Wednesday, May 21, 2008

Homology: The Problem

See this four minute video on "Darwinism's Homology Problem."

5 comments:

John Stockwell said...

...no mention of hox genes there, either.
Nothing in that film is accurate, either.
FYI body segmentation is controlled
by the repetition of hox genes in all
species, and clocks that turn them
on, off.

You really should take a little break
and read Sean B. Carroll's books.
They are a good read.

Sarah Scott said...
This comment has been removed by the author.
Sarah Scott said...

Stockwell,

[Corrected version]

The presence of hox genes does not prove evolution or disprove design. All that is suggested by such a discovery is that there is something in the DNA of kingdom anamalia that tells the embryo what to form. How does this sophisticated information coding lend support to the theory that a whale's flipper became a terrestrial foot? It does not. Rather, it suggests something of a much grander scale.

Consider the Cambrian explosion. In the fossil record, we *all of a sudden* have most animal forms which date to about the same time, whereas there is little evidence of them prior to that time. If hox genes theoretically lend support to the existence of gradual, large-scale (macro) evolution, wouldn't these little information centers need massive amounts of time thousands of generations to actually transform a flipper into a foot or a hand into a wing? In fact, why do we find supposed descendents of the whale at the same geological level as the whale? Why is the descendent of the horse (eohippus...eerily like the modern African hyrax) ABOVE the modern horse when the older structures are supposed to be below? It seems as though the geological record does not leave adequate time for hox genes to play the role many wishfully assume.

This does not even go into the difficulties belonging to the poor creature that inherited a wing-like hand who could not fly or use its fingers. Such a mutation would likely cause this "missing link" animal to become an easy lunch for something else and thus forfeit passing on its mutation (though there is little evidence to support that passing on *true* mutations is possible, much less beneficial).

In short, hox genes do not provide an adequate link to the theory that homologous structures prove common ancestry.

Sarah Scott said...

When I said the eohippus was the descendent of the modern horse, that is horribly wrong. Rather, the reverse is true. The horse is *theoretically* the descendent of eohippus (though many top notch scientists do not buy that...I think it was/is a large rodent-like creature). I also am missing an "and": "massive amounts of time _and_ thousands of generations." Apparently I cannot and should not type late at night, for egregious errors tend to ensue.

John Stockwell said...

Sarah Scott wrote
The presence of hox genes does not prove evolution or disprove design. All that is suggested by such a discovery is that there is something in the DNA of kingdom anamalia that tells the embryo what to form.


The absence of a discussion of hox
genes in the sources which Dr. Groothuis
is quoting destroys the credibiilty
of any argument he or they might
make regarding any alleged failure
of homology.

Sarah continues...
How does this sophisticated information coding lend support to the theory that a whale's flipper became a terrestrial foot? It does not. Rather, it suggests something of a much grander scale.


Basically, the modern notions of hox
genes and "clocks" tell us that we
don't have to have wildly different
genetics to get a wing, a flipper, or
a hand. That rather that it is the
timing of the action of chemicals
released turing different phases
of the delopment of organisms that
is sufficient.

The traditional arguments claiming
a failure of homology are arguments
based on the expectation that wildly
different genetic sequences would be
needed to do the job of constructing
these structures. So, no "millions
of generations" are not required
for many changes that we see (wing,
flipper, what have you).

As to your comments regarding the
Cambrian explosion, I can only point
out that the "explosion" was about
10 million years in length. Furthermore,
there is considerable evidence that
many of the forms seen in the Cambrian
predate the "explosion" well into
the Neo-proterozoic (pre-Cambrian)

See for discussion:

Wang DY, Kumar S, Hedges SB., Divergence time estimates for the early history of animal phyla and the origin of plants, animals and fungi. Proc Biol Sci. 1999 Jan 22;266(1415):163-71. [Pubmed] [PDF]

So, basically, we have no cause to
abandon descent with modification,
in favor of, what?, the assertion that
organisms appeared magically from
nowhere?

The fact that there is no massive
"genetic break" between the descendents
of organisms that appear in the fossil
record before the Cambrian explosion
with those that are the decendents of
those that appear during or after
the Cambrian explosion, basically tell
us that common descent is the most
viable explanation for the apparent
relatedness of species.
(The alternative to common descent is
separate descent, and at all levels
nobody has had to abandon the notion.
Quite the reverse, common descent
organizes a vast disparate collection
of data into a unified structure.)