The Demography of a Learned Society
Most academies are closed societies: members are admitted by election and remain until their death, and the total population usually remains constant over a given period. The demography of a closed body of this kind is simple: the annual intake is strictly determined by the annual “exits”, i.e. deaths, which is an exogenous variable. As a result, the rate of intake and the length of service in the institution are fully related, and also depend on age at election. In a context where the length of life is increasing (via the fall in mortality at ages above 60), the mean age of the population can only rise — unless the Academy elects ever younger members, which, in turn, reduces the rate of renewal. A more efficient solution is to set an age at which a seat is declared vacant.
This article begins with a summary of the main mechanisms at work in a stationary population. We then provide a brief overview of the history of the Académie des Sciences between 1666 and 2001 and a reconstruction of the evolution of its population (1,039 members over this period). After some comparisons with other academies, we conclude with the results of 30-year projections based on different hypotheses for changes in entry and exit rules — in particular the changes resulting from the amendments to the statutes adopted in 2002.