Institut
national d'études démographiques
Séminaire "Démodynamiques"
Demographic and Biological Limits to
Human Longevity: A Biodemographic Perspective
Jay Olshansky(*)
Jeudi 18 avril 1996 de 14 à 15 h (salle du 3e étage)
(*) Professeur à l'Université de Chicago
Résumé
Demographic entropy in the life table is a well known
phenomenon that has been demonstrated repeatedly in the scientific
literature. This phenomenon is demonstrated again using data from
France in 1990-92. In order for the average duration of life of
France to reach 85 years, total mortality would have to decline by 52
percent at every age. The average life expectancy of France can
exceed 85 years, but only if most major causes of death are eliminated
or sufficiently postponed (e.g., a 74 percent reduction in death rates
at every age). Even if the rapid declines in total mortality observed
at every age in France from 1900 to 1990 were to occur again from
prevailing levels of mortality, the average life expectancy of the
population would not even reach 90 years. Given the inescapable
mathematics of the life table and the fact that there are no known
lifestyle interventions or medical technologies available today that
are capable of reducing total mortality by these specified levels, the
practical limits to life expectancy at birth in France and other
developed nations are rapidly being approached. Life expectancy at
birth can rise beyond 85 years, but it is suggested here that this
would require significant new advances in medical technology that
"manufacture survival time" by decelerating the basic rate of aging
itself and postponing death through medical interventions.
The expression of demographic entropy in the life table is
directly related to biological forces that influence the onset and
rate of increase in intrinsic mortality. Although a species lifespan
may not be directly programmed by natural selection, the pattern of
death from intrinsic causes may be an inadvertent product of natural
selection operating on other aspects of a species life history -- such
as reproduction. Although evolutionary biologists have provided
strong theoretical arguments for why senescence occurs among
individuals and when in the lifespan it should be expressed, empirical
research has not been focused on explanations for why consistent
patterns of intrinsic mortality are observed among many sexually
reproducing species. I will discuss recent research in which we test
the hypothesis that the onset and rate of increase in the intrinsic
death rate is calibrated to attributes of a species reproductive
schedule (using data on humans, dogs, and mice). In addition, I will
discuss how our findings address the concept of a "law of mortality"
as originally proposed by Benjamin Gompertz and Raymond Pearl, and how
our findings suggest that in low mortality populations the lifespan of
the species may have actually been surpassed.
Animateur de la séance Nicolas Brouard,
brouard@ined.fr
On peut trouver le programme du séminaire sur http://sauvy.ined.fr/seminaires/demodynamiques ou le recevoir sur la liste(listserver) demodyn@sauvy.ined.fr
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