I realize that most evolution Freepers aren’t startled by the virtual absence of new phyla after the Cambrian explosion. But the concern is real – and not just to Intelligent Design supporters or Young Earth Creationists.
Virtually all of the body plans originated in the Cambrian explosion – a hiccup of time in the geologic record. Imaginative Sci-Fi writers propose a host of body plans in their fiction. So if man can think up novel body plans, why didn’t nature - if evolution is random, given all the time passing, some 500 million years?
The question is amplified by a number of intervening mass extinctions which would have provided ample environmental opportunity for new body plans to emerge and survive.
Notably, the “no new body plans” mystery is a concern among scientists as well. The best theorizing I’ve seen so far comes from this NASA website.
StJacques, you and I began our verbal debate over the mutability of regulatory control genes. I claimed they were highly immutable, you disagreed. I pointed to an article on eyeness evolving concurrently between vertebrates and invertebrates, i.e. between phyla. You objected that they weren’t using the words, ergo concepts, that I was using. It wasn’t worth carrying the argument any further – we had just met.
However, I’d like to bring the point forward at this time.
Back then, I argued that the meaning is clear, evolution is not random. The lowest life forms have no eyes and the eye gene with many sites has exponential possible combinations of amino acids. And yet the same combination of amino acids are selected for vision in all animals – vertebrates and invertebrates – across phyla.
Gehrig uses the term master control genes. I still prefer the term, regulatory control genes (but can’t recall where I first read it).
IMHO, if such control genes were largely immutable (since the Cambrian) it would explain not only concurrent evolution of eyeness across phyla but also the absence of new phyla (body plans) – though it would strike fatally at the notion of happenstance.
In the above NASA article, which also doesn’t use my lingo (no surprise there), the author suggests that microevolution cannot account for the fossil record and discusses the models of macroevolution (genetic drift, etc.) - but strongly suggests that environmentally linked hormonal induced changes in the control genes can create the observed effect of quickly emerging and successful phyla.
That would make sense to me also provided that a stability – or immutability – of control genes sets in after the Cambrian, otherwise body plans would be cropping up and dying off in the intervening 500 million years – especially so during the periods of mass extinctions.
In the alternative, if one presumes that regulatory control genes have remained every bit as mutable as ever in the intervening 500 million years (business as usual) then there is a big problem. As far as I know (and I have been watching) - there is no solar system or geologic evidence for a one time only, body-plan inducing environmental circumstance which has not since recurred. For me “the absence of evidence is evidence of absence”.
At any rate, the lack of new body plans – as with the eyeness across phyla – point to control, regulation, design, direction or whatever term you wish to use, but not happenstance.
I agree that this is interesting, but I don't know if it "rises to the level" (Clintonian expression) of a serious concern. To put the issue a different way, we might well ask why no new hominid has emerged in the last 5 million years. There were a few, very few, and now there are no new ones to be found. Is this a problem for evolution? I don't think so. It's just an observation of what's developed. The domain of what hasn't developed is infinite, but I don't see the need to worry about why each possible development hasn't appeared.
"No new body plans" may be overstating things. The phylum of vertebrates existed in the Cambrian, but the only vertebrates in the Cambrian were fish. Since then, fish have evolved into amphibians, reptiles, mammals and birds. That's not exactly "no new body plans" unless you think we all look like fish.
On your post #608, I will respond, but I have just exhausted my "freeper time" for the afternoon responding to DannyTN. I will try to get to it tonight, or possibly tomorrow. I can't say right now, but I will get back to it. I see some of my answers already, but I want to be careful.