On Sat, 10 May 2008 15:04:35 +0100, Andrew <thecroft@[EMAIL PROTECTED]
>
wrote:
>On 2008-05-10 14:41:50 +0100, Antares 531 <gordonlrDELETE@[EMAIL PROTECTED]
>
said:
>
>> On Sat, 10 May 2008 12:03:59 +0100, Andrew <thecroft@[EMAIL PROTECTED]
>
>> wrote:
>>
>>> On 2008-05-10 01:06:23 +0100, Antares 531 <gordonlrDELETE@[EMAIL PROTECTED]
>
said:
>>>
>> (snip)
>>>
>>> "Mutation" as such is only a very small part of Darwinian evolution.
>>> Once a mutation is in the gene pool most of the work of natural
>>> selection is done by non-mutative variation within a population. The
>>> only 'tangible' benefit required is that a variation gives one member
>>> of a species a better chance of surviving than others.
>>>
>> Andrew, I quite agree on this, as far as we've taken it, but there is
>> still that nagging set of questions as to how a creature or clan of
>> creatures could survive and sustain a very complex and long drawn out
>> sequence of Darwinian evolutionary changes that didn't produce any
>> benefits for a very long time and after being passed along through a
>> large number of generations.
>>
>> I'm talking about things like the development of eyes in so many
>> different species. The useful visual properties didn't (couldn't) show
>> up until the very complex and very extensive series of eye structure
>> mutations had gone to completion. That would have taken thousands of
>> generations, and millions of years.
>
>I don't agree. Even if an organism simply has a few light-sensitive
>cells that allow it to get out of the way when a predator comes
>prowling while its fellows get eaten would provide the kind of
>advantage that Darwin suggested. A complete eye with all its structures
>would no doubt provide a significantly greater advantage, but there is
>no need to posit a complete eye as a necessity for evolutionary
>advantage.
>Also, eyes do not have to develop independently in all organisms that
>have them. As long as rudimentary visual organs developed in the common
>ancestor.
>
Andrew, this seems reasonable but there are still some questions. How
would those first creatures with only light sensitive cells know where
"out of the way" was, relative to their present position? And,
wouldn't that predator also have to "see" "smell" "taste" "hear"
"feel" or otherwise detect the creature that it was hunting?
How did the predator develop these capabilities, using only Darwinian
natural selection? The problem I'm having with this is that none of
these complex sensory organs just popped into being with only one
simple mutation. Each required a VERY LONG chain of successful
mutations over a span of thousands or millions of generations. And,
how would Darwinian selection follow through those first mutations,
before any of the sensing cells came into being?
A similar set of questions surrounds the Darwinian development of
other organs such as the heart, kidneys, lungs, etc. These organs
didn't just pop into a functional state with one simple mutation. They
needed dozens or hundreds of successful, successive mutations with no
killer mutations interlaced with the successful mutations, before they
were able to provide the host some level of Darwinian natural
selection. For example, a light sensitive skin cell that was also very
susceptible to early in life development of cancer wouldn't work.
Gordon
>
>>
>> What I'm saying here is, for example, an eye system, complete except
>> for the lens, would not provide any Darwinian advantages and would not
>> likely have continued to evolve. The process had to go all the way to
>> completion before any Darwinian advantages came into play. What
>> attributes of Darwinian selection kept this process going during those
>> first generations, long before any benefits could be realized?
>>
>> Eye development doesn't seem to have had a singular mutation source.
>> That is, for example, the octopus (phylum mollusca) has eyes that use
>> specialized skin cells for the retina, with the optic nerve attached
>> to the back of the retina. Humans and other creatures of the phylum
>> chordata have eyes that use specialized brain cells for the retina,
>> and the optic nerve penetrates the retina then attaches to the front
>> side.
>>
>> These two eye development Darwinian processes seem to have occurred
>> independently of each other. There must have been some positive
>> effects, early on, but what were these positive effects. Gordon
>
>Although the eye development processes have occurred independently they
>may have arisen from a single mutation in a common ancestor.
>
This is the part that baffles me. How would one single mutation
provide any Darwinian selection advantage? Wouldn't the Darwinian
natural selection process require some functional advantage and
wouldn't this functional advantage require an unbroken chain of MANY
mutations before it began to provide the required Darwinian natural
selection functional advantage? Gordon
>
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