Martian human species

[Tom DiBenedetto]

Ken Kinman wrote:

>Tom,
>    When you state "both species retain the same relationship with the
>ancestral species," to me this is at best misleading.  The way I would look
>at this Mars man example, Mars mankind budded off of Homo sapiens (Earth
>mankind), and the current consensus (although contested) is that Homo
>sapiens budded off of Homo erectus.
>    H. erectus is thus paraphyletic with respect to H.
>sapiens, and the latter would be paraphyletic with respect to the new
>species of Mars mankind.  Therefore, Mars mankind is only related to H.
>erectus through the genetically intermediate species H. sapiens.  I really
>cannot understand why cladists find this viewpoint so
>disconcerting.

Because to me, your approach represents an artificial decision to deny
the very reality that we are trying to capture. What is it that makes
the taxon "sapiens" what it is? Empirically, we can talk about the
evolutionary novelites (apomorphies) by which we diagnose the taxon,
but ontologically, it seems clear to me that what "sapiens" is, is a
terminal lineage in the historical branching pattern of evolving life.
If some descendants of this lineage branch go off to form a new taxon
(a new terminal branch), then how on earth can anyone claim that they
are no longer part of "sapiens"? *Nothing* that can ever happen to a
descendant of sapiens will ever cause it not to be part of sapiens.
That, it seems to me, is what taking evolution seriously is all about
in the world of systematics. Snakes are still tetrapods, even though
they have no limbs, Birds are still reptiles even though they fly
around in feathers. Whales are still mammals even though they have
returned to the sea, and lost (almost) all of their hair. If they now
lose their mammary glands, go through a massive bout of reductive
evolution to the point where they become single-celled, crawl into a
thermal vent and start sucking sulfur, they will still be part of
Mammalia, because Mammalia refers to a *historical lineage*., as do all
taxa.
The martian humans would be part of "sapiens" for the same reason. It
makes absolutely no sense to me to try to deny the "sapien-ness" of
those martian humans. So the martians are historically part of sapiens,
and so would the humans who remain on earth. "Sapiens" is, quite
obviously,  now a taxon that is more complex than a simple terminal
taxon. It is a higher taxon, encompassing a terminal taxon (a species)
on mars, and a terminal taxon (a species) on earth. You can call them
"Sapiens terrestius", and "Sapiens marsii" (with deep and profound
apologies to the Latin scholars). This, it seems to me, is the most
accurate approximation of what would be really going on with these
historical lineages.

>     If you raise H. sapiens to superspecies status, then I
>assume you are going to give Earth mankind a new species
>name.  If Earth mankind has not changed (having stayed in the original
>environment of Earth), then erecting a new name is misleading.

But its *relationships* have changed!. We use characters, and
appearances to guide us in understanding historical relationships, but
it is the relationships which are the ultimate criterion for
classifying. Pre-split, H. sapiens was a terminal taxon; all of its
historical relationships with other taxa were external relationships
(i.e. it had no internal hierarchical structure). In other words, it
was a taxon which we rank as a species. But once it diverges, its set
of relationships is different.
Once again, I would like to emphasize that the notion of taxa being
promoted up the ranking system seems like an obvious point to me, for
any system that recognizes that evolution happens. Once upon a time
there was a single species of mammal; the ancestral mammalian species.
If systematists would have been around at that time, they would have
recognized it as a terminal taxon, a species. Perhaps they would have
called it Amniotus mammalia. By now, this taxon is a very high level
taxon, encompassing many lower level groupings and thousands of
terminals. It has become a higher taxon for one reason only; the
divergence of its descendant taxa. With each new divergence, Mammalia
encompasses more complexity, it moves higher up the hierarchy of
diverging life. The same would be true for the taxon "sapiens" in our
example.

>     And given the continuity of evolution (with rare exceptions, like
>polyploidy), I fail to see how your viewpoint is not also arbitrary.  Can
>anyone say at what point in time Mars mankind became completely
>reproductively isolated from Earth mankind.

No we cannot. But I dont see this as a real problem. Cladistics,and
systematics in general, is about classifying on the basis of historical
relationships between diverged groups. Hennig was very explicit about
the distincition between tokogenetic relationships and phylogenetic
relationships. And he mapped out the "grey area" during divergence,
when reticulation events might still happen. Our classifications
"settle down" when the divergence is complete and irreversible, as best
we can infer.

>     If you have adequate data, I think mother-daughter species are a more
>accurate model, and that sister-sister species should be used when adequate
>data is absent.

But even Mayr has acknoweldged that there is no data by which to
identify any particular ancestor-descendant relationship. Empirically,
we can identify sister groups, and we cannot identify A-D
relationships. And nomenclaturally, we recognize lineage branches. I
dont see the conceptual space in which there is a need, or any sense,
to identify, with a name, cut-off lineages (i.e. "mother taxa").