david ford wrote:
>> James G. Acker <jacker at us.net> on 4 Aug 1997 in talk.origins in
> "Rodhocetus (for David Ford)":
>> > The following three paragraphs are quoted from "New whale from
> > the Eocene of Pakistan and the origin of cetacean swimming"
> > by Philip Gingerich, S. Mahmood Raza, Muhammad Arif,
> > Mohammad Anwar, and Xiaoyuan Zhou,
[snip discussion of early whale]
>> 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,
As you mention below, you know precious little about genetics. I
suppose that you have only learned creationist genetics, which has
little resemblance to scientific genetics?
[snip Darwin's bear to whale quote]
>> > 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.
>> "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.
Most of these require modification of existing genes rather than
invention of new ones from scratch. In particular, modification of
amounts and modification of the developmental processes. The number of
'genes' one needs to change for a particular phenotype could be as
little as one nucleotide on an existing gene. Think of how much
variation exists within the human species. And it is this existing
information that selection works upon. But once the 'norm' has been
moved by directional selection, new variation away from this new norm
appears by the normal process of mutation.
>> 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?
Absolutely not. Nearly any gene has a whole slew of small numbers of
essentially identical (in terms of function) variants. Typically, no
one makes the effort to find these variants because they are clinically
insignificant.
> For genes coding for proteins, must all the
> nucleotides be exactly right?
Same question. Same answer. Absolutely not.
> How many triplet codons typically make up
> a structural gene, and how many typically make up a gene coding for a
> protein?
These are the same question (in general). 300 nucleotides and 100 amino
acids are rough enough. There are smaller by an order of magnitude.
There are much larger proteins, but few much larger than an order of
magnitude more.
>> > 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.
> >
> > Submitted to talk.origins by James Acker, 8/4/97
