DNAunion@aol.com writes
in message <24.c500da6.272b151b@aol.com>:
>>>First, let's start from the building blocks and see if we get life
>>>...
> >
> > >THadley: Given an energy-efficient tendency in life to
> > >evolve multiple dependencies among parts, as well as tendencies
> > to lose structures or mechanisms that are not essential to
> > current functioning, I would think that the individual parts
> > of any given organism are far more likely to "die" on their own
> > than do anything else.
> >
> > Take, for example, many kinds of symbiosis. Prior to the
> > symbiotic relationship, the two organisms are able to function
> > independently. After the relationship has been in existence
> > for any significant length of time, however, the symbiotes will
> > die if seperated. Dependencies have evolved and preexisting
> > structures vital for independent existence have been lost or
> > diminished.>>>
> DNAunion: I am not exactly sure if you are arguing against my
> statements, supporting them, or neither.
I'm disagreeing that the example you described is actually
a good attempt at testing the hypothesis that life could evolve
solely from what we classify as the building blocks of life.
> Let me point out though
> that I was discussing a fully-autonomous bacterium, and not one
> involved in any form of symbiosis. If one were to take a single
> fully-autonomous bacterium - keeping it supplied with the
> nutrients, like sugars, it needed to survive all the time - and
> lysed it, the "guts" (cytosol, ribosomes, circular DNA, etc.)
> would leak out : the vital concentration gradient would be
> gone, the cellular reactions would cease, and the cell (and all
> its components) would be dead (this is in fact one method employed
> by bacteria to kill others: they produce an oligopeptide that
> forms a leaky pore in the other bacterium). This process is
> irreversible (following "times arrow"): the chemical reactions
> will not self-organize back into a sustained metabolism capable
> of supporting life and the bacterium will not re-assemble from
> its now disorder "parts". This is true even if one heats the
> petri dish, or exposes it to intense UV, or jars it around, or
> supplies any other kind of undirected energy.
It's true, but there isn't necessarily any sort of law that
prevents it from reassembling into a new life form as much as
the logic that, if individual bacteria parts existed seperately
at any time, they would have now evolved to be incapable of
"living" on their own.
Recall Margulis' Symbiotic Theory for the origin of eukaryotes as
an example of a larger organism forming from smaller, "live" parts.
The original prokaryotic host cell may have eaten or otherwise
ingested aereobic bacteria (which may also have been a parasite),
which reproduced such that subsequent generations of this new cell
would also contain the newly ingested bacteria. These aereobic
bacteria survived via the nutrients from the host prokaryotic cell,
while multiple invaginations of the cell membrane helped prepare
the aerobic bacteria for their new roles. Over time, both the
prokaryotic host as well as the bacteria endosymbionts developed
a mutually satisfying or benefical existence and both entities lost
their ability to function without the other. The ingested aerobic
bacteria, which by definition are pro-oxygen, controlled and made
possible the oxidative metabolism of what was the prokaryotic host
cell. These aerobic bacteria may have begun to utiltize and
adapt their former roles to very similar functions within the
prokaryotic cell. These bacteria may have been the origin of
mitochondria.
So, under this hypothesis, the right way to break down a eukaryote
into its original parts would be to break it into a prokaryote
and assorted aerobic bacteria. Of course we can't do that and
actually have two living organisms because of the result of
evolution over time on symbiotic relationships. Thus, the idea
that we can break down living organisms and disprove anything
by not seeing their parts reassemble has a problem.
However, it would be true that if we could supply the mechanisms
and structures that evolution likely has erased, we could break
a eukaryote cell into two simpler, living organisms that could,
subsequently, reform given the right environment (assuming the
hypothesis is correct). And if symbiosis played other roles,
we might also expect the same reasoning to apply to many of the
individual "building blocks" of life.
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