Real species and ideology

Richard Jensen rjensen at SAINTMARYS.EDU
Wed Apr 21 08:37:03 CDT 2004

Rich's comments remind me of one of Popper's descriptions of scientific
discovery - the explanation of the known by the unknown.  The extant entities
that we are aware of are the known and our attempt to explain their existence
(and their relationship) requires that we delve into the unknown.  How we do
this, in my view, is a direct function of our personal interpretation of
patterns of variation; to address the question at hand (cline versus
hybridization; this is the unknown), we must first define cline and
hybridization, then ask which definition the data fit.

In my experience, the morphocline/hybridization problem may be addressed by
looking at the relationships among sets of characters.  If we have simple clinal
variation within a single entity, then the relationships (e.g., as determined by
correlations) among characters tend to remain the same; on the other hand,
hybridization tends to disrupt the patterns of relationships among characters.
I have a couple of empirical examples from my own data that support this view,
but others have argued against this based on simulation studies.  Anyone else
have data that might be used to support or counter my hypothesis?



Richard Pyle wrote:

> I certainly understand the logic in that, but I want to come back to two
> critical words I used in my first sentence above: "known extant".  Suppose
> that B & C both had restricted population sizes, and both went extinct due
> to human-induced habitat destruction.  If that happened, then A & D would
> become "sister species" within the context of "known extant" populations.
> Would the extinction events of B & C open up the possibility that gene flow
> between A & D could be thought of as a morphocline, instead of introgressive
> hybridization?  I can't see why it would, because the extermination of all
> individuals of B & C has no effect on the evolutionary relationship between
> A & D.

Richard J. Jensen              | tel: 574-284-4674
Department of Biology      | fax: 574-284-4716
Saint Mary's College         | e-mail: rjensen at
Notre Dame, IN 46556    |

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