Between Zeus and the Salmon The Biodemography of Longevity (1997) / Chapter Skim
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2 Trajectories of Mortality at Advanced Ages
2 Trajectories of Mortality at Advanced Ages
Pages 17-37
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From page 17... ...
For humans, the scattered data available suggested that mortality decelerated at the highest ages, but questions about data reliability precluded strong conclusions. For other species, virtually nothing was known about mortality at advanced ages because the populations studied had been too small to permit dependable estimates of death rates at ages that only a small fraction of the starting cohort reached (Carey et al., 1992~.
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From page 18... ...
For example, Buffon, the eighteenth century French naturalist, hypothesized that each species has a characteristic maximum life span and that this maximum life span is six or seven times the duration of the period of growth. A long stream of variants on this theme culminated with Fries (1980)
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From page 19... ...
(1992) , the trajectory of mortality rises, peaks, and then falls to a low level around which it hovers until the last fly died at an age of 171 days (compared with an average life span in the experiment of 21 days)
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From page 20... ...
Following up on this pathbreaking initial study, the Carey laboratory completed life-span analyses on an additional 1.6 million medflies, raised under a variety of conditions. Again, mortality decelerated at older ages.
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From page 21... ...
. In James Curtsinger' s laboratory, the life spans of tens of thousands of Drosophila melanogaster have been studied in various controlled experiments.
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From page 22... ...
FIGURE 2-3 (A) Semilogarithmic plot of death rates for 5751 male Drosophila melanogaster from inbred line.
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From page 23... ...
She has compared the mortality trajectory of the so-called wild-type nematode, the genotype usually studied, with mutant strains that differ from the wild type by a point mutation at a single locus known as DAF2 (Larsen, 1993~. As shown in Figure 2-5, her experiments show a sharp rise in mortality in the wild-type strain, but a much slower increase, with signs of a rough leveling off, in the DAF2 genotypes.
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From page 24... ...
and perhaps the flour beetle Tribolium confusum and the common house fly Musca domestica (Wilson, 1994~. Death rates are such that many individuals in these various species survive well past the ages when reproduction usually ceases or drops to very low levels.
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From page 25... ...
The age-trajectory of mortality reflects both the underlying age-trajectories of mortality for individuals in the population and the effects of compositional change as the frailer individuals drop out of the population. Some of my colleagues and I have devoted a lot of thought to this problem over the past two decades (e.g., Vaupel et al., 1979; Vaupel and Yashin, 1985; Vaupel and Carey, 1993~.
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From page 26... ...
In fact, even if death rates are increasing with age for every individual in a population, the age-trajectory of mortality can level off or even decline as a result of compositional change. The Gompertz exponential formula could hold for individual medflies, even though death rates for cohorts of medflies fall substantially at older ages.
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From page 27... ...
Many biologists seem to believe that it is possible for organisms to approximate the "one-hoss stray" of Oliver Wendell Holmes that ran perfectly until one day when all of its pieces fell apart simultaneously (e.g., Fries and Crapo, 1981; Dawkins, 1995~. This is one of the suppositions used to justify the belief in species-specific maximum life spans.
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From page 28... ...
Polk and Company did so for July 1, 1941, and then for July 1 of every year from 1947 to the present. These data, which are closely analogous to population count data collected by national statistical offices and census bureaus, have been assembled and analyzed by Vaupel and C.R.
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From page 29... ...
m = central death rate. carefully.
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From page 30... ...
In sum, although living organisms and equipment share only a few common attributes, demographers and biologists may nonetheless be able to learn something from reliability engineers. There is already a splendid example of this the statistical methods used to analyze survival data were to a considerable extent developed by reliability engineers interested in analyzing failure-time data.
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From page 31... ...
m = central death rate. THE EVOLUTIONARY THEORY OF AGING REVISITED The discussion so far has addressed a number of explanations for the observed deceleration of mortality in the five species for which large populations have been studied.
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From page 32... ...
Perhaps the biggest current challenge is to clarify the mystifying puzzle of why the evolutionary theory of aging does not appear consistent with the empirical observation that mortality decelerates at older ages. "Nothing in biology makes sense except in the light of evolution," Dobzhansky (1973)
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From page 33... ...
They share, however, an interest in populations. A1though many demographers rigidly restrict demography to the study of human populations, the methods and concepts of demography are useful in studying
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From page 34... ...
Liedo, and J.R. Carey 1995 Mortality Deceleration and Longevity in the Mexican Fruit Fly (Anastrepha ludens)
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From page 35... ...
1973 Nothing in biology makes sense except in the light of evolution. American Biology Teacher 35:125-129.
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From page 36... ...
Liedo, and J.R. Carey 1997 Early mortality surge in protein-deprived females causes reversal of sex differential of life expectancy in Mediterranean fruit flies.
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From page 37... ...
JAMES W VAUPEL 37 Williams, G.C.
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