[ExI] Are Limited Lifespans An Evolutionary Adaptation?

Rafal Smigrodzki rafal.smigrodzki at gmail.com
Fri Jun 19 18:28:05 UTC 2015

On Fri, Jun 19, 2015 at 5:05 AM, BillK <pharos at gmail.com> wrote:

> The “mutation accumulation” theory, where the repair mechanism wears
> out and the “antagonistic pleiotropy” theory, where traits that are
> beneficial in early life are detrimental in later life.

### I don't know about any specific problems with these theories,
especially the mutation accumulation one. Do you?

> The simulation shows "evolution favors shorter lifespans in
> environments where resources are scarce and when pressures to
> procreate are particularly intense". That might well not be the
> complete answer. But traits that benefit species survival rather than
> individuals seem likely.

### What evolves is not "genes for shorter lifespan" but rather "absence of
genes for long lifespan" - this is an important mechanistic distinction
which those population-level simulations completely miss.

> Assuming a species had a very long lifespan, then what might the results
> be?
> Reproduction beyond the capacity of the environment to support them is
> obvious, (boom and bust) so that would be a limiting factor. Long-life
> species would grow to match their environment and become slow
> reproducers, so they would have less evolution. A change in the
> environment would wipe them out.

### That's why long-lived species do not usually evolve in environments
with frequent environmental change, unless they are highly adaptable. The
arrow of causation goes from the environment, which co-defines the range of
the possible, to phenotypes, which fill in the space of possibilities. You
can't start your analysis at "Assuming very long lifespan ...", you need to
start at "Assuming the conditions allow long survival..."

> In the continually changing early world environment, there would be no
> evolutionary benefit to very long lifespan.

### And generally no benefit from having evolved genes actively limiting
lifespan - the changes in environment would wipe out individuals long
before they had the opportunity to use such genes.

The alleles that shorten human lifespan (and obviously there are many) are
all side-effects of evolution under conditions where long survival is
uncommon, not evolved adaptations against long survival.

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