Michael Ragland  wrote:

> Michael Ragland  wrote: 
> 
> Species- One kind of organism. Of sexually reproducing organisms, one or
> more natural populations in which individuals are interbreeding and are
> reproductively isolated from other groups. 
> Is this a sufficient definition of species? I've been reading some of
> the controversy over this term and as far as I can see this is an apt
> definition of biological species. It doesn't take anybody with a little
> general knowledge of Darwinism and embryology that we were once
> "different" species. Over a long gradual period of time we
evolved from
> other life forms or "species". If one sticks to our current definition
> of species I think there is no contadiction with evolution. However,
> strictly in terms of evolution the term "species" is fluid and ever
> changing. There is no question, assuming we don't destroy ourselves,
> that in a billion years we won't resemble anything like what we do now
> in terms of internal and external morphology. Nevertheless, as
> incredible as it may seem there will likely be vestiges of us remaining
> a billion years from now...to use an analogy like the human embryo at a
> certain early stage briefly resembles or is like a fish. 
> There is no question evolution can be externally influenced by future
> genetic engineering and this in itself will be a new form of evolution.
> Natural selection won't be controlled but will be gradually influenced
> and at some point in the far off future replaced completely by
> artificial selection via genetic engineering. 
> Does everybody agree with the aforementioned definition of species? Do
> people agree on an evolutionary scale the term and meaning is fluid and
> subject to change? 
> 
> Michael Ragland 
> 
> 
> There are around 25 distinct "definitions" of the category
"species" in
> the literature at present. The biospecies definition has been criticised
> a lot, and there are a number of "isolation" conceptions in
play. One of
> the problems with it is that it is a synchronic, or
"time-slice" concept
> that fails over any length of time and sometimes over geographic
> distance, and it is rarely operational in diagnosis. 
> 
> RAGLAND:
> I agree. 
> 
> Evolution conceptions of species tend to follow Simpson's "lineage with
> a unique evolutionary fate and tendencies", while phylogenetic concepts
> fall either to "autapomorphies" (unique constellations of characters
> that all and only that species' members bear), or to a species being
> merely the terminal node on a phylogenetic tree. 
> 
> RAGLAND:
> Wouldn't a terminal node on a phylogenic tree indicate an evolutionary
> dead end? I think the jury is still out regarding Homo Sapiens. Have
> there been instances where we can predict a particular "species" is a
> terminal node on a phylogentic tree. For example, many species are
> endangered by human development and encroachment. On that basis can we
> possibly determine a particular species will be a terminal node on a
> phylogenetic tree. I know this is simplistic but if we have the ability
> to determine a particular species is endangered can't we also project
> and determine a particular species is a terminal node on a phylogenetic
> tree. 

A terminal node on an evolutionary tree is simply a node that has not
yet speciated or gone extinct. If it goes extinct, then yes, it is a
dead end. If it speciates, then it is not. Terminal nodehood applies at
a given time index. At a point slightly earlier than the present, Homo
erectus was a terminal node on the tree. You are misled by the
terminology here.
> 
> I realize there can be many agents for a particular "species" to be a
> terminal node in a phylogenetic tree. Competition from other species is
> just one possibility. 
> 
> How does one actually determine autapomorphies" (unique constellations
> of characters that all and only that species' members bear)? At first
> glance I'm very critical of this. Are we not the evolvement of numerous
> organisms before us? We're just another product of evolution. What we
> classify as unique constellations of characters that all and only that
> species members bear...in "us" what would be considered the
> autapomorphies? 

Species that have no (apparent) autapomorphies are referred to as
"metaspecies" - for example, a species that is ancestral to many
subsequent species, all of which combined bear all the states or
characters of the ancestor and which the ancestor has no state not found
in the descendents, is a metaspecies.

Autapomorphies are found by investigation. There is an argument that,
whether *we* can diagnose it or not, *any* species must have
autapomorphies, or it would not be a species in the first place. An
example is the Rana pipiens complex of frogs in SE USA - *they* could
tell the differences (in terms of mating calls) even though *we* thought
they were all one species until Littlejohn and Oldham discovered that it
formed a "species complex" of about ten (?) distinct mating groups:

Littlejohn, M. J. and R. S. Oldham (1968). "Rana pipiens complex: mating
call structure and taxonomy." Science 162: 1003-1005.

You have to distinguish between what we use to diagnose and what has
causal efficacy - autapomorphies are usually spoken of in the diagnostic
sense, but they represent actual traits or properties of organisms that
maintain species as distinct lineages
> 
> WILKINS:
> There are genetic definitions such as Templeton's cohesion conception,
> and so on. 
> Each of them has their own problems.
> 
> RAGLAND:
> Yes, I'm sure. I get the impression the complexity of it renders any
> single definition of species moot. It's too rich and diverse a subject
> to be limited to one definition. Nevertheless, do you have any one or a
> "handful" which you agree with more than the others.

In my paper

Wilkins, J. S. (2003). "How to be a chaste species pluralist-realist:
The origins of species modes and the Synapomorphic Species Concept."
Biology and Philosophy 18: 621-638. [there is a production error that
repeats the last paragraph]

I argue this: yes, each of the species concepts (bar the purely
artificial ones) have some purchase in the actual world; but the notion
of a "species" as the lowest division is, under evolutionary theory,
something general - it literally means something that is not yet divided
into independent lineages. A species is any lineage that has differences
in some synapomorphies that causally maintain that lineage as distinct
from its nearest neighbours. This includes the biospecies, evospecies
and the various phylospecies conceptions under a (chaste) pluralism. We
now find that it is an *empirical* issue what sort of species a species
is, without needing to formulate prior definitions of that conception
other than "separate in evolution". I think of this (the SSC) as a
marriage of evolutionary and phylogenetic species concepts.
> 
> WILKINS:
>  I recommend you get hold of Jody Hey's (2001). Genes, concepts and
> species: the evolutionary and cognitive causes of the species problem.
> New York, Oxford University Press. It will introduce you to many of the
> issues. If you would like to look at some of the questions regarding
> speciation, try 
> Schilthuizen, M. (2001). Frogs, flies, and dandelions: the making of
> species. Oxford, Oxford University Press. 
> 
> Do a web search for "James Mallet" and you should locate an
essay o fhis
> on the species concepts (I add a couple and reject one of his, but it's
> damned good as it stands). 


-- 
Dr John S. Wilkins, www.wilkins.id.au
"I never meet anyone who is not perplexed what to do with their
 children" --Charles Darwin to Syms Covington, February 22, 1857
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