From: Hal Finney (hal@finney.org)
Date: Fri May 10 2002 - 11:47:17 MDT
> DURHAM, N.C. -- The lifespans of people in developed nations are
> increasing at a remarkably constant rate, suggesting that there is no
> natural limit on life expectancy, said a Duke University researcher in
> an article in the May 10, 2002, Science. Data analyzed by the scientists
> indicate that the maximum human lifespan will reach 100 in about six
> decades, which policymakers should consider as they make critical resource
> decisions affecting older adults.
Robin Hanson earlier pointed to a successful model which makes different
predictions:
> Age-specific mortality rates have fallen at a steady exponential rate for
> the entire last century. The classic source on this is
>
> Modeling and Forecasting U. S. Mortality, by Ronald D. Lee,
> Lawrence R. Carter, J. American Statistical Association,
> 87(419):659-671, Sep., 1992.
>
> There was also a recent Nature article showing that this model applies
> also to a half dozen other countries.
>
> Given the initial age distribution, this steady exponential decline in
> age-specific rates produced a rapid decline in life expectancy in the
> early part of this century, and a slower decline in the later part. But
> the fundamental trend has remained amazingly steady.
I can't read the new Science report, but it doesn't sound like their
statistical analysis is as "deep" as the Lee&Carter result. OTOH, L&C's
methodology has apparently been shown to systematically underestimate
longevity increases when applied to past data (although by a small
amount).
I found an interesting article,
http://www.demog.berkeley.edu/~tmiller/papers/p2000.immortality.us.html,
about what would happen to future population if we suddenly achieved
immortality. This is a common topic for debate, in terms of its impact
on overpopulation. From the article:
Sudden medical breakthroughs in 2001 could have relatively large
impacts on population size this century. For example, a sudden 20
year gain in life expectancy would boost US population size by 21% at
mid-century and 23% by 2100 over the baseline forecast. By historical
standards, such sudden breakthroughs are unprecedented. The largest
single year gain in US life expectancy was 8 years (a rebound following
the flu epidemic of 1917). Single year gains in life expectancy exceed
1.0 in 12 of the 98 years in the last century. They exceeded 2.0
only twice.
The achievement of immortality in 2001 would lead to a tripling of the
current US population and a more than quadrupling of the current world
population by the end of the century. (That is, the world population
would twice double in size).
Assumptions about future fertility and immigration levels can have
much more dramatic effects on future US population size than can
assumptions about mortality. For example, the US Census Bureau's high
projection foresees a US population of 1.18 billion by the end of
the century -- due to their assumptions of high fertility (TFR=2.6)
and high immigration (3 million net immigrants admitted in 2100).
In contrast, we project a US population of only 800 million at the
end of the century -- even assuming that immortality is achieved next
year! This is because our projections assume lower fertility (TFR= 1.9)
and lower immigration (900,000 per year) than the Census high forecast.
So immortality would have a significant impact, but it is generally
small compared to fertility level. If people responded to life extension
by dropping fertility it might have no impact at all.
Hal
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