Re: [asa] Advice for conversing with YECs (Cheek turning)

> OK, I had this book on my shelf, next in line to read. I just picked it up
> and read it. Well written chapter. However, if Figure 1 was an accurate
> description of the total story, it would show all the extinct phyla. I find
> two different numbers, anywhere from 40 to 70 total phyla appeared in a
> rapid period of time, and then many of them died out...down to our present
> 25 or so, with none of them new. In other words, no new phyla have evolved
> since about this time.

The estimate of 70 phyla, most then going extinct, is rather high. A
little over 30 living animal phyla are known, though some of them are
tiny obscure worms with no fossil record.
Several of the bizzare Cambrian things are being fit into phyla with
better data from additional specimens or studies. There are also a
handful of phyla with good evidence for Precambrian origins from the
fossil record (although the average molecular clock has no statistical
validity, there are some calculations of this sort that also support
earlier origins to most phyla), so the fact that no new ones clearly
originate later does not mean that all originate out of nowhere in the
early Cambrian.

There are several factors that make the early appearance of higher
taxa such as phyla expected, some of which are evolutionary.
Non-evolutionary aspects include the fact that, as phyla are more
inclusive, they will on average appear earlier than less inclusive
groups and that it may be possible to identify a given fossil to a
higher but not to a lower category. Also, differences in environment
may affect fossilization patterns-the Cambrian is different from both
the Precambrian and postcambrian in predominant patterns of
preservation. The first appearances of phyla in the fossil record
closely track times of good preservation of soft parts. Evolutionary
aspects include cladistic classification, which does not want to have
one group arising from within a group of equal rank. For example,
acanthocephalans and pentastomids are highly specialized parasitic
worms. Current data (mostly DNA) indicate that they derive from
rotifers and crustaceans, repectively. Therefore, cladistic
classification demotes them to a class or subclass. Another aspect is
that, in trying to create broad taxonomic categories, the features
that delimit different groups most consistently would, under an
evolutionary scenario, be expected to be the features that evolved the
earliest. Older classifications tended to put barnacles and
brachiopods with the mollusks because they all have calcareous shells.
 However, more recent studies suggest that the jointed legs of
barnacles (at least as larvae and non-parasitic adults) is a more
fundamental character uniting them with arthropods, and in turn the
molting of an outer cuticle is a feature going back to the common
ancestor of several phyla including arthropods but not mollusks or
brachiopods. Likewise, the lophophore of brachiopods is a key
feature, associating them with phoronids, and the brachiopod shell
differes in several ways form bivalves. Yet another is that there's
limited evolutionary room for major innovation, whether in animal
morphology, or environmental niche. Another is that increasing
specialization and stability can be favored-it's generally better to
keep basic existing features that work while modifying the details,
rather than trying to invent something totally new.

Many more factors are at play, too.

> Molecular evolution too, David? There are five different types of molecular
> convergence. There are hundreds of examples in the literature now. They are
> not expected, and not consistent with the neoDarwinian model. The most
> remarkable is systemic convergence, the independent emergence of entire
> biochemical systems, and there are numerous examples of this.

Yes, molecular convergence is expected. I don't know exactly what
your categories of molecular convergence are, but it is expected
evolutionarily. Similar environmental pressures can be met with
similar solutions, such as stronger oxygen binding in hemoglobin forms
used by organisms in lower oxygen settings. DNA has only four bases
to choose from and proteins have a little over twenty amion acids to
choose from, so short identical sequences are quite likely to turn up
randomly. Starting from the same origin, two organisms will have
certain similarities and will likely arrive at similar points
independently on some counts, such as the use of related proteins in
the eyeballs of vertebrates and cephalopods. They're useful enzymes
that happen to be optically nice and have independently been used as a
lens filler in the two groups. Oysters and scallops indpendently
evolve from shell proteins producing mother of pearl to ones producing
foliated calcite in the inner layer-close parallelism from the same
starting point and similar environmental pressures.

> Truly, even with God being directly involved, this confuses me. It certainly
> doesn't look Darwinian, but why would God do it this way, and not more like
> the Darwinian model? I don't have the answer for that. I just don't think
> that neoDarwinian evolutionary concepts explain this very well at all.

I don't see just what the problem is for evolution. If you specify
exactly what the feature is and why it seems problematic for
evolutionary explanations, I might follow your arguments better.

For example, I don't see what the point is of listing examples of
convergence. I know lots of them but don't know of any particular
problems for evolution among them.

-- 
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"
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