S49 Periodicity of demographic events - Périodicité des phénomènes démographiques
Organiser: Sauvain-Dugerdil Claudine (Working Group on Biology and Population)
LaboDémo, Universite de Genève, Uni Mail, 1211 Genève 4, Switzerland
Tel: +41 22 705 8921
Fax: +41 22 705 8939 (781 4100)
Email: Claudine.Sauvain@ses.unige.ch
Outline: Demographic events are not random. The regularities in their occurrence have been widely documented. The timing of birth, death, marriage and migrations through the day, the week, the month and the year is suggestive of natural, physiological and socio-cultural cycles. The working of these rhythms has mainly focused on traditional societies among which individual life and social events are strongly contingent on the seasonality of agricultural activities and an adapted calendar of cultural customs: few conceptions at the time of heavy work load and, in Catholic countries, at Lent, marriages in winter time, migrations at harvest time and seasonal nomadism of pastors. The periodicity of demographic events has therefore mainly been interpreted in terms of socio-cultural expression of natural cycles on a yearly basis and seasonal differences in mortality and morbidity. This was also reflecting a naive conception of the effect of non-cultural variables, such as the variation of external temperature.

Less familiar evidence of recurrence of demographic events, shift from a rural system based on agriculture to an urban mainly tertiary economy, changing values and new scientific tools are however pointing towards factors behind this periodicity. This session will therefore focus on birth and mortality/morbidity periodicity, their mutual interactions and links with nuptiality and mobility, along three lines:

  • Bio-cultural interconnections: birth seasonality in line with the concept of energy balance between input and output necessary for women to reach the fecund threshold level (Ellison paper at the Beijing session); cultural and biological factors - genetic and non-genetic - of cycles in human morbidity/mortality (virus/bacterial cycles linked with climate and with human activity and interventions and varying human susceptibility due to genetic and non-genetic factors, i.e. malaria).
  • These interconnections in a period of a widening gap between humankind and natural rhythms. Periodicity in modern populations in which activities are increasingly independent from natural cycles and where there are less seasonal differences in type of food, as well as a more protected immediate environment (buffering effects of new cloth and increasing time spent in aseptic and/or air conditioned offices and means of transportation).
  • The meaning of old and new traditions and preference: Evolution of marriage season parallel to the modernisation process. Beliefs associated with particular period, or specific day, and their effect on births and suicides. Chinese years considered as more or less beneficial, but what about the peak of weddings in Switzerland on 8.8.88.

This will be considered by discussing further evidence and, above all, intriguing examples of periodicity of demographic events, such as:

  • Longer cycles: revisiting secular recurrence of epidemics
  • The Millenium effect: Leridon on the demographic events on Jan. 1st 2000
  • Epidemiological factors (in the line of Bittles’ work on the influence of mother’s birth season on birth defects)
  • Poulain’s on the season of birth of centenarians

By providing further information on the factors linked with periodicity of demographic events and the present changes in this respect, this session will also contribute to give new insights into the interactions between biological factors and socio-cultural ones and the respective importance of environmental constraints and individual heterogeneity in fertility and mortality.