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1 up, 1 reply
Evolution is defined in biology as change in the frequency and nature of heritable traits in living organisms over successive generations, cumulatively resulting in biodiversity by means of selective pressures. Evolution, therefore, is a fact of population genetics which has been directly observed happening out in the real world in the current day and age on numerous occasions, whether it be by natural, sexual, or artificial selection. In my time I've met few creationists who deny this fact. Creationists, however, claim that when it comes to biodiversity, this evolutionary process has arbitrary limits beyond which it is impossible for two species to have shared a common ancestor. And so I must ask the question; where do you draw this arbitrary line?
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1 up, 1 reply
I suppose I should have specifically said "macro-evolution" instead of just "evolution". The definition you gave had two parts: "change in frequency" and "change in nature" of heritable traits. I hold that both of these are constrained by real, non-arbitrary limits.

The change in frequency for heritable traits is known as "micro-evolution", and is in-fact scientifically observable. However, it is limited to selecting only from pre-existing genetic traits. While many combinations of genetic traits are possible within the genome of any given species, these are merely new organizations of already-present genetic information. One of the main limits of this re-organization is that species generally cannot mate successfully with other species (and in the few cases they can, the offspring are infertile)

As for the change in nature of heritable traits, there are only a few ways that this occurs: mutation, and a few extra-genetic factors. The vast majority of mutations are harmful to the creature mutated, or at the very least result in decreased fertility. I must admit that I do not know much regarding extra-genetic factors, but if I'm not mistaken, most of them have relatively small effects (such as making the descendants of an alcoholic more prone to alcohol addictions).

It's honestly been a while since I've brushed up on this stuff, so please correct me if any of the information I've given is incorrect.
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1 up, 1 reply
I'll start by clarifying the distinction between macro and micro evolution; microevolution is the change in allele frequencies within interfertile populations, whereas macroevolution refers to evolutionary processes on the scale of one or more speciation events, though the line between the two often becomes blurred. Both are the result of change in the frequency/nature of alleles over successive generations. And yes, speciation events and macroevolution have been observed occurring in real time. But creationists contend that such observed instances of macroevolution are "insignificant;" it's always one species of lizard diverging into more lizard species, or a species of finch diverging into multiple, but never a big change like a species of lion evolving from a species of mouse (which of course, is not how evolution works.) This is what I mean by creationists setting arbitrary boundaries; they might accept, for example, that all snake species are descended from one or several original "snake kind(s)." But they'll argue that snakes and other squamata (such as lizards) are just "too different" to have a common ancestor.

Your comment that mutations are mostly harmful isn't correct; the overwhelming majority of them have inconsequential effects. And while harmful mutations are still more frequent than beneficial ones, sufficient beneficial ones do occur for selective pressures to increase biodiversity. The only constraint imposed by the rarity of beneficial mutations is how long evolution takes, not what can evolve in the first place. You also mentioned extra-genetic factors. These factors are called epigenetics, and they mutate far more easily and quickly than DNA. They control whether a gene or trait is expressed, so they can have a very significant and diverse effects on organisms, though Genetic mutations remain the strongest driving force for evolution.

As for change in frequency of alleles within a population, the main way this happens besides natural selection is what's called "genetic drift." That is, allele frequencies within a population tend to vary somewhat randomly over time. If a population splits into two, some traits will happen simply by chance to be exclusive to one splinter group, meaning the two groups will be genetically distinct populations. And once the two groups are separate gene pools, different mutations build up in each one over generations to the point that the two groups are no longer interfertile, resulting in speciation.
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1 up, 2 replies
It sounds to me like speciation is going in the wrong direction for the molecules-to-man evolutionary narrative. The way you describe it, it sounds like it just creates more restrictions on the exchange of genetic information. If one was to use the process of speciation to try and point out a common ancestor for all life, then that common ancestor would need to have had a far more expansive and diverse gene pool than any creature alive today, which makes the question of spontaneous generation even more far-fetched than it already is in the main-stream evolutionary narrative.

The only way around this is to show that macro-evolution could occur through beneficial mutations that add genetic information. I have yet to hear of any such mutations, but I would be interested if you have any specific examples.

You cite "selective pressures" as a cause for producing beneficial mutations, but I fail to see how natural selection could possibly motivate mutations, seeing as they are not some sort of voluntary action. Natural selection is a process of destruction, breaking down what doesn't work and giving no guarantee of creating anything new to take their place. It might pressure a creature to learn new patterns of behavior, which might go on to have epigenetic effects, but it cannot cause the generation of mutations (it can only destroy any mutation that proves unsuccessful).

Finally, you say that speciation through the combination of mutations with regular genetic processes is capable of explaining the decent of all life from a common ancestor. You also claim this to be a very gradual process. If this is as gradual a process as you claim, then why are there distinct species at all, as opposed to some genetic spectrum? Why are there neatly divided and classified groups of inter-fertile creatures, as opposed to all individual creatures having overlapping ranges of fertility?
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2 ups
Let me clarify a few things. I didn't say that selective pressures create mutations, I said they act upon them. If a mutation has a positive effect on an organism's survivability or reproductive fitness, then that organism is more likely to pass on its genes to the next generation. For this reason, beneficial traits will typically become more frequent in a gene pool over time, whereas deleterious traits tend to be weeded out. So the statistical process of natural selection not only selects against harmful traits, but selects for advantageous ones. Additionally, you mention the "molecules to man" narrative and "spontaneous generation." Of course biologists don't believe in spontaneous generation today, which has long since been replaced by theories of abiogenesis, but ultimately it's actually not relevant to the veracity of evolution. Evolution does not deal with the non-life to life transition, though such a transition would be a continuum with no clear-cut point at which biogenesis ends and life begins. So one could assume that God created the first life, and evolution would still be a fact.

I think a point of confusion here might be your idea of "new information." You seem to imply that you think change in genetic function, or "new information," must entail an increase in genetic material, which it does not. Mutations can simply change the function of existing codons, rather than adding new ones or removing an existing ones. Though there are in fact evolutionarily significant ways of increasing the amount of DNA in an organism's genome (such as transcription errors and parasitic DNA,) this is somewhat beside the point. Mutations result in new traits without any need for a larger genome. One example of a beneficial mutation can be found in a species of bacteria that lives in the waste water of a nylon plant. A functional error in a DNA repair protein had resulted in an extra nucleotide being inserted into the bacteria's pOAD2 plasmid; this nucleotide insertion resulted in a series of what are called frame shifts, which resulted in the DNA coding for a brand new enzyme that allowed the bacteria to digest the nylon present in the water.
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2 ups, 1 reply
As for your question concerning genetic spectrums. Speciation occurs due to various forms of reproductive isolation such as the example I gave in my last comment, where a population has splintered into two groups which no longer interbreed. This reproductive isolation almost always occurs for geographic reasons, such as by geographic barriers. The concept of genetic spectra does occur frequently in nature, but this can still result in speciation over time, since one end of a spectrum will not be interfertile with the other. For example, population A may be able to breed with population B, and B may be able to breed with population C, but population C will be too genetically distinct to breed with population A. Then, for example, population C and adjacent groups of population B might be struck by a disease which only certain members of population C happen to be resistant to. All effected groups of populations B and C that don't happen to breed with the resistant members of population C will be at a severe survival disadvantage, and will either become assimilated into the gene pool of the resistant C population or be severely reduced in their population size. All B members outside the disease's range can then continue to breed among themselves and with population A unharmed. The result is that the spectrum has become so polarized that simple genetic drift and population movements can break the population continuum altogether, resulting in speciation. What I have delineated here is one rather specific example of many possible ways a gene-pool spectrum can be broken. As I said, it's often as simple as one group migrating away from the original population.
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1 up, 1 reply
Okay, I was under the impression that you were trying to assert that selective pressures can increase the chances of mutations occurring in the first place, as opposed to maintaining mutations after they occur. I think we are now on the same page with that definition of selective pressure and its functions.

As for my point on mutations and new information, I am well aware that many mutations take away or simply reorganize DNA. What I was trying to say is that mutations based on addition of information would be required to fit the narrative of evolution from abiogenesis, since abiogenesis favors the idea of the first living creature being relatively simple with as little DNA as possible. If one wishes to debate from a standpoint of theistic evolution as opposed to naturalistic evolution, then the discussion is completely different (since matters of doctrine or theology would be much more "on the table" in such a discussion).

Your response to my question on genetic spectrums makes a lot of sense.
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0 ups, 1 reply
You said that abiogenesis favors the idea of the first living creature being relatively simple with as little DNA as possible; this isn't quite accurate. Theories of abiogenesis involve a long series of developmental steps between simple organic molecules and anything that can be categorized as life. In these series of steps, the development of DNA happens well before organic chemistry fits every category that constitutes life, at a stage more akin to a protobiont or virus; so the first organisms that could be christened life would already have a sizeable amount of DNA. And primitive unicellular organisms happen to be quite proficient at increasing the size of there genome through gene transfer or absorbing outside genetic material. And as I mentioned earlier, new chunks of genetic material can be added to a genome by parasitic DNA (typically from viruses) or through transcription errors in which chunks of a genome are duplicated. In some organisms, such as many plants, the entire genome can be doubled through a single duplication event.

And I am still arguing for naturalistic evolution, my point was just that a naturalistic theory of evolution does not require a naturalistic explanation for the origin of life, and would not be proven false if the latter were impossible.

But I'm glad my explanation on speciation made sense, I was a little worried that I may have made it a little hard to follow XD
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1 up, 3 replies
Honestly everything you are saying is making good sense to me. However, that is not the same as me saying that it is convincing. I think speciation and mutation are insufficient for explaining how all life could have a common ancestor (a naturalistic explanation fails to account for things such as specified complexity, while a theistic approach makes very little sense ant all)

I am not debating on the existence of speciation or genetic drift (I affirm both), but the idea of universal common descent. Universal common descent is not inspired from any compelling evidence (fossil records rather show multiple different kinds of creatures existing as soon as the first life), but rather seems to me to be a way to avoid figuring out how abiogenesis could occur multiple times to give rise to distinct kinds (naturalistic abiogenesis is far-fetched enough as it is, so saying it has happened multiple times is almost unthinkable)

I am not certain exactly where I would draw the lines on which creatures are parts of which "kinds" (since Genesis does not give specific classifications, but rather uses general terms like "creeping things" or "livestock"), but I am fairly certain that many types of creatures are simply too different to be descended from the same ancestor (for instance, a scorpion and a cow).
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0 ups
Concerning a point at which common descent is impossible, let me put it like this… The physiology and function of all life is determined by DNA. The DNA content of organisms is constantly changing over successive generations through mutations and natural selection, resulting in speciation. As more and more time passes, more and more genetic differences accumulate, and the number of speciation events that have occurred continue to pile up. Therefor, given enough time, is it not the case that large physiological and functional differences between various organisms will not only be ultimately possible, but inevitable? I think I'll also note that on average, the genes of vertebrates like cows and arthropods like scorpions are 60% identical, that's how similar they are.

Then there's the issue of specified complexity. All theories concerning Dembski's proposal of "specified complexity" are manifestly false. Information Theory demonstrates that Dembski's hypotheses cannot be mathematically substantiated, and his entire thesis hinges on a strawman argument; namely, that a simple smooth mathematical function cannot increase in information. While correct, this is not relevant to evolutionary theory, which functions by a combined system of branching replication and selective mapping, and thereby his entire argument collapses. He also misuses statistics and Information Theory through his use of arbitrarily specific outcomes.

And while I'm here, I think I'll address the similar problem of irreducible complexity as well. The irreducible complexity argument states that complex systems of interdependent parts cannot possibly evolve, because the omission of any one component will result in the system failing to perform it's function. The main reason why this argument fails is because it assumes that new functions cannot be derived by repurposing something which originally had a different function, a phenomenon which is very commonplace in nature. All biological systems claimed to be "irreducibly complex" have since been shown to be composed of parts that have already been used for some biological function in the past.
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0 ups
Also, I'm not sure what you're talking about when you say "multiple different kinds of creatures existing as soon as the first life…" as this is not what we see. The first two and a half billion years of life consisted of nothing but primitive unicellular organisms. Life then spends the next billion years evolving cooperative unicellular organisms like algae mats, then yet another hundred million years evolving the most primitive multicellular organisms. Only then do we get the so called "Cambrian Explosion," which I suspect is what you were referring to. It's called an explosion because it's a period in which we see the sharpest increase of biodiversity in Earth's history, not because it happened all at once. In fact this "explosion" was about fifty million years long, and left a rich fossil record that shows a logical evolutionary progression of biodiversity. The reason for why this increase in diversity was so "quick" compared to previous eras of life's history is likely that life had finally evolved a system of complex cooperative tissues, allowing for a much grater range of evolutionary possibilities. And life took full advantage of these possibilities, with life being as of yet relatively unspecialized, and almost all evolutionary niches unfilled; evolution has never since had so much room to play with biodiversity.
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0 ups, 2 replies
I cry every time :'(
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1 up
Sorry for my absence, I've been booked between finals, graduation, and a full-time job
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1 up, 1 reply
I'll have my next reply in the debate ready in a few days or so, maybe.
0 ups
No worries mate. Best of luck!
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