X-Message-Number: 2101
From:	Ralph Merkle <>
Subject: Optimality, mutation and the evolution of ageing
Date:	Mon, 12 Apr 1993 16:34:26 PDT


"Optimality, mutation and the evolution of ageing", by L. Partridge
and N.H. Barton, a review article in Nature, Vol 362,
March 25th 1993, page 305.

The abstract:

Evolutionary explanations of ageing fall into two classes.  Organisms
might have evolved the optimal life history, in which survival and
fertility late in life are sacrificed for the sake of early
reproduction and survival.  Alternatively, the life history
might be depressed below this optimal compromise by deleterious
mutation:  because selection against late-acting mutations is weaker,
these will impose a greater load on late life.  Evidence for the
importance of both is emerging, and unravelling their relative
importance presents experimentalists with a major challenge.

>From the article:

"Because ageing reduces the genetic contributions of individuals
to future generations, it is opposed by natural selection.  But
as Medawar first pointed out [omitted references], the natural
selection that maintains survival and fertility becomes weaker
through the life history.  Even without ageing, organisms are at
risk of death and impaired fertility from disease, predation and
accidents.  If the genes affecting survival and ferility are to
some extent age-specific in their effects, then those that
influence later life will be subject to weaker selection because,
by the time they take effect, more of the original carriers will
already have died or become infertile for other reasons[omitted
references]."

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