The interacting effects of prices and weather on population cycles in a preindustrial community

Abstract

The exogenous cycles and population dynamics of the community at Penrith, Cumbria, England, have been studied (1557-1812) using aggregative analysis, family reconstitution and time series analysis. This community was living under marginal conditions for the first 200 years and the evidence presented is of a homeostatic regime where famine, malnutrition and epidemic disease acted to regulate the balance between resources and population size. This provides an ideal historic population for an investigation of the direct and indirect effects of malnutrition. Throughout the period studied, a short wavelength oscillation in grain prices was apparently the major external factor that drove exogenous cycles in mortality, birth rate, and migration. In particular, the different responses of children to variations in food supply are emphasised; fluctuations in poor nutrition correlated significantly with the variations in mortality rates for infants (probably indirectly during pregnancy and directly during the first year of life) and for young children (via susceptibility to lethal infectious diseases). Migratory movements contributed to the maintenance of homeostasis in the population dynamics. A medium wavelength cycle in low winter temperatures was associated with a rise in adult mortality which, in turn, promoted an influx of migrants into this saturated habitat. A model incorporating these interacting associations between vital events and exogenous cycles is presented: grain prices were an important density-dependent factor and constituted the major component of the negative feedback of this population and drove the exogenous, short wavelength mortality cycles. Cycles of births and immigration provide a positive feedback for the build-up of susceptibles and the initiation of smallpox epidemics and increased population size.

PIP: This study examines the impact of prices and weather as exogenous community factors and cycles of famine, malnutrition, and epidemic disease on population size in England. Data were obtained from published records of baptisms, burials, and marriages in Penrith, Cumbria, England during 1557-1812. Seasonal mean temperatures during 1659-1811 in central England were obtained from Manley (1974); national grain price indices during 1450-1749 were obtained from Bowden (1967, 1985); and annual wheat prices during 1600-1812 were obtained from Stratton (1970). The time series analysis techniques of Shumway (1988) were used. It is hypothesized that cycles of grain prices and availability of food were major factors influencing the short wavelength cycles in births and deaths. Wheat prices followed a short cycle of 5-6 years and a medium cycle of 13-16 years. Medium cycles were correlated with seasonal weather conditions. Short cycles of wheat prices correlated with economic factors, such as a good or bad harvest or fungal epidemics. Short wheat cycles were key factors influencing mortality cycles in Penrith. Mortality followed short 5-year cycles. Adult and child burial cycles corresponded to famines. Adult mortality was linked with both the short wheat price cycles and longer cycles of climatic conditions. Child mortality was only associated with short cycles of regular epidemics, famine, and malnutrition. Neonatal mortality lagged by one or more years, but postneonatal mortality corresponded to wheat prices. High annual burials corresponded to low baptisms. Evidence suggests that immigration replaced adult burials. The medium cycles of prices had less impact on adult mortality than the short cycles, especially from 1670 to 1760. Mean annual births equaled mean annual deaths. After 1750, population growth increased due to lower mortality rates, especially among young children.