Re: Trees of Life


"alwaysaskingquestions" <alwaysaskingquestions@xxxxxxxxx> wrote in message news:5es4crF39tl6pU1@xxxxxxxxxxxxxxxxxxxxx
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.

I could quibble with some points so far, but I generally agree with your
conclusion. The first lifeforms were chemosynthetic autotrophs. Not
everyone agrees though.

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.

Big mistake here. Being in the water is no reason not to be a photosynthesist.
In fact, photosynthesis probably originated in the oceans. Even today, oceans
receive >70% of the sunlight and do about 30% of the photosynthesis. When you
eat beef, go ahead and pay homage to the gods of land photosynthesis for giving
us plants. But when you eat fish, thank the gods of ocean photosynthesis for
giving us cyanobacteria.

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.

Oh, it was a major step, for sure. That is why plants get their own kingdom.
But the step wasn't the origin of photosynthesis. Not by a billion years.
Plants arose because an amoebo-like heterotroph absorbed a cyanobacteria
which already had photosynthesis and developed a symbiotic relationship with
it.

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?

Start here and follow some links from the section on evolutionary origins.
http://en.wikipedia.org/wiki/Chloroplasts

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?

Short answer: Yes, it is totally impossible. It is just as impossible as that a
bunch of different cities would all independently choose 911 as their emergency
response phone number because that number happens to work well for that
purpose. There are plenty of other numbers that would work.

So the only possibilities that are reasonable are common descent, common design,
or rampant horizontal transfer. Parallel evolution makes sense in some
cases, but not this one. Just too many coincidences.

.

Relevant Pages

  • Re: Trees of Life
    ... It seems to me that the first forms of life, by definition, had to be ... The only way they could get energy was either by photosynthesis ... As far as I can see, chemosynthesis is the more likely of the two as most ... the Theory of Evolution generally assumes that life ...
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  • 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)
  • 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 ... the first life forms on land which developed into plants had ... from chemosynthesis to heterotrophy to photosynthesis which is even more ...
    (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)