Re: limit of selection???

From: dkomo (dkomo871_at_comcast.net)
Date: 08/25/04 

Date: Wed, 25 Aug 2004 04:41:37 +0000 (UTC)

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. If Wilkins were still around, he'd light up this
fallacious way of speaking in a big way.

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.

> 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"!

     --dkomo@cris.com

Relevant Pages

  • Re: limit of selection???
    ... > selection can push an adaptation, ... > 1) Childbirth is a problem, ... repeats seem to control head size, the more repeats, the bigger the ...
    (sci.bio.evolution)
  • Re: limit of selection???
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