The body plan of a creature seems to me to be definitive of the original created Kind that shows the impossibility of evolution from one Species or Kind to another. Something I read suggested that the body plan is not genetically coded in the DNA itself but it some other part of the fertilized cell. However the usual idea seems to be that it is in fact part of the DNA, that it is governed or regulated by a certain set of genes called Hox genes, or homeobox or homoeotic genes, and I'm not at all clear about the differences among these terms.
Homeobox genes were apparently discovered in fruit fly experiments in which changes to this particular set of genes would alter the body structure of the fruit fly, such as by locating the antennae on the lower body instead of the head. These genes occur on different chromosomes and are found in the DNA of most animals.
Googling around this topic I found at least one source that says mutations to these genes distort the body structure, such as in the case of the relocated antennae of the fruit fly, and that most mutations to this set of genes are lethal.
That being the case I'd think it makes evolution impossible. You can't get changes to the body plan that are at all beneficial, and the body plan to my mind is definitive of the creature itself. The body plan of a cat is absolutely recognizably distinct from the body plan of a dog for instance, also the body plan of a chimp from that of a human being though I'm sure we'd have quite a discussion about that one. If each creature has a distinctive defining body plan and changes to the genes that govern it are always deleterious, evolujtion from one species to another, from one Kind to another, is genetically impossible. I make a different case for the genetic impossibility of evolution in the post before last, so this is another way it's genetically impossible.
A common discussion of these things focuses on the supposition that they evolved to be what they are, through the whole history of supposed evolution from one species to another. This is taken for granted although of course there has never been any proof of this and can never be, it is simply assumed based on the Theory of Evolution. The actual facts, such as this one that mutations have only destructive effects on the hox genes or the body plan genes, seem to belie the whole theory but they'll of course go on asserting it as if it were true anyway.
As I recall I originally got interested in the body plan or structure or morphology of a creature as the definition of the Kind when I was thinking about the trilobites in the fossil record. Trilobites are found in most of the geological time periods all the way up the ladder, each time period containing its own perculiar type of trilobite. Of course these differences up the time scale ladder are taken as evidence of evolution from one type of trilobite to another, just one of the many supposed evidences of the reality of evolution itself.
Looking at the different kinds of trilobites it's quite clear that what they all have in common despite some radical variations, is their body plan or basic morphological structure. They are all clearly Tri- Lobe-ites, they all have the spines that usually though not always wrap around the side lobes and they all have the head and eyes in the same place. The variations in that respect are clearly extremely minor. Nothing has changed the basic nature of the trilobite itself over those supposed hundreds of millions of years of "evolution" up the geological time scale ladder.
Of course to my mind this is to be expected since from the biblical creationist perspective a trilobite is a trilobite is a trilobite and there is no such thing as evolution, but it's nice to have this kind of confirmation from the fossil record. In other words what we see in the fossil record is the enormous number of variations on the trilobite theme built into the trilobite genome. The variations are quite dramatic, which one would expect from a pre-Flood creature. After the Flood although we still get some pretty dramatic variations, the loss of all but a pair or seven individuals of a Kind would have to mean that the variations possible after the Flood are dramatically decreased from theose before the Flood. As I've argued many times, I think this must be expressed at the genetic level in a great loss of heterozygosity or genetic diversity in each creature including human beings but I don't want to get off on that topic here.
This observation that the trilobite body plan is a constant no matter how great the number of variations that differ from population to population, got me thinking about how body plan is likely the way to definte the Kind, meaning the individual creature scrupture presents as having been separately created. Often believers in evolution make this a big challenge, suggesting that there is so much similarity, which they take as part of the vidence for common descent, defining the Kind would be impossibly difficult. Nevertheless I have no problem calling Cat a Kind, or Dog. But it was the trilobite's consistent definitng morphology that showed me it is the body plan I'm seeing as definitieve of the Kind. The cat body plan is absolutely distinctive. A cat is a cat is a cat, from the lion to the housecat. The catness of cats. Likewise the dog body plan is definitively distinctive. And it includes wolves and foxes and dingoes.
The Linnaean system of classifivation confuses these things. It classifies according to morphology but not in this definitive way that struck me with the trilobite and dots and cats. It breaks down "Aves" in a way that obscures the fact, for instance, that the entire group of "Aves" all share the same body plan. A Bird is a Bird is Bird. I had to look at the skeletons of some ambiguous representatives such as the penguin and the ostrich, and sure enough the body plan Bird is shared by them too. Except for the webbed feet of ducks and swans so do the swimming birds, and the bill instead of a beak, though they are the only subgroup that gives me pause about its placement in the Kind. Probably shouldn't, the body plan is quite evidently Bird.
Since I'm going blind I'm not too likely to be spending much time on other creatures to see which should be classified as a Kind. I don't see any need for most of the Linnaean cateogries, Order, Family etc etc. Seems to me we have a Kind which could also be called a Species, and many subspecies. I have to figure out how to divide the Unbulates, compare body plans of cattle, sheep, deer and so on. If they share a body plan they are all of the Kind. Off the top of my head the bovine Kind must be separate from whatever the deer-elk Kind is, but I immediately think of objections to that idea. .
Current politics is driving me crazy so I'm probably going off on evolution to take a rest from it. Not that I've stopped thinking about it bit O don't want to write about it right now.
Maybe tomorrow.
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