[Taxacom] The Reality (or not) of Species (again!)`

Richard Pyle deepreef at bishopmuseum.org
Sat Sep 13 19:58:14 CDT 2008


I've broken this out into another thread, so as not to distract from the
other (very interesting) discussion started by Bob Mesibov.

Although we've had this discussion many, many times on this list before, I
have some new ideas about how to articulate my own perspective, so I will
try again.

As with so many things we argue about, a lot of the aspects of this argument
boil down to perspectives and semantics.  

I think most of us will agree that, as far as we know, most/all life on
Earth has a common origin.  Working on that premise, then all living things
today are connected to each other by a *continuous* and *unbroken* chain of
reproductive events.  Unless we regard all of Life on Earth as a single
species (not very practical for purposes of communicating about
biodiversity), then we must draw boundaries between species at points along
this *unbroken* continuum of reproductive events.

>From the perspective of someone who is primarily interested elucidating
phylogenies (which, I presume are intended to be congruous with some sort of
evolutionary history -- though after reading Bob's earlier post re-launching
the tracking characters thread, I'm not so sure anymore) -- species are
"real" entities because surrounding us in nature there are seemingly
unambiguous "sets" of organisms that cluster very tightly together in their
characteristics, and we do *NOT* see continuous spectra between these sets.
For example, we cannot find in nature today a continuous spectrum of
organisms representing intermediates between humans, chimpanzees, and
orangutans (Please, John -- I imply no phylogenetic affinities here).  The
"fuzziness" between species, from this perspective, can be thought of
primarily as a short-live phenomenon that happens only during periods of
speciation (which are assumed to be very short, relative to periods between
speciation events). In the example given, this "fuzzy" period lasted only
during the time that the shared ancestor between humans and chimps (or
between humans and orangs, or between orangs and chimps) was diverging into
distinct species, and thereafter the three lineages can be thought of as
"real" units of nature. From this perspective, it's quite appropriate to
think of species as "real", which can be authentically represented by nodes
at the tips of cladograms.

The perspective of someone who operates in the world of alpha taxonomy is
quite different.  From this perspective, the "non-reality" of species is not
about comparing humans to chimps (or to orangs, or whales, or palm trees),
it's about making decisions that seem utterly arbitrary.  People in this
world are constantly operating in the realm of the "fuzzy" -- dealing with
boundary effects between "putative" species.  They don't spend their time
thinking about whether we should treat humans as a different species from
chimps (...or orangs, or whales, or palm trees....).  They worry about
things like "how many species of orangutans are there?"  I'm not a primate
taxonomist, but as I understand it, until recently there was only a single
species, with two recognized subspecies (one on Borneo, the other on
Sumatra).  Now (I guess) those are recognized as full species, but some
maintain that the Bornean species can be further divided into three
subspecies.  Are there two species of orang? Four? One?  The notion that
nature has the "correct" answer to this question, and that it's our job as
taxonomists to continue studying the situation until we "discover" the
"correct" answer, seems utterly naïve from this perspective.  Rather, from
this perspective the "correct" answer is the one that best facilitates
communication among humans.  That is, species boundaries are *defined* by us
(not "discovered" by us), and as such, are not "real" entities in nature.
Species are "real" only in the sense that at any given moment of time, the
derivitives of evolution (i.e., organisms) form a clumpy pattern, rather
than smooth continuum.  But when you look at it across time, the pattern is
extremely smooth -- down to the resolution of a single generation against a
background of billions of years.

So which perspective is correct?  The obvious answer is "both" (or
"neither", depending on whether you're the glass-half-full type, or the
glass-half-empty type).  I know what perspective I have, and it reflects the
nature of the world I live in, and the questions that interest me.

As I tried to express in my previous post, it boils down to the question of
what proportion of all evolutionary history is characterized by the "fuzzy"
regions of speciation.  I already said that the "species are real"
perspective generally assumes that the "fuzzy" zones are proportionally
small on the grand scale of things.  [The only way you can eliminate the
"fuzziness" altogether is to maintain that every single speciation event
begins with an individual offspring that is not conspecific with its
parent(s).]  But when you talk to people who operate from the other
perspective, you find that many of them see the "fuzziness" as the dominant
mode.  In my world, I see plenty of examples where the fuzziness of one
speciation event has not yet attenuated while another apparent speciation
event is already beginning.  In such cases, the entire pattern is fuzzy.
And I can say that about a group of vertebrates -- which are typically MUCH
"cleaner" in terms of having what we might perceive as "real" species than
many/most other groups (e.g., plants).

Sorry, Curtis -- I stand by my assertion that the image of the billowing
smoke is a MUCH closer representation of the "reality" of the contunuum of
life through the ages than the stick-figure cladograms we see so often.
Sure, in the broadest/crudest sense, the stick-figures can be characterized
as "representations of reality". But to those of us coming from the other
perspective, such a notion is patently, laughably, absurd. Don't get me
wrong -- cladograms are a GREAT tool for communication, in the same way that
taxonomic nomenclature is a great tool for communication.  And they're a
very convenient and intuitive short-hand method for representing hypotheses
about gross historical patterns of descent.  But the danger, as others have
already pointed out, is in allowing oneself to believe these stick figures
represent "reality".

Aloha,
Rich






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