@benkirk… Yes yes … but you do remember that the fellow wanted explanations, right? How can body plans just CHANGE?!?
Here you mention that the nostrils on whale embryos are just like ours … and yet genetically, those nostrils are instructed to move!
It is certainly easy enough to explain … proto-whales that suffered genetic mutation for pushing their nostrils around … found great relief when the nostril ended up HIGHER on the head …
What sounds like a strange arrangement to us is just what whales needed.
Do you suppose he will agree that God thought of that?
I really don’t understand how someone who complains that he does believe animals can evolve/speciate with God’s help … and yet at the same time repeats incessantly his objections about this or that change that he just doesn’t believe is possible via Evolution.
It is a senseless set of positions to assert simultaneously !
Phyla are not equated to body plans. There are phylum-level body plans (or perhaps more accurately, phylum-level characters) and there are class- and family-level body plans. Some lineages are named after the characteristic body plan, tetrapods being the most obvious example. Tetrapods are not a phylum.
[quote=“gbrooks9, post:22, topic:29879”] @benkirk… Yes yes … but you do remember that the fellow wanted explanations, right? How can body plans just CHANGE?!? [/quote]
Hi George,
“Body plan” is just a rhetorical goal post that can be moved anywhere depending on what has been shown to evolve. As a biologist, I would say that there are 2 body plans: protostome and deuterostome.
Sort of, but I’d describe it less anthropomorphically. So which is the real “body plan”–before or after the nostrils move? Or does that mean that one organism has two body plans?
It’s just hopelessly vague, which is why it is a favorite rhetorical weapon of denialists.
I have no idea what you mean. How can any organism “suffer genetic mutation for pushing their nostrils” or anything else? Those verbs and nouns don’t go together.
Moreover, by invoking mutation, you’re again forgetting the relative amounts of existing variation and new variation (mutations). What is that ratio again?
I have no idea. It would seem that if an omnipotent God thought of that, there’s no reason to have the nostrils move. He would just build them in the place where they are in the adult. Evolution, OTOH, works very differently.
Cognitive dissonance.
[quote]It is a senseless set of positions to assert simultaneously !
[/quote]Like asserting that new mutations must account for things like this, given the known fact of the ratio between existing genetic variation and new mutations!
There is a real concept lurking here. I think we all agree that there were a large number of different “body types” that appear in the Cambrian explosion. I do not think it is “all possible permitted by physics”, but there were certainly a lot, and more than we see walking (or swimming and flying) around today.
I think that is the key point, which is real, that is being referred to when Gould, Morris, and Hugh Ross (yes him too!) talk about “body plans.” Though, I do not think there is a good way to get much more specific than this.
As for the point about tetrapods being a “new body plan”. I don’t think a definition that includes tetrapods is really relevant here. It is clear that tetrapods are just a tweaked body plan from something that came before that looked very very similar. I think the point of “novel” body plans is that they do not have any obvious (even they do exist) precursors.
Of course, we can talk about the non-obvious precursors and we can even debate whether or not any body plans truly are “novel.” I think evolutionists, for the most part, would argue almost all body plans are not novel. Hugh Ross I am sure would key on specific cases (or classes of cases like the the Cambrian Explosion) where the specific precursors are less clear.
So I do think that “body plans” is a real concept even if a precise definition is elusive. I would say that the difficulty in defining them is part of the point too. The more fossils we see, the weaker the divisions seem.
I think I’m the one who mentioned tetrapods, and I wrote a whole series about their evolution right here on BL. I didn’t say that they represent a “new body plan,” and certainly never would claim that the tetrapod body plan (or any other body plan) arose without precursors. No, the point was that “body plan” is a phrase that does not mean “phylum” any more than it means “class” (tetrapods are a class, technically a superclass) or “family”, both of which are taxonomic categories that are often identifiable specifically by body plan. The Tiktaalik paper, describing one of the most famous fossil finds of our time, is titled “A Devonian tetrapod-like fish and the evolution of the tetrapod body plan.”
The tetrapod body plan, like everything else in the biological world, was new at some point in history. How it arose and why/how/if it has been successful — those are worthy and interesting questions. Whether it or anything else poofed into existence is not, to me, any more worthy a question than the Omphalos hypothesis. YMMV.
Oh, it is more complicated, which is my (badly articulated) point. However, it’s not complicated as a rhetorical tool in the hands of a pseudoscientist.
As we know … the snail and the octopus are both members of the Phylum “Mollusca” !!!
And so they share a common ancestor… the first mollusk… whatever it was.
The Octopus has 8 limbs… the snail? Does it even have ANY limbs?
The Octopus has 2 prominent eyes and a highly developed brain. The snail? A very different kind of brain (if we can call it that) … and while it has eyes … are they at all like the eyes of an octopus?
