Talk:Polyphyly

The "lower land vertebrates" are a polyphyletic group.

This is a nice image, but I don't think it actually describes a polyphyletic group. The common ancestor of amphibians and mammals was a land vertebrate, and although the illustration does not show this, the lower land vertebrates are usually meant to include it. As such, this is a paraphyletic group, comprising all its descendants except the mammals (and I would think the birds). Might a better illustration might be the warm-blooded animals, highlighting Mammalia and Aves separately? Josh

Well, are you sure that the warm-blooded animals are a polyphyletic group? Was the most recent common ancestor of birds and mammals warm-blooded or cold-blooded? I think this picture actually shows a paraphyletic group, doesn't it? Because the yellow curve includes the fork between Mammaila and Aves? I don't know, I'm no biologist. Keenan Pepper 19:50, 21 July 2005 (UTC)

I'm not sure what to make of that picture. It's generally understood that the ancestral amniotes were cold-blooded, and crocodylians are too. Also, although it technically falls under the definition we give for paraphyletic, that group would still be polyphyletic since it leaves out connecting forms - the difference is whether the tree is topologically connected. I'm not entirely sure how to word this. Josh

How about this text? A picture highlighting mammals and birds separately would go great with it. Keenan Pepper 23:12, 22 July 2005 (UTC)

That sounds fair. The image would be easy to adapt, but it's on the commons and I don't know where the update should go. Josh

New image, based on the discussion here. There is also an svg source for the image on commons, so it should be very easy to correct. Zeimusu | Talk page 15:40, 30 September 2005 (UTC)

Examples of Polyphyly

These examples aren't clear to me. The definition of polyphyly here requires not including the common ancestor, but these examples don't state whether the nearest common ancestor is a member of the group or not. Rather, these examples say that the descendants of the common ancestor are not all included. Isn't that just paraphyly? Octavo (talk) 20:10, 26 November 2007 (UTC)

Yeah, it sure seems that way. Let me think about that. — the Sidhekin (talk) 17:11, 6 February 2008 (UTC) Meanwhile ...

Last example is misleading... seems to imply that primates are the descendants of birds and bats. This is not true - the MRCA was a non-flying reptile of some sort. 75.110.136.111 (talk) 16:18, 6 February 2008 (UTC)

Seems to me it's saying birds and bats are descended from primates ... but then, the second example seems to say plants and bacteria are descended from animals. Seems a few "descendents of" have gone missing ... hang on ... fixing ... better now?

Of course Octavo's objection still stands. — the Sidhekin (talk) 17:11, 6 February 2008 (UTC)

"However, the number of paraphyletic groups and polyphyletic groups is exponentially larger than that, on the order of N²" - Not an expert, so don't want to modify this page, but N² isn't exponentially larger -than N -Gargletheape (talk) 14:49, 7 December 2008 (UTC)

Wrong definitions of polyphyly

Polyphyly is defined by characters: A polyphyletic group is a taxon defined by convergent characters (homoplasies), while a paraphyletic group is defined by primitive characters (plesiomorphies), and monophyletic groups by shared derived characters (apomorphies) (ref: Hennig, 1950). The definition and examples given here are instead *tree-based*, but in tree-based definitions there is only monophyly and non-monophyly, as there is no difference between paraphyly and polyphyly. This is why there is confusion above whether the cited examples are para- or polyphyletic. —Preceding unsigned comment added by 130.242.24.193 (talk) 10:19, 26 May 2010 (UTC)

There IS a difference between paraphyly and polyphyly in tree-based definitions, as these terms are currently used. Taking monophyly to be synonymous with holophyly (as it is in current use), then a paraphyly is a monophyly minus one or more (usually one) sub-monophylies. A polyphyly is any other kind of non-monophyly other than a paraphyly. In other words there is the classification of classifications:

• monophyly
• non-monophyly

• paraphyly
• polyphyly

Now it can well be argued that this rather distorts the derivation of the words: something which is 'not mono' should be 'poly', but we have to describe consensus usage, whether or not this is what we would wish it to be. Peter coxhead (talk) 15:46, 6 December 2010 (UTC)

Why have three articles?

Please see Talk:Monophyly#Why_have_three_articles where I have asked why there should be separate articles on monophyly, paraphyly and polyphyly. Please leave comments there. Peter coxhead (talk) 15:57, 6 December 2010 (UTC)

Incorrect definition

The definition currently given in the first sentence ("A polyphyletic ... group is one whose members' last common ancestor is not a member of the group") is obviously incorrect. Imagine that in the very first diagram the blue-purple area were extended to include the region around the word "Amniota". In other words a group was defined as "all amniotes up to but not including Sauropsida + all mammals and their ancestors + all Aves". This group would not be polyphyletic according to this definition, whereas it clearly is.

The problem is that a short but correct definition can, as far as I can see, only be negative: a polyphyletic group is one that is neither monophyletic nor paraphyletic. A longer but correct definition is "a polyphyletic group is one that excludes some of the descendants of the nearest common ancestor of the members of the group and also excludes at least one of the members of the sister groups of the excluded members" (based on Oosterbroek, Pjotr (1987), "More Appropriate Definitions of Paraphyly and Polyphyly, with a Comment on the Farris 1974 Model", Systematic Biology 36 (2): 103 –108, http://sysbio.oxfordjournals.org/content/36/2/103.abstract ). However, this definition is incomprehensible without a lot of explanation.

I still believe that attempting to have separate articles on monophyly, paraphyly and polyphyly is a serious mistake; the three terms cannot be properly understood except in terms of each other. Peter coxhead (talk) 12:46, 4 October 2011 (UTC)