In article <Pine.SGI.3.95.970808001626.26526C-100000 at umbc9.umbc.edu> david ford <dford3 at gl.umbc.edu> writes:
>From: david ford <dford3 at gl.umbc.edu>
>Subject: Genetics and the Bear--> Whale Transformation
>Date: 8 Aug 1997 00:43:16 -0400
>James G. Acker <jacker at us.net> on 4 Aug 1997 in talk.origins in
> "Rodhocetus (for David Ford)":
David's reply begins here:
>If you want me to discuss something, your best bet is to post and e-mail
>what you'd like replied to. I'm a firm believer in open, public
>discussion. The "fact" that all manner of plant and animal structures
>came into existence through non-intelligence directed means using
>changes in organisms' DNA falls to pieces in the light of genetics, and
>that is the angle I'm going to be approaching this claimed discovery of
>an intermediate between a land animal and a whale. Since we'll be
>discussing genetics, I've included some appropriate newsgroups. To
>those in those groups, talk.origins is moderated, and if you want your
>posts to show up, you might want to put talk-origins at moderators.uu.net>after the "To:" in your e-mail. I don't like the idea of participating
>in a thread named after me, so I've taken the liberty of changing the
>title. The title gets its inspiration from the following remark by
>Charles Darwin.
>"In North America the black bear was seen by Hearne swimming for hours
>with widely open mouth, thus catching, like a whale, insects in the
>water. Even in so extreme a case as this, if the supply of insects were
>constant, and if better adapted competitors did not already exist in the
>country, I can see no difficulty in a race of bears being rendered, by
>natural selection, more and more aquatic in their structure and habits,
>with larger and larger mouths, till a creature was produced as monstrous
>as a whale."[_On the Origin of Species_ (1859), original edition, 184.]
Acker:
>> It is my contention that all of
>> the changes described above are modifications of existing structures,
>> and therefore there is no obvious genetic barrier to such changes.
Ford:
>"There is no obvious genetic barrier to such changes." In the
>transformation of a land animal into a whale, approximately how many new
>genes would you guesstimate were required? Some areas where new genes
>perhaps would be required are in the appearance of the tail fluke, for
>any new enzymes or proteins (e.g., perhaps for the whale's skin), for
>the new structure that would allow the baby whale to drink milk
>underwater, for the cap that is around the nipple, for the organ making
>spermaceti, for the muscles and flaps that allow the blowhole to be
>closed off when the whale dives, for the baleen filtration system in
>baleen whales, for making the mother's milk the composition that it is,
>and for the melon.
>Geneticists, biologists, please help us out. Jim and I know precious
>little about genetics. With genes coding for structures, is it
>necessary that every nucleotide be present, or else the structure coded
>for develops malformed? For genes coding for proteins, must all the
>nucleotides be exactly right? How many triplet codons typically make up
>a structural gene, and how many typically make up a gene coding for a
>protein?
Acker:
>> Mr. Ford is
>> therefore invited to quantify the genetic barriers to such changes
>> that will preclude such microevolutionary modification of the body
>> plan of a terrestrial ungulate into that of a modern, fully-aquatic
>> whale. If he is unable to do so, he will make tacit admission that his
>> definition of microevolution encompasses the body plan modifications
>> that are seen in the evolutionary transition from four-legged
>> terrestrial ungulate to modern whale. He will also admit that
>> Rodhocetus, as stated by the authors, represents an evolutionary
>> intermediate in this process.
Response to David Ford, 8/10/97
I have several points I'd like to make. First of all, David
likes to quote Darwin and his suggestion that a population of
bears could become whale-like. That's the reason for the title of
the thread. I'll tolerate that because he didn't want his name
in a thread, but I want to point out that I believe David intends
this to be a subtle form of ridicule. If David were playing fair,
he'd called it something like the Terrestrial --> Aquatic
transition. No one is claiming that whales evolved from bears!
The claim, for which there is substantial evidence predating
the discoveries made in the 1990s, is that whales are descended
from primitive terrestrial ungulates called artiodactyls. These
are also supposed to be ancestral to the pig, cow, and hippopotamus
(among others).
Next point: David quoted a lot of things necessary in the
full transition to modern whales. However, the fossil under
consideration is Rodhocetus, and that is what I would like to focus
on. David said that evolution does not bring new organs and
body plans into being. In the case of whales, he's quite right.
The body plan of whales is a highly modified version of the body
plan of a terrestrial ungulate. Considering the transition step-by-
step lead us directly to Rodhocetus.
Therefore, what we have to consider initially is if there
are genetic barriers to what is seen in the transition from a fully
terrestrial ungulate to Rodhocetus. Obviously, since Rodhocetus is a
skeletal fossil missing limbs (notably a tail, so that even the anchor
points of a possible tail fluke can't be examined), only a few features can
be examined. Therefore, I'd like to perhaps speed up the discussion
by considering the changes that are seen specifically in Rodhocetus.
So, let's return to the quote from the Gingerich et al. paper published
in Nature which led off the discussion. I'm leaving out the second
of the three paragraphs, which notes that the fossil was found in
deep neritic shelf deposits. It's an important point to keep in
mind.
"Rodhocetus is important for three reasons. First, it is an early
archaeocete that retains high neural spines on anterior thoracics
and a pelvis articulating directly with the sacrum. These are
primitive characteristics of mammals that support their weight on
land, and both suggest that Rodhocetus or an immediate predecessor
was still partly terrestrial. At the same time, cervicals are short,
enhancing rigidity of the anterior body, sacrals are large but unfused,
enhancing power and flexibility, and the femur is reduced, stream-
lining the lumbocaudal trunk. These are derived characteristics of
later archaeocetes and modern whales associated with aquatic
locomotion. Thus the morphology of Rodhocetus is intermediate,
as might be expected of a transitional form evolving from land to
sea."
[delete 2nd paragraph]
"Finally, most modern whales have robust lumbar and proximal
caudal centra, and all lack fusion of sacral vertebrae, making the
lumbocaudal column seamlessly flexible. High dorsal neural spines
and long ventral chevrons limit vertebral excursion but provide leverage
for powerful axial and abdominal muscles. Rodhocetus has all of these
functional features. This indicates that the characteristic cetacean mode
of swimming by dorsoventral oscillation of a heavily muscled tail evolved
within the first three million years or so of the appearance of
archaeocetes. Terminal caudals are lacking in the type specimen
of Rodhocetus and we cannot assess the possible presence of a caudal
fluke, but it is reasonable to expect development of a fluke to coincide
with shortening of the neck, flexibility of the sacrum, and reduction of
hind limbs, first observed in Rodhocetus. This idea can be tested when
a more complete tail of Rodhocetus is found."
So, what we are talking about (primarily) are modifications
of the spinal column and femur that made Rodhocetus an adept
swimmer that was still partly terrestrial (perhaps to bear young,
like elephant seals, walruses, and sea lions do in modern
times). The cervical (neck) verterbrae are shortened. The
central spine and muscular anchor points are strengthened. The
sacral vertebrae are unfused, making the tail more flexible, and the
femur is considerably reduced in size. (I also know that the nostrils
of Rodhocetus are upturned and set slightly back on the snout. This
feature is visible but undiscussed in the diagram of the Rodhocetus
skeleton found in the Nature paper.)
So, I ask David: do you truly want to find out if there are
any genetic barriers to the above modifications? I contend that it
is obvious at this point that there is no new information, and all of
the observed changes are strictly modifications of existing structures.
Will you concede that there is no genetic barrier from a terrestrial
ungulate to the changes described by Gingerich for Rodhocetus?
If you do not concede the point, where do you think attention should
be focused -- which is the likeliest modification to represent a
genetic barrier?
I note as I finish this on 8/10/97 that I have already seen
a reply from Howard Hershey -- definitely a qualified geneticist --
and I am also anticipating David's discussion of Hershey's post.
I also appreciate the reply from St. Andrew, which echoed some
of the thoughts expressed above.
JGA
-----------------------------------------------------------------------------
This posting was the opinion, like it or not, of: James G. Acker
---> jacker at us.net
QUOTE OF THE .SIG: "Whenever you have eliminated the
impossible, the possible, however improbable, remains."
Sherlock Holmes
