cladism's greatest weakness

Hubert Turner turner at RULSFB.LEIDENUNIV.NL
Wed Sep 22 09:03:56 CDT 1999

>On Tue, 21 Sep 1999, Richard Jensen wrote:
>Given that you have used a specific criterion in your example
>(reproductive isolation), then I would argue that the taxon Homo sapiens
>is still a species (those on Earth), and those on Mars represent a new
>species of Homo (H. ares?).  Those on Earth still behave as a single taxon
>consisting of a large number of reproductively compatible individuals.
>I don't see the necessity of raising H. sapiens to a higher taxon.  As you
>say, nothing has gone extinct or disappeared.  If a have a species, and
>nothing goes extinct or disappears, then I still have a species.

Why dignify the population on Mars with the new name? We would be equally
well justified to rename the earthbound population and keep the name H.
sapiens for the martians. The point is of course that the two lineages are
assumed to have become permanently split, so that each evolves
independently of the other. In that sense both can be seen as separate
entities that are no longer the same as their most recent common ancestral
lineage. (Old) H. sapiens, H. ares and 'H. terrestris' are now a
monophyletic clade (of lineages), but which lineage(s) are recognized as
species (based on e.g. fixation of character state, a novelty for a new
species, a plesiomorphic state for the 'ancestral' species) to which the
name 'H. sapiens' might be  applied, is a matter of taste.

Dr. Hubert Turner
EEW, Sect. Theoretical Biology & Phylogenetics
PO Box 9516, 2300 RA  Leiden, The Netherlands
Visiting address: Van der Klaauw Laboratory, Kaiserstraat 63, Leiden
Phone: +31-71-5274904    Fax: +31-71-5274900
E-mail: turner at

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