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Sigh. Yes. Again, so what? How do you know that there are viable modest changes that will keep taking you farther away from a particular existing species?evolution works by modest changes. large changes = modest changes over time.
if we are talking about the refinement of major traits then a gene that gives you 1% better vision or 1% better immunity is better than the status quo and is thus beneficial. fifty 1% improvements a million years later lead to a highly refined and specialized organ.Sigh. Yes. Again, so what? How do you know that there are viable modest changes that will keep taking you farther away from a particular existing species?
Yes, we're talking about speciation -- that's what the thread's about. Even most creationists will accept that evolution can produce closely related species. But can you extrapolate that to the large-scale differences seen in the range of species seen in nature? My point is that you cannot automatically extrapolate, because you cannot know a priori whether there is a viable pathway that leads to all of these forms from a single ancestor. You have to find actual evidence for universal common descent; the mere fact that microevolution occurs won't tell you whether universal common descent is a possible explanation.if we are talking about the refinement of major traits then a gene that gives you 1% better vision or 1% better immunity is better than the status quo and is thus beneficial. fifty 1% improvements a million years later lead to a highly refined and specialized organ.
If we are talking about speciation. gene differences between populations accumulate naturally over time. eventually there are too many differences for reproductive compatibility.
Speciation has been observed on several occasions so that's a moot point.Yes, we're talking about speciation -- that's what the thread's about. Even most creationists will accept that evolution can produce closely related species. But can you extrapolate that to the large-scale differences seen in the range of species seen in nature? My point is that you cannot automatically extrapolate, because you cannot know a priori whether there is a viable pathway that leads to all of these forms from a single ancestor. You have to find actual evidence for universal common descent; the mere fact that microevolution occurs won't tell you whether universal common descent is a possible explanation.
There seem to be a couple of confusions here. First, evolution is not a global optimization algorithm; all species are in the vicinity of local optima, not some global optimum (if that even means anything biologically). Second, while evolution is stochastic, it is strictly a local search procedure, at least in metazoans. Evolution will explore slightly suboptimal solutions, but strongly suboptimal ones will never last long enough for a species to move through that trough, and lethal solutions are impassible. Are there workable paths between the regions of viability? That question can only be answered empirically at this point, not by the kind of abstract argument you're using here.
Larger jumps (large insertions and deletions, for example) are possible, but as their effect gets larger, the probability of their hitting a viable solution drops sharply. This is true not only because the great majority of genome space is not viable (so picking random points is a very bad strategy), but also because offspring inherit not only a (possibly modified) genome from their parents, but also a developmental environment (e.g. the chemical environment of a fertilized egg). That environment is unlikely to support development of a very different organism.
No, it's not evidence for common descent that I want -- I'm a geneticist who specializes in the genetics of natural selection, so I'm reasonably familiar with the actual evidence. What I want is for you (or anyone else) to support the particular argument that is the subject of this thread. I think it's a bad argument, at least as it stands, and so far no one has made a serious effort to make it better.if it's evidence for common descent that you want, that can be found in the mtDNA, nucleic DNA, Molecular biology, protein sequences, and endogenous retroviruses. all of these are the result of heredity and show that species are related to each other, therefore common descent.
No, it's not evidence for common descent that I want -- I'm a geneticist who specializes in the genetics of natural selection, so I'm reasonably familiar with the actual evidence. What I want is for you (or anyone else) to support the particular argument that is the subject of this thread. I think it's a bad argument, at least as it stands, and so far no one has made a serious effort to make it better.
I agree that evo-devo provides the right framework for thinking through a lot of these issues, and is where many of the questions will end up being settled. One thing that seems likely is that simpler multi-celled organisms have much greater flexibility and can accommodate larger changes in body plans than can more complex organisms, which have complicated and more brittle developmental pathways.But as you state climbing a fitness peak is one thing. Crossing the valley between fitness peaks is another. However, I think there are a few things that make this feasible, one of which is not genetic.
First, Evolutionary Developmental Biology (Evo-Devo) has shown us that natural selection can not directly see developmental pathways.
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I agree that evo-devo provides the right framework for thinking through a lot of these issues, and is where many of the questions will end up being settled. One thing that seems likely is that simpler multi-celled organisms have much greater flexibility and can accommodate larger changes in body plans than can more complex organisms, which have complicated and more brittle developmental pathways.
Should it even be? I mean, what if there aren't always beneficial mutations like that? The organism gets stuck and/or goes extinct without descendants.Yes. So? The argument of the OP amounts to the claim that there are always beneficial mutations that take you farther away from the starting genotype for an organism. No one has showed that that is the case.
If there are enough cases when not all paths are blocked then the fact that not all point As have a reachable point B is quite irrelevant.If it isn't, then all beneficial mutations are going to do is permit an organism to track modest changes in the environment, or compensate for deleterious mutations that may have fixed by chance.
True. So the question is, are there enough cases? Looking at the evidence of common descent, it's clear that there are, in fact. My point is not that common descent is in any trouble, but that you really can't just assume there are no barriers that prevent microevolution from accumulating into macroevolution.Should it even be? I mean, what if there aren't always beneficial mutations like that? The organism gets stuck and/or goes extinct without descendants.
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If there are enough cases when not all paths are blocked then the fact that not all point As have a reachable point B is quite irrelevant.
You do seem to make sense... as I'm nowhere near a geneticist (though I'm slowly steering towards evo-devo right now) I think I'll accept your point.True. So the question is, are there enough cases? Looking at the evidence of common descent, it's clear that there are, in fact. My point is not that common descent is in any trouble, but that you really can't just assume there are no barriers that prevent microevolution from accumulating into macroevolution.
That is, the existence of microevolution is very weak evidence that macroevolution explains the diversity of life. The only reason we know that microevolution can accumulate to cause macroevolution on the global scale is that we know independently that macroevolution actually happened.
Now a geneticist, formerly a physicist. (Before that I was going to be a literary critic, but that didn't survive one year in grad school.)(BTW... in this thread you wrote you are a geneticist. IIRC in the thread that recently got here from Christian Apologetics you wrote you were a physicist. Are you both?)
True. So the question is, are there enough cases? Looking at the evidence of common descent, it's clear that there are, in fact. My point is not that common descent is in any trouble, but that you really can't just assume there are no barriers that prevent microevolution from accumulating into macroevolution.
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