In phylogenetics, a grouping of organisms is said to be paraphyletic (Greek language ''para'' = near and ''phyle'' = race) if all the members of the group have a common ancestor, but the group does not include all the descendants of the most recent common ancestor of all group members. Groups which include all the descendants of the most recent common ancestor are commonly termed monophyletic or holophyletic. The former is more common, but sometimes paraphyletic groups are also considered monophyletic, in which case the latter is used. A paraphyletic group can be fixed by expanding it, and including other clades. A class which is descended from more than one root form is called ''polyphyletic''. Many of the older classifications contain paraphyletic groups, especially the traditional 2-6 kingdom (biology) systems and the classic division of the vertebrates. For example, the class reptile as traditionally defined is paraphyletic because that class does not include two groups of its descendants, birds (in class Aves, birds), and mammals (in class Mammalia). Paraphyletic groups are often erected on the basis of plesiomorphies (ancestral similarities) instead of upon apomorphies (derived similarities). In most cladistics-based schools of taxonomy, the existence of paraphyletic groups in a classification are regarded as errors. Some groups in currently accepted taxonomies may later turn out to be paraphyletic, in which case the classifications may be revised to eliminate them. Some, however, feel that having paraphyletic groups is an acceptable sacrifice if it makes the taxonomy more understandable. Others argue that paraphyletic groups are necessary to have a comprehensive classification including extinct groups, since each species, genus, and so forth necessarily originates from part of another. It has been suggested that paraphyletic groups should be allowed but clearly marked as such, for instance in the form Reptilia*. The term paraphyletic is also used in historical linguistics, with similar meaning. For example, centum and satem are paraphyletic groups of Indo-European languages. == References == * Phylogenetics
''In biological taxonomy, a grouping of organisms is said to be paraphyletic if it does not represent all the descendants of some common ancestor. Most schools of taxonomy advocate that groups reflect phylogeny instead, and so view the existence of paraphyletic groups in a classification as errors. Taxonomic groups that do share a common ancestor are called monophyletic.'' :I'm a little confused here. The last sentence seems to indicate monophyletic means "all share a common ancestor", but the first sentence seems to indicate that paraphyletic means "does not provide complete coverage of the set of all descendants of some common ancestor". Is the first sentence instead intended to mean "contains members which may not all share the same set of ancestors"? User:Chas zzz brown 11:21 Dec 6, 2002 (UTC) :Thanks for the clarification, Steve User:Chas zzz brown 07:51 Feb 12, 2003 (UTC) ---- ''This does not necessarily mean that older biologists meant to create them; more often it was just that they needed to have some taxonomy in order to organize the huge number of species in a way they could understand, and without modern scientific evidence, guesswork was required that later turned out to be wrong.'' I don't think this is true. Older taxonomies in many cases contain groups which are obviously ''intended'' to be paraphyletic. For instance, it has long been understood that mammals and birds evolved from reptiles (making the reptiles paraphyletic), but only recently has the class Reptilia been objected to on these grounds. :I really did not like that paragraph but wondered how best to change it. The most charitable interpretation of it seems to be at the genus level, where many paraphyletic genera have been erected because of they have been classified by overall similarity, which necessarily includes plesiomorphies, rather than by recognizing apomorphies by a cladistic analysis. ---- ''In phylogenetics, a grouping of organisms is said to be paraphyletic if all the members of the group have a common ancestor but the group does not include all the descendants of the common ancestor.'' This is a tautology, any group of organisms is vacuously paraphyletic as defined here (let A be a common ancestor, let B be a parent of A, and let C be a sibling of A sharing parent B. Then C is not in the group, but it is the descendent of a common ancestor of the group, namely B). It should probably read "In phylogenetics, a grouping of organisms is said to be paraphyletic if the group does not include all of the descendents of the most recent common ancestor of all the members." I would change the page but I don't want to introduce an error, in case this isn't what the author intended to say. --User:A5 00:25, 26 Mar 2004 (UTC) ---- Another confused reader here... what does this mean? :''Groups which include all the descendants of a common ancestor are commonly termed monophyletic, although this term is sometimes taken to apply to paraphyletic groups as well, in which case they are called holophyletic.'' The primary culprit is the unclear "they", but the whole sentence is as clear as mud. Should probably be broken into two carefully worded sentences. Perhaps it would be better to have three parallel definitions: paraphyletic, monophyletic, holophyletic, to make it clearer exactly how they're used and what the distinctions are. I'm not a science dunce, I promise! This just needs refining. User:CatherineMunro\User_talk:CatherineMunro ">User:CatherineMunro|User:CatherineMunro\User_talk:CatherineMunro 07:06, 28 Nov 2004 (UTC)
----
User:A5 is exactly right, the definition as it was made no sense:
:''In phylogenetics, a grouping of organisms is said to be paraphyletic if all the members of the group have a common ancestor but the group does not include all the descendants of the common ancestor.''
To see why this makes no sense, consider this: some amphibian is a common ancestor for all members of Mammalia. Yet all reptiles are also descendants of this same amphibian, and therefore by this definition Mammalia is paraphyletic.
You can generalize the conclusion to any group, which shows the definition is obviously broken.
I'm not a biologist, but I would rather leave a definition that I believe to be correct than one I know to be wrong. (You know, Wikipedia:Be bold). So I've made the change, feel free to comment. --User:Saforrest 00:35, Jan 28, 2005 (UTC)
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In phylogenetics, a grouping of organisms is said to be paraphyletic (Greek language ''para'' = near and ''phyle'' = race) if all the members of the group have a common ancestor, but the group does not include all the descendants of the most recent common ancestor of all group members. Groups which include all the descendants of the most recent common ancestor are commonly termed monophyletic or holophyletic. The former is more common, but sometimes paraphyletic groups are also considered monophyletic, in which case the latter is used. A paraphyletic group can be fixed by expanding it, and including other clades. A class which is descended from more than one root form is called ''polyphyletic''. Many of the older classifications contain paraphyletic groups, especially the traditional 2-6 kingdom (biology) systems and the classic division of the vertebrates. For example, the class reptile as traditionally defined is paraphyletic because that class does not include two groups of its descendants, birds (in class Aves, birds), and mammals (in class Mammalia). Paraphyletic groups are often erected on the basis of plesiomorphies (ancestral similarities) instead of upon apomorphies (derived similarities). In most cladistics-based schools of taxonomy, the existence of paraphyletic groups in a classification are regarded as errors. Some groups in currently accepted taxonomies may later turn out to be paraphyletic, in which case the classifications may be revised to eliminate them. Some, however, feel that having paraphyletic groups is an acceptable sacrifice if it makes the taxonomy more understandable. Others argue that paraphyletic groups are necessary to have a comprehensive classification including extinct groups, since each species, genus, and so forth necessarily originates from part of another. It has been suggested that paraphyletic groups should be allowed but clearly marked as such, for instance in the form Reptilia*. The term paraphyletic is also used in historical linguistics, with similar meaning. For example, centum and satem are paraphyletic groups of Indo-European languages. == References == * Phylogenetics
Paraphyletic
''In biological taxonomy, a grouping of organisms is said to be paraphyletic if it does not represent all the descendants of some common ancestor. Most schools of taxonomy advocate that groups reflect phylogeny instead, and so view the existence of paraphyletic groups in a classification as errors. Taxonomic groups that do share a common ancestor are called monophyletic.'' :I'm a little confused here. The last sentence seems to indicate monophyletic means "all share a common ancestor", but the first sentence seems to indicate that paraphyletic means "does not provide complete coverage of the set of all descendants of some common ancestor". Is the first sentence instead intended to mean "contains members which may not all share the same set of ancestors"? User:Chas zzz brown 11:21 Dec 6, 2002 (UTC) :Thanks for the clarification, Steve User:Chas zzz brown 07:51 Feb 12, 2003 (UTC) ---- ''This does not necessarily mean that older biologists meant to create them; more often it was just that they needed to have some taxonomy in order to organize the huge number of species in a way they could understand, and without modern scientific evidence, guesswork was required that later turned out to be wrong.'' I don't think this is true. Older taxonomies in many cases contain groups which are obviously ''intended'' to be paraphyletic. For instance, it has long been understood that mammals and birds evolved from reptiles (making the reptiles paraphyletic), but only recently has the class Reptilia been objected to on these grounds. :I really did not like that paragraph but wondered how best to change it. The most charitable interpretation of it seems to be at the genus level, where many paraphyletic genera have been erected because of they have been classified by overall similarity, which necessarily includes plesiomorphies, rather than by recognizing apomorphies by a cladistic analysis. ---- ''In phylogenetics, a grouping of organisms is said to be paraphyletic if all the members of the group have a common ancestor but the group does not include all the descendants of the common ancestor.'' This is a tautology, any group of organisms is vacuously paraphyletic as defined here (let A be a common ancestor, let B be a parent of A, and let C be a sibling of A sharing parent B. Then C is not in the group, but it is the descendent of a common ancestor of the group, namely B). It should probably read "In phylogenetics, a grouping of organisms is said to be paraphyletic if the group does not include all of the descendents of the most recent common ancestor of all the members." I would change the page but I don't want to introduce an error, in case this isn't what the author intended to say. --User:A5 00:25, 26 Mar 2004 (UTC) ---- Another confused reader here... what does this mean? :''Groups which include all the descendants of a common ancestor are commonly termed monophyletic, although this term is sometimes taken to apply to paraphyletic groups as well, in which case they are called holophyletic.'' The primary culprit is the unclear "they", but the whole sentence is as clear as mud. Should probably be broken into two carefully worded sentences. Perhaps it would be better to have three parallel definitions: paraphyletic, monophyletic, holophyletic, to make it clearer exactly how they're used and what the distinctions are. I'm not a science dunce, I promise! This just needs refining. User:CatherineMunro\
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