Re: Trees of Life

On Jul 2, 6:03 am, "alwaysaskingquestions"
<alwaysaskingquesti...@xxxxxxxxx> wrote:
Thanks for the technical terms to describe what I was talking about but
humour me for a moment whilst I get my basic thinking straight.

It seems to me that the first forms of life, by definition, had to be
autotrophs. The only way they could get energy was either by photosynthesis
or chemosynthesis.

As far as I can see, chemosynthesis is the more likely of the two as most
researchers in abiogenesis think that the first life forms probably formed
in a primordial sea or in the vicinity of hydrothermal vents. If I
understand it properly, the Theory of Evolution generally assumes that life
began in water and spread to land; therefore, it seems likely that the
earliest life forms used chemosynthesis.

If you do not restrict the molecules that the first lifeforms depended
on they most likely used what you call chemosynthesis. They probably
did not use the molecules that current hydro vent ecologies depend on,
but carbon based molecules that may have included things like sugars
and amino acids.


In that case, the first life forms on land which developed into plants had
to make a switch from chemosynthesis to photosynthesis which is a major
evolutionary step and not one that I can easily picture happening in gradual
steps. Don't get me wrong here, by the way, I'm not suggesting this as some
form of 'Irreducible Complexity' - I don't buy into that rubbish.

Evidence indicates that the evolution of photosynthesis occurred in
water. Fossil blue green algae are known (photosynthetic
prokaryotes). There had to be photosynthetic prokaryotes before
eukaryotes because chloroplasts are prokaryotic in origin.

For gradual steps just think of the fact that a lot of molecules
absorb light and transfer energy. Pigments can do this. They also
have other uses like protecting the organism from damage by light.
You do not need the entire chain of the current apparatus to do things
for the cell. Likely no one knows the events that led to the
evolution of photosynthesis, but those no ones include creationists,
and science has some real answers like photo protection and electron
transfer. What do creationists have for their alternative?


On my original point about when did organisms start consuming each other -
which I now know is called heterotrophy :) - if this happened before
marine forms of life made it onto land, then that means that plants went
from chemosynthesis to heterotrophy to photosynthesis which is even more
complex. I note that you say that "Plants, for example, are descended from
heterotrophs" - can you point me to some reading on this?

Consuming other organisms isn't complex. Whatever they bumped into
they probably got as much as they could from it. I don't know how
long this period lasted, but until the first lifeforms could extract
energy from readlily availble chemicals their metabolisms would be
limited to what they could find in their environment, which would
include each other.

Unless they can be replenished such systems have finite periods of
time where they are viable. Whale carcasses create mini ecosystems
when the fall to the bottom of the sea, but when the carcass is gone
the organisms have to find another source of food.


I take the point made by both you and Ron O make about plants and animals
having so much similarity in things like DNA, genetic code and membrane
structure which are very strong arguments in favour of a common ancestor,
but is it totally impossible that they started off from different bases and
developed those similarities because those are the very things that work?

Structural similarites can be accounted for by convergent evolution.
The genetic code isn't such an entity. The code can change, but the
changes are all nested within the original. This is due to the fact
that once lifeforms reached the level that they had a certain number
of genes, it would have been difficult for the code to change without
messing up quite a lot.

Independent evolution of the genetic code and the machinery to make it
work are not likely, just from the stand point of why would only one
code work? Just look at the code and try and figure out why AGA and
AGG have to code for arginine while AGT and AGC code for serine, and
then note that in some mitochondrial genomes AGA and AGG do code for
serine. Why should TTG and TTA code for Leu while TTT and TTC code
for phe. There are four other codons that code for leu CTA, CTG, CTT
and CTC. There are four other codons for ser and arg.

There may have been many lifeforms with partial genetic codes or parts
of the machinery to do something with it that combined to form our
common ancestor, but they combined before plants and animals split.

Ron Okimoto


.

Relevant Pages

  • Re: Trees of Life
    ... Photosynthesis and chemosynthesis are not means of life developing. ... They are terms used to describe how organisms extract energy from ...
    (talk.origins)
  • Re: Trees of Life
    ... It seems to me that the first forms of life, by definition, had to be ... As far as I can see, chemosynthesis is the more likely of the two as most ... photosynthesis probably originated in the oceans. ... That is why plants get their own kingdom. ...
    (talk.origins)
  • Re: Trees of Life
    ... Photosynthesis and chemosynthesis are not means of life developing. ... They are terms used to describe how organisms extract energy from ...
    (talk.origins)
  • Re: Trees of Life
    ... Photosynthesis and chemosynthesis are not means of life developing. ... They are terms used to describe how organisms extract energy from ...
    (talk.origins)
  • Trees of Life
    ... do we try to construct a tree of life originating back to a single ... As organisms using photosynthesis and chemosynthesis are entirely ...
    (talk.origins)