Metaphors for Evolution

[Richard Pyle]

As promised (threatened) in my last post, here is my take on an evolutionary
metaphor, in response to Curtis' river metaphor.

> >That's fine, but I guess I fail to see the analogy to the
> current topic of
> >discussion (let me know if you'd like me to elaborate on why I
> think it is
> >misapplied).
>
> It's a metaphor about the difference between discreteness and reality.

In the case of the forked river, there are "discrete" molecules of H20,
which maintain physical consistency throughout their journey from the fork
to the disparate destinations.  There is a clean and simple way to map the
"lineages" of the water pathway -- a water molecule went by either one path,
or another.  But the paths of evolution are not traveled by matter.  Any
particular physical substance only participates in teeny, tiny sections of
the path.  So when we speak of evolving life, what we're really talking
about is the (imperfect) transference of information.  The only thing that
connects us to our grandparents, or to the most recent common ancestor that
we share with chimps and orangutans, or to the 90%+ of non-human cells that
inhabit our bodies -- is intangible information.

And that, I think, is why we have a hard time getting our collective heads
around what is REALLY going on during the evolutionary process.  We try to
visualize it in physical terms -- lineages of physical molecules, organisms,
populations, taxa -- but the only real lineage is of something that exists
purely in the abstract.

The best metaphor I know of for evolution is a variant of that old
grade-school game where one student whispers a short story to the next
student, and the story gets passed from student to student until it comes
back to the first student, by which time it has changed considerably.  The
variant is that the student whispers the story to several other students,
each of whom whisper it to several others -- until the story has been passed
around to everyone in the country.  Sometimes a particular person will hear
the story from more than one source.  If the two versions are nearly
identical, the student will pass on a single version to the next listener
(genetic recombination and gene flow). If the two versions of story have
diverged a little bit but are still identifiable as the same story, then
both versions will be blended, selecting certain facts from one version and
other facts from the other, and the amalgamated version will be passed on to
the next person (hybridization). In other cases, the alternate versions of
the story will have diverged so much that the person will maintain them as
two separate stories when passing them on to the next person (reproductive
isolation). Sometimes, a listener will overhear bits and pieces from a
storyteller passing the story to a different listener (lateral gene flow).
In many cases, a particular version of the story never gets passed on at all
(extinction).

It's easy to assume that the individual people in this story-passing network
represent organisms; but actually they don't.  The people represent the
reproductive process (e.g., recombination, meiosis & mitosis, etc.) -- i.e.,
where all the mutations and alterations occur. Organisms, in this metaphor,
are represented by the sound waves that travel from the storyteller's mouth
to the listener's ear.  They are ephemeral conduits that perpetuate the flow
of information.  They are formed when the storyteller generates the sound
waves (comparable to my "assemblage of matter"), and after they encounter
the ear of the listener (initiate the reproductive process), they disperse
into the "ether", losing all trace of the information they once transmitted
(comparable to my "entropy" thing).

To tie it back into the original discussion, my contention is that we don't
yet fully understand how the information flows over the course of evolution.
My hope is that some day we will have the technology and "intellectual
fortitude" to gather up all of the stories that are still being told,
analyze them word-for-word, and through the use of sophisticated algorithms
be able to reconstruct how the various versions of the story relate to each
other.

O.K., it's Monday -- the weekend is over.  I need to get some work done...

Aloha,
Rich

=======================================================
Richard L. Pyle, PhD
Ichthyology, Bishop Museum
1525 Bernice St., Honolulu, HI 96817
Ph: (808)848-4115, Fax: (808)847-8252
email: deepreef at bishopmuseum.org
http://www.bishopmuseum.org/bishop/HBS/pylerichard.html