meanderings, riparian and philosophic

Curtis Clark jcclark at CSUPOMONA.EDU
Mon Apr 5 21:26:14 CDT 2004

At 12:40 2004-04-05, Richard Pyle wrote:
>So, when we're talking about
>lineage-splitting, are we really thinking the same thing?

Maybe. Dealing with lineages often requires inference, because we can never
observe all the matings. A lineage split would result from members of two
groups of potential parents never mating with one another. A consequence of
this is that the distribution of homologies fits a tree better than it fits
a network.

> > That's not the only way to look at it. You could talk about population
> > lineages.
>But a population is defined by the set of individual organisms that it
>contains (across time and generations).  So referring to a population can
>only be thought of as a short-hand for referring to a collective set of
>individuals.  The individuals are he ones who reproduce; not the population.

Tell that to a population geneticist. We can know things about populations
without knowing about their individuals. I, like you, tend to be
individual-centric, but that's not the only way of thinking of things.

>In the ideal world, those sets of individuals constituting populations would
>be "discrete" (there's that word again), with distinct boundaries -- both in
>terms of individuals and the gene sequences they contain.

Only in Aristotle's ideal world. Again, population geneticists model the
fuzziness, rather than bemoan it.

>Maybe more accurate, but certainly not more precise.  As my wife says, it's
>generally better to be vaguely correct, than precisely wrong -- so I see
>your point.  But one of the downsides of accurate vagueness is that
>different people might try to extract different precision specifics from it.

Good point.

> > I am convinced that I
> > am real, and I suspect the same of you, but I'd be hard-pressed to
> > demonstrate that I were discrete.
>Well....yes and no.  Yes, I do indeed believe that I am real.  As for being
>discrete, I would say that we, as individual organisms, are certainly more
>discrete that populations or species are.  We are temporally discrete in the
>sense that we have reasonably precise starting points (the union of sperm
>and egg) and ending points (death).  We are spatially discrete in the sense
>that we are mostly contained within the boundary layer of our epidermis
>(plus some hair).

I'll get metaphysical here...Linnaeus (for example) is physically dead, and
never visited California, but in a sense he is here now. My point being
that discreteness is often a fruitless thing to characterize, since it
doesn't really address what's important. I suspect that our overemphasis on
being discrete relates to our ability to "recognize individuals", which is
a consequence of our being behaviorally complex social organisms.

> > The requirement of discreteness is IMO
> > one of those Aristotelean leftovers that hinders modern science. Certainly
> > the particle physicists have gotten over it.
>I'm not sure if it hinders modern science, but it certainly seems to be
>hindering me! :-)  I semi-jokingly made reference in an earlier post to
>carrying on the argument all the way down to superstrings, so I know where
>you're coming from on the particle physics thing.  But I think it's still
>fair to use the word
>"discrete" in the sense of, "individual organisms are more discrete than
>populations or taxa".

But why does it matter, except to our ability to define boundaries?

> > I claim this as an *outcome* of lineage-splitting.
>Hmm....are you saying that the lineage is the "reality", and the pedigree is
>merely an outcome of that real lineage?  I tend to think of it the other way
>around -- that the "reality" is that organisms have reproduced generation
>after generation, and we are trying to see the evolutionary patterns (what I
>think of as linage splitting) that itself is the outcome of this long trail
>of reproductive events.

I guess what I'm saying is that the *phylogenetic* consequence are an
outcome of lineage-splitting; without that, we wouldn't be building trees
very effectively.

> > My ramblings are based on the idea that we don't know that for
> > certain, but
> > that we have well-established theories of the ways that "traits" (genetic
> > or morphological) can be transferred longitudinally or laterally. One
> > approach to non-congruence is to throw up our hands and say "It's too
> > complicated, so I'm going to stuck with my 'expert taxonomic opinion'."
> > Another is to postulate unknown forces at work. I maintain that
> > the best is
> > to analyze the data in the context of accepted mechanisms and see whether
> > we can make any sense of it.
>A agree -- but how is the last sentence ("...make any sense of it") any
>different from "expert taxonomic opinion"?

It's the same as expert taxonomic opinion, but differs from "expert
taxonomic opinion". The former is substantiated with data, the latter with

>Well....I think we have our heads around the periodic table pretty well.

And fortunately it seems to be the same now as it has been since a week or
so after the Big Bang.

>course, in evolution, we are talking about histories (things that have
>happened in the past), and there is NEVER any certainty in that.  But there
>are varying degrees of certainty.  And I guess when you cut through all the
>verbiage in my long posts, my ultimate point is that the level of certainty
>associated with most arguments about phylogenetic history is considerably
>less than that expressed by many of the participants in such debates.

I agree totally. To me, the whole point is to craft elegant testable
hypothesis that have no ego-investment at all, and then test them to

Curtis Clark        
Web Coordinator, Cal Poly Pomona                 +1 909 979 6371
Professor, Biological Sciences                   +1 909 869 4062

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