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Author Topic:   What is a "kind"?
Meldinoor
Member (Idle past 4808 days)
Posts: 400
From: Colorado, USA
Joined: 02-16-2009


Message 36 of 42 (531320)
10-17-2009 12:47 AM
Reply to: Message 33 by Arphy
10-16-2009 7:38 PM


Re: The kind: comedy gold
Hello Arphy,
First off, I want to congratulate you on your recent POTM nomination. You and slevesque have mustered the courage many creationists lack, and defined the term "kind". Pats on the back for both of you.
Now some comments on your post.
Your additive criteria seem to be the standard definition of "kind". If two animals can reproduce, they are a "kind". I have no problem with this definition as far as sexually reproducing species go.
However, to conclusively show that a species does not belong to a kind you need to use your subtractive criteria. This is your definition's weak spot. As far as I can tell from slevesque's excerpt, gaps in the fossil record are all that is necessary to exclude a species from a kind.
The problem is that new fossils are found continuously, and gaps are gradually filling up. If scientists were to dig up enough links between land-living animals and whales that even creationists would have to concede their relation to each other, then pakicetus would join the whale kind.
If you base a definition on gaps in current knowledge, your kinds will be continuously redefined as new findings come in.
slevesque's article writes:
Are the natural and hybridized forms within the group separated from organisms outside the group by gaps that are significantly greater than intra-group differences?
But how do you quantify these differences? If, say, you defined gorillas and chimps as being one kind (not saying you do), what steps would you take to show that humans are significantly more different from that kind than gorillas are from chimps? (I think, on a molecular level, chimps and humans are closer than chimps and gorillas genetically).
The key to genetic relationships lies with molecular evidence, not so much morphology. Your method should reflect this.
-Meldinoor

This message is a reply to:
 Message 33 by Arphy, posted 10-16-2009 7:38 PM Arphy has replied

Replies to this message:
 Message 37 by Arphy, posted 10-17-2009 2:32 AM Meldinoor has replied

  
Meldinoor
Member (Idle past 4808 days)
Posts: 400
From: Colorado, USA
Joined: 02-16-2009


Message 38 of 42 (531332)
10-17-2009 4:27 AM
Reply to: Message 37 by Arphy
10-17-2009 2:32 AM


Genetic similarity vs Morphology
Thanks for your reply, Arphy.
Arphy writes:
But yes, it is possible that revisions may have to be made as new evidence turns up.
Fair enough. That is true for any scientific model.
Arphy writes:
I think that possibly this should be looked at as in, if you are going to lable two species as being distinctly different kinds because they fulfill the other subtractive criteria, then you had better make sure there aren't any fossil intermediates.
Good point, Arphy. However, I'm not sure why the author of that article chose to place a lack of fossil evidence under negative criteria. Absence of proof is not proof of absence, and just because we don't have the fossil links doesn't mean they don't exist. I get the feeling it was thrown in just to fluff up the list of criteria.
Arphy writes:
yes, but what gaps? The gaps between kinds or the gaps between members of the same kind? I would say it is the latter.
Hahaha... If they filled the gaps between different kinds they would no longer be different kinds Any fossil links must per your definition be within a kind. So your distinction makes no sense. Respectfully.
Arphy writes:
Consequently, species appear much more similar than they would if you examined their morphology, thus the use of DNA sequence information biases the systematic results towards similarity that is purely genetic.
I still have a problem with this. We are essentially discussing genetic or evolutionary (you would probably say micro-evolution) relationships when we're talking about kinds. While morphology may be useful for grouping types of animal, it is horrible when it comes down to figuring out how animals are related.
Take dogs for instance. They differ enormously in their outward morphology, yet their DNA is still very uniform. If we were to define dogs merely by what they look like, ignoring all other factors, we might be tempted to put them in different groups, possibly even in your case, different kinds.
But dogs can interbreed. This shows us that morphology plays very little role in determining whether two animals can hybridize. It's all in the DNA. The more differences, the less likely two individuals will be able to produce viable offspring.
Arphy's reference writes:
Consequently, species appear much more similar than they would if you examined their morphology, thus the use of DNA sequence information biases the systematic results towards similarity that is purely genetic.
But isn't it the genetic similarities that matter? Who cares how dissimilar two species look? There are many proven cases of closely related animals (like dogs) that look wildly different. There are also cases where animals that look similar have proven to be distantly related genetically (like marsupial squirrel gliders, and placental flying squirrels). If you group these marsupials and placentals into the same kind, and do not put chimps and humans together, you've got some serious problems with your definition of kinds.
-Meldinoor
Edited by Meldinoor, : Trying to remember to give my posts good titles

This message is a reply to:
 Message 37 by Arphy, posted 10-17-2009 2:32 AM Arphy has replied

Replies to this message:
 Message 40 by Arphy, posted 10-18-2009 4:13 AM Meldinoor has not replied

  
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