Re: limit of selection???
From: A.C.H. (br.hessels_at_planet.nl)
Date: 08/25/04
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Date: Wed, 25 Aug 2004 23:10:49 +0000 (UTC)
dkomo <dkomo871@comcast.net> wrote in message news:<cgh5a1$1ot2$1@darwin.ediacara.org>...
> A.C.H. wrote:
>
> > "Malcolm" <malcolm@55bank.freeserve.co.uk> wrote in message news:<cg7u10$236v$1@darwin.ediacara.org>...
> >
> >>"A.C.H." <br.hessels@planet.nl> wrote
> >>
> >>>The following reason is, i believe, not in those lists:
> >>>
> >>>because an adaptation is caused by its selection pressure, it can not
> >>>escape its selection pressure.
> >>>
> >>>Again:
> >>>The adaptation is linked to whatever selects it, it can not outperform
> >>>it.
> >>>
> >>>Again:
> >>>an example: a prey will never be able to definitely outperform its
> >>>predator, because there is no selection beyond what's actually doing
> >>>the selecting (the predator).
> >>>
> >>
> >>There is no point in having something that is more effective than needed.
> >>For instance, most animals that are adapted to temperate climates are
> >>unlikely to go for more than a day or so without finding water. If they were
> >>transplanted to a desert then they would starve because of lack of food
> >>anyway, so elaborate systems for conserving water have not evolved.
> >>There is also very frequently a cost associated with an improvement. For
> >>instance spiders could spin bigger webs and catch more flies, but they would
> >>need to produce more silk to do it. The actual web size is probably a very
> >>good compromise.
> >>Then evolution is a dynamic process. For instance childbirth is very
> >>hazardous for human females, because head size has expanded faster than hip
> >>size. In several millions of years this will be solved, by selection for
> >>women with wider hips or for more premature births. However the adaptive
> >>process has not yet caught up.
> >
> >
> > The issue i was trying to pose was what this would mean, how far
> > selection can push an adaptation, how perfect it'll become.
> >
> > [moderator's note: I can't be the only one thinking of Fisher's
> > Fundamental Theorem here, can I? The rate of evolution is proportional
> > to the product of the selection gradient, the genetic component of
> > phenotypic variation, and the heritability of the trait. Does no one
> > else think this is relevant here? - JAH]
> >
> >
>
> Maybe, but I see a philosophical problem with talking about selection as
> though it were a physical force like electromagnetism, using phrases
> like "pushing an adaptation." Selection is not a force. It is only an
> abstraction.
Well its about the hard, painfull & difficult lives of individuals
surviving or not surviving.
If Wilkins were still around, he'd light up this
> fallacious way of speaking in a big way.
o.k. its just a metaphor for natural selection, the differential
survival & reproduction of variating, replicating units (genes,
individuals). If an environmental factor influencing this has a
certain consistancy, you might want to express that as a force
(someting having a certain direction and a certain strenght).
>
> The only thing that *physically* happens is that population of animals
> acquire different traits through mutations and have different numbers of
> offspring as result, causing some traits to become more common, and
> others less. There's nothing out there in the environment that reaches
> out and "selects" one animal versus another.
Think about a predator catching a prey. In this case the environment,
the predator, most defenitely reaches and selects.
>
> > Compare these two situations:
> >
> > 1) Childbirth is a problem, females die during birth. Evolution by
> > natural selection is happening, which is the cause of adaptation
> > (easier childbirth).
> >
> > 2) Women are perfectly adapted to giving birth, childbirth is no
> > problem at all, no women die giving birth.
> > In this case, the natural selection, which caused the adaptation in
> > the first place, falls away.
> >
> > Therefore the state of perfect adaptation (all women give birth easy)
> > cannot be reached, because, paradoxically, the cause of the
> > adaptation: natural selection, falls away when you approach this
> > state.
> >
> > So i predict: child birth will be less hazardous, but will never be
> > easy.
> >
>
> I think this argument is specious. If you insist on talking about
> natural selection as though it were a concrete force, then I would say
> the exact opposite happens: selection doesn't "fall away" for women
> better adapted to giving birth, it *increases*. These women have more
> offspring -- they are more strongly "selected"!
>
>
Natural selection is about the differential survival of individuals.
If all individuals survive (and reproduce) there is no natural
selection.
> --dkomo@cris.com
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