To some extent I could agree with the original author, but possibly not
for quite for his reasoning. The original taxonomic classification of
birds (and organisms generally) was based on physical and sometimes very
superficial, traits. The classification of species was not the problem;
the problem was the higher classifications, Genus, Family and Order
(of the Class Aves in the case of birds). In many/most cases the
general evolutionary relationships weren't too badly done, but the
classification into Genera, Families and Orders was based mostly upon
physical characteristics and behavioural (and other) traits, and the
taxonomists own bias. So if a species appeared to be too different it
was placed in a different higher category.
Now DNA sequence analysis has allowed a much more objective delineation
of species and of the shape of the evolutionary tree but in most cases
the positioning of the higher classification boundaries has been
retained for historical reasons. There has been some fiddling where
there are glaring inconsistencies but very few wholesale rearrangements,
and certainly no implementation of a standard for definition of Genus,
Family, Class etc.
So back to the original published report. I hope the authors return to
the original data to determine estimated times of divergence and not
simply rely on taxonomic classification.
I also note that they used the phylogeny based upon the DNA-DNA
hybridization results of Sibley and Ahlquist. This method has now been
so discredited with regard to the reliability of the results that I
wonder how they ever managed to get the manuscript past the reviewers,
let alone being able to rely on any results and conclusions.
Andrew Hobbs
Andrew Taylor wrote:
On Tue, Jun 27, 2006 at 05:25:17PM +1000, Graham Turner wrote:
These traits came first, then the birds were slotted into taxa. Thus
it becomes bleeding obvious that the reson these birds are
grouped together is that they are similar.
You should read the paper. They used genetic not phenetic phylogenies
- grouping by DNA similarity not traits. I've appended part of the
paper's introduction to give you a flavour of it. Most of the paper is
taken up with the methods. Testing hypotheses like this quantitatively
is challenging. Claiming a hypothesis is obvious is much easier -
but doesn't help when opinions differ about what is obvious.
Andrew
A large body of work on [phylogenetic tree imbalance] has given rise
to a plethora of biological explanations for why there is so much
variation in clade richness, defined here as the number of extant species
within a lineage. These have invoked a wide range of lineage-specific
characteristics to explain the observed variation in clade richness,
including body size (refs), life history (refs), sexual selection (refs),
ecological generalization (refs), ecological specialization (refs),
behavioral drive (refs), and geographical range size (refs). Tested
in isolation, some of these hypotheses have received empirical support
(refs), while others have been widely refuted (refs). The most striking
aspect of these tests, however, is that, although some of the associations
are statistically significant, the proportion of variance explained is
generally rather small (refs).
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