I described my own interaction with the horses in an article for Answers, Horse fossils and the nature of science. In a nutshell, using baraminology techniques, I found (to my surprise) that all fossil equids appear to belong to a single baramin, and are thus descended from an ancestral pair of horses on the ark. To be blunter than I could be in Answers, the evolutionists got that one right, and we creationists appear to have gotten it wrong.
Unfortunately, saying such provocative things tends to stir up more emotion than thoughtful commentary. Some say that we should never say stuff like that because scoffers will use it to mock us. I say, what won't scoffers use to mock us? Others simply refuse to give up their belief that horse evolution is bunk. I don't see what the big deal is, but that's the way it goes I guess. Every now and then, though, I find someone who can converse in a civil manner about controversial topics. There's one such commentator (Kevin N) over on Paul Garner's blog. He is definitely not a young-age creationist, but in the interest of promoting civil interaction, I asked Paul if I could post a response to his questions here. (I also thought his questions were really interesting and thoughtful.) So here we go:
The rate of evolution needed to go from Hyracotherium to Mesohippus to Merychippus to Pliohippus to Equus (or whatever other path one presents) in just a few centuries after the Flood is extreme, to say the least. The changes between these organisms is not just a matter of changes of size, but also significant changes in their limb bones and teeth.
You are definitely correct, and I wish I could give you a really good answer. My stock answer is that all the speciation mechanisms we know about today are not adequate to explain this kind of rapid change and we need to develop a new one. I suspect it has something to do with genomic rearrangements via transposable elements induced by environmental stress, but this is based primarily on work in bacteria (here and here). You might say I'm turning into a radical neo-neo-Lamarckian. In short, I speculate that with the correct kinds or threshold of environmental stress, genomes will spontaneously reorganize and produce novel morphologies which can become new species. It is not random change; the changes must be directed and are designed to happen.
In the western United States, where the horse series is preserved, the thickness of Tertiary sediments is often hundreds of meters. How did a "subtropical forest" develop during a time when the sedimentation rate averaged perhaps a meter or more per year? How did browsers/grazers survive?
Unfortunately, that question is way outside of my expertise, so I can only offer a few meager comments. First, I would suggest that the post-Flood residual catastrophism was episodic or punctuated rather than continuous. So perhaps it is not sufficient to think merely in terms of an overall average sedimentation? If this is correct, then the regional catastrophes that produced huge sedimentation would leave survivors in other regions of continents or the world. I suppose this is a vaguely Cuvierian mode of thinking, with periods of relative calm ended by regional "revolutions" that wipe out many, many species. Survivors from other regions then repopulate the devastated areas.
There is also a problem of ecological succession. The subtropical forest not only had to develop in a time of ultra-high sedimentation rates, it had to do so without a well-developed soil as a starting point. Being that this would be an instance of primary succession, rather than secondary succession, the forest would have taken decades (or centuries?) to mature to the point that is preserved in the fossil record. But the soil couldn’t have developed as more sediments were continually added.
That is a very interesting and important question, but I don't have an answer. I've definitely thought about it, though.
In the wild, post-Flood world that you advocate, how did the proto-horse (Hyracotherium or whatever) migrate all of the way from Ararat to Nebraska?
I've wondered that myself, especially since Hyracotherium appears in Europe and America. I think you'll find my answer kind of hokey: I suspect they might have rafted on mats of debris left in the oceans from the Flood. There's a paper in the fifth ICC Proceedings that describes this hypothesis. I know that it does not explain everything, and it's not entirely satisfying, but it has a certain sense to it. We know that animals and plants can use debris rafts to cross the oceans. It's reasonable to assume that a global Flood would leave behind enormous debris rafts, some of which could be quite stable. Since these could be the centers of recovery for plants along the shores, anywhere one came close to the shore, herbivores would be attracted (and carnivores to the herbivores). As I said though, I have many concerns. One is the efficacy of the model to explain mammal migration. Reptiles and maybe birds? Sure. But mammals are a whole different issue, given their near constant need for fresh water. But I suppose it's possible that a debris raft large enough to stably transport mammals could have pools of freshwater accumulated from rainfall (which would have been plentiful). Another issue is whether such rafts would actually explain modern animal distributions. For example, we know that there are currents running between Europe and North America today, but what about after the Flood when the ocean temperature was much warmer and the continents were presumably in a slightly different configuration? And while we're on that topic, what was the continental configuration after the Flood? Lots of unanswered questions, but I think we have an interesting start to look for answers. And the theory does have quite an explanatory power when you look at macrobiogeography.
Microevolution needs variation to work with. Variation is a property of populations, not of individuals or a pair of individuals. Where did the variation come from to allow the rapid diversification of horses in just a few centuries?
First, horse evolution is not microevolution. Although it's a vague term, microevolution generally refers to evolutionary changes within a species. Horse evolution produced new species, genera, and even subfamilies. I'll probably get a lot of flak for saying this, but horse evolution counts as a kind of macroevolution.
Second, as I mentioned in my answer to your first question, I don't believe any known speciation mechanisms are adequate to explain the kind of speciation that we see in baramins. That means that microevolutionary changes accumulating and becoming macroevolutionary changes is not a realistic answer to the question of intrabaraminic diversification, in case that was what you were thinking. As I said, I suspect that much of these changes must have been designed to happen.
Third, even though I don't think simple "variation" is enough to explain intrabaraminic species diversification, there is the fact that modern horses have sequence variations in their orthologous genes. This is an area that we really need original research on. I've tinkered around with some unpublished data, but I have no definitive conclusions.
So that's what I have to say. What excites me most about this post is the amount of stuff we don't know. There are many questions to be answered and many opportunities for future creationists to make important contributions to creation research. If we had all the answers, that would be boring.