[Taxacom] Evolutionary misconceptions (was Ladderising phylogenetic trees)

[Kenneth Kinman]

Hi Jim,
       I would agree with that scenario in many cases, especially when a
species has a wide geographic distribution and lots of subspecies.  The
most clearcut such cases would be a circle of subspecies, where one or
more intermediate subspecies die out, and therefore gene flow is
interrupted between the subspecies on either side.                   
     If the extinction happens to more centrally located subspecies, the
surviving remnants are very clearly sister species by anyone's
definition.  However, if the extinction is rather asymmetric, and the
original species is separated into a big group of subspecies on one
side, and just a small subspecies or two on the other, it is rather
subjective whether to label the surviving populations (if they achieve
species status) as sister species or the more widespread species as the
mother to the small daughter species.        
      Unfortunately any such extinction-derived speciations tend to be
more controversial (less clearcut) than the far more asymmetric examples
(tiny allopatric populations invading islands, or diploid species giving
rise to polyploid species).  In those cases, death of intermediates is
less likely to occur or be such an important consideration, especially
polyploids where intermediates don't typically exist (being one of those
relatively sudden punctuations that Stephen Jay Gould liked to point
out).
        ----------Ken

------------------------------------------------------------
Jim Croft wrote:
     I am a negative-space kinda guy (also some would claim, a negative,
space-kinda guy)... speciation happens not with reproduction, but with
death - the joining bits in the middle die out.. et voila! species
happens.  :) 
It is death, not birth that holds all the good cards... 
building biodiversity - one death at at time... :) 
jim