Bruce Toback writes:

> Denys writes:
>
>  >Besides here in Houston, we consume spiders (also known as crawdads or
>  >mudbugs, but an arachnoid by any other name, like crabs and lobsters.)
>
>  Wirt is no doubt composing a much more detailed reply, but meanwhile,
>  lobsters and true crabs aren't arachnoids. Horseshoe and king crabs are
>  cousins to spiders, but crustaceans such as lobsters and crayfish are not.
>
>  I look forward to Wirt's exposition of the precise evolutionary
>  relationship among the three groups :-).

I really doubt that anyone is TRULY looking forward to this, but I'll answer
Bruce's comment anyway. To begin with, arachNOIDs are not living organisms.
They are human-engineered, giant, eight-legged metallic Japanese
transformer-like creatures that live in the glens just outside Osaka and
ravage the cities and the citizenry of Japan at night.

ArachNIDs, on the other hand, are spiders, mites, scorpions and solpugids
(sun spiders) --  but crawdads nor crabs are not, exactly as Bruce states.
Arachnida is the scientific name of the Class name given to these animals.
Arthropoda (jointed-leg animals) is the name of their Phylum, a more
inclusive set of animals yet again (which does include crawdads, lobsters,
insects, and horseshoe crabs, among others).

We are now virtually 100% convinced that life arose on this planet just once
(or if it didn't, whatever other forms that may have temporarily existed
early on were outcompeted by the form that we find present here now). We've
come to this conclusion because all of the code, for every living species, is
essentially identical and can be arranged in a nearly perfect hierarchy.

The mechanism that has allowed such a great diversity of speciation and
diversification is nothing more complicated than the invention of
object-oriented, hierarchical code reuse. To quote the great biologist, Art
Bahrs, the architecture of life is much like:

     "32 bit extensions and a graphical shell [on top of] a 16 bit patch to
an
      8 bit operating system originally coded for a 4 bit microprocessor,
      written by a 2 bit company, that can't stand 1 bit of competition."

Every cell in your body contains all of the information to build another you
(with a few minor exceptions, of course. Red blood cells, for example, are so
sacrificial that they lose their nuclei, where the DNA of inheritance
resides, soon after maturity). Nonetheless, every piece of dandruff you
slough contains all of the code that defines not only you, but also your
essential mammalian nature, that was built on a reptilian platform,
originally coded for a far simpler chordate (an animal with a spinal chord),
built out of a differentiated colony of originally free-living nucleated
cells -- that could never stand one bit of competition, at any prior stage of
complexity.

The oldest code in your tissues is now estimated to be at least 3.5 billion
years old and is associated with your cells being simply a eucaryote (a fully
nucleated, extremely complex cellular structure). And nature, just like Bill
Gates, makes do with what he has available to him at the time. Genes come in
families -- and occasionally superfamilies. One of these superfamilies is the
opsin family. These genes encode the proteins that are the bleachable
pigments that allow you (and every other animal) its vision. However, the
invention of the intitial opsin gene is now believed to be about a billion
years old, a quarter-billion years before multicellularity itself (the
Metazoa/Metaphyta/Fungi) was invented and half a billion years before the
first primitive, image-forming eye was evolved.

This code re-use hierarchy is noted in the most basic Linnean classification
scheme (which Linneaus only guessed at -- but which we can now verify with
near certainty). Linneaus' basic hierarchy is (using, for example, HP's
former spider-of-the-month):

     Kingdom (Animalia)
         Phylum (Arthropoda)
            Class (Arachnida)
               Order (Araneae)
                  Family (Araneidae = Argiopidae)
                     Genus (Argiope)
                        Species (aurantia?)

This path makes the process seem unusually short and direct -- but there are
2 million to 100 million species of animals currently present on the planet
(most estimates range in the 8-20 million numbers, but we really have no
idea. We're racing to at least catalog most species before we finish paving
over the planet). All of these animals are in the same Kingdom. And there are
five Kingdoms that are generally recognized (Animalia, Plantae, Fungi,
Monera, and Protista).

There is an extraordinary resource available on the web that directly
demonstrates this process of hierarchical code re-use. Its URL is:

     http://www3.ncbi.nlm.nih.gov/htbin-post/Taxonomy/wgetorg?id=2759

The human genome is not the only genome that is being sequenced. For every
species shown in the National Institute of Health's taxonomic hierarchy
above, at least some fraction of the species' genome exists and can be read
out. What you're looking at is a database, organized by commonality of
descent -- but one where all of the code is similar and branches from one
common point of origination.

You may find that may have some trouble navigating the hierarchy simply
because Linneaus' hierarchy is broken into a great many more divisions than
I've shown above. But don't be discouraged. Most biologists couldn't navigate
it with ease either (in part because people keep changing the names). The
pointer above begins at the point of commonality of code that is the
Eukaryotes (the fully nucleated cells that are characteristic of plants,
animals and fungus). The earth was only ca. 1.5 billion years old at the time
of the formation of this cell type.

To get to HP's spider (or as close as we can for the species represented),
find the Fungi/Metazoa group and click on it. At this level of code
commonality, we, as a species, are indistinguishable from mushrooms. On the
following screen, click on Bilateria (a subdivision of Metazoa, which is all
of the bilaterally symmetric animals that you can see with your naked eye --
and a lot that you can't). At this level, we're indistinguishable from Denys'
crawdads.

On the next screen, click on Arthropoda (the jointed legged animals). This is
the point where we, as chordates, diverge from the crawdads (about 500-530
million years ago). On the next screen, click on Araneae, the order of true
spiders -- and we're basically home: if HP's spider were listed. The end
point is a binomial name for a species (e.g., Homo sapiens, Rattus rattus, or
Argiope aurantia).

To get to Denys' crawdads, back up to the Arthropoda and click on the
Eucarida, of which the Decapoda (ten-legged animals) are a subdivision. It's
important to note, however, that this NIH hierarchy is a little misleading.
Of all of the animals large enough to be seen, 97% of the 10 million species
are in the Phylum Arthropoda. Only a very small portion of all of these
animals are listed here.

Wirt Atmar

(If anyone finds any of this upsetting or significantly off-topic, I have set
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