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| The Purpose of Names and Paraphyletic Clades | |
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| Tweet Topic Started: Oct 6 2013, 06:09 AM (1,931 Views) | |
| Ursus arctos | Oct 6 2013, 06:09 AM Post #1 |
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Autotrophic Organism
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The article Disguised Queries is great at making us think about the purpose of a name or label. Imagine that you have a peculiar job in a peculiar factory: Your task is to take objects from a mysterious conveyor belt, and sort the objects into two bins. When you first arrive, Susan the Senior Sorter explains to you that blue egg-shaped objects are called "bleggs" and go in the "blegg bin", while red cubes are called "rubes" and go in the "rube bin". Once you start working, you notice that bleggs and rubes differ in ways besides color and shape. Bleggs have fur on their surface, while rubes are smooth. Bleggs flex slightly to the touch; rubes are hard. Bleggs are opaque; the rube's surface slightly translucent. Soon after you begin working, you encounter a blegg shaded an unusually dark blue—in fact, on closer examination, the color proves to be purple, halfway between red and blue. Yet wait! Why are you calling this object a "blegg"? A "blegg" was originally defined as blue and egg-shaped—the qualification of blueness appears in the very name "blegg", in fact. This object is not blue. One of the necessary qualifications is missing; you should call this a "purple egg-shaped object", not a "blegg". But it so happens that, in addition to being purple and egg-shaped, the object is also furred, flexible, and opaque. So when you saw the object, you thought, "Oh, a strangely colored blegg." It certainly isn't a rube... right? Still, you aren't quite sure what to do next. So you call over Susan the Senior Sorter.
So now it seems we've discovered the heart and essence of bleggness: a blegg is an object that contains a nugget of vanadium ore. Surface characteristics, like blue color and furredness, do not determine whether an object is a blegg; surface characteristics only matter because they help you infer whether an object is a blegg, that is, whether the object contains vanadium. Containing vanadium is a necessary and sufficient definition: all bleggs contain vanadium and everything that contains vanadium is a blegg: "blegg" is just a shorthand way of saying "vanadium-containing object." Right? Not so fast, says Susan: Around 98% of bleggs contain vanadium, but 2% contain palladium instead. To be precise (Susan continues) around 98% of blue egg-shaped furred flexible opaque objects contain vanadium. For unusual bleggs, it may be a different percentage: 95% of purple bleggs contain vanadium, 92% of hard bleggs contain vanadium, etc. Now suppose you find a blue egg-shaped furred flexible opaque object, an ordinary blegg in every visible way, and just for kicks you take it to the sorting scanner, and the scanner says "palladium"—this is one of the rare 2%. Is it a blegg? At first you might answer that, since you intend to throw this object in the rube bin, you might as well call it a "rube". However, it turns out that almost all bleggs, if you switch off the lights, glow faintly in the dark; while almost all rubes do not glow in the dark. And the percentage of bleggs that glow in the dark is not significantly different for blue egg-shaped furred flexible opaque objects that contain palladium, instead of vanadium. Thus, if you want to guess whether the object glows like a blegg, or remains dark like a rube, you should guess that it glows like a blegg. So is the object really a blegg or a rube? On one hand, you'll throw the object in the rube bin no matter what else you learn. On the other hand, if there are any unknown characteristics of the object you need to infer, you'll infer them as if the object were a blegg, not a rube—group it into the similarity cluster of blue egg-shaped furred flexible opaque things, and not the similarity cluster of red cube-shaped smooth hard translucent things. The question "Is this object a blegg?" may stand in for different queries on different occasions. If it weren't standing in for some query, you'd have no reason to care. Is atheism a "religion"? Is transhumanism a "cult"? People who argue that atheism is a religion "because it states beliefs about God" are really trying to argue (I think) that the reasoning methods used in atheism are on a par with the reasoning methods used in religion, or that atheism is no safer than religion in terms of the probability of causally engendering violence, etc... What's really at stake is an atheist's claim of substantial difference and superiority relative to religion, which the religious person is trying to reject by denying the difference rather than the superiority(!) But that's not the a priori irrational part: The a priori irrational part is where, in the course of the argument, someone pulls out a dictionary and looks up the definition of "atheism" or "religion". (And yes, it's just as silly whether an atheist or religionist does it.) How could a dictionary possibly decide whether an empirical cluster of atheists is really substantially different from an empirical cluster of theologians? How can reality vary with the meaning of a word? The points in thingspace don't move around when we redraw a boundary. But people often don't realize that their argument about where to draw a definitional boundary, is really a dispute over whether to infer a characteristic shared by most things inside an empirical cluster... Hence the phrase, "disguised query". In the context of this forum- how useful then are the commonly used paraphyletic labels? A couple of glaring failures of course are in ancestry and genetics. However, such things as endothermy vs ectothermy, limb posture, or niche and associated adaptations ("panda") do often offer a sizable cluster of traits. |
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| Varanus | Oct 6 2013, 09:05 AM Post #2 |
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Autotrophic Organism
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Funny. I just learned this lesson. There will never be a perfectly objective classification system. We need to classify things, but nature doesn't. The only thing we can do is try to find the system that works best, and I guess you guys found it. |
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| coherentsheaf | Oct 6 2013, 10:46 AM Post #3 |
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Kleptoparasite
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Nitpick: "Paraphyletic clade" is an oxymoron. As for the questions how useful paraphyletic groups are: Most of them are completely useless in terms of achieving coherent categorization. One has to struggle to find useful ones and those are easily outgunned by categorization based on single characteristics, like "thunniform", or "ectotherm". In terms of communicating with ignorant people they have their uses. |
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| Ursus arctos | Oct 6 2013, 07:09 PM Post #4 |
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Autotrophic Organism
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I definitely disagree with their use for categorizing. On that note, I probably should have left "clade out" and stuck to examples like "panda". Perhaps a very loose example is "aquatic", which evokes the idea of a host of traits. Maybe I should move this thread to an area for less serious discussion? The question was possible usefulness of words to refer to groups of animals that together do not form a complete clade. How often I've seen "non-avian theropod" used suggests that there must be some use for such a word. |
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| coherentsheaf | Oct 6 2013, 07:20 PM Post #5 |
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Kleptoparasite
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Yes non avian theropod seems useful, as does prosauropod - saying nonsauropod sauropodomorph seems just tedious and these animals share a boatload of characteristics. On the other hand nonavian reptile/dinosaur often involves a lot of nonsense (In non avian theropods we see so many avian traits that they feel a lot closer to birds than to the rest of reptilia). In the end it is just like in life: Words that are useful will be used often and we should discourage words that might be useful but at the same time are confusing and hinder progress. Example: I am sure that traditional notions of the word reptile were responsible for us not recognizing similarities between the respiratory system of birds and gators until 2012. |
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| SpinoInWonderland | Oct 6 2013, 10:32 PM Post #6 |
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The madness has come back...
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Paraphyletic clades? I think paraphyletic labels are useful, having to say "non-therapsid synapsid" takes more time and energy than saying "pelycosaur", which doesn't take longer to write or speak and has the same meaning. It's okay to use paraphyletic labels, as long as you do not start getting them mixed up with clades. |
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| SpinoInWonderland | Oct 6 2013, 10:39 PM Post #7 |
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The madness has come back...
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You can use "stem-avians" then, like how the non-mammalian synapsids are called "stem-mammals" |
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| theropod | Oct 6 2013, 11:42 PM Post #8 |
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palaeontology, open source and survival enthusiast
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Yes, paraphyletic GRADES are sometimes just practical. I still haven't adapted to saying "I wanna eat an actinopterygian today" whenever I want to eat fish. They become a problem when they are used in a scientific context eg. to argue some point holding true for certain animals or to pronounce arbitrarily drawin lines between animals. On a much (MUCH MUCH) smaller scale we still have this problem with genera and species, however they are necessary at the moment and their definitions work reasonably well as opposed to taxa of various ranks. |
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| maker | Feb 19 2015, 07:08 PM Post #9 |
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Apex Predator
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Can this be moved to Zoological Debate & Discussion? Birds and mammals should be considered reptiles: Whales should be considered even-toed ungulates: By Michelle Spaulding, Maureen A. O'Leary, John Gatesy [CC BY 2.5 (http://creativecommons.org/licenses/by/2.5)], via Wikimedia Commons And apes considered old world monkeys and humans apes. Edited by maker, Mar 12 2015, 07:10 AM.
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| Mesopredator | Feb 19 2015, 10:14 PM Post #10 |
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Disaster taxa
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Interesting discussion. I feel my knowledge on this subject is lacking and so I do not understand everything. With food there is a similar thing going on. Peanuts are not nuts but legumes, but are considered in cuisine to be nuts. Etc.
Or. We forget about reptiles and start to call chelonia turtles, lepidosauria [word for lizards + snakes], crocodylia crocodiles. In folk biology reptiles are however unlikely to disappear. Or is this not the issue dude? |
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| Jinfengopteryx | Feb 20 2015, 06:55 PM Post #11 |
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Aspiring paleontologist, science enthusiast and armchair speculative fiction/evolution writer
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Amniota is not synonymous with Reptilia. There is a monophyletic Reptilia clade that doesn't include mammals. |
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| maker | Mar 12 2015, 07:10 AM Post #12 |
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Apex Predator
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Maybe not mammals, but definitely birds, if birds are not reptiles, crocodilians are not reptiles. Paraphyly is simply not good science. Edited by maker, Mar 16 2015, 05:14 PM.
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