[Taxacom] Tuataras are REAL (the relativity of reality)

[Richard Pyle]

Hi Ken,

I think we're talking about different things here.  The further back in time
and/or biological divergence one goes to find the most recent common
ancestor among extant organisms, the lower the probability (on average) of
future genetic exchange among them.  That tuataras seem more "real" and less
"fuzzy" (along with crossopterygians and other unique-ish extant organisms)
is merely an artifact of historical patterns of extinction and
diversification.  It's an illusion.  If there were such a broad array of
extant Tuataras that taxonomists had named 500 different species (including
_Sphenodon punctatus_), then there would be absolutely no more "reality" of
the distinction between _Sphenodon punctatus_ and other non-Tuatara critters
on the planet than there is now.  Yet somehow, because there is only one
extant species today, it seems more "real" to you. But if species were
"real" (in the sense of this debate -- that is, intrinsically evident
outside of the human imagination), then there would be only one possible
objectively correct answer to the question of whether or not there are one
species or two.

What you are talking about is not the "reality" of species, but the reality
of clades.  Most of us would agree (ignoring introgression, hybridization,
lateral gene flow and other confounding issues) that clades have some degree
"reality" to them.  Not in the sense of physical reality of the sort Pierre
alluded to, but historical reality in the sense that there is only one true
sequence of "begats" (reproduction events) that historically transpired.  In
other words, you can make a legitimate hypothesis that the most recent
common ancestor (however you define that) of all living tuataras is not an
ancestor of any living non-tuatara.  Save for the caveates already mentioned
(introgression, hybridization, etc.), we can assume that this hypothesis is
falsifiable through ever increasing amounts of testing.

But what is not really falsifiable or testable or a hypothesis is whether
all living tuataras should be classified as two separate species, or as two
subspecies within a single species, or simply as a single species with some
measure of population structure.  *THIS* is the sort of reality (or lack
thereof) we're talking about when we have these "endless arguments".

So, in a sense we do have "both" -- but they are different things.  We have
testable hypotheses about phylogenetic relationships, which can (in the
context of evolution) be mostly regarded as "real"; while still
acknowledging that the line we draw to circumscribe a set (or class) of
individuals that we regard as a "species" is, in *all* cases, ultimately
arbitrary.

Aloha,
Rich

> -----Original Message-----
> From: taxacom-bounces at mailman.nhm.ku.edu 
> [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Ken Kinman
> Sent: Friday, June 01, 2007 5:09 PM
> To: taxacom at mailman.nhm.ku.edu
> Subject: [Taxacom] Tuataras are REAL (the relativity of reality)
> 
> Dear All,
>       These endless arguments about whether species are real 
> (or not) seem largely to be semantic exercises which largely 
> rest upon on which particular species one is talking about.  
> The fuzzier they are, the more likely they are to be branded 
> a class of objects rather than a real entity.
> 
>       The tuatara is an excellent example.  Admittedly, we 
> could probably argue endlessly about whether there are 
> actually one or two species of extant tuataras.  HOWEVER, 
> tuataras are so distinctive that I cannot see how anyone can 
> argue against the reality that they constitute a REAL clade 
> of organisms which share descent from a common ancestral 
> population of tuataras (whether it is one or two distinct 
> species just distracts from the reality of the clade).  Such 
> a clade seems to me to be BOTH a class AND an individual.  
> It's like having your cake and eating it too, but some seem 
> intent on denying that we can have our cake and eat it too, 
> even in such clear-cut cases.
> 
>       Why can't it be both, rather than only one or the 
> other?  It is only in a minority of cases that we can do 
> this, so why not celebrate them rather than insist that it 
> has to ALWAYS be only one or the other just because many 
> cases are not so clear-cut?  In a Universe full of continuua, 
> it seems such a waste of time arguing over a term like 
> "reality", when it is such a relative term and dependent on a 
> given context and perspective.
>     ----Ken Kinman
> 
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