have been fraught with difficulties due to the long chronological period of time that this era encompasses. A population of 2,500 for Scotland has been suggested, contrasting sharply with overall British population estimates which range from between 20,000 to 100,000 (McEvedy and Jones 1978; Brothwell 1972).
These now outdated estimates were based on known burial populations which are likely to be severely biased due to selective burial practices (Bradley 2007). They also fail to take into consideration that it is unlikely that population numbers would have remained static over such a long period of time, particularly due to increasing evidence of climate change, shifting patterns of land-use and movements of people within northern Britain. All of these factors would have had implications to the Bronze Age population, namely the economy and diet, spread of disease and its effect on mortality rates.
Population structure: age categories and distributions
It is common practice to split age distributions into discrete biological age intervals, measured in units of months, years or multiple of years since birth. The simplest subdivision is to separate the lifespan into three groups based on chronological years and physiological development: sub-adult or child, adult and mature adult (Chamberlain 2006). The boundaries between these basic age groups can vary between the sexes but are thought to be founded on biological indicators, such as the development of sexual maturity in females.
There is little agreement on the definitions used to describe the age of children within archaeological populations (McLaren, forthcoming; Sofaer Derevenski 2000), however, demographic conventions define children as individuals less than 15 years of age (Chamberlain 2000, 207). Within a stable population, demographic models suggest that the segment of the total population constituted by children could vary from about 36% in a low life expectancy population to about 19% in the highest life expectancy populations (Chamberlain 2000, 207). This has profound implications to the wider population, as a higher infant mortality rate will result in fewer individuals reaching adulthood.
Survivorship is a useful demographic concept that expresses the probability that an individual will survive to a specified age. This is a contested subject; some argue that the small number of individuals over 45 years of age identified amongst the population is an indication that people died young. Others suggest, that this paucity of older and elderly individuals is, in fact, a product of bias in skeletal-age estimation which has failed to recognise old-adult individuals (Chamberlain 2006, 34). This is clearly an area which needs more work to clarify.
Health and disease
As the accuracy of osteological analysis of Bronze Age skeletal remains advance, the recognition of markers of disease, injury and dietary problems increases. Such palaeopathological studies provide important information for Bronze Age lifestyles and health and are vital to gaining an understanding of the demography of early prehistoric populations. In very few cases can the cause of death be determined, but useful information can be observed regarding joint disease due to physical stress, chronic infections, trauma and deficiency in diets (Shepherd and Bruce 1986, 17).
Degenerative joint disease
Osteological analysis of skeletal remains has demonstrated an increase in the frequency of joint disease during the Bronze Age, indicating increased stress on the joints due to strenuous physical activities, believed to be related to intensification of farming and exploitation of the land (Roberts and Cox 2003, 77). This includes evidence of spinal joint degeneration such as that on a 35-40 year old adult male at Cnip, Lewis (Bruce and Kerr 1995, 283) and Blackhills, Tyrie (Shepherd and Bruce 1986, 36), osteoarthritis of the wrist of an adult male at Grainfoot, Longniddry (Lorimer 1991, 114), degeneration of the hip joint such as that of a young adult male from Keabog, Pitdrichie (Shepherd and Bruce 1987, 37). Spinal lesions known as Schmorl nodes, a further indicator of degenerative spinal disease either due to age or as the result of heavy manual labour is known in a small number of individuals such as two adults from Grainfoot, Longniddry (Lorimer 1991, 113-4), Boyndlie, Aberdeenshire, Culduthel, Invernesshire and Kilspindie, East Lothian (Shepherd and Bruce 1986, 36-7).
Infection is likely to have been a major cause of death at all ages, but rarely leaves traces on the bones of the skeleton (Shepherd and Bruce 1986, 19).
Severe dental wear and disease is a characteristic feature of the Bronze Age population, reflective of the stresses inherent in a coarse diet (Roberts and Cox 2003, 80). Dental caries and abscesses have been observed on numerous individuals including a 35-40 year old adult male at Grainfoot, Longniddry (Lorimer 1991, 114) and adults from Boatbridge Quarry, Thankerton (Clarke et al. 1984), Mains of Leslie, Borrowstone and Persley Quarry, Aberdeenshire (Shepherd and Bruce 1986, 36), to name a few.
Evidence of physical trauma is limited in the Scottish burial population during this period, but a few examples are known. Severe injuries could either as the result of repeated physical exertion, accidental injury or deliberate violence but is impossible, in most cases, to determine the cause (Roberts and Cox 2003, 80). Possible skull fractures have been noted in adult males from Hillhead and Ord, Aberdeenshire (Shepherd and Bruce 1986, 36) and a severe and extensive facial injury was noted on the skull of an adult male from Cnip, Lewis (Bruce and Kerr 1995). A healed skull fracture and a possible fracture of the thoracic spine has been observed on an adult male from Keabog (Shepherd and Bruce 1985).
Indications of childhood illness and possible dietary deficiency can be observed in some instances from the skeletal remains in the form of enamel hypoplasia (banding on tooth enamel), cribra orbitallia (pitting on the roof of the orbits), harris lines (banding on long bones). These can only be formed during childhood, whilst the skeleton is still growing and typically indicate a period when growth has been severely impaired. Although not common, examples have been noted from a child at Auchlin, Aberdour (Reid 1924; Shepherd and Bruce 1986, 36). A peak in occurences in children around 2-3 years of age has been suggested as the result of weaning (Fuller et al. 2003). Possible instances of scurvy and rickets have been noted in south-west England (Mays 2007; Keith 1920).
Mortality, or death rate, is defined as the proportion of the population that dies within a specific chronological interval. Although no accurate mortality figures are available for Bronze Age Scotland, high infant mortality is expected (Goodman and Armelagos 1989). It has been suggested that up to 40% of children born in prehistory, died before reaching 5 years-of-age (Goodman and Armelagos 1989, 225). Mortality rates are expected to peak at this early stage of childhood, then decease to minimal levels in late adolescence and early adult, and then rise steadily into old age (Chamberlain 2006, 25).
One notable exception to this is high death-rates in young adult females. Margaret Bruce’s study of Beaker associated burials from North-East Scotland identified a greater proportion of young-adult females amongst the deceased. Greater quantities of adult males appear to have survived into middle-age or later which is in contrast to adult females, a greater proportion of which appear to have died in early adulthood, between 15-25 years of age (Shepherd and Bruce 1986, 18). It is likely that this is directly related to childbearing and childbirth.
Mortality rates are not only tied to age and biological sex but would also vary according to socioeconomic status and other population parameters. This is more challenging to interpret in the case of Bronze Age Scotland due to the possibility of selective burial practices.
Migration and movement
There is increasing evidence for large-scale movement of peoples in the Bronze Age. In Scotland, indications of movement of individuals to and from Ireland are suggested by similarities in material culture. This movement of peoples into and out of Scotland could have had a profound affect on the population depending on the extent of such migrations, not only creating the possibility of increased pressure on settlements and resources but also effecting the distribution of disease.
Particularly during the Earlier Bronze Age there is evidence of the movement of peoples within and outwith Britain, demonstrated by Jane Evans and Janet Mongomery’s strontium isotope analysis programme conducted through the Beaker People Project. Strontium isotope analysis looks specifically at tooth enamel which is formed during early childhood. This enamel retains the isotopic signature of the underlying geology, absorbed by the body through water consumption, which relates to the early years of the individuals life (Fuller et al. 2003). Unfortunately, this process has its limitations as it is not possible to detect individuals that move between regions that have the same underlying geology (Chamberlain 2006, 9).