Re: (long-branch attraction)

["David Marjanovic" <david.marjanovic@gmx.at>]

----- Original Message -----
From: <Dinogeorge@aol.com>
To: <dinosaur@usc.edu>
Sent: Saturday, April 07, 2001 1:06 AM
Subject: Re: Triassic Sauropods


> And this long-branch problem afflicts molecular analyses perhaps even
worse
> than it afflicts morphological analyses, since amino-acid sequences and
DNA
> sequences are more like discrete coin tosses than are morphological
> characters.
>
> I'd like to hear comments about how cladistic analyses might get around
this
> problem.

More taxa, more characters, better characters. There was an article in
Science last November, "A Kingdom-Level Phylogeny of the Eukaryotes" or so
(I've lost the copy :.-( :.-( ), which was based on 4 genes (instead of just
SSU rRNA); it got microsporidians as fungi instead of as basal eukaryotes
and also put other simplified parasites into crown clades, along with more
surprising but well-supported results. Now it is universally accepted that
trees that show microsporidians as basal eukaryotes suffer from long-branch
attraction.
        However, I think that morphological trees are less prone to
long-branch attraction, because they are traditionally based on hundreds of
characters that won't vary randomly. Of course, this does not completely
rule out the problem.