Farewell to Species - reticulation

Richard Jensen rjensen at SAINTMARYS.EDU
Wed Feb 2 08:19:41 CST 2000

I don't think Tom Lammers needs someone else to speak for him, but I
suspect his statement that cladistics assumes dichotomies arises (in part)
from the fact that if there is a lineage split of any sort, then each
lineage (whether two or three or more) is viewed as a new taxon.  This is
a hard one for many of us to accept.  For example, a wide-spread species
(species here used in the context of a taxon that can be viewed as a basic
evolutionary unit) experiences the loss of a peripheral population that
undergoes rapid evolutionary change and is now readily recognizable as a
taxon in its own right.  Does the original wide-spread species cease to
exist?  Do we still have two taxa or three?

As has been explained to me by many cladists, after this "speciation"
event, we now have three taxa: the original wide-spread species (now
relegated to at least nomenclatural extinction) and its two "daughter"
species.  My view is that, unless both daughter species have evolved
autapomorphies with respect to the original species, then after the split
there are still two species: the original is unchanged and there is the
new isolated species that takes off on its own evolutionary pathway.

Richard J. Jensen      |   E-MAIL: rjensen at saintmarys.edu
Dept. of Biology       |   TELEPHONE: 219-284-4674
Saint Mary's College   |   FAX: 219-284-4716
Notre Dame, IN  46556  |

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