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Member (Idle past 1724 days) Posts: 20714 From: the other end of the sidewalk Joined: |
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Author | Topic: Definition of Species | |||||||||||||||||||||||||||
penstemo Junior Member (Idle past 5524 days) Posts: 13 From: Indiana, USA Joined: |
Link to ICZN:
International Commission on Zoological Nomenclature Link to ICBN: International Code of Nomenclature for algae, fungi, and plants - Wikipedia I'm not sure how cladistics is going to bear on taxonomy. That's something that I haven't done much research on. DNA testing is the way of the future, I believe, for both plants and animals.
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penstemo Junior Member (Idle past 5524 days) Posts: 13 From: Indiana, USA Joined: |
From a brief read here:
Taxon - Wikipedia I don't believe cladistics is going to have much effect at the species level and the next two higher taxonomic ranks- genus and family. But at the higher levels of class, phylum etc. it probably will be important. Field botanists like myself work at the lower levels- species, genus, and family- and leave the higher levels to the so-called experts who often disagree. That's why I think DNA testing will be important in sorting out some, if not all, taxonomic problems. Edited by penstemo, : No reason given.
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penstemo Junior Member (Idle past 5524 days) Posts: 13 From: Indiana, USA Joined: |
Some clarification why I don't think cladistics is going to have much effect on lower taxonomic levels. Plants in a single genus usually have a close phylogenetic relationship, i. e. they evolved from a common ancestor. Plants in a single family usually have a close phylogenetic relationship, i. e. they evolved from a common ancestor. So it seems to me that this is consistent with cladistics.
I offer the following quote from Wikipedia in support of the above statements. (Cladistics - Wikipedia)
Since the early 20th century, Linnaean taxonomists have generally attempted to make at least family- and lower-level taxa (i.e. those regulated by the codes of nomenclature) monophyletic. A monophyletic group is one which evolved from a common ancestor. Thus we see that under the Linnaean system of taxonomy a basis for a cladistic interpretation is in place at the lower taxonomic levels, although there are probably some exceptions. Despite the growing popularity of cladistics, the traditional Linnaeansystem is not likely to be replaced in the near future. More info here: PhyloCode - Wikipedia Edited by penstemo, : More info added Edited by penstemo, : Added more info
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Dr Jack Member Posts: 3514 From: Immigrant in the land of Deutsch Joined: |
Despite the growing popularity of cladistics, the traditional Linnaean system is not likely to be replaced in the near future. I disagree. There are already university's that teach Linnaean classification only as a historical interest. Plus pretty much all recently published classifications use cladistic approaches. At the Genus-species level, it'll continue, above that it's already broken down. A fixed number of named ranks simply doesn't make sense.
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herebedragons Member (Idle past 1177 days) Posts: 1517 From: Michigan Joined: |
Hi Razd - I have finally been able to spend some time on this and post a response. I also found several other threads on similar subjects and have read through them. So here are my thoughts, observations, ponderings, questions, etc.:
First of all, I see defining a species is very subjective and difficult to nail down precisely, since there is no one "perfect" rule to apply. It seems to me that it is important define species accurately and with a fair amount of precision. Someone commented that species is the only thing that matters in an ecosystem, but a deeper, more accurate understanding of species and what makes them different would help us understand how life has developed and why.
{ramble} Wouldn't it be easier to use genetics to define a species similar to the morphological definition, as "a population of individual organisms with 99% identical DNA" for instance? What about: "a species is a population of individual organisms with similar hereditary traits in common, separated from other species by different hereditary traits and biological barriers preventing breeding." In both cases it comes down to how much needs to be the same and how much needs to be different to differentiate one species from another. {/ramble} I wasn't sure what you were meaning by this (the {ramble} part made it confusing what your intention was), but yeah, maybe in some ways it would be more accurate to classify organisms that way, although the amount of work involved would certainly not make it "easier". And, as you pointed out, it still comes down to subjectivity - "how much needs to be the same and how much needs to be different?"
We also see with horses, donkeys and zebras, that there is a genetic barrier to hyridization that has occurred since they separated from a common ancestor, one that results in infertile or poorly fertile offspring that most ofted die without reproducing, thus demonstrating genetic reproductive isolation being acquired.
That is similar to the genetic species concept in Message 1, using one specific gene. I think I'd want to do some kind of cladistic analysis of more units, perhaps at a chromosome level, and then focus on the one showing the most difference to provide the cutoff information. This would have to be done first for species that are closely related but just not breeding compatible -- horses/zebra/donkey and whitetail/mule deer -- to see what a genetic level of difference was necessary. This hasn't been done? Kinda surprising that it hasn't. Obviously, the fossil record becomes even more imprecise and speculative and subject to error.
Part of the problem is the degree of dis-similarity that can occur in a species, whether you are a lumper or a splitter, and how good the evidence. Add the ego-boost of being able to describe a new species fossil for the first time, and you can see that defining species for fossils can be a problem.
Not that this is definitively wrong, we need to be able to categorize them in some way - in the best way we know how. But there are just too many unknowns in the fossil record to be certain that species are categorized correctly. For example, the marsupial flying squirrel and the placental squirrel example you gave me. If fossils were found of these animals they would most likely be considered very similar animals. Like wise the Tasmanian wolf and common grey wolf would be thought to be very close cousins. However, we know they are very different animals. Similarly, if fossils for a Saint Bernard and a Chihuahua were found they would certainly be classified as quite unrelated, however we know them to be of the same species. (maybe Saint Bernard and Chihuahua aren't great examples because I can't imagine them actually breeding in the wild - or in captivity for that matter ![]() Secondly, I realized that I was actually trying to define "kind" and I now see that it is just not that simple. Our observations in nature don't seem to match up to any idea of a kind. But I am thinking it is important how we classify organisms. I see you are a fan of cladistic classification. Doesn't this system assume common ancestry? What I mean is you may have sufficient evidence that a horse and a zebra have a common ancestor, but is there that degree of certainty for all known species. Where would you put species that were uncertain? Would they be left out or placed in an approximate or assumed clade? Would it be noted that they were uncertain until sufficient evidence was presented? I do need to have a better understanding of cladistics, so I'm not drawing conclusions, just questioning. A newer system of classification I found some information on is Baraminology. You probably have already looked at it and drawn your own conclusions but here is the link: What are the Genesis kinds? - ChristianAnswers.Net It is a system of classification that some are trying to develop. It is highly criticized and considered to be junk science. But, all the criticism I read was in regard to their conclusions and starting assumptions not the actual data or the "science" they were doing. This is a very new line of research and I would think it should be given a chance, unless there are fundamental flaws in how they do the research. This quote:
quote: The page you were looking for doesn't exist (404) gives some degree of confidence that they are willing to base their conclusions on the data and not pre-conceived notions (whether they do what they say is another matter). You could say that they believe in creation is a pre-conceived notion. But I would also include that I feel evolutionists base their conclusions on the fact that they believe evolution to be true. Its all a matter of perspective - but, I guess that's a discussion for another thread. Their research has confirmed equid fossil series is a legitimate example of species evolution. This is a series that creationists have long been critical of. They have also verified the evolution of the subtribe Flaveriinae. The problem is that he interprets both cases as post-flood diversification. So not only did he say the "f" word, but the biblically implied <6000 Woods:
quote: A mechanism for Darwin's theories was not known for what, 50 years after his publication of Origin of Species, when DNA was discovered. Yet his theories weren't arbitrarily thrown out. So, could you give me a brief overview of your opinion of Baraminology and an idea of where I can find some objective information on the subject? One problem with the debate between creation and evolution is it is so polarizing. There just doesn't seem to be a neutral side. It's one or the other. Anyway, I think it is good and beneficial to our understanding of life that we are exploring different ways of classifying and identifying organisms. With our ever increasing understanding of how complex and interconnected life is, we need better and more accurate ways to identify, at the very basic level, species.
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Dr Jack Member Posts: 3514 From: Immigrant in the land of Deutsch Joined: |
But there are just too many unknowns in the fossil record to be certain that species are categorized correctly. For example, the marsupial flying squirrel and the placental squirrel example you gave me. If fossils were found of these animals they would most likely be considered very similar animals. Like wise the Tasmanian wolf and common grey wolf would be thought to be very close cousins. However, we know they are very different animals. This is completely untrue. Any trained palaeontologist could easily distinguish a marsupial from a placental mammal because they don't look at crude morphology but at much more taxonomically useful features such as the structure of bones in the skull and the teeth.
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herebedragons Member (Idle past 1177 days) Posts: 1517 From: Michigan Joined: |
Yes, Mr.Jack, I am sure they could and I certainly didn't mean to imply that a trained palaeontologist couldn't do their job. But those particular examples are modern specimens and I wasn't meaning that we find modern specimens that we know what the differences in structures should be. I was using it as an example of the information that is missing from the fossil record. Scientists regularly debate as to how to classify a fossil specimen and often ultimately disagree. It is not easy to classify fossils for the very reason I cited - missing information. But your point about not just looking a crude morphology was well taken.
Thanks Edited by herebedragons, : No reason given.
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herebedragons Member (Idle past 1177 days) Posts: 1517 From: Michigan Joined: |
Mr. Jack, I have some more evidence to support my statement.
quote: http://www.macroevolution.net/marsupials.html Again, my primary point was the difficulty of categorizing extint fossil specimens accurately. So, clearly, there is a large amount of uncertainty in the fossil record. Thanks
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Dr Jack Member Posts: 3514 From: Immigrant in the land of Deutsch Joined: |
Please use credible sources as opposed to crank websites.
I particular like the way your source neatly elides the difference between "few" and none, and the differences common to all marsupials and features that can be used to distinguish marsupials - that quality quote mining.
Again, my primary point was the difficulty of categorizing extint fossil specimens accurately. So, clearly, there is a large amount of uncertainty in the fossil record. Yes, there's a large amount of uncertainty in the fossil record, but let's not exagerate the kind of uncertainty or the nature of that uncertainty.
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Blue Jay Member (Idle past 3017 days) Posts: 2843 From: You couldn't pronounce it with your mouthparts Joined: |
Hi, Herebedragons.
I don't think I ever welcomed you to EvC. So, welcome to EvC! It's good to read true open-mindedness for a change!
HBD writes: First of all, I see defining a species is very subjective and difficult to nail down precisely, since there is no one "perfect" rule to apply. On this, I agree. There is a fair amount of subjectivity involved in biological classification, no matter which system you use. -----
HBD writes: It seems to me that it is important define species accurately and with a fair amount of precision. On this, my agreement is not so strong. As an entomologist, it irritates me to no end that many people with advanced degrees in entomology do not know how to distinguish families or even orders of insects from one another, and I am a strong proponent of requiring insect taxonomy for all aspiring entomologists. However, as an ecologist, I also do not deal directly with taxonomy on a frequent basis, beyond identifying small arthropods under a microscope. In ecology, the only purpose in classifying organisms is the organization of biological information so that we can generate predictions that help in testing our hypotheses. In the end, classification only needs to be precise enough that we can predict which groups of organisms can serve as models for our predictions about the behavior and function of other organisms, and so we can predict which hypotheses apply to which organisms. Within phylogenetics, the point of classification is to uncover the history and principles of the evolution of life. But, all biologists acknowledge that this is not really a means of objectively delineating the boundaries between species or other organisms. Quite the contrary, in fact: if phylogenetics has taught us anything, it is that such boundaries simply do not exist. That is why our attempts to classify are inevitably saturated with subjectivity: because the entire concept of categorization is itself subjective, and does not actually represent the reality of the situation. -----
HBD writes: A newer system of classification I found some information on is Baraminology. Baraminology is actually just a new name for the oldest system of classification that exists. The concept is essentially identical to the concept used by Linnaeus: it groups things according to patterns in morphology, then groups those groups according to coarser patterns. The only difference is that baraminology asserts that there will eventually be found a point beyond which groups cannot be combined together into larger groups, and the primary thrust of baraminology is to identify these points of distinction. My complaint with this field of study is that valid, empirical reasons for suspecting the existence of such breaks have never been presented, and so, the entire field of baraminology can be summarily defined as the search for something that we have no reason to suspect even exists. As a lifelong Christian, I would be very interested if such data were uncovered, but I cannot honestly characterize the basis of the field of baraminology as anything greater than wishful thinking, so I am required by my personal sense of integrity to reject it as a legitimate academic pursuit. Maybe the future will change my mind, I'm not sure, but my skepticism for that is currently very high. -Bluejay (a.k.a. Mantis, Thylacosmilus) Darwin loves you.
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herebedragons Member (Idle past 1177 days) Posts: 1517 From: Michigan Joined: |
Belief that the term species and other taxonomic categories represent real distinctions in nature and not just subjective divisions for human convenience is difficult to pin down and defend with any certainty.
quote:SIUC University Carbondale Although the most popular and widely excepted definition seems to be the Biological species concept,
This concept states that "a species is a group of actually or potentially interbreeding individuals who are reproductively isolated from other such groups." but both speciation and reproductive isolation remain problematic issues. "Reproductive isolation", widely considered an essential ingredient in defining the word species, is itself vaguely and inconsistently defined. Exactly when does reproductive isolation occur? what are the actual mechanisms that bring it about? is geographic isolation enough to develop reproductive isolation? what does potentially interbreeding individuals actually mean? etc. Truly reproductive isolation is quite ill defined.
quote:Then throw into the mix hybridization. If you fail to observe interbreeding in a given case, is it safe to assume there no members of the population that do not interbreed? It is possible that interbreeding does occur at some place other than what has been observed or that it may occur at some other time? There are numerous cases of forms that are treated as separate species and were not previously known to hybridize but are now know to do so. Some examples here:http://www.macroevolution.net/reproductive-isolation.html The author gave an analogy that I think clearly illustrates the problem and also the problem of presupposing or historically considering a form to be a separate species despite there ability to interbreed as are the Spanish sparrow (P. hispaniolensis) and the house sparrow [P. domesticus].
quote:It seems to me the concept of species is very illusive and there is no one size fits all approach. In addition, I’m not sure it has any value in the real world other than for our convenience in discussing different animals. IOW when I say ‘zebra’ you know I am talking about an animal that lives in Africa and has black and white stripes and when I say ‘horse’ you know I am talking about a domesticated animal that is primarily used for human recreation. Whether they are clearly distinct species may be irrelevant. The problem with a statement like that, from an evolutionist’s point of view, is that if a species distinction is irrelevant, that kinda makes speciation irrelevant too, since after speciation occurs the results would be irrelevant. penstemo writes: DNA testing is the way of the future, I believe, for both plants and animals. I have been doing some reading about DNA sequence analysis and feel there is a lot of promise to resolve some of these problems and give us a clearer picture of lineage and thus history, but I have a feeling evolutionists (specifically gradualists) and creationists alike are going to be disturbed by the results. Any other input on DNA sequencing would be helpful as I know very little about the terminology or theory behind it. Good Day All
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Coyote Member (Idle past 2425 days) Posts: 6117 Joined: |
Baraminology is actually just a new name for the oldest system of classification that exists. The concept is essentially identical to the concept used by Linnaeus: it groups things according to patterns in morphology, then groups those groups according to coarser patterns.
Actually baraminology seeks to justify the biblical concept of kinds, and to make it sound scientific at the same time. The only difference is that baraminology asserts that there will eventually be found a point beyond which groups cannot be combined together into larger groups, and the primary thrust of baraminology is to identify these points of distinction. It is not a field of research because no conclusions can be arrived at other than those specified in scripture. It is pure religious apologetics. An example: From "Baraminology—Classification of Created Organisms," by Wayne Frair, which appeared in the Creation Research Society Quarterly Journal, Vol. 37, No. 2, pp. 82-91 (2000), and which appears on the christiananswers.net website.
quote: Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.
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herebedragons Member (Idle past 1177 days) Posts: 1517 From: Michigan Joined: |
Please use credible sources as opposed to crank websites. I particular like the way your source neatly elides the difference between "few" and none, and the differences common to all marsupials and features that can be used to distinguish marsupials - that quality quote mining. My apologies, Mr. Jack, but what consitutes a "credible" source as opposed to a "crank website"? I am avoiding "creationist" sites as they are "crank" or "bogus". But this was not a creationist site. I don't believe I quoted anything out of context. I did edit some content because I felt it was unnecessary to the discussion and sorta lengthy. So I don't see how I am guilty of quote mining. I looked over the entire site, and the author appeared to be credible, at least as credible as I could determine. So what is a "credible" source? Does it have to agree with popular or prevalent ideas? I will concede the point regarding distinguishing marsupials, as it is actually irrelevant to the disscussion, but would like clarification on "credible". I am trying to be a responsible and thoughtful part of this forum and don't feel that I am just spouting nonsense that is "cut and pasted from creationist propaganda". Thanks
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herebedragons Member (Idle past 1177 days) Posts: 1517 From: Michigan Joined: |
It is not a field of research because no conclusions can be arrived at other than those specified in scripture. It is pure religious apologetics.
Thanks Coyote, but thats the criticsm I've already heard. I don't think scripture puts a huge "restaint" on the research though as there are very few "types" actually described. That man is a seperate "type" seems to be the most problamatic for evolutionists. I was hoping there would be something a bit more condemning, like "they don't wear gloves when they handle evidence." lol ![]() The scripture only sets the outer boundaries, not the entire realm of possible conclusions they could arrive at. So I'm not sure it's fair to say "no conclusions" because scripture really doesn't draw too many conclusions on it's own. For instance, the horse evolution series and the subtribe Flaveriinae both confirmed evolution. I'm sure many a creationist will be uneasy about those conclusions. Creationists are constantly being asked to define what a "kind" is. I personally am not sure it is really necessary or practical or maybe even possible, but if a group of creationists are attempting to come up with a definition, maybe their work should be based on the data, not on the fact they are trying to define "kind". Thanks
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Coyote Member (Idle past 2425 days) Posts: 6117 Joined: |
Creationists are constantly being asked to define what a "kind" is. I personally am not sure it is really necessary or practical or maybe even possible, but if a group of creationists are attempting to come up with a definition, maybe their work should be based on the data, not on the fact they are trying to define "kind".
If creationists are trying to define "kind" they first need to determine whether they are trying to arrive at a scientific definition or one that must agree with scripture above all. If it is the latter case, then they are doing religious apologetics, not science. They can only claim to be doing science if they follow the scientific method and accept the results, whether or not those results agree with scripture. The method determines which of these two fields of endeavor is being practiced. When one is required to conform to scripture one is doing religious apologetics--the exact opposite of science. Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.
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