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Re: AMARGASAURUS SATTLERI (pretty long)



Jeffrey,
I have always thought that ring species are the perfect example of speciation in action. Even though the ends of the ring don't interbreed, they can still exchange genes indirectly through intermediates in the ring.
If you wipe out enough of the intermediate populations, that genetic link is lost and they become two species. But if a barrier appears in the middle of the ring, then you are faced with the question of how long before they become two species. As long as the possibility exists that the barrier could disappear again, the genetic ring could be reestablished if no isolating mechanisms have had time to develop. One biologist will declare them two species, and another will say they are still one, but actually it can depend on how long the barrier will remain. In such cases, the true answer cannot be answered with certainty in the present, being dependent of historical contingencies that have not yet unfolded. It could go either way in the future. A great example of incipient speciation confounding the experts, and the blurriness of species boundaries.
I think semi-species are really fascinating: "Two species or not two species, that is the question!"
----Ken Kinman
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If telling two species apart seems like something a six year old could
do, consider ring species. In northern europe live two species of gull, the
herring gull and the lesser black-footed gull. They are clearly distinct in
appearance, and they do not interbreed. In North America, there is (for
the most part) only the herring gull. However, as you move across northern
North America across northern Siberia and into northern europe, you
encounter an almost continuous, interbreeding gradation from the herring
gull to the lesser black-footed gull. To someone explaining the gradational
changes and the difficulty in drawing species boundaries along the gull's
distritbution, one might scoff "I refuse to accept that I can't tell a
herring gull from a lesser black-footed gull" and be right...but still
missing the point.
Could you tell an ostritch from its ancestor 10,000 years ago? 50,000
years ago? 1 my? 1.5 my ago? If you moved back in time in 10,000 year
increments along the ostrich family tree back to its common ancestor with
me, and then moved forward in time in the same 10,000 year increments, you
would encounter a continuous series of pretty much indistinguishible,
interbreeding forms. If we want to ignore evolution doesn't exist and just
compare living ostriches and humans, then sure, distinguishing them looks
easy. However, if we want to look at the entire family history of of life,
and use a system of classification that looks at the entire history of life,
the divisions as we start moving up and down the branches start seeming
fairly arbitrary. Fortunately for taxonomy, most of the intermediates have
gone.


LNJ
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Outlawing drugs in order to solve the drug problem is much like outlawing
sex in order to win the war against AIDS.
-Ronald Siegal

No matter how far you have gone on the wrong road, turn back.
-Turkish proverb
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Jeffrey W. Martz
Graduate student, Department of Geosciences, Texas Tech University
3002 4th St., Apt. C26
Lubbock, TX 79415
(806) 747-7910
http://illustrations.homestead.com/Illustration.html
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