(09-24-2013 07:25 PM)JOwl Wrote: I think the (very cool) link I put in post #15 on this thread helps illustrate the difficulties of observing g cross-superclass evolution like fish to amphibian. Fish were around for about 160million years before the appearance of the first species we'd call an amphibian. That's an _extremely_ long time, full of lots of little differences.
But there do exist species like the lungfish (some of which use both lungs and gills to breathe) that are suggestive of how amphibians may have developed lungs ( http://www.ucmp.berkeley.edu/vertebrates...ipnoi.html )
A bit of introspection here leads us to the heart of the issue.
Darwin did believe in speciation, but his qualms came from the implications of his work as applied to the fossil record. Given the slow, steady transformation implied by his theory, he expected to see in the fossil record transitional forms between species indicating slow and steady changes. The fossil record of his time didn't record this. Darwin expected that, as time passed and more fossils were found, the transitional forms would be found. It didn't happen that way. More and more fossils species were found, but it only increased the number and variety of species known; transitional types were far and few between. This caused some consternation among biologists, and eventually in the latter part of the 20th century the concept of "punctuated equilibrium" was proposed. It stated that, rather than slow and steady gradual changes to organisms, evolution instead tended to happen very quickly and dramatically. If that's the case, one wouldn't expect to find transitional forms, because their lifespans over geologic time would be very brief, and thus the odds of their forms being preserved in the fossil record would be very low.
That's all well and good, and may even be correct. Strictly speaking, however, it isn't scientific. That's because for a theory to be scientifically valid, it has to be falsifiable. Punctuated equilibrium can't be falsified, because evidence that might disprove it may have simply never been preserved in the geological record. So you can believe in unguided evolution, and RiceDoc can believe in a deity specifically intervening to create species, and there's no scientific reason to deny either of your viewpoints. The problem comes in when people try to use science to invalidate either viewpoint. It's like using a hammer to pound a screw into place. There is a better tool available, but as the old saying goes, to someone who has a hammer, every problem looks like a nail, even if it's actually a screw.
One caveat that must be mentioned regarding speciation is that in recent years the whole concept of "species" is coming under scrutiny; the previous posts about Darwin illustrate this. Originally defined as a group of organisms capable of interbreeding with each other and producing fertile offspring, such a definition doesn't suffice for all known types of organisms and can intergrade with hybridization, but that's another subject....
[Incidentally, your example of the lungfish is not very helpful to your argument. It's presently believed that the Dipnoi are only distantly related to modern amphibians. Stegocephalians (the clade containing tetrapods, of which modern amphibians are part) have significant differences in their skull structures from dipnoids. Furthermore, lungfish have internal gills like fish, while modern amphibians in their aquatic phases have external gills, and the lungfish maintains its dual respiratory abilities throughout its life as opposed to amphibians, who undergo metamorphosis from gills to lungs for respiration. The evolutionary pathways for the Dipnoi and Amphibia to acquire dual respiratory abilities were likely quite different from each other.]
(09-24-2013 09:24 PM)jwn Wrote: (09-24-2013 08:43 PM)Caelligh Wrote: I have another theory about the controversy. Perhaps denying the Christian creation story is perceived by creationists as a step on the slippery slope to denying the rest of Genesis. As I recall, the whole point of baptism (the first sacrament) is freeing the recipient from original sin. If you deny the creation story, perhaps you also deny original sin, you deny baptism, and you ultimately raise questions about the church's definitions of good and evil and even the reason for Jesus' crucifixion. I can see how a religious institution might want to avoid that.
Perhaps, but the Catholic Church, one of the primary proponents of both original sin and the salvific effect of baptism, stated over 60 years ago that with respect to evolution and the creation narrative, a Catholic was free to believe in a range of explanations for the creation of the world and physical body of humans so long as one maintains that "souls are immediately created by God." In effect, the Catholic Church takes a mostly agnostic stance on the issue.
Now, Pius XII, in the same document, also takes a firm stance against polygenism, the theory that humans descend from multiple "first parents," in order to preserve the doctrine of original sin from the "first Adam." That was popular back in the 1950s, but I think more recent research regarding mitochondrial DNA has shown that all humans descend from, very few mothers, and perhaps just one. I will admit to both not being well read on this topic and not having the article I'm thinking of at hand, so someone is free to prove me wrong on that.
You are correct in regards to the "evolutionary bottleneck". From studies of mutations in mitochondrial DNA, the rate of which is well-known, and the relatively low genetic variability in modern humans as compared to other species, it can be shown that all humans on Earth presently are descended from a very small number of humans that lived in Africa aproximately 70,000 years ago. Being that a number of fossils of
Homo sapiens have been found that are considerably older than that, it would seem that something happened that extinguished most human lineages no later than 70,000 years ago. It should be noted that the timing of this bottleneck depends on what part of the genome one studies for variability, but the existence of the bottleneck seems to be proven.
Your remarks concerning the Catholic Church, I think, highlights one of the issues about this debate. Without getting into too much detail, the Catholic understanding of Scripture embodies four distinct
senses: the literal, allegorical, moral, and anagogical (leading to a destination) senses. Proper exegesis of Scripture must take into account each of these four senses. It seems to me that the people trying to get evolution out of textbooks and/or get creationism in them (who are typically Protestant) tend not to use all of these senses in their exegesis (quite often using only the literal sense). I suspect this is an artifact of the Protestant understanding of Scripture (and I can think of other issues in which certain Protestant communities take certain stances apparently using only the moral and/or allegorical senses of Scripture).