Re: What did the first single-celled organisms eat?


"r norman" <r_s_norman@xxxxxxxxxxxx> wrote in message news:pkl843lg8i5sp82ugmvdnlmnkqbk0fbuhm@xxxxxxxxxx
On Fri, 11 May 2007 14:41:21 +1000, j.wilkins1@xxxxxxxxx (John
Wilkins) wrote:

Perplexed in Peoria <jimmenegay@xxxxxxxxxxxxx> wrote:

"John Wilkins" <j.wilkins1@xxxxxxxxx> wrote...
Perplexed in Peoria <jimmenegay@xxxxxxxxxxxxx> wrote:

"John Wilkins" <john@xxxxxxxxxxxxx> wrote...
John Harshman wrote:
snex wrote:

On May 9, 12:25 pm, Terry <Kilow...@xxxxxxxxxxx> wrote:

What did the first single-celled organisms eat?

each other.

They lost money on every deal, but they made it up in volume?

No, seriously, they had to have some source of energy and carbon.
There are many possibilities, some of which are still working
today. There are many inorganic processes that make high-energy
molecules, some of whose energy can be extracted. Currently living
bacteria make use of all of them. Look up, for example,
"chemautotroph".

Original organisms probably evolved as a community that was overall
autotrophic. It is speculated (for we cannot know for sure) that
they worked off volcanic flows containing H2S, but I am betting that
they would happily reuse each other's high entropy molecules as well
if they could.

I didn't notice it the first time, but I think you meant that they would
reuse high *energy* molecules. Or else *low* entropy molecules.
Unless you really did mean 'high entropy', in which case this whole
subthread is based on my misreading.

And I am betting that they would if they could, but they couldn't.

Why?

Well, using foreign molecules for energy doesn't make sense to me for the
early days because my biochemical intuition says that getting useful
energy by fermentation takes some pretty sophisticated enzyme-like
machinery. Doing that came later.

I do not see why it has to be fermentation. If you have a lysed membrane
then whatever are the contents of that vesicle will be biologically
valuable, whether sugars or whatever. Since we are postulating
relatively primitive systems, it's likely that the intake of food
particles will be by vesicles forming on the membrane that transport
material internally, so they will almost certainly - some of them -
subsist on processed polymers from other organisms.

I'm going to combine my replies to Wilkins and r_norman into this one
response. I hope this is agreeable.

We (John and I anyways) seem to be in agreement that we are not going
to be discussing extraction of energy by fermentation. And discussion
of some kind of heterotrophic assimilation of 'building blocks' mostly
takes place following my next paragraph. But I want to respond now
to your suggestion that food *particles* were ingested by some kind of
vesicle. That kind of phagocytosis or pinocytosis almost certainly
came much later in evolution - long after the first true cellular organisms.
What I think we should be talking about here is much lower level - the
passage of individual molecules into membranes or through membranes.
Recall that you need this movement of individual molecules through
membranes even if you have pinocytosis of vesicles, since the interior
of the vesicle is still biochemically *outside* the cytoplasm.

That leaves somehow absorbing whole molecules to become self-biomass.
Sure, that saves some kind of metabolic effort if the molecule you absorb
is something you would have needed to make anyways. But consider that
absorbing it is probably a mistake if it is not one of the molecules
normally made by your biochemistry. It may gum up your operations. So,
it is only safe and advantageous to absorb the molecule if it came from an
unfortunate member of your own 'species'. But if you think about it, that
defeats the whole reason why you postulated that they all evolved as a
community. And developing the machinery for discriminating useful foreign
molecules from the unuseful ones is also something that my intuition tells
me must have come much later. Simple inorganic foodstuffs are much easier
to 'recognize' and use in the right way.

Maybe. Organic material will denature into oligomers that are
functionally indistinguishable from abiotic organic molecules that are
of high energy or substrate-material value.

Sure they will. But I am also denying that there are any abiotic organic
molecules of high energy or substrate-material value. So your claim that the
stuff that escapes from dead organisms is functionally indistinguishable
from stuff that I claim doesn't exist doesn't really affect me. We are in
agreement that organisms will treat the two kinds of things the same. I
say that organisms will simply ignore such stuff.

Suppose there are protobionts that routinely die in the environment, and
thus release their material, or are even predated by some simple system
that can lyse lipid membranes. The entropy of those molecules released
will be valuable to some systems, and selection will rapidly drive them
to become eficcient at it. No matter how far back you go, there has to
be an ecological web.

No there doesn't! Not one with multiple species. Why do you suggest
there must be one?

I assume that you meant to write something like "the negentropy of those
molecules would be valuable". But valuable how? Something is valuable
only if you know how to use it - if you have the auxiliary machinery
necessary to make use of it. Value depends on context. A Pentium chip
is quite valuable, pound for pound, but if you give one to a man on a
desert island he probably wouldn't think you had given him anything
very valuable. Value also depends on purity. If you contract to sell
a hundred Pentium chips to a computer manufacturer, and then ship him
a large box filled with tens of thousands of chips that had failed the
testing process mixed together with a hundred that had passed - well, I
think that your customer would consider the value of the good chips to have
been pretty seriously damaged by your co-shipment of all those bad chips.
Sure, he can restore the value by testing and culling, but that takes
work and complicated testing machinery.

What an abiogenesis scenario needs is to to cut back as far as possible on the
number of different kinds of machinery needed. I claim that the hypothesis
of heterotrophy (whether you are eating organics produced abiotically or
by other organisms) INCREASES the number of different kinds of machines
you need. Early organisms were simple. They didn't have complicated testing
machinery to separate the wheat from the chaff. They didn't need them. They
took in simple inorganics that didn't need to be tested, and they used a
small number of reactions to turn those organics into simple wheat with just
a little chaff as a byproduct. Selection in those early days was oriented
toward coming up with machines that produced more wheat and less chaff; not
with coming up with machines to separate abiotic wheat from chaff. And then
only when organisms became very good at producing pure wheat did it become
advantageous for other organisms to become good at stealing the wheat. Because
if wheat is mixed with a large enough proportion of chaff, it has no value at
all.

Also, I'm assuming that almost all early biomolecules were lipids, and it
is not easy energetically to pull a lipid molecule out of one membrane
(even a 'dead' one) and insert it into your own membrane. And fusing your
membrane with that of another organism runs into the same issue of "same
species, safe but ecologically pointless; different species, unsafe".

I don't see why almost all molecules that are ingested have to be lipids

Under my assumptions, there was no point in ingesting anything else. Early
organisms, I claim, consisted of nothing else.

(although I can see how free-floating lipids in a medium might be
valuable to the formation of the predator's membranes).

I am claiming that membranes, in the first organisms, were not just a
skin for separating the good stuff inside from the outside world. I am
claiming that they WERE the good stuff, and that there was nothing of any
interest inside (if there even was an inside). And I suppose that I am
also claiming that there were too few free-floating lipid molecules in the
medium to make much of a difference. They just aren't soluble enough in the
medium to accumulate in any quantity. So, I am postulating an ecosystem
in which dead organisms did not get recycled, except perhaps through a
purely geological kind of carbon cycle.

And now for my responses to r_norman.

The earliest true biological organism must have been a very
sophisticated device filled with complex (but not irreducibly so)
machinery. To meet the definition, it must have had a molecular
biology that used genetic information both to construct and to
duplicate itself. There must have been an enormous amount of prior
"evolution" of this machinery in protocells.

I'm glad you put "evolution" in scare-quotes. Because I think that
equivocation regarding that word is at the heart of much of the
confusion over abiogenesis. Oh, there are some other sources of
confusion - most notably various kinds of sorites. So I am happy
we have John here with us. Equivocation and misuse of sorites are
definitely within the province of philosophy. Why, one might even
say that they are a specialty of philosophers. ;-)

The key question, of course, is just what kind of 'evolution' it
was that you say took place 'prior'.

Was it evolution under natural selection? If so, then I, at least,
would prefer that you changed your implicit definition of a
'true biological organism' to include those things - whatever they
were - that had been evolving 'prior'.

If not, then we have a problem. Because you are saying that this
"evolution" led to a very sophistocated device filled with complex
machinery. We all three know that evolution under natural selection
can lead to exactly this result. As far as I know, no other kind
of 'evolution' can produce this kind of result. And since we don't
actually know anything about how it happened - since we are just guessing -
I don't see any reason to guess that some unknown evolutionary process
was involved. Producing complex machinery is something that evolution
under natural selection does. No other known kind of evolution does it.
So you are engaging in a kind of subconscious equivocation when you
even introduce the word 'evolution' to describe some unknown process.

My own inclination (shared with Tim Tyler over at sbe, by the way, though
we reach different conclusions) is to try to come up with the simplest
possible machinery which can grow and reproduce and evolve under natural
selection. If we can come up with something simple enough, then maybe
we don't need some mysterious evolutionary process to produce it the
first time. Maybe it will be simple enough that it could have resulted
from 'chance'.

At the same time, the
earliest true biological organism must have had a biochemical
metabolism, both catabolic to use chemicals as a source of energy and
anabolic to use chemicals as substrates for building its own
structure.

A quibble. I would say that the word 'catabolic' should only be used
if it is *organic* molecules that are being broken down to be used as
a source of energy. I don't think that simple autotrophs really have
a catabolic section to their metabolism. And what they do have is
oriented toward recycling of carbon skeletons (of amino acids, say)
rather than toward energy production. At least prior to the origin of
energy storage compounds like starches.

Again there must have been an enormous amount of prior
"evolution" of this machinery.

If it was not evolution under natural selection, one wonders why you
think that this kind of evolution would lead to 'machinery'. And if
it was evolution under NS, then one wonders why we are not instead talking
about whatever 'organisms' it was that were being selected, instead of
talking about this horribly complex monstrosity that you are talking
about.

And the earliest true biological
organisms must also have had cell biological functions of transport
and responsiveness to the environment, also required a lot of prior
"evolution".

Why 'responsiveness to the environment'? Just what definition of
'true biological organism' are you using, anyways?

So the earliest true organism "ate" whatever those
protocells ate including the protocells themselves using the existing
machinery. At some point in the process, it was obviously necessary
to ensure that autotrophic protocells maintained themselves in the
environment in sufficient quantity to drive the entire system,

Er.... And what drove the entire system before that point? Before
autotrophic protocells became necessary in quantity.

quickly
becoming incorporated into the early true cells themselves. The only
question is whether that piece was necessarily part of the very first
true cell if there were enough protocellular autotrophs already
available.

Ah! So you are claiming that autotrophic 'true cells' originated by
a kind of symbiogenesis between heterotrophic true or proto- cells and
autotrophic protocells. Well, I suppose that could happen. But I
am curious as to why you are so incurious as to the origin of those
autotrophic protocells. Because those little babies strike me as the
key players in the whole needlessly complicated story. It is almost
obvious to me that they came first and the heterotrophs came later.
And that heterotrophy arose without the need for any kind of symbiotic
union by simple evolution of a pure autotroph into an autotroph with
a lot of salvage pathways, and then into a facultative heterotroph, and
then finally into a full heterotroph.

The details are rather less important. Whether fermentation as we now
know it or some other biochemical process was the major energy
providing pathway is irrelevant; the protocell chemistry developed
some pathway that was effective. Glycolysis seems very likely since
it is so widespread in modern forms and anaerobic metabolism seems
necessary since free oxygen was lacking. However the early protocell
metabolism must have been capable of dealing with a wide variety of
chemicals both as energy sources and for synthesis, perhaps through
the expediency of developing tools to reduce just about any complex
molecule to a relatively small set of simple organic building blocks.

Again, I think you are approaching the problem wrong. You are making
the earliest proto-organisms as complicated as you can - presumably
to increase their fitness. I would prefer to make them as simple
as I can (even if that means restricting them to uncommon and particularly
beneficent environments) just to have a better chance that they could
originate.

The title of this thread is "What did the first single-celled organisms
eat?" You seem intent on transforming the question (which clearly is
predicated on an apparent paradox) into a different question about what
some highly evolved LAST universal ancestor ate. The OP, it seems to me,
was clearly asking about what the FIRST universal ancestor ate.

The membrane transport problem also necessarily had to have been
already solved by the protocells so that the earliest cells already
had the ability to incorporate molecules that were not lipid soluble.

Ah! You say that it was a 'problem' and that it was 'solved'. Those are
sure signs to me that you are thinking in terms of natural selection as
the mechanism for protocell evolution. Unless I am missing something here.

In other words, the problem is pushed back one step. The earliest
organisms used existing machinery to solve their problems of living.
The problem is how the separate pieces of machinery developed;
pieces of metabolism in this entity, pieces of membrane function in
that one, genetic mechanisms in a third, all capable of merging and
separating and thus sharing the accumulating techniques of how to
manage it all. Since energy drives the whole process, autotrophy in
the sense of taking some "inorganic" form of energy to build organic
chemistry must have been present from the outset.

Ok. But why do you hypothesize that the different kinds of machinery
evolved in different entities? Why postulate symbiogenesis? Why
not, as I suggested above, autotrophy to facultative heterotrophy to
heterotrophy all in one single lineage? If symbiogenesis, are you
assuming that only one of the proto-cells had ribosomes and the genetic
code? If so, are you suggesting that the heterotrophic partner had it
and the autotroph did not? If so, what, exactly, was the autotroph
contributing to the eventual partnership if she did not contribute any
genes?

.

Relevant Pages

  • Re: What did the first single-celled organisms eat?
    ... high-energy molecules, some of whose energy can be extracted. ... Original organisms probably evolved as a community that was ... passage of individual molecules into membranes or through membranes. ... machinery for discriminating useful foreign molecules from the ...
    (talk.origins)
  • Re: What did the first single-celled organisms eat?
    ... No, seriously, they had to have some source of energy and carbon. ... molecules, some of whose energy can be extracted. ... Original organisms probably evolved as a community that was overall ... If you have a lysed membrane ...
    (talk.origins)
  • Re: What did the first single-celled organisms eat?
    ... entropy molecules as well if they could. ... machinery for discriminating useful foreign molecules from the ... We are in agreement that organisms will treat ... autotrophs which are 'social' in some sense. ...
    (talk.origins)
  • Re: Lets be more exact.
    ... does the energy come from. ... > Why would an RNA replicator or any replicator need protein? ... molecules that "need" it by the self-organizing properties of membranes ... situation as with reproducing organisms. ...
    (sci.bio.evolution)
  • >>>> DISTINGUISH BETWEEN <<<<
    ... Distinguish Between Living And Nonliving Organisms ... Distinguish Between Effective And Efficient Communication ... Distinguish Between Organic And Inorganic Compounds ... Chemical Tests To Distinguish Between Molecules ...
    (de.rec.film.misc)