There seems to be a lot of confusion about what different models to explain the origin of higher taxa actually posit. This thread is not so much to argue which one is correct but to understand what the theories themselves actually are. Taxa refers to the different classifications with species (or subspecies and breeds) being the lowest taxa and genera, families, orders, kingdom, etc,....being higher taxa.
1. The dominant theory of evolution is the Modern Synthesis also commonly referred to as NeoDarwinism. I have typically abbreviated this to Darwinism and explained why, but most here seem to insist on just calling it "evolution" despite evolution being defined as a microevolutionary process involving the change in the frequency of alleles. Of course then, a mere change in the frequency of alleles is not necessarily the origin of higher taxa, and so working with that label does not address the topic at hand.
Whatever one wants to call it (I shall use ND for brevity's sake), ND posits sequential speciation however one wants to define species as the process that occurs evolving the higher taxa. One species evolves into another and then another and so forth until you have different genera, different families and so forth. However one wants to describe the process is besides the point. There is a clear process envisioned of small genetic changes adding up over time in populations to produce new species, genera, families and so forth. We can get into that in more depth later.
2. The next model, so derided by evos, is creationism or special creation. Contrary to what many evos think, creationists generally do advocate evolution as well, though perhaps not all, and many especially object to ND's emphasis on allelic mutations as the mechanism for evolution. Their idea is evolution happens but is limited within a kind. So all bears or cats or some other creatures (using animals to help bring clarity to the concept) can and did evolve into all the other bears, cats, etc,....but evolution is limited to a range, evolution within a kind, or "baramin" as some have labelled it.
This is why creationists scoff at evolutionists that talk about microevolution (not originally a creationist term as some presume) being exclusive evidence for evo theory as if creationism does not incorporate microevolution as well. Creationism is divided into young earth creationism (YEC) and old earth creationism as well as further differences in those groups. But they generally advocate a special creation act of the kinds, some advocate progressive creation acts.
Please keep in mind the point of this thread is not to initially jump into debating the validy of models but to actually understand what they say.
3. Front loading and related theories: This is generally an Intelligent Design model. ID actually encompasses creationism but includes models separate from it. Front loading accept common descent as a general principle, though not necessarily monophylogenetic, meaning there can be more than one common source. That is something often suggested but more as a suspicion. The idea is that the environmental pressures play just a small role in the pattern of life that has emerged. Instead as Broome said there is a Plan or pattern that was already embedded into organisms to direct, but just in a general sense, the path of evolution. So something like the similarities between marsupial and placental pairs is not the result of ND evolution (environmental pressures selecting the designs) but a product of internal mechanisms directing the evolution into common designs.
The basic idea is the first organisms contained a basic program so that certain common designs would emerge; that there is a direction to evolution.
Front loaders generally do not believe macroevolution is occuring any more but is a process that has largely or completely spent itself out.
There is a further division in front loading which is worth noting. Some incorporate allelic mutation more than others. Others like John Davison, and likely Goldschmidt and Grasse (who might be termed a front loader today in his advocacy of "internal mechanisms) suggest that random allelic mutation plays almost no role in the emergence of the higher taxa; that something else causes the reordering of DNA. In other words, their model is a form of "saltionism."
So creationism can actually accept speciation within a kind (though some differ), but saltationists do not accept gradual evolution of this sort. It's an important distinction to note.
Epigenetics and the idea of looking at chromosomes more as a means of speciation is based on a revival of this older theory of evolution front loaders and other saltionists advocated but evos involved with it do not consider epigenetics as exclusive of ND but an addition to it (no saltionism), somewhat outside ND but merely adding to it.
4. Saltationism without Intelligent Design....it's worth noting that we don't know if some scientists in the past that rejected Neodarwinism such as Goldschidt, Otto Schindewolf, Pierre Graase, etc,...would accept the label "Intelligent Design" today. You'd have to look at their writings and comments more extensively to see if they viewed the process as the result of design and purpose or purely random. Also, keep in mind saltionism is not full-blown Lamarckianism, nor even Lamarckian at all. Epigenetics though can be seen as somewhat Lamarckian.
5. Intelligent Design: This is really a very broad umbrella including theories accepting common descent and not, but can generally be thought of a model based on the assumption that there is Intelligence behind design; that there is purpose in the creation both of biological life and the universe itself. It's a model involved in areas besides biology such as information theory, mathematics, physics, astrophysics and cosmology. I believe theistic evolutionists should rightly be considered a form of ID but they'd object to the label.
Hope that is helpful.
