In order to believe Micro but not Macro evolution, you must...

[sfs]

evolution works by modest changes. large changes = modest changes over time.

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?

 

[CACTUSJACKmankin]

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?

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.

 

[sfs]

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.

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.

 

[CACTUSJACKmankin]

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.

Speciation has been observed on several occasions so that's a moot point.

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.

 

[Loudmouth]

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.

Apparently, there are 6 billion different ways of making a human. As you state elsewhere, genome space within a species is quite large. At the same time there is no doubt that mutations do result in non-viable offspring, or offspring that are incapable of producing offspring which is the nearly same thing in the eyes of natural selection. Microevolution is very doable.

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. An embryo is not selected for or against by environmental factors until after their development. This allows for novel changes to occur in developmental pathways. These changes can occur early in a developmental cascade which would produce larger changes or farther down in the cascade which would produce smaller changes.

Second, stable environments produce specialists which climb their fitness peaks to the point that they can no longer go back to the valley floor and cross to another fitness peak. However, drastic changes in environments kill off specialists which opens up niches for generalists who occupy the positions closer to the valley floors. In addition, areas at the edge of a ecological range also provide areas where valleys can be crossed which is why Gould and Eldridge proposed Punctuated Equilibria as a mode of evolution that can produce macroevolution.

 

[sfs]

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.

 

[Loudmouth]

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.

The only way to make it better is to look for viable transitional steps that link two divergent morphologies. IOW, more research is needed. Darwin played the same "Devil's Advocate" game. He referred to the eye as one example. He showed that there were viable steps in the evolution of the complex eye, using the brachiopods as an example where one can see very simple to very complex eyes with obvious transitional states.

 

[sfs]

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.
[...]

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.

 

[Loudmouth]

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.

I completely agree. Complex metazoans built upon the basal developmental pathways seen in less complex organisms. These became the foundation for the major clades. Once further developmental adaptations were built upon these foundations it became impossible to go back and change the foundation without completely disrupting the developmental pathways that sat atop them. This is somewhat analogous to specialists who can not descend their fitness peaks to the valleys below.

 

[Naraoia]

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.

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.

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.

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.

 

[sfs]

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.
[...]
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.

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.

 

[Naraoia]

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.

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.

(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?)

 

[sfs]

(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?)

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.)

 

[Naraoia]

Now a geneticist, formerly a physicist.

Thanks for clarifying.

(Before that I was going to be a literary critic, but that didn't survive one year in grad school.)

 

[Loudmouth]

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.

Yep, I agree. For example, it would be very difficult to nigh impossible for a mammal to evolve into a tetrablastic organism. However, it would be much easier for a basal triploblastic organism to evolve into a tetrablastic organism. There really can be barriers (see evo-devo) that microevolution would have a tough time crossing.