Re: Trees of Life

On Jun 30, 6:56 am, "alwaysaskingquestions"
<alwaysaskingquesti...@xxxxxxxxx> wrote:
"Ron O" <rokim...@xxxxxxx> wrote in message

news:1183203066.953173.103560@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

On Jun 30, 6:02 am, "alwaysaskingquestions"
<alwaysaskingquesti...@xxxxxxxxx> wrote:
There are two ways we know in which life can develop purely from
non-living
matter - photosynthesis and chemosynthesis.

Photosynthesis and chemosynthesis are not means of life developing.
They are terms used to describe how organisms extract energy from
their environment.

I worded that badly. The point I was trying to make was that they don't need
other pre-existing forms of life for their energy source.





Why then, do we try to construct a tree of life originating back to a
single
point? As organisms using photosynthesis and chemosynthesis are entirely
independent, would it not be more logical to have two separate trees of
life - basically one for plants and one for animals, or do we have real
evidence of a common ancestor? (I'm consciously leaving cyanobacteria out
of
this as I don't think it affects my underlying point.)

Science claims that the evidence indicates life going back to one
point (the lifeform that developed the genetic code that all known
extant life uses), but it is acknowledged that we know nothing about
how many different types of lifeforms may have combined during the
evolution of that common ancestor.

You don't, know much about chemosynthesis and photosynthesis if you
claim that they have to be two separate trees.

That's why I'm asking here :)

Just look up the
bacteria that produce H2S (chemo) and the ones that produce H20
(photo). You will note that they both use the same genetic code and
have similar electron transport systems.

What I'm wondering is whether they inherited the genetic code and electron
transport system from a common ancestor or whether they could have evolved
them separately.

http://en.wikipedia.org/wiki/Genetic_code

Anything is possible, but what we have to try and figure out is what
actually happened.

We have no evidence that there were multiple lifeforms that developed
the genetic code independently. We have evidence that the code did
evolve and did go through some selection. It is possible that there
were several different lineages that were working on a triplet code,
were coevolving and stealing bits from each other. With natural
selection giving a boost to the best combinations at the time.


Science doesn't even claim
that it knows what the first lifeforms used as an energy source. My
bet would be on chemosynthesis. Lifeforms probably just took up
molecules from their environment and did things with them. Some of
those chemicals may have been photoactivated, probably not in the
organism, but maybe they were.

A secondary area intrigues me. Outside of those basic organisms that use
photosynthesis or chemosynthesis, all other forms of life grow and
develop
by consuming other organisms - cow eats grass, man eats cow, etc.

What is so intriquing?

Because it seems to me that that organisms starting to consume other
organisms could have been a major stepping stone in evolution.

Basic biology of food webs and chains. The chains are dependent on
the lifeforms that can extract basal energy from their environment.
Deep sea vent ecosystems are dependent on chemotrophs, but the first
lifeforms were probably not chemotrophs that could extract energy from
salts. Most of the scenarios that I've seen had the crude lifeforms
using more complex molecules floating around in solution. These
lifeforms would naturally take any source that they bumped into. So
the basal (in terms of chemosynthesis and photosynthesis) lifeforms
that our current food webs depend on did not exist and evolved later.
The first lifeforms were likely scavengers. Other lifeforms would
have been the richest sources to plunder.

SNIP:

Ron Okimoto

.

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