Re: Experiment on Natural Selection

Sorry for the delay, I only just saw your reply.

"Zoe" <muze10@xxxxxxx> wrote in message
news:65fk93tv9ddjehg2h6ok00iu5ajefu4oab@xxxxxxxxxx
On Sun, 8 Jul 2007 23:07:29 -0400, "mel turner"
<mturner@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
[snip]

I agree. I want to know your position on the power of NS.

It's really pretty impressive. It might make sense to think of
evolution by natural selection as a vast excercise in "trial and
error" on the part of the evolving populations. Lots and lots of new
random variations [random with respect to selective values of the
traits and to evolutionary trends] is continually being generated by
mutations, etc., and are continually "tested" against the organism's
environment, and whatever happens to work especially well will
automatically tend to be kept whereas all those that don't work well
are automatically discarded.

until a series of "beneficial" mutations bring a trait to the point of
being advantageous,

Why assume that there is any such requirement for a series of
mutations before a trait begins to be advantageous? Perhaps instead
there'd always be incrementally increasing small advantages as each
related change is added to the mix.

It's true that it would be problematic if traits always needed a
series of independent changes before any benefit was possible, but
no one else assumes that it's the case.

what does natural selection do about such
intermediate changes? Does it also select "not-yet-advantageous"
changes?

No, and do we actually know of any real evolutionary changes that
required a preceding series of several changes each with no possible
benefit, perhaps including ones that would be harmful without the
whole package being present?

If any such examples do exist, we don't seem to know of them yet.

And I am referring to morphological changes that allow you to classify
a species as no longer belonging to its original genus.

Genera are pretty arbitrary words for groups of related species.
There is no set level of difference marking a "genus", it's very
subjective and arbitrary. One classifier's "genus" is another's
"subgenus" or a "section" within a genus. The nested series of
groups within groups within groups of related species are real,
the names and ranks assigned to them are artificial.

Organisms
that, say, can eat faster than others does not mean that they are a
new species; they are just a healthier, better functioning member of
the same species.

Or they can eat different kinds of foods unavailable to others. There
are neat bacterial examples, like the bacterial mutants that now can
eat man-made industrial nylon plastic waste.

Bacteria that resist antibiotics will always be
recognized and classified as bacteria, so they don't qualify as
evidence for macroevolution.

"Macroevolution" by definition is any evolution of new species and
groups of related species from common ancestral species. All the
bacteria have to do is to become new species of bacteria for it to be
"macroevolution".

Anyway, there are a great many recognized, named genera and families
and orders, etc. of bacteria, so much "macroevolution" would have
been required for them to arise from a common ancestor.

http://tolweb.org/Eubacteria/2
http://www.ucmp.berkeley.edu/bacteria/bacteria.html
http://www.ucmp.berkeley.edu/bacteria/bacteriasy.html

Until they evolve some morphological
changes that take them out of the recognizable category of bacteria,
then they have not yet given evidence for macroevolution.

That's not any definition of "macroevolution" as used by scientists.
It's their term, so they get to define it.

"Bacteria" are one of the three main groups of life.

http://tolweb.org/tree?group=Life_on_Earth&contgroup=

They are enormously diverse, morphologically but especially at
the molecular/physiological level. To say their radiation from a
common ancestor is not "macroevolution" is _worse_ than saying that
the evolution of all multicellular animals [humans, insects, worms,
jellyfish, sponges, etc.] from our last common ancestor wasn't
macroevolution because they're all "still animals".

Besides, the way groups are defined in modern classifications, nothing
can ever evolve so much that it no longer belongs to a group. Groups
are defined as the set consisting of a specified common ancestral
species and all of its descendants. It doesn't matter what the
descendants look like, by definition they will always belong to the
group.

[snip]
we are back in the early earth of the evolutionary worldview,
remember. There are no populations yet. Just your first common
ancestor.

If it's a "first true cell", let it and its progeny reproduce for a
few days and we can talk about a population of millions or billions
of cells. Any modern bacterium can do that. Then we'll see the
possibility of selection acting on all the genetically-determined
differences that will be arising among them.

so is it possible to use bacteria today in an experiment that will
follow them for millions of generations to see if natural selection of
"beneficial" mutations will begin to morph some of the bacteria into a
category that is no longer identified as bacteria?

Well modern bacteria are remarkably diverse, and much of that diversity
is morphological. It should easily be possible to select for great
morphological changes instead of just physiological and/or biochemical
changes. It's been done in the lab with a single-celled green alga
Chlorella. Exposing them to organisms that eat the normal single-celled
form caused them to evolve a new strain that existed as multicellular
clumps.

http://www.talkorigins.org/origins/postmonth/jul00.html

Changing from single-celled to multicellular is a pretty major
morphological change. One of the biggest. There have been only a very
few groups of life that have ever made that transition. [Animals,
fungi, green plants, red algae, brown algae all did it independently].

Chlorella isn't a bacterium, however, but it is a simple single-celled
microbe.

Natural selection only works at the population level. It doesn't apply
to any single cell or any single organism, whether bacterium or whale.

this I do not get. Mutations affect the individual first before it
can pass on its mutated gene to offspring.

Sure.

It is at this level, it
would seem, that natural selection would operate, retaining the
individuals that have the advantageous mutations until you have a new
population of duplicates of the first mutated individual.

But the selection itself arises from the _differences_ among
genetically different individuals within a population as they interact
with their environment. The advantageous, "better" traits are only
"better" in comparison to the less-advantageous "not-better" ones.
With just one organism we don't have any differences to compare.

It's simply not a race unless there are at least two runners
participating. "Selection" by definition involves "choosing" among
genetically different individuals in a population. We can't have that
with just a single individual or a single genotype.

So it would
be the individual that first evolves,

No, by the definition of "evolution". Single individuals indeed do
first get each new mutation, but it's not "evolution" until the
population as a whole changes over generations.

and its offspring population
would then supposedly become classifiably different from the original
population.

Are you speaking of strictly asexual organisms? If the organisms are
breeding with one another or otherwise somehow exchanging genes, it's
a matter of the new advantageous trait spreading throughout the
original population over a number of generations. In strictly asexual
organisms we'd be looking at the "population" of descendants of the
original mutants gradually outcompeting and replacing their relatives
that don't have the advantageous trait.

[snip]
I've reordered my thinking in that respect. We are now working with a
simple cell.

Okay, but if we later want to go back to abiogenesis, the basic idea
NS would also apply to any "population" of self-replicating pre-life
molecules.

how does natural selection work on a pre-life molecule to bring it
across the divide into life?

Much as it works with life as we know it:

If we have a pre-life "genetic" molecule or system of interacting
molecules that is capable of imperfect self-reproduction, then there
will be selection among the variant versions of the molecule that
arise. Any new variations that happen to reproduce themselves just a
little more efficiently, perhaps survive just a little longer so as
to have a few more offspring on the average, etc., will automatically
tend to become increasingly more common in the overall "population"
of reproducers. Similarly, all variations that don't help will
automatically tend to be lost. Many of the basic features of early
cells might well be things that first arose as changes that helped
pre-cell reproducers survive and reproduce.

[snip]
Perhaps we should be talking about the _last_ common ancestor of all
currently-existing life? We can say a whole lot more about it than
your ill-defined "first common ancestor".

first common ancestor is ill defined because I am waiting for you to
define it. It is really your common ancestor concept, you know, not
mine.

Okay, but there won't be much known about the transition from
pre-cells to the first cells. Or about pre-cells, for that matter.

what little do you know about the transition, please?

Not much at all. I do know that the evidence strongly indicates that
it must have happened well over 3 billion years ago, and I know that
only one line of cellular life that we know about survives, so that it
either happened only once, or all other independent lines simply
didn't survive to the present.

I also know that there are numerous scientists who have proposed
various ideas over the years about what early pre-cell self-reproducers
would be like and about how they may have first arisen and how they
would have functioned:

http://www.talkorigins.org/faqs/abioprob/
http://www.talkorigins.org/faqs/abioprob/abioprob.html
http://www.resa.net/nasa/origins_life.htm
http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0030396
http://www.geocities.com/CapeCanaveral/Lab/2948/orgel.html
http://www.talkorigins.org/origins/postmonth/jan02.html
http://www.talkorigins.org/origins/postmonth/apr98.html
http://www.infidels.org/library/modern/richard_carrier/addendaC.html

We clearly don't know too much about it, and we might never have a
very clear idea of exactly how it happened [or we might]. [This lack
of knowledge of course will never be evidence that natural abiogenesis
didn't happen.]

But this is digressing from issue at hand, which is evolution and
natural selection. Even if we all fully agreed that the first life
simply had to be supernaturally created by a deity or by the IDers
deity in disguise, it still will have evolved ever since, and natural
selection will have been a big part of the story.

cheers



.

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