On 07/09/12 01:33, pnyikos wrote:
> On Sep 6, 2:48 pm, Richard Norman <
r_s_nor...@comcast.net> wrote:
>> On Thu, 6 Sep 2012 11:28:34 -0700 (PDT), pnyikos
>>
>>
>>
>>
>>
>> <
nyik...@bellsouth.net> wrote:
>>> On Sep 6, 1:08 pm, Richard Norman <
r_s_nor...@comcast.net> wrote:
>>>> On Thu, 06 Sep 2012 08:22:20 -0700, John Harshman
>>
>>>> <
jharsh...@pacbell.net> wrote:
>>>>> On 9/6/12 7:26 AM, pnyikos wrote:
>>>>>> Originally I thought to use "milestones" instead of "benchmarks", but
>>>>>> that creates the impression that these benchmarks are about evenly
>>>>>> spaced, whereas I think the difficulties in getting between successive
>>>>>> benchmarks are very different quantitatively.
>>
>>>>>> In fact, the first thing I'd appreciate reader feedback on is this.
>>>>>> Try ordering the various moves from one benchmark to the next, in
>>>>>> order of difficulty.
>>
>>>>>> I'd like even creationists to play along here. Even if you don't
>>>>>> think evolution bridged the gap from one benchmark to the next, you
>>>>>> might at least have some idea as to which ones pose the biggest
>>>>>> obstacle to "abiogeneticists" and "evolutionists".
>>
>>>>>> Here are the main benchmarks:
>>
>>>>>> B0. Prebiotic soup, with amino acids, purines, pyrimidines, and
>>>>>> various other simple organic compounds that we know can be formed
>>>>>> spontaneously under early earth (before life) conditions, having
>>>>>> produced them in the lab and having found them in meteorites.
>>
>>>>>> B1. prokaryotes (bacteria, archae)
>>
>>>>>> B2. sexually reproducing eukaryotes
>>
>>>>>> B3: metazoans
>>
>>>>>> B4: lower chordates
>>
>>>>>> B5: primitive tetrapods
>>
>>>>>> B6: prosimians
>>
>>>>>> B7: *Homo sapiens*
>>
>>>>> As far as I can tell, you have picked 5 random points along a particular
>>>>> pathway from no life at all to one particular extant species. I see no
>>>>> reason to suppose that these points are special, even along that
>>>>> pathway, or that the particular pathway is in any way generalizable.
>>>>> What is served by such an exercise?
>>
>>>> To play the game as proposed, taking it seriously, I do think that
>>>> some form of B0, B1, B2, and a modified B3 (the origin of complex
>>>> multicellular organisms) are indeed major stages. Given that pretty
>>>> much all of evolution as ordinarily studied relates to plants and
>>>> animals, that most living things are really prokaryotes is important
>>>> biology but not what interests most of us.
>>
>>>> I would separate the origin of eukaryotes from the origin of true
>>>> sexual reproduction (meiosis + fertilization/syngamy) as separate
>>>> steps.
>>
>>> That's another good benchmark. Let's put it in:
>>
>>> B1.5 the first eukaryotes
>>
>>> I think the move from B1.5 to B2 was much more difficult than the move
>> >from B1 to B1.5. How about you?
>>
>>>> Once you have multicellularity, it seems the rest is pretty
>>>> easy to explain and even multicellularity doesn't seem to be that much
>>>> of a problem.
>>
>>> Did you read what I wrote about Stage 3 in my second post? Metazoans
>>> have far more going for them than mere multicellularity.
>>
>>>> The first step in particular encompasses all of what we
>>>> call abiogenesis and seems like an enormous leap compared with all the
>>>> rest.
>>
>>> I fully agree. See my reply to Harshman a few minutes ago for more
>>> details.
>>
>> The real issue is as John pointed out: what is the purpose of this
>> analysis?
>>
>> You can point to any number of "stages" in the development of life.
>> There is really nothing to be gained by searching for qualitative
>> features measuring the "difficulty" of any step.
>
> Richard, talk.origins is not a scientific research forum; we are here
> to talk about evolution in various ways, and I thought this would be a
> nice little intellectual excercise.
>
> That said, I do have an application in mind, but I'd rather hold off
> talking about it because that would distract others from the main
> theme of this thread.
>
>> It is obvious that
>> at every branching point in evolution there is some "change", some
>> "development" -- this branch has such and such whereas that branch
>> lacks it or has some other. Follow the branching tree and you get a
>> series of "benchmarks".
>
> Sure, but the Stages 1 through 7 are levels that some branches may
> attain, and others not. The number of branches that have gotten from
> one stage to the next is surprisingly small.
>
> In fact, I can't think of a single example of a set of four organisms
> at one stage giving rise to an organism at the next stage unless two
> or more of them are in a direct line of descent from each other.
That's because each of your stages is a clade. Of course it will have
been reached only once. It's one thing when you do that up to metazoans,
but why is "primitive chordates" a benchmark ? It's important to us
because we're chordates, and the chordate body plan does seem more
suited to large organisms, i.e. large brains, i.e. intelligence, but if
you went back to the Precambrian and looked at the first chordates among
the trilobites I'm not sure you'd go "Aha ! A benchmark has been reached
! Surely the descendants of these creatures (and only of these
creatures) will be the only ones to develop the large brains
intelligence requires". And in fact they aren't, if you consider the
octopus an example of intelligence (and even if you don't think much of
the octopus' intelligence, they clearly have as much potential for
intelligence as chordates do, from a Precambrian perspective).
Same thing with "primitive tetrapods". If your benchmark was "complex
land life" you'd see it be reached quite a few times. Even "chordates
moving onto land" has happened more than once (though to be fair nothing
holds a candle to tetrapods in that respect).
And I completely fail to see the significance of the "prosimian"
benchmark, as opposed to any other clade that's between tetrapods and
Homo sapiens.
The question really is what those are benchmarks *to*. If I were setting
benchmarks for life on Earth in general, some thing I'd include would be
: oxygen metabolism, hard shells, land plants, land animals, vascular
plants, wood, presociality, eusociality, pack/tribal structures, flight,
flowers, C4 photosynthesis, Nitrogenase, neocortical-like structures,
domestication, thermoregulation...
>
>
>> There is no measure for how "difficult" any step might be.
>
> As I told John, my purposes on this thread are more qualitative than
> quantitative. The main emhasis is just on comparing pairs of
> successive benchmarks, and saying which "move" is the easier.
>
> And you came through very nicely in your first post.
>
>> There is
>> only a measure of how much we know or understand about the processes
>> and stages and mechanisms that lead to each stop.
>
> How would you measure (in the sense of "quantify") your knowledge or
> understanding? It seems far harder than quantifying the difficulty of
> getting from one step to the next.
>
> I'm here to gather infomation about the processes; it is only in that
> way that we can be confident about the comparisons we make about the
> difficulty.
>
>
>> It is clear that
>> the earliest steps are little understood where the more recent steps
>> are well documented.
>
> We do know something about getting from prokaryotes (B1) to the most
> primitive eukaryotes (B1.5).
>
> In the textbook _Biology_, Eighth Edition, by Campbell
et.al., there
> is a section, "The Evolution of Mitosis" on page 237. It shows a
> hypothetical pathway from the way bacteria reproduce to the mitosis
> that occurs in most eukaryotes, including Plantae and Animalia.
>
> There are two intermediate stages, representied by dinoflagellates,
> then diatoms and yeasts. In the latter stage, the nuclear membrane
> remains intact and the microtubules stay within the nucleus,
> separating the chromosomes as in plant and animal cells, whereas the
> microtubules in dinoflagellates anchor the nucleus to the cell wall
> the way proteins are believed to anchor the daughter chromosomes to
> the cell wall before fission is complete. In the mitosis you generally
> see in textbooks, the nuclear envelope breaks down during mitosis.
>
> One thing missing from this hypothesis is how the single chromosome of
> bacteria might have become replaced by paired chromosomes. Might a
> mechanism like polyploidy be involved?
>
> Peter Nyikos
> Professor, Dept. of Mathematics -- standard disclaimer--
> University of South Carolina
>
http://www.math.sc.edu/~nyikos/
> nyikos @
math.sc.edu
>