From: Cliff Lundberg <cliff@cab.com>
>Richard Wein wrote:
>
>>In case anyone should think that Cliff is representative of philosophical
>>naturalists in having a "built-in prejudice in favor of naturalistic
>>explanation", I'd like to point out that I don't share his prejudice. I
>>reject the ID explanation precisely because it is *less* parsimonious.
>>...
>>The most parsimonious explanation is not simply the one which can be
>>stated in fewest words.
>
>There must be some correlation between parsimony in the real
>world and description of the real world. Simpler mechanisms and
>fewer assumptions should mean fewer words in the description.
>
>>It's the one which leaves least unexplained.
>
>That sounds like the 'most complete' explanation.
Perhaps I'm mixing up "parsimony" and "explanatoriness". But I think the two
concepts are quite intertwined, and it's not easy to separate them. The
point still remains that there's no need to appeal to a personal prejudice
to reject non-natural explanations. There are good reasons to reject
non-natural explanations based on the rational principles of parsimony and
explanatoriness.
>I never liked this topic--I recall having to learn terms like explicans
>and explicandum, definiens and definiendum, terms which are never
>employed outside of philosophy of science courses and which are
>forgotten after the exam. It just seemed to me that in a general sense
>ID was a highly parsimonious explanation, as it relies totally on one
>simple assumption and it can explain anything and everything.
Taking this to the extreme, those who are satisified by such explanations
can simply explain everything with the 3 words "God did it"! Or even shorten
that to the single word "God!". ;-)
[...]
>>I think "weird" is understating it. It's bizarre! Still, I suppose bizarre
>>things do happen. But have you thought out any plausible scenarios for how
>>this could have happened in the case of particular organs?
>
>To me the origin of metazoan or cellular complexity is so completely
>opaque I expect the real truth to be rather weird and unexpected,
>counterintuitive and possibly gross.
>
>I don't have theories about particular organs, but I can certainly imagine
>an aquatic ecosystem of organisms with specialized abilities to move, to
>filter, to perceive and react, to digest, to emit chemicals etc living in
>tight symbioses.
But if these abilities can evolve in organisms living in tight symbiosis,
why can't they all evolve in a single organism?
>How could genomic integration of metazoa occur? I'd have
>to presume successful zygosis of disparate organisms would involve
>endomitotic duplication of each chromosome to form the normal diploid
>set. Subsequent reproduction would be through the familiar means.
>Against objections I can only say things may have been a little wild
>during the formation of our metazoan fauna.
>
>>>It's logically more satisfactory than thinking these complexes evolved
>>>gradually.
>>
>>Why? What's your objection to gradual evolution of organs? Do you deny
that
>>*any* complexity can evolve gradually?
>
>Maybe.
If you don't think that *any* complexity can evolve gradually, then there
must have been a vast number of cases of symbionts merging, in order to
account for today's huge complexity.
If you think that *some* complexity can evolve gradually, then why not all?
Where do you draw the barrier?
(Note: I'm not denying that there may have been *some* merging of symbionts,
such as in the formation of the eukaryotic cell.)
>If 'complex' means having many parts, how do you *gradually* move
>from having x number of parts to having x+1 number of parts?
I don't use "complex" to mean having many parts. I would consider
duplication of an existing part to be only a small increase in complexity.
The point being that this can occur through a small genomic change.
Consider, for example the way that a small genomic change can result in an
extra pair of legs in a fruit fly, or a 6th toe in a human.
Likewise, the merging of two symbionts may have required only a relatively
small genetic change, which is why I don't necessarily consider it to be a
big increase in complexity.
>Objections to
>the gradual evolution of interdependent complexes are familiar, they're
>basically
>about the problem of incipience.
>
>As with the number of bones we have, the number of organs seems to be
>diminishing. We see vestigial organs, but do we see nascent incipient
>organs? Anybody sprouting a handy eye in the back of the head? This
>implies to me that there was a special formative era, and that subsequent
>evolution is a limited refining process distinct from the wilder original
>time of 'creation'.
How do you recognize an incipient organ? We can see creatures with eyes of
various stages of complexity, from a pit lined with light-sensitive cells up
to the human eye. Wouldn't the former qualify as an incipient eye?
It may well be the case that, as organisms become more complex, it becomes
more difficult for them to evolve new organs, because so many interrelating
parts would have to change. That would explain why we don't see changes in
basic body-plan in the more complex species. Whereas a small genomic change
may give a fruit-fly an extra pair of legs, it would require many
simultaneous changes to give a human being a functional extra pair of legs.
(Nevertheless, it's amazing how flexible the human body plan is. I believe
humans are occasionally born with an extra pair of toes. And have you seen
pictures of healthy Siamese twins with shared limbs and organs?)
Richard Wein (Tich)
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