re: massive cladistic retaliation.

[Nick Longrich <longrich@stardot.com>]

Wagner wrote:

>        And no, cladistic groups are NOT NECESSARILY REAL!

>   Such as?  What monolphyletic group of animals cannot be expressed as
>a common ancestor and its decendants?  Oh, are you stuck on that old "what
>if three species of birds are isolated at the same time" thing?  Answers to
>this are available in the litterature.  Check Sereno 1990.

        I'm asking about species A and species B which come from a common 
ancestor. Then they produce species C:

            C
            |
            |
           / \
          /   \
         /     \ 
        A       B
         \     /
          \   /
           \ /
            |
            |
            |
             
        Does cladistics allow for this? I've never heard 
anybody mention it. Rosemary Grant (her and her husband's work is 
detailed in Beak of the Finch) argues that this could be an important 
force in speciation. We know it works like this for hundreds of natural 
and artificial plant species. You breed species A and species B and get 
species C which is interfertile with other hybrids but not other members 
of A and B. What is the relationship between species C and a species D 
which branches off from B or A? 
        Dawkins mentions a fact in one of his books (Blind Watchmaker) 
that peas have hemoglobin, of all things. How in the heck did that 
happen? Maybe the transfer of that sequence was through a bacterial, 
viral or other kind of vector. How does this fit into a cladogram? 
        My junior adviser was talking to me about the evolution of 
eukaryotes and the archaea. We were discussing about how the features 
shared by eukaryotes and archaea argue for common ancestry that would 
exclude the prokaryotes. But she also said that some sort of chimaeric 
evolution is also possible. 
        Too long we've been looking at these diagrams that 
just show branching, branching, branching. But evolution doesn't 
just drive things apart. What about eukaryotes? If some of the genes of 
chloroplasts and mitochondria have found their way into the nucleus... 
then what? The common ancestor of a magnolia and someother plant can be seen 
as a cyanobacteria, another line of prokaryote, whatever the heck common 
ancestor it was we shared with the archebacteria for the host cell... 
        To use Kuhn's vastly overused and kind of annoying word paradigm, 
cladistics and branching phylogeny is a paradigm. It is one that does not 
fit all the evidence in front of us
         There is evidence that viable species of animals (to say
nothing of plants) can be created from hybrids. That either argues
that we need to revamp our phylogenetic system or our concept of
species. The intimate symbiosis of the eukaryotic cell cannot be
represented in a cladogram, as far as I know.  There is the distinct
possibility of gene exchange between very different groups of animals.
        I am not very well educated in cladistics, but none of what I
have seen suggests to me that these relationships can be elucidated or
even described by the cladistic method. If it's preventing us from
seeing the true phylogeny of our genetic packages- our diverse origins
in various domains of life- then we need to divorce ourselves from the
concept of cladograms as able to describe "reality".

[ Given what we know of genetic mechanisms it seems highly unlikely
  that any of the species of import for this group arose via
  hybridization with other known species.  Stegosaurs mating with
  theropods only happens in Godzilla movies.  If the dinosaur fossil
  record were more complete, you'd have a legitimate beef. -- MR]

        nick L.