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Re: Cladistics (was Sci. Am. - present)

>Christopher Brochu <cbrochu@fmppr.fmnh.org> wrote:
>> I'm not sure why this is.  In the vast majority of cases, DNA sequence
>> and morphology tell  you more or less the same thing.  Molecular data are
>> no less subject to selective pressures, and levels of homoplasy given
>> sets of the same size are no different.
>> 10 years ago, the question was "should it be molecules or morphology?"
>> Today, the answer is "yes!"
>Yes, but there are certainly examples where our morphologically-based
>phylogenies have been disproven by DNA sequence data.  For example, recent
>DNA research has shown today's elephants to share a common ancestor with
>hyraxes, manatees, dugongs, aardvarks, golden moles, and (I love this one)
>elephant shrews.  Nobody predicted such a family.

Actually, morphological data *did* predict most of this, and AFAIK the
elephant shrew bit is poorly-supported by a few genes - this is not a case
of morphology being overturned by molecular data.

>It would appear that we will never get the DNA sequence data required to
>put our morphologically-based dinosaur phylogenies to a proper test.

Or, conversely, that we'll never have sufficient morphological variation to
test molecular phylogenies for, say, bacterial strains.  Morphology and
molecules both preserve a phylogenetic signal.


Christopher Brochu

Postdoctoral Research Scientist
Department of Geology
Field Museum of Natural History
Lake Shore Drive at Roosevelt Road
Chicago, IL  60605  USA