[Taxacom] Type of Homo sapiens (was: Are species real? Doesn't matter.)

Sun Jun 3 15:03:57 CDT 2007

Rich Pyle wrote:
>"...We do NOT have any reason to believe that "species" exist."

Hi Rich,

I believe Vazrick has provided a good rejoinder, but I wonder...are you writing about species as taxa in a Linnean hierarchy or species as the terminal branches of clades?  These are not necessarily the same, although I think most of us, as practicing taxonomists, view them that way; i.e., extant species (not as ranks in the hierarchy but as the products of evolution) are the end points of clades. 

I have every reason to believe that species exist as real entities in nature. As Laurent wrote, "But species... are merely objects that are part of a (sometimes strongly) simplificatory model - the taxonomic system - that is used to
describe these products and, indeed, communicate about them."  Laurent chided me for my use of "...species, thought of as products...", so I will restate that simply as "species, as the products of biological evolutionary processes", are just as real as any other "objects" we may encounter.  Laurent's use of object is important - referring to something as an object is to recognize its reality as perceived by our senses.  Thus, species = objects = something perceived to be real.

If a clade has reality, then its reality is a function of the spatiotemporal continuity of a particular biological phenomenon; let's call it a gene pool. The best evidence we have for the existence of a clade is its current manifestation as a gene pool.  We determine, by various criteria, that there is this particular gene pool that appears to exist independently of other such gene pools and we can recognize individuals having the properties necessary to be considered part of this gene pool. The last is where the clade gets its reality - a clade is defined by the real individuals that have existed and do exist. By the way, I used "appears" above because in most instances we are unable to document that gene pools are fully independent; that's why we have a variety of proxies (e.g., morphological species, phylogenetic species, ecological species] that allow us to communicate with others.

Thus, when I write about Quercus palustris, common pin oak, I am referring to hypothesized relationships among a collection of localized populations that, despite their widespread occurrence throughout eastern North America, are all recognizable as members of a single morphological (and apparently biological) "species".  Each individual is real (there's one, right outside my window, that I have watched grow for over 25 years), each population (these are admittedly fuzzy because we don't know the extent of gene flow) is comprised of real individuals, and the extant species as a whole is comprised of the same real individuals.  To deny the reality of the species (= clade) is to deny the reality of the individuals!

Cheers,

Dick J     

Richard Jensen, Professor
Department of Biology
Saint Mary's College
Notre Dame, IN 46556

tel: 574-284-4674

----- Original Message -----
From: Vazrick Nazari <nvazrick at yahoo.com>
To: taxacom at mailman.nhm.ku.edu
Sent: Sun, 3 Jun 2007 05:13:30 -0400 (EDT)
Subject: Re: [Taxacom] Type of Homo sapiens (was: Are species real? Doesn't matter.)

Richard,
I have a hard time placing the existence of a clade in the same category with the existence of atoms or existence of multicellular organisms. To me, clades are just as real as species. The scientific reasoning (and support) for existence of different clades can be variable to a great extent, just like species can be delineated with various degrees of certainty (re. Tautaras, versus whatever species-complex out there that works for you). Unlike your other examples, the existence of a clade (defined as a group of biological taxa that includes all descendants of one common ancestor) can just as easily be threatened as the existence of species. Reproductive events cannot be the definable and mostly unambiguous boundary of a clade. Monophyly is the only definable and mostly unambiguous boundary of a clade. As far as I know, any violation of the principle of monophyly will undermine the existence of a clade, and this violation happens quite regularly in phylogenetics
 and taxonomy. Clades are being re-shaped or nullified all the time, just as species are being shuffled into various genera or synonymized with one another all the time. Existence of any clade is dependent upon the amount of data available and the methodology used for inference, just as existence of species depends upon the amount of data available and the species definition adopted.

For what it is worth 

Vazrick Nazari, PhD student
Department of Integrative Biology
101 Axelrod Building, University of Guelph
Guelph, Ontario, Canada N1G 2W1
Phone: (519) 824-4120 ext. 52226
http://www.uoguelph.ca/~vnazari

Richard Pyle <deepreef at bishopmuseum.org> wrote: 
Hi Dick,

We have good scientific reason to believe that subatomic particles exist.
We have good scientific reason to believe that atoms exist.  We have good
scientific reason to believe that molecules exist.  We have good scientific
reason to believe that living cells exist. We have good scientific reason to
believe that multicellular organisms exist. We even have good scientific
reason to believe that clades exist.  We do NOT have any reason to believe
that "species" exist.  What separates the first six things from the last is
that they all have definable and mostly unambiguous boundaries (in the case
of clades, these are reproductive events -- as in the most recent
reproductive event that is shared in the evolutionary histories of all
extant organisms within a defined set).  Specifically, they have boundaries
that exist whether or not human beings exist.  The boundaries that we define
for species (i.e., the circumscription of all individual organims -- alive,
dead, and yet-to-be-born) are simply that -- definitions that we create.
Subatomic particles, atoms, molecules, cells, multicellular organisms and
probably even clades are units that exist in nature whether or not humans
are here to observe them.

Aloha,
Rich

---------------------------------
TV dinner still cooling?
Check out "Tonight's Picks" on Yahoo! TV.
_______________________________________________
Taxacom mailing list
Taxacom at mailman.nhm.ku.edu
http://mailman.nhm.ku.edu/mailman/listinfo/taxacom