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Re: Digit Loss (kiwis and tyrannosaurs)



(Tracy Ford)
>>Given a choice between an explanation that provides a relationship between a
cause and an effect and another explanation that asserts only the action of
random chance, I prefer the former.<<
Just because B follows A does not mean that A and B are casually related.  Every
year the Himalayas are taller, and my computer is slower, but neither of these
instances has anything to do with the other.  Time passed and certain lineages
of dinosaurs lost fingers, but these two instances need not be casually related
either.

(Jaime Headden)
>>  Horns are four-fold or more in structure, at least: underlying
bone, surface blood vessels and soft-tissue, laminar tissue at
the base with skin, and the caratin itself, also strongly
innervated with blood.<<

Alright, horns are complex, but not nearly so much so as functional digits,
where every piece of tissue must fit together in order for any functionality.
Horns may have complex layers of keratin and soft tissue, but they have no
muscles, no tendons, no nerve endings, all of which _must_ be present and shaped
the right way for a digit to work.

>>A positive effect can even be selected against. <<
If the effect is positive, by definition, it is selected for.  Features selected
against are negative, even if they have potential for being positive.

>> It is not
required, but stays; therefore it is being positively selected
for.<<
...or has not yet been mutated out of existence.  If the genes haven't been
altered, no change occurs, no matter the selective pressures.

>>In either of the
first two cases, have thge monkey do another random act to your
car. Purring, nothing, or explosions, repeat. Now your car is
evolving. Nature is not sentient, and the monkey is your genome.<<
Almost exactly my analogy.  Now extend the analogy into the argument and see my
point.  No matter how much you want some specific adjustment to your car (for
instance, you might want nitros added in), that adjustment will _never_ appear
unless chance directs the monkey to make the appropriate modifications.
Selective pressures are not the cause of every evolutionary development,
mutation is.  No matter how high a selective pressure is, it cannot direct the
development of adaptation without mutation.

Not that I'm trying to get the last word or anything, but it seems that our
argument is  getting bogged down by particulars, so we should probably end this
thread.  If  people wish to know more about my standpoint, read Steven Jay
Gould's _Full House_ (from which my opinions were drawn), that shows most
evolutionary trends were not driven by any pull _towards_ a maximum (a right
wall) but push _away from_ a minimum (right wall).  There is no trend towards
larger size in horses, but since horses began near the minimum horse size, a
randomly diverse speciation of these animals produced animals larger than the
precursers.  I think this same argument can be applied to tyrannosaur evolution
as well.  If one studies the full house of diversity of maniraptors through
time, and not just the extremes to large size and small arms, I doubt you will
see any trend at all.

Dan