On 2008-05-10 16:27:17 +0100, Antares 531 <gordonlrDELETE@[EMAIL PROTECTED]
> said:
> 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?
Not necessarily. There are plenty of plants that respond to stimuli on
a much more basic level than that. As to where "out of the way" is, it
probably doesn't matter if you're moving when a predator approaches and
your fellow prey are sitting still.
>
> 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?
I think the problem you're experiencing is that you're focussing on
what we experience as the "end product" (a thoroughly non-Darwinian
concept, but there you go). The lens, for example, in an eye need not
have sprung from a mutation, but froam the gradual specialisation of
cells through natural selection. The same applies to most of the rest
of the structure.
>
> 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
I see the problem, but I think it stems from an over-emphasis on the
role of mutation in your understanding of evolution. Mutations are a
very very small part of the overall process.
>>
>>>
>>> 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
Not necessarily.
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