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