From: kck+@cs.cmu.edu (Karl Kluge)
Subject: Re: Origin of carnivorous plants
Organization: School of Computer Science, Carnegie Mellon
Date: Sun, 27 Sep 1992 02:15:18 GMT

> From: alanf@tekig6.PEN.TEK.COM (Alan M Feuerbacher)
> Subject: Re: Origin of carnivorous plants
> Date: 26 Sep 92 18:37:28 GMT
> 
> In article <Bv4A3p.H3B.2@cs.cmu.edu> kck+@cs.cmu.edu (Karl Kluge) writes:
> >Why do you think this is a new argument?
> 
> I'm well aware this is not a new argument. 

Sorry, didn't mean to snap. 

> It's just that in my
> attempt to understand evolution (admittedly incomplete) I don't recall
> reading a really good explanation of the problem, by which I mean one that
> I finished reading with a feeling that I really understood the answer.

I'll have to defer to the professional biology types such as Chris for
more specific pointers to the literature.

> I understand the idea of adapting preexisting structures.  Let me try to
> better explain my difficulty in understanding.  First let me state that I
> reserve judgement about whether a creator exists or not, and that I accept
> all the evidence that evolution has occurred.  It was, in fact, the discovery
> that my former religion had completely misrepresented the evidence for
> evolution, as well as about other things in science, that led me to give
> it up.

As a theistic evolutionist, let me say that I hope you won't throw the baby
out with the bath water (although you will find those on t.o who will argue
that there was never any baby to begin with). 

> There are an extremely large number of possible mutations, given the
> complexity of DNA.  I would think that if were true that a major mechanism
> for evolutionary change is the adaptation of preexisting structures to new
> uses, most populations would display a tremendous number of structures
> that are partially formed, in the sense of not being used, such as the
> radial seismoid bone in bears.  It's not that such things don't exist,
> but that I would expect there to be a *lot* more of them.  Only then would
> there be enough "raw material" to adapt to a random environmental change.

Borges once wrote an essay called "Kafka and his precursors" in which he
pointed out that every writer creates his own precursors -- that we read
these other, prior texts differently, and see their common threads, solely
because Kafka wrote his stories. The same point applies here. There is
nothing partly formed or useless about that wrist bone in the other bears --
it serves whatever function it does in articulating the joint. If we didn't
know about pandas, we would never think to view it as a transitional stage
to something else. So one answer to your question is that we don't see such
things because in the absence of knowledge of what they will become we have
no reason to see them as transitional stages. If aliens had happened to
visit Earth during the evolution of mammal from reptile-like forbearers,
they would have no way to look at the jaw structure of the transitional
forms and see that as a "partial set of inner ear bones."

The other problem is that a relatively small number of humans devote any
significant amount of time to looking at an animal kingdom with orders of
magnitudes more animals in them out in the world. Who knows what is going on
in the deep (2 mile+) oceans, or in the more inaccessible parts of the rain
forests and jungles which remain?

On the other hand, I do see your concern. There has been some work on
comparative functional anatomy of the visual system, for instance, which
puts forward the following theory: Visual areas originate in a way analogous
to the way new proteins evolve. An existing structure is replicated due to a
mutation or other type of variation. The new structure then is specialized
in different ways by other mutations or variations, and natural selection
picks one. Why don't we see more animals with duplicated visual areas that
haven't specialized? One answer is that we spend very little time looking.

Yet another answer is to appeal again to the distinction between the fact
and theory of evolution. Creationists would have us believe that homologous
traits are due to design reuse. Unfortunately, the nested structure of
homologies within a trait combined with the concordant patterns of homologies
between traits would require that we accept a rather Panglossian view of the
world. We would have to believe that it just happens to be that case that
the appropriate distribution of variations on the basic leg design just
happens to match the appropriate distribution of variations of visual system
functional anatomy and so on and so on. Evolution, on the other hand, HAS to
work this way. We are forced to believe either that evolution occurred, or
that a creator, engaging in separate acts of special creation, just happened
to choose to create in a way indistinguishable from evolution. You can
believe either one, but *those* are the choices. 

> You said above:
> 
> >            I could try to construct "just-so" stories, but I won't. I'll
> >simply point out that any theory to explain the advantage of these partial
> >stages has the advantage over creationism of being testable. 
> 
> Can you point me to examples in the literature where such a theory has
> been proposed and tested?

A number of other people more familiar with the literature about the
specific question at hand have already posted about sources on the evolution
of carnivorous plants. In general terms, for a nice experiment testing a
specific theory about the fitness of differing ages of reproductive maturity
given predators which prefers individuals at different life stages, see US
NEWS AND WORLD REPORT 8/13/1990. I like this one as a very elegant example
showing that natural selection isn't a tautology, and that theories about
fitness can be tested.

Also, Gould's essay on the Panda's thumb, and some of the essays in HORSE'S
TOES AND HEN'S TEETH examine the idea that single mutations can lead to major
morphological change (though changing relative growth rates of parts, for
instance). In general, if you haven't, try to read THE PANDA'S THUMB, EVER
SINCE DARWIN, H.T.&H.T., and BULLY FOR BRONTOSAURUS -- the essays cover many
of the issues which get discussed frequently here.

Karl
Newsgroups: talk.origins