Re: Experiment on Natural Selection

In message <os2393tovqp70hqe8f6um0rj6ul0414f8k@xxxxxxx>, Zoe <muze10@xxxxxxx> writes
On Sun, 8 Jul 2007 09:55:06 +0100, Ernest Major
<{$to$}@meden.demon.co.uk> wrote:

In message <lqb093tjggblbobl60f8ilk9tmot7vh737@xxxxxxx>, Zoe
<muze10@xxxxxxx> writes
You're welcome(ish) to talk about origins, but when by origins you mean
abiogenesis, it's misleading to write about testing the methodology (I
think you mean mechanism) of evolution.

I am talking about the origins of the first new species of cell that
supposedly evolved from the old and first cell-type organism. Is that
better?

Elsewhere - I've lost it in the thread - you claim that you're talking
about the time before there were populations. So I'd better make the
following clear ...

It may or may not be meaningful to speak of the first organism as a
single individual - the line between life and non-life may be fuzzy. But
assume for the sake of argument there was an identifiable (by an
omniscient contemporary observer) first organism. This may accumulate
mutations as it lives - DNA repair is likely to relatively inefficient
at this stage - but these mutations are unlikely to transform it into a
new species.

how much apparatus are you prepared to give to this imagined first
common ancestor, please? Does it have at least an immune system to
protect it from its hostile environment?

I don't understand why these questions appear; they seem non-sequiturial.

However, the answer may depend on what you call an immune system. However by the common understanding of the term an immune system primarily defends the organism against parasites. If you use this relatively broad conception of an immune system then perhaps bacterial restriction enzymes (which digest foreign DNA/RNA) qualify. At this remove, it's hard to identify the properties of the earliest organisms, but my guess would be that they didn't have an immune system.

However this first individual doesn't remain a single individual. It
reproduces, and its daughters reproduce, and so on, and a population
forms and grows (at first exponentially), and individuals drift away to
other places and form other populations, and in a geologically short
time there are billions of near copies of that first individual.

(Evolution requires life as a precursor; natural selection requires that
there be at least two living organisms.)

okay.

Now, back to the original question. It appears that your not so much
asking about natural selection, but about the efficacy of natural
selection in achieving speciation. It happens to be the case that many
different processes can be involved in speciation; at one extreme
natural selection is involved, at the other extreme natural selection
is, if you draw the box in the right place, the only process involved.

For the example of the first extreme, consider allopolyploidy by the
union of unreduced gametes. Organisms normally produce gametes (eggs and
sperm) with half the number of chromosomes of the parent, which, when
they unite, regain the parental number of chromosomes. In some
organisms, e.g. plants, the process of the formation of gametes is
erratic, and there is an appreciable rate of production of gametes with
twice, or even four times, the normal number. An unreduced gamete from a
plant of one species can fertilise an unreduced gamete of another
species. This produces an allopolyploid offspring, which contains
complete sets of chromosomes from both parents. If it is viable, and
self-fertile, it is a member of a third species. (This particular
example doesn't apply to your question, as you're talking about the time
before sexual reproduction and even before there were two species.)

true, so strike that example and moving on...

It's important that you understand that natural selection is not the only process involved in speciation, and the degree to which it is involved varies between instances.

For an example of the second extreme, consider a population the
morphology of whose members clusters about a mean morphology. Now
imagine that the environment changes so that the mean morphology is no
longer favoured, but that two or more atypical morphologies are
favoured. After time we know have a metapopulation whose members are
clustered about several different morphologies.

do you have examples of this in the current world that can be
extrapolated back to the early earth scenario?

Your qualification to the request for examples doesn't seem to make sense. Do you have any reason to doubt that the process was possible in the early earth situation?

Now to answer your question. Speciation occurs in the modern world -
we've seen it happen perhaps 100 times - and a variety of processes are
involved.

would you be less vague, please? What exactly occurs in the
speciation you are referring to? Do you mean adaptive changes where
the species retains its morphology but copes with its environment more
successfully? Or do you mean morphological changes that distinguish
one part of a population from another part of the same population?

Both and neither. Speciation is the replacement of one species by two. Either or both of adaptive morphological and non-morphological change may be present, but neither is essential.

Why couldn't those processes (or rather the subset of them
that were operating at the time) have resulted in speciation in the
ur-population.

pardon my ignorance, but what does "ur" stand for? I imagine you are
referring to the new population, but not sure what "ur" specifically
refers to.

ur is a prefix which denotes the first or original; for example in creationist belief Adam was the ur-human.

The ur-population would have spread into different
environments, in these different environments the descendant populations
would have accumulated, by drift and selection, different genetic
changes. When sufficient genetic changes have accumulated you have new
species.

please for examples from today's populations that can be reasonably
extrapolated back to an unknown time?


Your qualification to the request for examples doesn't seem to make sense. Do you have any reason to doubt that the process was possible in the early earth situation?
--
alias Ernest Major

.

Relevant Pages

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