Subject:
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Re: Problems with Darwin's theory
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Newsgroups:
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lugnet.off-topic.debate
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Date:
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Mon, 5 Feb 2001 21:49:15 GMT
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Viewed:
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433 times
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Sproaticus wrote:
>
> In lugnet.off-topic.debate, Steve Chapple writes:
> > Yet again, I remind you that what I'm asking for evidence of is the
> > theory regarding evolution OF species from one to another - part of
> > what I've "defined" as Darwinism - NOT evolution WITHIN a species.
>
> For anyone to give you that, you also need to "define" what a species is --
> specifically, what criteria there are to decide where one species stops and
> the other starts. So much of your point depends on establishing a discrete
> categorization of groups of organisms. This unfortunately is very fuzzy
> even within the scientific circles.
I was going to post a reply to an argument last week concerning species
concepts in the macro-evolution/creation debate, unfortunately other
responsibilities got in the way. Thanks for bringing it up.
As Sproaticus said, there are many, many different concepts of what
constitutes a species. Each of them has their own strengths and
weaknesses.
The first species concept was put forth by Plato/Aristotle. They
regarded species as unchanging entities with one underlying type. They
explained variation within a species as imperfect copies of that type.
This is known as the Typological Species Concept.
A second concept is the morphological concept, which is actually an
extension of the Typological. It drops the idea of single true type and
uses morphological similarity as a basis for calling a group of animals
a species.
A widely used concept is the Biological Species Concept, which states
that species are groups of actually or potentially interbreeding natural
populations that are reproductively isolated from other such groups
(Mayr 195?). This concept can be readily used in most areas of biology.
There's also the evolutionary species concept which basically says each
individual has a evolutionary path, but nothing about how to group
existing organisms.
The cladistic (or phylogenetic concept) looks at evolutionary history
(e.g. the fossil record) and determines species identity by where
members appear and disappear.
Finally, there is the Cohesion Species Concept which defines a species
as the smallest group of organisms able to maintain genetic and
phenotypic cohesion through intrinsic isolating mechanisms(i.e. genetic
drift and NS). This one is kinda conceptually hard to grasp, but it
typically does a better job at explaining the natural world then the
other ones IMO. I use this along with the Biological Concept in most of
my thinking.
(there are some more concepts, these were the ones that were at the top
of my head)
> For example, a common definition of a species is a group of related
> organisms capable of interbreeding. However, breeding issues -- genetic
> compatability, physical compatability, parasitic compatability, etc. --
> abound. Consequently, a common complaint with the current definition of
> species is the fact that many different dog (and even wolf) species can
> breed with each other. A similar point involves a breed of arctic waterfowl
> (arg, arctic tern?), which members' sizes increase gradually as one
> traverses the globe longitudally, with neighboring groups cabable of
> interbreeding, until there is an area where small and large breeds meet and
> *can't* breed due to the size difference. Where is the division of species
> then?
>
> Or is the division merely arbitrary, a virtual cubbyhole system to simplify
> accurate note-taking. It's easy to see that while our though processes are
> often dichotomic, the world rarely is. If so, then how can the division of
> species be taken seriously?
>
> I find your argument provoking, but I feel that this is one area where you
> *really* need to clarify your stance.
Both sides really need to clarify their species stance. I hope these
brief descriptions give a good starting point.
-chris
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Message is in Reply To:
 | | Re: Problems with Darwin's theory
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| (...) For anyone to give you that, you also need to "define" what a species is -- specifically, what criteria there are to decide where one species stops and the other starts. So much of your point depends on establishing a discrete categorization (...) (24 years ago, 5-Feb-01, to lugnet.off-topic.debate)
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