what is a species et al.

Jim McKenney jimmckenney@jimmckenney.com
Thu, 13 Dec 2007 06:46:43 PST
Warning: ranting old guy alert!

Dylan wrote: "Whatever the evidence employed, once substantiated
monophyletic groups are worked out then the rank of those groups becomes
"academic". Hence the subjective nature of taxonomic schemes and hence the
everlasting hope of armchair botanists for more suitable arrangements."

Well said, Dylan, although I want to quibble about one aspect of this

First, let's take another look at this concept species. Here's my version of
the history of the concept in a nutshell: from the time of Plato and his
concept of eidos (form) up until not quite a century ago, gross morphology
was the only criterion generally considered in delimiting species. 

Then, as biologists began to realize the implications of what studies in
genetics were telling them, the concept of population genetics arose and
from it the idea that species were delimited by breeding behavior. In this
view, two entities were members of the same species if they shared the same
gene pool. The beauty of this concept is that it is relatively objective.
Whereas in the old system based on morphology all of the traditional
Linnaean ranks (species no more or less than the others) were determined
subjectively, the "species as an interbreeding population" concept was not
subjective in the same way: membership, so-to-speak, in a species was not
subjectively determined by a taxonomist but rather by the breeding behavior
of the entity in question. Those studying populations didn't determine what
the breeding arrangements would be, the simply reported what they observed.
This approach seemed to eliminate the main objection to traditional taxonomy
- namely that it was subjective. 

I like to contrast the differences in these two approaches in this aphorism:
two entities are not members of the same species because they look alike
(that's the old taxonomic approach); it's the other way around - they look
alike because they are members of the same species (i.e. they share the same
gene pool). That's the insight derived from genetic studies. 

Although the gene pool concept resolved the main objection to traditional
taxonomy (i.e. that it was blatantly subjective) and seemed to provide a
modern, objective species concept which could be used for all sexually
reproducing populations, it did not resolve the challenge posed by
evolutionary studies. The problem, if it is one, with the gene pool concept
is that it portrays species as a snap-shot of real life - the species so
delimited is valid for only an instant. 

And what are the challenges posed by evolutionary studies? Unless you
believe in special creation, then all existing species evolved from other
species. When one species evolves from another, it's a gradual process.
There is probably never a clear break. It's not as if the new species
suddenly separates from the existing one; the ancestral species merges
imperceptibly over time into the new species. Think about that for a moment:
there is no boundary separating the ancestral and derived species. There has
been an unbroken succession of parents and progeny over time. That they are
distinct "species" is an illusion. Darwin himself seems to have been aware
of this- and I cite Darwin only because he wrote a century and a half ago
and some people still don't seem to have caught on. 

There really is no such thing as species in a purely objective sense except
in the momentary sense - the gene pool concept does give us an objective
view of species, but because natural populations are constantly shifting and
changing, that view is valid only at the moment it is made. 

It's a lot like the conundrum posed by analytic a priori knowledge: the more
certain you can be about something, the less relevance it has to the real

As you can see, I take the view that species is as much a philosophical
question as a purely scientific one. I don't expect DNA studies to resolve
the species question. Every generation has had those who look to the latest
technological innovations to solve the "species question". When I was a kid
it was chromosome studies. Technological innovations provide wonderful
insight, but they won't solve the species problem. 

We old guys sure do go on, don't we! I'm 64 now, and for the first time in
my life I have that vague feeling that I wish I were younger, not just
younger but at the beginning of my intellectual life. Why? Because of all
the amazing technological innovations: where is it all going? I so envy
those of you who can look forward to another fifty years: I can't even
imagine what that world will be like. 

Thanks Joe for providing some links to broaden our horizons. 

One final thing. Dylan mentioned "the everlasting hope of armchair botanists
for more suitable arrangements." But really, Dylan, isn't that what we all
want? You can rest assured that the DNA guys will be making arrangements
which suit them.

I'm all for things making sense. 
Jim McKenney
Montgomery County, Maryland, USA, USDA zone 7 where Iris unguicularis
continues to bloom.  
My Virtual Maryland Garden http://www.jimmckenney.com/
BLOG! http://mcwort.blogspot.com/
Webmaster Potomac Valley Chapter, NARGS 
Editor PVC Bulletin http://www.pvcnargs.org/ 
Webmaster Potomac Lily Society http://www.potomaclilysociety.org/

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