Paraphyly is real (+ "strict cladist" defined)
kinman at HOTMAIL.COM
Mon Jan 14 16:22:46 CST 2002
Tom DiBenedetto wrote:
If a lineage divides into two daughter lineages then the daughters are
sisters. What logical or conceptual system are you employing that can see
this as a mere convention?
The above can perhaps be a useful Hennigian convention for cladistic
analysis, but that is not what *really* happens. There is one mother and
only one daughter in a cladogenic event. The daughter species has at least
one synapomorphy that the mother species lacks (otherwise they would still
be the same species).
The paraphyletic mother species persists, and it is only Hennigian
convention that converts her into a second (but unchanged) daughter. You
say the mother persists as a "higher taxon", but this is another semantic
convention, and it just obfuscates the paraphyletic nature of cladogenic
events. The paraphyletic mother persists as the original species, separate
from her daughter species (the exgroup).
This becomes even more apparent when you examine the process at the
level of populations or even individuals. Remember how Hennig breaks down
the concept of "hologeny" into ontogeny, tokogeny, and phylogeny.
To put it simply, the only "real" cladogenic events (which are
inevitable if evolution is to continue) are when a mother paraphyletically
gives rise to a single daughter. "Single paraphyly" is the reality. Even
if a mother species occasionally does give rise to two daughter species,
they are two separate cladogenic events at the level of populations or
individuals. Cladogenic events happen all the time at that level, but they
rarely give rise to new species.
Single paraphyly is as *real* as it gets (in my opinion), and the rest
are just convenient conventions that are erroneously thought to be real
evolutionary events. Doubly paraphyletic groups are not real (nor
inevitable), but their use is occasionally useful and warranted (I therefore
avoid multiple-paraphyletic groups wherever possible). My ideas are a
little different from Mayr and Ashlock on this point.
Wish I had time to explain this better, but that's all the time I have
for now. But let me quickly define what I mean by a strict cladist so there
is no confusion:
DEFINITION: A "strict" cladist is one who never recognizes formal
paraphyletic taxa (apparently due to the strange notion that they are unreal
"mistakes" that must always be done away with). In my opinion, they are the
ones who got it wrong, and universities should be giving students both sides
of the story. Maybe with the Internet, both sides of the story will
eventually get out and discussed.
---- Ken Kinman
MSN Photos is the easiest way to share and print your photos:
More information about the Taxacom