Definitions for a Newbie

I am a newbie to this group, and have no formal education in biology or paleontology, or geology, but have been in 'informal' student most of my life.

What is the definitions of polyphyly and paraphyly? I have done several web searches, but the dictionary sites I've tried come up with no matches. Is there a dictionary site that can handle the words used in this group?

Thanks, Mark Lewis

: there a dictionary site that can handle the words used in this group?

Start with monophyly: a monophyletic group includes an ancestor and all of its descendents (cladist definition), or as Mayr put it in 'This is Biology,' monophyly is 'the descent of a taxon from the nearest common ancestral taxon of the same or lower rank.' Mayr's is more a traditional Darwinian definition, but both say essentially the same thing.

Paraphyly: a paraphyletic group does not include all of the descendents of a single ancestor (the group 'tree' excludes one or more of the branches), or again from Mayr: 'Paraphyletic: a taxon that includes a lineage leading to a derived taxon,' which is I suppose about as reductionist as you can get but is terribly unclear, IMO.

Polyphyly: a group that includes the descendents of at least two different ancestors, or a group whose common ancestor is in another taxon. (Mayr doesn't address that one).

Remember that 'group' in the above usage means 'group' that we backwards humans have invented to describe some assemblage of species that we think through various analyses are related by descent. We get into trouble when we try to name the group and describe its content. We got into trouble doing that long before Darwin, and we'll still be in trouble decades from now. No two scientists can ever agree on anything 100%, and that goes double for the history of evolution and its consequences. Though we don't agree on the history of evolution, the fact is that there _is_ a history and we may never know what it is. Evolutionary biologists lose sleep and grow old early remembering that. Hence the various approaches to understanding it, all of which may come up empty (or not), but all of which have some truly vicious attackers (and defenders).

It's important to understand that cladistically inclined scientists regard monophyetic groups as the only natural groups, because monophyletic groups trace the evolution of whatever group you're talking about without any unauthorized side trips into artificial constructs. Cladists regard paraphyletic groups as artificial, but traditionalists tend to regard them as inevitable natural consequences of evolution. Nearly everybody hates polyphyly, which is probably why Mayr didn't even mention it.

What is often lost in the murk is that our knowledge of evolution in real terms is still so rudimentary that all of this may eventually come to

Actually I think the term monophyly should be abolished. What cladists call monophyly is best referred to as holophyly (a common ancestor and all of its descendants). Paraphyly is when a such a group is made incomplete by the formal removal of one or more exgroups. Reptilia (traditional) is paraphyletic because two exgroups (mammals and birds) have been removed. Amphibia (traditional) is paraphyletic because one exgroup (amniotes) is removed. Unfortunately the term monophyly used to mean either holophyly or paraphyly (i.e., a group with a common ancestor whether any exgroups are removed or not). Therefore not everyone uses the term monophyletic to mean the same thing. As for polyphyly, it depends on who you ask. If an anonymous poster calling himself 'Cal King' gives you a definition, take it with a grain of salt. As recent post demonstrate, polyphyly is not easily defined or diagnosed.

Thanks, Sean and Kenneth.

I DO have one more question! *S* Where can I find the FAQ/Charter for this NG? That way I can avoid some embaressin' questions. *S*

Mark