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RE: Challenge to Cking

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Posted by: CKing at Fri Oct 3 22:14:26 2008  [ Report Abuse ] [ Email Message ] [ Show All Posts by CKing ]  
   

>>Okay Cking, I have a final challenge for you. Tell me whether B and C form a paraphyletic or polyphyletic group in this example:
>>
>>The relationships among the taxa are ((A,B)C)(D,E). The character matrix is:
>>
>>A - 000
>>B - 111
>>C - 111
>>D - 000
>>E - 000
>>
>>Lets assume that 1000 other characters support the above relationships perfectly (i.e. no homoplasy), so the relationships are not ambiguous.>>

Those 1000 characters are meaningless without knowing what they are. They could be symplesiomorphs, or they could be synapomorphs or they could be homoplasies (convergences, parallelism or reversal) or a mixture of different combinations of these types. A naive cladist may be impressed by the claim of 1000 similarities, but I am not.

A similar claim has been made concerning birds and dinosaurs. The cladists like to impress their followers and the uninitiated as to how many similarities there are between birds and dinosaurs. The real deciding character, however, is feathers. The oldest known reptile with feathers is Longisquama insignis, a Triassic organism. On the other hand, there is no known dinosaur that has feathers. All the so-called "feathered dinosaurs" come from a period long after birds have diversified into many different types, and none of them predated the oldest known bird, Archaeopteryx. Some of the "feathered dinosaurs" have proven to be forgeries. Other "feathered dinosaurs" have filamentous structures that are similar to the collagen fibers found in the skin of vertebrates that do not have any trace of feathers. Yet other "feathered dinosaurs" are actually secondarily flightless birds.

>>Using a character based definition of para and polyphyly (which you appear to prefer),>>

How else can you identify paraphyletic and polyphyletic groups unless you examine the taxonomic characters of the members of a particular group, be they molecular or morphological characters?

>>I argue that there is no way to distinguish between between para or polyphyly,>>

If that is the case, then you don't know enough to make a taxonomic proposal. The prudent thing to do is to leave the existing taxonomy as is but investigate further.

>> but it is clear that these two species do not form a monophyletic (i.e. ancestor and all descendents) group.>>

That does not bother me. I am not obsessed with holophyletic groups. Paraphyletic groups are perfectly fine. Polyphyletic groups, however, should not be recognized as valid taxa. In fact, holophyletic groups are kind of boring because nothing much new has evolved from them to warrant the erection of a new higher taxon. If life never evolved beyond the bacterial stage on earth, then we have a rather uninteresting holophyletic group, and neither you nor I would be typing at a keyboard or going out herping. We would all be extracting energy from some inorganic source and be single celled organisms. Evolution produces paraphyletic groups, therefore the cladists should stop destroying paraphyletic taxa.

>>This is what I suggested could happen, while you denied it is possible.>>

I never said that it is not possible to be unable to figure out the truth. I only said that if there is not sufficient information, then do not make a hasty taxonomic proposal. If a taxonomist claims that a taxon is not monophyletic, then he should exlain to us whether he/she means the taxon is paraphyletic or polyphyletic. If he/she does not know, then say so. Don't hide behind the term "not monophyletic."

>>In this case it is clearly correct to state that B and C are not monophyetic (unless you and I disagree on the definition of monophyly), but it is not clear whether they are para or polyphyletic. Hence the appropriate use of the term non-monophyltic. If you can prove that there is a way to tell whether B and C are para or polyphyletic, I am very interested to see this proof.>>

I am not interested in your example, because a hypothesis of relationships is only as good as the taxonomic characters used to support such a relationship. Without knowing the goodness of the taxonomic characters, even 1000 similarities does not impress me and these similarities do not prove anything. If there is not enough information to determine whether a group is paraphyletic or polyphyletic, then just say that there is not enough data. Don't declare the group "not monophyletic."


   

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