Comments on: Why Weird Animals Matter, Continued: Untangling the Branches

By: John Monfries

John Monfries — Mon, 05 May 2008 04:47:45 +0000

Thanks from a layman for the explanation of long branch attraction.

I read about this in Dawkins “Ancestor’s Tale” but didn’t quite get it. This explanation is clearer.

By: Doug

Doug — Fri, 02 May 2008 12:38:31 +0000

Hi Carl,

Your picture of a ctenophore in this post reminds me of this NASA drawing of the Heliosphere.

Is motion at such vastly different scales coincidental or related to mechanics?

By: Derek Sikes

Derek Sikes — Thu, 01 May 2008 22:26:59 +0000

“The long branch of the original comb jelly now became split in two, reducing the amount of long-branch attraction.”

If the new comb jelly joined near the top of the branch, as I expect it did, then although the branch may be cut into two pieces the pieces are not of equal size, and the long bit will remain problematic.

By: Allen Collins

Allen Collins — Thu, 01 May 2008 15:34:03 +0000

I am confident that Dunn et al. tested for long-branch attraction problems and carefully assessed their data in order to discern any systematic bias.

Nevertheless, my gut tells me that this early diverging ctenophore result is most likely spurious. That said, it is perfectly appropriate for it to have been published. The data presented certainly indicate that this is the case. Personally, I would be more worried about taxon-sampling issues. What happens when all or most of the longer-branched bilaterians are excluded from the analysis? What will the results be when more opithokont protists are included in future analyses? We shall see.

By: Diego

Diego — Thu, 01 May 2008 01:40:17 +0000

Well, at least the authors used Maximum Likelihood. ML is not immune to long-branch attraction, but it is much less susceptible to that particular problem than parsimony.

By: My Sockpuppet's Concern Troll

My Sockpuppet's Concern Troll — Thu, 01 May 2008 00:15:23 +0000

Good post, Carl, but I have to take issue with this:

As I wrote in the Boston Globe Monday, earlier studies had generally pointed to sponges as belonging to the oldest lineage.

All tips are equidistant from their most recent common ancestor (MRCA). The oldest lineage doesn’t make sense when comparing extant taxa. I think it would be more appropriate to refer to sponges/comb-jellies as the outgroup to all other mammals (whichever one happens to be the right one).

And if I didn’t do this, Ryan Gregory would have.