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True cladograms & Black swans



At 07:43 PM 2/24/98 EST, Dinogeorge wrote:

><<However, we can only reconstruct these events: they are gone now.  We might
>have some model (parsimony, maximum likelihood, biomechanical, etc.) to
>choose one of the three schemes over the other, but we cannot stop there and
>say "This is the *right* answer."  The best we can say is "This is the right
>answer, given current data".  The addition of new data could potentially
>cause us to reject the currently accepted scenario in favor of one of the
>other two.>>
>
>Right. But there is only one True answer (multiple choice question), and a
>cladogram that indicates a different phylogeny from the True answer is wrong,
>regardless of whether we can discern it and regardless of the perfection or
>interpretation of current data.

Correct.  I agree that there is a true reality (as opposed to an untrue
one?), external to us.  (Actually, that is the basic fundamental assumption
of science).

However, where we disagree is whether we, with limited knowledge, can ever
reach a state of certainty that we can say that we have absolutely,
irreversiblely reached that Truth.  The basics of the fundamentals of
science is that we can test and test and test an hypothesis to the point
that it is perverse to consider other options (i.e., that gravity won't
operate tomorrow morning).  HOWEVER, if we were to wake up tomorrow and find
that gravity had reversed, we would have to revise our previous hypothesis
based on new data.

This is what I meant by saying we cannot know, for absolute certainty, the
"real" answer.  Any answer we find may be backed up by extraordinary amounts
of supporting evidence, and every test done up to a certain point verifies
it, but we have to recognize that the potential exists that we may find new
data which will cause us to revise it.

Or, to go explicity to Karl Popper here, if we keep on finding white swans,
we won't have proven that all swans are white.  Finding a single black swan
would falsify the hypothesis that all swans are white.

>If we believe, for whatever reasons, that we
>have a true cladogram when in reality it is wrong, then we are living in a
>fool's paradise.

No. We are still wrong, but we are wrong for the right reasons.  There is
nothing shameful in this.

>I would say it is worthwhile to dedicate some research toward
>solving the problem of verifying the Truth of cladograms, especially since the
>number of choices is quite finite, rather than wishy-washily dismissing the
>issue as insoluble.

PLEASE go back the archives: Brochu & others have posted references for
various papers on exactly this topic for time to time.  Or, stop by and look
through the last several volumes or twenty of Systematic Biology/Zoology,
Trends in Ecology and Evolution, Cladistics, etc.

No one claims that a problem is insoluble.  It may not be soluble with
current data, but this is just an invitation to additional data.  The
operative concept here is "multiple working hypotheses": the field is
narrowed down to fewer options, and we can look for additional means for
testing them.

(This is hardly unique to cladistics: I first learned that phrase with
regards to structural geology...).

>The possibility of living in a fool's paradise makes me
>edgy (no snide comments here, please; I've anticipated them all already).

No snide comment, just noting (as I stated earlier in this post) that the
concept that science does not give absolute final answers makes some people
uncomfortable.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661