RE: [asa] Platypus- a transitional creature?

From: asa-owner@lists.calvin.edu [mailto:asa-owner@lists.calvin.edu] On
Behalf Of Rich Blinne
Sent: Thursday, May 08, 2008 1:09 PM
To: David Campbell
Cc: Dehler, Bernie; asa@calvin.edu
Subject: Re: [asa] Platypus- a transitional creature?

Since its initial description, the platypus has stood out as a species with
a blend of reptilian and mammalian features, which is a characteristic that
penetrates to the level of the genome sequence. (*snip*)

To add a little more detail here (and this is from the paper and not the
review articles which is kinda strange): Synapsids (mammal-like dinosaurs)
and Sauropsids (bird-like dinosaurs) split 315 Mya, Protherian and Therian
Mammals split 166 Mya, Therian Mammals split into Marsupials and Eutherian
Mammals 148 Mya. Platypus is a monotreme which a kind of Protherian Mammal.
Another monotreme is echnida. This part bird and part reptile is nonsense.
Archosaurs (birds) and Lepidosaurs (reptiles) split from Sauropsids (no date
given in the paper). Platypus is in a completely different branch than
either of these. The bill of a platypus is a classic example of analogy
rather than homology.(*snip*)

Notably, duplications in each of the beta
<http://www.nature.com/__chars/beta/black/med/base/glyph.gif> -defensin,
C-type natriuretic peptide and nerve growth factor gene families have also
occurred independently in reptiles during the evolution of their venom47
<http://www.nature.com/nature/journal/v453/n7192/full/nature06936.html#B47>
. Convergent evolution has thus clearly occurred during the independent
evolution of reptilian and monotreme venom48
<http://www.nature.com/nature/journal/v453/n7192/full/nature06936.html#B48>
.

I ask:

Since the platypus is part of the protherian mammals (higher up the tree
than the bird/reptile splits from the Sauropsids), why then the
pervasiveness of reptilian features "that penetrates to the level of the
genome sequence"? In several defenses of evolution I've read recently, the
argument is made that if a fossil or creature were discovered which had
characteristics that didn't fit with the predicted phylogenic sequence (i.e.
characteristics from a different branch, instead of diverging from a common
branching point), it would mean trouble for the evolutionary theory. Yet,
this article speaks of "convergent evolution" to justify the fact that this
protherian mammal has evolved the same features that reptiles have
apparently evolved independently.

Now, I'm certainly willing to give the experts due reverence in their fields
of expertise, but isn't this perhaps a little begging the question? We are
told that the phylogenic tree is descriptive of common ancestry, but when
features appear on two different branches that don't follow the path of
common ancestry, we are told that "convergent evolution" can occur? Before
I jump to conclusions, isn't this what the article is saying?

On the other hand, if modern evolutionary biology can tell us with a
straight face that convergent evolution is a possibility, then isn't it a
little disingenuous for them to turn around and claim that consistent
phylogenic lineages is sure evidence that the evolutionary model is correct?
I'll grant the possibility that a gene might mutate the same way twice in
two different lineages, or a duplicate feature might emerge regardless of
the genetic similarity, but what are the odds?

Jon Tandy

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Received on Thu May 8 23:35:23 2008