gary_s wrote:OK, then. Parse it out. What would the model look like if you ditch the entire concept of shared heredity over time?
Look, I don't think there is much reason to doubt a common decent. But there are other possibilities like parallel but independent lines of development that are not so far fetched that they are out of the realm of possibility.
You are referencing convergent evolution here, where genetically desperate species evolve morphological similarities. A good example of this is the wolf and the Tasmanian tiger. This is an important element of evolutionary theory, but is not as far reaching as common descent. You could probably remove this element and the theory would still stand up pretty well, although you would still need to explain the observed evidence. But this is not
common descent. Common descent is far more significant. It explains the vast amount of genetic heredity across the spectrum of life. So you wiffed on this one. Try again. The most important point here is that without common descent, the evolutionary model would look very different. So what would it look like?
And regardless it certainly doesn't mean that you cannot support some parts of the theory and not others. After all the evidence is not just one type but quite varied and thus there is evidence for other parts of theory such as natural selection that is quite independent.
Perhaps I misstated my point on this one. Certainly there are lots of moving parts to this theory, and rejecting one does not require you to reject all the others. That is not what I'm trying to convey. But can we agree that every aspect of evolutionary theory is there for a specific purpose, to explain some observation? And can we agree that the alteration of any element would change the model, even if only slightly, while the removal of some would radically change it. This is not so far fetched a proposal and shouldn't be a cause for disagreement. I'm just saying that a model is built to explain observable evidence. If the evidence remains, but you throw out any part of the model, you then need to explain he evidence in some other way, thus changing the model. Rian states that she does not accept common descent (or doubts it or whatever she says), but does not offer any suggestion of how else to explain the evidence used to support it. That's all I'm asking for. How else does she explain the evidence, or does she refute the validity of the evidence altogether? What does her evolutionary model look like because it certainly does not look like the one I know about.
You do need to be careful about going overboard with general statements like that which just are not supportable.
I modified my statement to be more clear, but my meaning is still the same and you have not made a case that I'm saying anything unsupportable. In fact, I'm almost certain that I would be supported by any evolutionary biologist you might ask.
gary_s wrote:Mitch, Rian is drawing into question the single most important aspect of the theory, the idea that species evolve over deep time and therefore are all related at a genetic level to various degrees. Without this, what is left? She still supports natural selection, but that alone cannot support the modern evolutionary model. A different model would emerge.
Gary, how you assign importance and significance to parts of the theory is not itself a matter that can be objectively established.
I'm using the two words to mean the same thing, but significance is probably a better word because it means that it represents a significant aspect of the overall theory. Again, I ask if you remove common descent, how do you then explain the genetic similarities between all the myriad species of the world? What is the mechanism? If that isn't "significant", then I don't know what is.
Furthermore I don't even agree with you. I think the principles of natural selection, shifts in the genetic pool, and other things are more applicable to a greater number of observations. I think this issue of common decent is just something that has particular philosophical importance to you.
Please don't pretend to understand my motivations. You are always complaining about others for doing the same thing. I am stating my understanding of evolutionary science and supporting what I know, not defending some philosophy. And certainly those other elements are quite significant, but we aren't discussing them because Rian has not drawn them into question. Anyway, genetic shifts explains some parts of the model that are not accounted for in common descent. Natural Selection is also quite a major element of the model. It explains how creatures respond to environmental pressures and how speciation occurs. Without Natural Selection, the model would be quite different. And the same goes for common descent. In fact, without common descent, Natural Selection only explains changes on a much smaller scale and doesn't allow for the deeper genetic relations of species that are quite divergent, such as why humans share genes with grass. If anything, this is Rian's reasoning. She has voiced acceptance of Natural Selection on a "micro" scale, but questions the "macro" scale of evolution despite the overwhelming evidence. If anyone is defending a philosophy because it is important to them, it clearly isn't me. I'm only expressing the consensus view of science.
Sure, that part of evolutionary theory is really important to you
I take great offense at this statement, Mitch. It implies that I am defending this topic out of emotional reasoning and that couldn't be further from the truth. You simply do not understand my motivations and do not know why I choose to debate certain topics. You have often criticized others for deigning to known the motivations of others and to criticize them. And yet that is exactly what you are now doing. If this is all you can muster, then nothing else you have to say on this subject is of any interest to me.
I can agree that there is little reason to doubt common decent and I still don't share your estimation of its importance to the rest of the theory. Remember that I support not only evolution but abiogenesis as well so I also think that abiogenesis and common decent is the most reasonable explanation for the origin of life on our planet. But I still would not say what you have said.
Then you do not understand evolutionary theory as well as you think you do. I disagree with you and you have made no statement worthy of changing my opinion on the matter.
gary_s wrote:can you imagine saying you don't buy the theory of relativity because you just don't buy the idea that space-time is curved? If you leave that part out, you don't have much of a theory left.
YES, I CAN. It even has a name. It is called the Special Theory of Relativity. So I am afraid what you are saying is incorrect.
I was speaking of General Relativity, not Special. Take space-time curvature out and the model is not the same. Special Relativity doesn't even need space-time curvature. You call yourself a physicist?
gary_s wrote:That's what I said, or at least inferred (I said "so far as I know"). I said nothing of possibilities. There are no known alternative theories that hold up under scrutiny, so there's nothing scientific to replace the model of evolution.
Yes I can get behind you on that statement, but I don't see how that changes my objections to what you said to Rian. Sorry.
I don't need you to "get behind me". I know I'm right about this and I don't need your approval. And the reason it should change your opinion is because you should know that if any portion of a theory is removed, then it HAS to be replaced by something else. The only reason for it being there is because it explains some element of the physical universe as we observe it. If the observations determine that that portion of the theory is no longer needed, then it could be removed, but this is just not the case with evolution. We know that species share genetic heredity. So how do they do that? It's called common descent. Now, reject the idea of common descent and try to explain the shared genetic heredity.