Talk:Paraphyly

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[edit] Unclear text

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"? Chas zzz brown 11:21 Dec 6, 2002 (UTC)
Thanks for the clarification, Steve 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. --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|Catherine\talk]] 07:06, 28 Nov 2004 (UTC)

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, Be bold). So I've made the change, feel free to comment. --Saforrest 00:35, Jan 28, 2005 (UTC)

the class Reptilia as traditionally defined is paraphyletic because that class does not include birds (class Aves), which are descended from reptiles.

This is not a good example since birds almost certainly came from warm-blooded dinosaurs, not reptiles. I haven’t changed it because a better example should be substituted. But someone should. David Shear, Oct 14, 2005.

Two points to this; classic Reptilia includes dinosaurs; how to reorganise the major subdivisions of Amniota is not something there is a clear agreement on, but promoting Dinosauria to the same level as Reptilia, Aves and Mammalia is not the only possibility. Second point, how about using apes as the example? - humans are descended from apes but not included amongst them. Of course, this could be on the creationist-avoidance principle Richard Gadsden 00:41, 23 September 2006 (UTC)

[edit] Paraphyly in linguistics?

I have removed the paragraph "The term paraphyletic is also used in historical linguistics, with similar meaning. For example, there are scholars who believe that centum and satem are paraphyletic groups of Indo-European languages". It is so because these terms are not believed (by some linguists) to be paraphyletic but polyphyletic rather. See Talk:Indo-European languages for details. --Grzegorj 16:55, 23 August 2005 (UTC)

The term is used in several Wiki articles on various languages, however.17:51, 29 November 2007 (UTC) —Preceding unsigned comment added by Adresia (talk • contribs)

[edit] Classification Logic

I'm quite curious: if one has to strictly apply the paraphyletic rule to name groups, there would logically be but one group, that is the group of the first species originated on Earth: such a group, containing the single species from which all others have originated, must contain all such species. So where is the limit really put? It's not really discussed in the article... Gbnogkfs 25 May 2006, 21:34 (UTC)

Could you be a little bit more specific? What is the paraphyletic rule? I know but one: do not include groups proven to be paraphyletic in the classification. Alexei Kouprianov 10:36, 26 May 2006 (UTC)
You say it's better not to include paraphyletic groups in classification. The problem is that you can't apply this rule to every group, except if you want to create only one group, which is of course against the scope of a classification in the first place.
To make an example: let's consider the Mammal and Reptile classes. Let's consider the most recent ancestor to all mammal and reptiles: in which class would you include it? If you put it in the Mammal class, then the mammal class is paraphyletic; if you put it in the Reptile class, then the reptile class is paraphyletic; if you put it in a third class, then that class is paraphyletic.
The result is that if you want to create only non-paraphyletic groups, you are forced to put mammals, reptiles and their common ancestor into the same class.
Eventually, repeating this process, all the living beings have to be put in the same class.
There is common agreement even among anti-paraphyleticists on the existance of more than one class: where do you put a limit in the refusal of paraphyletic groups? Gbnogkfs 26 May 2006, 22:18 (UTC)
No, you've got it all wrong. Just as the authors of the Wiki-article. The taxa do not include ancestors. Even the monophyletic ones. They include all (in case they are monophyletic) or some (in case they are non-monophyletic, i.e. para- and polyphyletic) terminal taxa (indivisible units of the analysis) believed to be descendants of the hypothetical most recent common ancestor. This comes from a logical premise that only sister-group relationships (and not the ancestor-descendant relationships) can be proven. Note, please, that I am just repeating an argument from the thirty-year old debates. It is all in the 1970--1980s. No matter for a discussion on this point any longer. Alexei Kouprianov 22:25, 26 May 2006 (UTC)
I can't really get the whole of your answer, but then if the article is wrong, why doesn't anybody amend it? Gbnogkfs 26 May 2006, 23:33 (UTC)
Well, I just did. I am sorry I was too technical (I was trained as a taxonomist). I hope that my reformulation of the article makes this less esoteric. Alexei Kouprianov 10:44, 27 May 2006 (UTC)
So taxa are used only for "clades", with the exclusion of common ancestors: that is, for exemple, that the most common ancestor of Mammalia and Reptilia (and all of the ancestors of this last, in fact) is not included in any class (while being, for exemple, a member of the chordates). That's interesting: it was not clear at all! Gbnogkfs 27 may 2006, 12:43 (UTC)
That's even more interesting. None of the still existing or fossil species could be unambiguously identified in principle as the most recent common ancestor of mammals, reptiles, mammals+reptiles, as well as of any other group. Hence, there is no real problem of classifying the ancestor. The real ancestor when discovered could pose a major problem, but no one is able to prove that this or that particular fossil really is the ancestor. The logically correct way to deal with fossils is to regard them as sisters (not mothers) of other fossil or recent groups. Alexei Kouprianov 13:57, 27 May 2006 (UTC)


Indeed: a very sperimental approach. Thanks for the biology lessons :) Gbnogkfs 27 may 2006, 20:42 (UTC)


[edit] Definition re-broken

I happened upon this page again and saw that the definition had been re-broken since User:Saforrest's fix long ago (and other intervening fixes by other users). It said: "In phylogenetics, a group of organisms is said to be paraphyletic (Greek para = near and phyle = race) if the organisms have the same common ancestor, and the group does not contain all the descendants of this ancestor." I changed it to: "In phylogenetics, a group of organisms is said to be paraphyletic (Greek para = near and phyle = race) if the group contains its most recent common ancestor, but does not contain all the descendants of that ancestor." The definition was most recently broken by User:Pgan002. Please take care when rewording the definition. Roughly, all organisms on Earth have a common ancestor, and no non-trivial group of organisms contains all of the descendants of this ancestor. I also fixed the reference to Polyphyly. A5 16:17, 19 August 2006 (UTC)

[edit] Logical Inconsistencies

It was shown, however, that the inclusion of ancestors in the classification leads to unavoidable logical inconsistencies

Alexei, you would have to concede that the above statement is a matter of debate even today. I think the article should be edited to highlight some of the aspects of the differing approaches. Ordinary Person 13:13, 30 November 2006 (UTC)

Well, I said everything I could in my posts from May 27. If one can prove that exactly this or that fossil bone is the actual ancestor of some recent group it's fine with me. I only doubt it is in principle possible. As soon as we include ancestors in the scheme, some taxa turn to be inherently paraphyletic. If the whole scheme was invented to avoid paraphyly, why let it back in? Alexei Kouprianov 14:14, 30 November 2006 (UTC)

That's a reasonable point. I wonder if some of this discussion can be worked into the article without dewikifying it. Ordinary Person 15:02, 30 November 2006 (UTC)

Well, it was. The problem is that the definition in the very first paragraph of the article is not under my full control. I am mostly active in Russian Wiki and I come here from time to time just to make few corrections here and there. Meanwhile someone usually replaces a more theoretically rigorous but somewhat obscure definition with something more agreeable from the common sense perspective. The situation is getting more complicated because an average zoologist or botanist usualy does not pay attention to such subtlities, and, especially in the textbooks, one may find rather commonsensical definitions for mono-, poly-, and paraphyly, which are a bit far from the rigorous logic of original theories back in the 1980s, when the cladistic swords weren't yet rusty being stained with blood of the pheneticists and evolutionary taxonomists... I'll try to come back in a couple of days to try and reformulate the definition agaun but I can not guarantee that it will stay for ever. (Note: I am not complaining! It is just the way the things are...) Alexei Kouprianov 18:15, 30 November 2006 (UTC)

[edit] "Paraphyletic to"

We should define the common usage "paraphyletic to", as in "reptiles are paraphyletic to birds". It is arguably clearer (especially for a general audience) to say "reptiles are paraphyletic, because they exclude birds" which is almost as concise, but the "paraphyletic to" wording is pretty common and baffling if you don't know the shorthand. The only thing holding me back is that the dictionaries and glossaries I consulted only defined paraphyletic, not the usage with "to". So I don't have a source. Kingdon (talk) 19:50, 14 March 2008 (UTC)