Re: Absolute or just relative fitness?

From: Tim Tyler (tim_at_tt1lock.org)
Date: 08/16/04 

Date: Mon, 16 Aug 2004 15:50:14 +0000 (UTC)

Jim Menegay <jimmenegay@sbcglobal.net> wrote or quoted:
> William Morse <wdmorse@twcny.rr.com> wrote in message news:<cehmdr$311e$1@darwin.ediacara.org>...

> > I agree that absolute fitness is a useful concept. We have often debated
> > whether there is a direction to evolution, and to a certain extent I
> > would argue that there is a general overall increase in absolute fitness.
>
> That may well be a useful concept, but the name for it should not
> be "absolute fitness". Both you and Tim Tyler are confusing things
> by giving it that name.
>
> You seem to want a name for a kind of fitness that is always
> increasing, in the sense of Fisher's fundamental theorem. Or,
> perhaps you are looking for a concept to use as the ordinate for
> "altitude" in one of Wright's fitness landscapes.
>
> However, my understanding is that Wright saw his landscapes as
> varying, not fixed, on an evolutionary timescale. They may only
> be thought of as fixed over the course of a few generations.
>
> Similarly, Fisher emphasized that the continual increase in fitness
> from natural selection (assuming variance in fitness exists) is
> generally counterbalanced by the fact that mutation usually decreases
> fitness and more importantly by the fact that the environment is
> continually deteriorating. So the concept that you are looking for
> is, in some sense, a fitness that would result if the environment
> (including competition with conspecifics) were held constant.
>
> Clearly, since the environment is not held constant over the course
> of evolution, such a concept is purely theoretical.
>
> Absolute fitness, as the term is most standardly used, is not
> measured with the environment held constant. It is measured
> using the current environment. Hence, it does not really make
> sense to compare absolute fitnesses, or any other measurable
> kinds of fitnesses, between past and present, nor between
> present and future.

The argument that fitness is increasing suggests that organisms are
having more babies survive to reproduce now than in the past.

That might well be true - the living world currently seems to be
expanding in scope and penetrating new habitats - and periods of
growth and expansion generally result in more kids surviving.

I don't think that's usually what I argue along these lines, though.

Usually what I'm claiming is that organisms are getting better at
turning energy gradients into offspring as time passes - i.e.
that evolution is progressive.

Such a process would *not* normally result in increased fitness as
time passes - since organisms are usually thrown into competition with
their relatives in resource-limited environments - and the only way
*everyone* can have more kids is if there is more rapid expansion and
growth all around.

The modern world /does/ happen to currently be exhibiting a lack
of resource limits - and rapid expansion and growth - but that's a
rather different issue to whether evolution is progressive.

However - there *is* a sense in which progress could be painted as an
increase in absolute fitness.

To give a specific (if somewhat hypothetical) example:

Recreate a number of historical time periods, millions of years apart.

Take a sample (using some sort of random sampling process) of organsms
from each time period - and test their survival in each of the other ones.

The hypothesis that evoultion is progressive in character in the way
I suggest would strongly suggest that the later organisms would exhibit
better survival (over all the environments) than the earlier organisms
would.

Such an experiment avoids the criticism that fitness must be evaluated
in the same environment before comparisons can be made - by evaluating
each organism in each environment.

I note that any such criticism isn't really valid in the first place:
in fact it is quite acceptable to ask whether modern organisms/ecosystems
exhibit better survival when transplanted into ancient environments than
ancient organisms/ecosystems do after transplantation into modern ones. 

-- 
__________
 |im |yler  http://timtyler.org/  tim@tt1lock.org  Remove lock to reply.

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