Scientific Evidence for Universal Common Descent

[Jim]

That one seeks to resolve perceived social issues by establishing a dialogue with different sides ...

I see now where the confusion might be. I was discussing with @usfan a social problem that I thought might be a common interest between us. You thought that in my discussions with people on both sides of this middle-school spitwad fight I was on some kind of peace mission. That isn’t what I think I’m doing but I’m resigned to people thinking that no matter what I say, possibly because (uncomplimentary theories about social dynamics self-censored). Even so, I will point out sometimes that what other people think I’m doing is not what I think I’m doing. Even after 20 years of never seeing that make any difference to anyone, I can’t be sure that it never will. Besides, it wouldn’t be fair to let people imagine false things about what I’m thinking without pointing that out sometimes.

 

[Thief]

roots of the tree are very murky due to horizontal gene flow.

and the flow of water

also horizontal

 

[usfan]

@usfan I’m still confused about what you think you’re doing. Are you picturing yourself as Davy Crockett at the Alamo? Husayn at Karbala? Sometimes I’ve pictured myself as a Man of La Mancha, the little drummer boy, or Dorothy of Oz.

Self image fantasies are irrelevant in a rational, scientific based discussion.

Whether i see myself as a trangender female eskimo, or a talking lion, or a Crusader for a Cause, has no relevancy to the topic. I find these kinds of questions to be ad hom (to the man) deflections.

Science. Facts. Evidence. Reason. Arguments. These are the tools of a rational, scientific debate about a scientific theory. Arguments of authority, ad hominem, poisoning the well, and other such fallacies really are out of place, in a scientific discussion.

"We need to calculate the fuel needed to thrust the ship out of the gravitational field, and establish the orbit.. what figures, Werner, have you compiled?

..but before you answer, are you gay? Your second cousin goes to a fundamentalist church.. I'm not sure we can trust your motives. How can these figures be trusted? You used to work for Hitler! Some people don't like you, Werner.. anything you say here will be filtered through the narrative they have created, not anything factual you have said.."

Werner:

Please give me an example of what you would count as evidence for common descent.

If common descent were true, there would be several things we would expect.

1. Gene creation. New genes would constantly arise, adding traits & variability.
2. Fuzzy speciation. Organisms would share many common genetic structures. The ability to reproduce would be essential in transferring the DNA to new species.
3. Plug and play genetics. Genes would be identical, across organisms. Chromosome pairs would have many exact matches, in ancestral organisms.
4. Obvious vestigiality. Remnants of descendancy would clearly be seen, not just speculated and imagined.
5. Difficulty in narrowing breeds. If genes are constantly being 'created!', by some mysterious, undefined mechanism, low diversity levels would be impossible. New traits and abilities would constantly pop up, giving the organism more tools for adaptation. Extinction would be difficult.
6. Observable, repeatable experiments that show the ability of new gene creation, increases of genomic complexity (or decreases), and forcing, under laboratory conditions, the 'evolution' of new genetic structures.
7. Chromosomes, genes, blood, organs, and other things that are unique to each genotype would be interchangeable and switchable. There would not be the hard wired blueprint we see in the DNA.
8. 'Missing Links', would be abundant, with transitional species constantly demonstrating the ability of organisms to evolve into more complex organisms.
9. Other evidence, that allegedly proves the validity of this theory. If it is so plainly true, why is there no evidence for this common phenomena?
10. Reason and scientific methodology would be used to support the theory, instead of outrage, hysteria, and jihadist zeal.

My arguments do not hinge on my self image, my sexual preference, the schools i attended, nor my heritage.

 

[usfan]

Besides, it wouldn’t be fair to let people imagine false things about what I’m thinking without pointing that out sometimes.

I can only try to stick with science and empiricism, in this exercise. Those tools are powerless in restraining lies, propaganda, and false caricatures. To address them anytime they come up, reduces the thread to bickering and dickery, which seems to be the goal of the anti-science disrupters.

..anything to keep the subject deflected, distracted, and disrupted is preferable to a calm, rational, examination of facts. That is the only goal of the hecklers, as far as i can see.

 

[Polymath257]

If common descent were true, there would be several things we would expect.

1. Gene creation. New genes would constantly arise, adding traits & variability.

Which we see. Mutations do exactly this.

2. Fuzzy speciation. Organisms would share many common genetic structures. The ability to reproduce would be essential in transferring the DNA to new species.

And organisms *do* share many common genetic features.

3. Plug and play genetics. Genes would be identical, across organisms. Chromosome pairs would have many exact matches, in ancestral organisms.

Nope, this is not a consequence of common descent. Instead, we should expect that there would be *families* of proteins coming from a common origin with mutations determining the differences of detailed function. And this is precisely what we find.

As for chromosomes, they can and do duplicate and merge. We have evidence for both.

4. Obvious vestigiality. Remnants of descendancy would clearly be seen, not just speculated and imagined.

And we see this.

5. Difficulty in narrowing breeds. If genes are constantly being 'created!', by some mysterious, undefined mechanism, low diversity levels would be impossible. New traits and abilities would constantly pop up, giving the organism more tools for adaptation. Extinction would be difficult.

Wrong yet again. If variability is produced at a constant rate, then selection pressure above that rate would lead to less variability. Selection pressure less than this rate would lead to more.

And this is what we see.

6. Observable, repeatable experiments that show the ability of new gene creation, increases of genomic complexity (or decreases), and forcing, under laboratory conditions, the 'evolution' of new genetic structures.

We cannot force the direction of mutations, nor is that expected. But we certainly *do* see increases of complexity, new gene creation, etc.

7. Chromosomes, genes, blood, organs, and other things that are unique to each genotype would be interchangeable and switchable. There would not be the hard wired blueprint we see in the DNA.

Well, DNA is NOT a blue print in any typical sense. And no, we would NOT expect interchangability because we expect there to be mutations along the way interfering with such.

That said, you do realize that humans and chimps share some blood types, right?

8. 'Missing Links', would be abundant, with transitional species constantly demonstrating the ability of organisms to evolve into more complex organisms.

Since speciation is expected to happen in small populations, this is an incorrect deduction. That said, we *do* see many such 'missing links' in a variety of different lines of evolution.

9. Other evidence, that allegedly proves the validity of this theory. If it is so plainly true, why is there no evidence for this common phenomena?
10. Reason and scientific methodology would be used to support the theory, instead of outrage, hysteria, and jihadist zeal.

And reason *is* used to support it, but knowledge of specialized terminology is required as well as some background knowledge. Too many people who criticize evolution don't have the required background knowledge.

The same is true, for example, with those who criticize quantum mechanics or the Big Bang model. In general, they have no knowledge of any of the details and so are incompetent to make any criticism at all.

 

[usfan]

I think an understanding of the chromosome & some of the terminology would be good to clarify. So much of the misunderstandings about genetics & living organisms are due to flawed beliefs about the DNA, how it is assembled, what it does, & how it can change.

We have evidence that the equid line has changed chromosome numbers. It is theorized that at some point, a chromosome pair detached at the centromere, & reattached at a telomere, presumably at the fertilized egg level. We have mtDNA to indicate actual descendancy, but the chromosome pairs are different. But, under further examination, the structure of the chromosome 'arms' are the same, just rearranged at the centromere/telomere level.

This is not absolutely proven fact, but is merely a theory for HOW the equid line changed at the chromosomal level. it does fit with the more empirical evidence of mtDNA descendancy, however, so it is a pretty good theory. But, we do not see the same thing with canids.. some, but not as much. Nor do we see it with hominids, especially humans. So a particular trait from one genotype does not mean it can be universally applied to ALL genotypes. Each genomic structure is different, with different rules governing their propagation.

Also, as i noted in the earlier post, the number of chromosomes is not an indicator of ancestry.

Here are some chromosome pairs numbers from wiki:
Fennec fox Animals Vulpes zerda 64
Horse Animals Equus ferus caballus 64
Spotted skunk Animals Spilogale x 64
Mule Animals 63 semi-infertile
Donkey Animals Equus africanus asinus 62

We have mtDNA evidence that asinus & caballus are related. But there is nothing to indicate any genetic relationship with the fox or skunk. So the mere number of chromosomes is not a significant indicator, but the GENETIC structure in it, is. Both the asinus & caballus are from the same root haplogroup.. they are descended from the same ancestor. Their genetic STRUCTURE is the same. the fox & skunk are not. They are a different genotype, from a different haplogroup.

So it is not the number of chromosomes, but their structure, that is the indicator of ancestry.

 

[Polymath257]

I think an understanding of the chromosome & some of the terminology would be good to clarify. So much of the misunderstandings about genetics & living organisms are due to flawed beliefs about the DNA, how it is assembled, what it does, & how it can change.

We have evidence that the equid line has changed chromosome numbers. It is theorized that at some point, a chromosome pair detached at the centromere, & reattached at a telomere, presumably at the fertilized egg level. We have mtDNA to indicate actual descendancy, but the chromosome pairs are different. But, under further examination, the structure of the chromosome 'arms' are the same, just rearranged at the centromere/telomere level.

This is not absolutely proven fact, but is merely a theory for HOW the equid line changed at the chromosomal level. it does fit with the more empirical evidence of mtDNA descendancy, however, so it is a pretty good theory. But, we do not see the same thing with canids.. some, but not as much. Nor do we see it with hominids, especially humans. So a particular trait from one genotype does not mean it can be universally applied to ALL genotypes. Each genomic structure is different, with different rules governing their propagation.

Also, as i noted in the earlier post, the number of chromosomes is not an indicator of ancestry.

Here are some chromosome pairs numbers from wiki:
Fennec fox Animals Vulpes zerda 64
Horse Animals Equus ferus caballus 64
Spotted skunk Animals Spilogale x 64
Mule Animals 63 semi-infertile
Donkey Animals Equus africanus asinus 62

We have mtDNA evidence that asinus & caballus are related. But there is nothing to indicate any genetic relationship with the fox or skunk. So the mere number of chromosomes is not a significant indicator, but the GENETIC structure in it, is. Both the asinus & caballus are from the same root haplogroup.. they are descended from the same ancestor. Their genetic STRUCTURE is the same. the fox & skunk are not. They are a different genotype, from a different haplogroup.

So it is not the number of chromosomes, but their structure, that is the indicator of ancestry.

You are wrong that this is not seen in human ancestry. In fact, humans have a chromosome that is a merged version of two chimp chromosomes. And it works very similar to how you described the equuid merger. It shows that humans and chimps are from the same root primate group.

And, of course, you are right. Chromosome number alone is a very poor sign of relatedness. It *is* the more detailed information *on* the chromosomes that is superior for determining this.

 

[Jim]

Self image fantasies are irrelevant inI find these kinds of questions to be ad hom (to the man) deflections.

"We need to calculate the fuel needed to thrust the ship out of the gravitational field, and establish the orbit.. what figures, Werner, have you compiled?

..but before you answer, are you gay? Your second cousin goes to a fundamentalist church.. I'm not sure we can trust your motives. How can these figures be trusted? You used to work for Hitler! Some people don't like you, Werner.. anything you say here will be filtered through the narrative they have created, not anything factual you have said.."

Werner:

Give me a break, preacher. You know that I’m not using it as an argument, or to deflect from ... from ... from what exactly? Am I interrupting something? Am I missing something? Are you involved in some kind of fruitful, beneficial discussion with someone who is listening and trying to understand what you’re saying? Pardon me, I didn’t notice. I was just curious, that’s all. I won’t trouble you again. Carry on with ... with ... whatever you’re doing here. I’ll go find another sandbox to play in.

 

[usfan]

Fake Science:

1. e.coli have evolved to a different species!
2. Neanderthal is a separate species!
3. Horse tree is proof of evolution!
4. Whale ancestor proves evolution!
5. Vestigial organs prove we have evolved!
6. the 'tail' in the embyo shows we came from a fish!
7. archaeopteryx is a transitional species between bird & reptile!
8. Time proves evolution! Given enough time, anything is possible.
9. Fruit flies prove evolution!
10. Canidae proves common descent!

Etc, & etc. There are a lot more, but this should prove the point.
Now, the Real Science:

1. e.coli are the same species, that have adapted to digest citrates
2. Neanderthal was a tribe of humans, & their dna is evident in living humans now.
3. The mtDNA in equus can be traced, & descendancy evidenced for some haplotypes, but many speculative 'horse ancestors' are just speculative. There is no evidence that they descended. That is believed, only.
4. Whales: ..same as equus or canidae. Just because you can imagine a sequence of drawings, does not provide evidence that it happened. There is no evidence, genetic or otherwise, that this is true.
5. Almost all of the original 86 vestigial organs listed in the 1800s have been proven to be necessary, important organs in the human anatomy. They are NOT vestigial, just assumed, wrongly. Ignorance of function does not prove 'vestigiality!'
6. It is not a tail. It is a developing embryo. Any imagined similarity to a tail is a 'looks like!' fallacy.
7. There are multiple, conflicting theories about archaeopteryx. It is impossible to make a definitive statement about this extinct creature, that has much more evidence of it being a bird with claws & feathers. ..like many living birds do.
8. Time has no mechanism to affect major changes in the genome. There is nothing evidenced to support this claim. It is a belief, not a scientifically evidenced theory.
9. Fruit flies, even after millions of generations, remain fruit flies. They are of the same haplogroup, & the same genotype.
10. Canids remain canids, after millennia of observation. Their variability has decreased, over time, and lower diversity levels are observed. Arctic wolves produce themselves, with little diversity.

That is the difference between asserted science, & critical examination. Fake science is merely declared, with no evidence. Real Science examines the claims, applying the scientific method. IF the 'theory' does not stand under scrutiny, it is debunked. If it is asserted without evidence, it is dismissed without evidence

 

[usfan]

You are wrong that this is not seen in human ancestry. In fact, humans have a chromosome that is a merged version of two chimp chromosomes. And it works very similar to how you described the equuid merger. It shows that humans and chimps are from the same root primate group.

And, of course, you are right. Chromosome number alone is a very poor sign of relatedness. It *is* the more detailed information *on* the chromosomes that is superior for determining this.

I dispute the assertion that the chimp and human chromosomes show identical structure, and have merely reattached at the telomere level, as in equus. That is believed and assumed, but the structure is not the same.

1. Caballus and asinus have mtDNA evidence of common descendancy.
2. Caballus and asinus can interbreed, though produce an infertile mule.
3. Chimps and humans have no indication of common descendancy from the mtDNA marker. All humans have this indicator of ancestry, but it does not extend to chimps or any other primates.
4. Humans cannot interbreed with any other primate, nor any organism. There is no indication nor evidence that we descended from another transitional form, nor that we are evolving into something else. Humans have always been humans, and though there are many morphological differences, we all can interbreed and we all are descended from the same ancestral mother.

 

[Polymath257]

I dispute the assertion that the chimp and human chromosomes show identical structure, and have merely reattached at the telomere level, as in equus. That is believed and assumed, but the structure is not the same.

In what significant way is it different?

1. Caballus and asinus have mtDNA evidence of common descendancy.
2. Caballus and asinus can interbreed, though produce an infertile mule.
3. Chimps and humans have no indication of common descendancy from the mtDNA marker. All humans have this indicator of ancestry, but it does not extend to chimps or any other primates.

What mtDNA marker? Which of many?

4. Humans cannot interbreed with any other primate, nor any organism. There is no indication nor evidence that we descended from another transitional form, nor that we are evolving into something else. Humans have always been humans, and though there are many morphological differences, we all can interbreed and we all are descended from the same ancestral mother.

And the evidence is exactly opposite of this conclusion.

 

[TagliatelliMonster]

If common descent were true, there would be several things we would expect

Well, this might be interesting...

1. Gene creation. New genes would constantly arise, adding traits & variability.

The process is rather simple when you know gene duplication can and does happen, after which the duplicate can go on to become different from the original one through further mutation.

2. Fuzzy speciation. Organisms would share many common genetic structures. The ability to reproduce would be essential in transferring the DNA to new species.

How is that not exactly what we observe in the world? The boundaries between species can, at times, be so fuzy that there's actual debate about how to define "species"...

Exactly what one would expect, from a gradual process such as evolution.

3. Plug and play genetics. Genes would be identical, across organisms. Chromosome pairs would have many exact matches, in ancestral organisms.

"plug and play genetics"? Not sure what you mean by that.

In any case, exact cross-species matches are found all the time and actually form the very basis of phylogenetic trees. The magnitute of "shared dna" also matches expectations of how young or old the common ancestor is.

4. Obvious vestigiality. Remnants of descendancy would clearly be seen, not just speculated and imagined.

And it is.
To just a couple such obvious examples:
- unusable muscles to move ears in the direction of sound
- non-functioning eyes covered by a thick layer of skin (basically eyelids that can't be opened)
- tailbone (and what I can only call a tail in a fetus)
- goosebumps

5. Difficulty in narrowing breeds. If genes are constantly being 'created!', by some mysterious, undefined mechanism, low diversity levels would be impossible

1. there's nothing mysterious about the mutation known as gene duplication
2. diversity of species and variation within a species, are not the same thing. One thing I immediatly think off, when in a stable environment a species enters "local optimum" (ie: there are no more plausible evolutionary paths towards further improvement for the niche they are in), then diversity would be low, but every new generation will still be born with pretty much the same amount of variation. It's just that natural selection at that point, will favour the status quo.

New traits and abilities would constantly pop up, giving the organism more tools for adaptation. Extinction would be difficult.

Only if you ignore the fact that a gradual process like evolution can only work through the accumulation of micro-changes over many generation. Which is by definition rather slow, especially in more complex life with greater lifespans. So if environmental parameters (=selection pressures) change, they would have to change at a pace that gives the evolutionary process of life enough time for life to adapt to that new reality. If the changes are too drastic too quick, extinction follows.

6. Observable, repeatable experiments that show the ability of new gene creation, increases of genomic complexity (or decreases), and forcing, under laboratory conditions, the 'evolution' of new genetic structures.

Basically every agriculture program has covered this.
Then there's also the e-coli lab experiment, in which brandnew metabolic pathways evolved, giving one the populations access to a food source that none of the other populations (including their ancestors) could digest.

7. Chromosomes, genes, blood, organs, and other things that are unique to each genotype would be interchangeable and switchable.

Why?

Or perhaps first, what do you mean exactly?

8. 'Missing Links', would be abundant, with transitional species constantly demonstrating the ability of organisms to evolve into more complex organisms.

First, the terminology "missing link", makes no sense. It's conceptual creationist, or at best sensationalist, jargon that has no meaning in the actual science.
Suppose you have datapoint A and C with "missing link" B for which there are no fossils.
Suppose we find B. Did you find the "missing link"? Not really. You found B, but in doing so, you just created 2 more gaps... between A and B and between B and C. So now that you found the one "missing link", you only thing accomplished is that now you need to find not one, but TWO more "missing links".

The correct term, would be a "transitional". A fossil that shares traits / features with ancestral species, as well as traits with its off spring, which isn't present in its ancestors.

And we got a ridiculous amount of those.

9. Other evidence, that allegedly proves the validity of this theory.

just so you know: in science, evidence supports theories - it never proves them.

If it is so plainly true, why is there no evidence for this common phenomena?

Ignoring the evidence doesn't make it disappear.

10. Reason and scientific methodology would be used to support the theory, instead of outrage, hysteria, and jihadist zeal.

The only outrage, hysteria and jihadist zeal I'm seeing when it comes to topic of evolution, is the outrage hysteria and jihadist zeal coming from fundamentalist theist who can't accept scientific explanations because it conflicts with their bronze age tale of makebelief.

My arguments do not hinge on my self image, my sexual preference, the schools i attended, nor my heritage.

It seems to me that any of the "10 arguments" in this post of yours, are rather hinged on good old ignorance of what the science actually is all about.

 

[usfan]

Reproduction is more like a slot machine. Each time you pull the handle on 2 machines simultaneously, they produce a child slot machine. This child has the combined odds of the parents. If you continue this process, without adding new parent slot machines, the available traits within the children becomes depleted & certain traits become dominant. Hair, eyes, & other traits, become dominant, pushing the lessor used traits further back into genetic obscurity. Some of those parent traits are still there, but they are dormant, or relegated to obscurity because of the odds of them coming up again. THAT is how natural selection works. It is the same as breeding. You don't have an infinite choice of traits every time you reproduce. You don't have 'new!' traits or genes being created by some mysterious process.
"Selection acts upon existing variability."
The 'selection' process slowly eliminates them from the gene pool. This is the reason for lower levels of genetic diversity. This is observable, repeatable science.

 

[usfan]

In what significant way is it different?

The 'connection' between chimps and humans is asserted, based ONLY upon the chromosome count, and the assumed telomere reattachment.
Equus has evidence for this, not just speculation.

 

[Polymath257]

The 'connection' between chimps and humans is asserted, based ONLY upon the chromosome count, and the assumed telomere reattachment.
Equus has evidence for this, not just speculation.

No, it is NOT *only* based on those. There is a lot of other evidence, but the merging of the chromosomes is a strong piece of evidence.

 

[usfan]

Give me a break, preacher. You know that I’m not using it as an argument, or to deflect from ... from ... from what exactly? Am I interrupting something? Am I missing something? Are you involved in some kind of fruitful, beneficial discussion with someone who is listening and trying to understand what you’re saying? Pardon me, I didn’t notice. I was just curious, that’s all. I won’t trouble you again. Carry on with ... with ... whatever you’re doing here. I’ll go find another sandbox to play in.

This thread is about examination of empirical evidence.. to see if the belief in common descent is warranted by scientific methodology. It is not for everyone. A certain amount of nerdy empiricism is needed, instead of the relationship based relating that is common in most personal discussion threads.

I mean no offense, i just hope to keep the thread topical. Philosophical debates over beliefs are legion, in this forum. This one is for empirical science.

 

[Polymath257]

Reproduction is more like a slot machine. Each time you pull the handle on 2 machines simultaneously, they produce a child slot machine. This child has the combined odds of the parents. If you continue this process, without adding new parent slot machines, the available traits within the children becomes depleted & certain traits become dominant. Hair, eyes, & other traits, become dominant, pushing the lessor used traits further back into genetic obscurity. Some of those parent traits are still there, but they are dormant, or relegated to obscurity because of the odds of them coming up again. THAT is how natural selection works. It is the same as breeding. You don't have an infinite choice of traits every time you reproduce. You don't have 'new!' traits or genes being created by some mysterious process.
"Selection acts upon existing variability."
The 'selection' process slowly eliminates them from the gene pool. This is the reason for lower levels of genetic diversity. This is observable, repeatable science.

Wow. It looks to me like someone needs some basic education in how reproduction works at the genetic level.

 

[usfan]

No, it is NOT *only* based on those. There is a lot of other evidence, but the merging of the chromosomes is a strong piece of evidence.

So you assert. Do you have any evidence of a reattached telomere? Or any evidence of ancestry?

I presented it with equus. The mtDNA maternal marker, and the ability to reproduce indicate descendancy. The 'reattached telomere!', is a valid theory for the divergence between caballus and asinus. There is only chromosome numbers for the chimp/human theory.

Are the spotted skunk and horse related, because they both have 64 chromosomes? No. There has to be something else, to indicate descent. Equus has that. Hominids do not. That is believed and asserted, with no corroborating evidence.

 

[usfan]

Wow. It looks to me like someone needs some basic education in how reproduction works at the genetic level.

If you dispute my description, show where it is wrong. Casting aspersions is an ad hom deflection. Snarky innuendo is not a fact based rebuttal.

 

[TagliatelliMonster]

Reproduction is more like a slot machine. Each time you pull the handle on 2 machines simultaneously, they produce a child slot machine. This child has the combined odds of the parents. If you continue this process, without adding new parent slot machines, the available traits within the children becomes depleted & certain traits become dominant. Hair, eyes, & other traits, become dominant, pushing the lessor used traits further back into genetic obscurity. Some of those parent traits are still there, but they are dormant, or relegated to obscurity because of the odds of them coming up again. THAT is how natural selection works

Ow boy, what a terrible analogy.
No mention at all of a fitness test and even completely ignoring that a new generation also comes with its own mutations (ie: variations that are brand new to that newborn; so genetics that weren't inherited by mom and dad, but which might very well be past on to off spring)

If you are simply going to ignore 2 of the core principles of a process, then yeah, sure, the process won't work.

It is the same as breeding

It's not. When you breed something, every new generation adds its own variability. There also WILL be a fitness test: first the individual needs to be able to survive and secondly there will be an (artificial) selection concerning which individuals will be allowed to produce a new generation.

You don't have an infinite choice of traits every time you reproduce.

It's not infinit, indeed. But it's also not non-existing.
Every generations comes with its own, unique and brand new, set of choices.

You don't have 'new!' traits or genes being created by some mysterious process.

Indeed not by "mysterious" processes. Instead, just through genetic mutation which is then a candidate for selection. Not mysterious at all.

"Selection acts upon existing variability."
The 'selection' process slowly eliminates them from the gene pool.

By favouring certain other things, which are not only kept in the genepool, but spread out in it until it achieves fixation.

Only focussing on how changes are discarded, is only going to result in you missing how changes are also kept and spread in populations.

This is the reason for lower levels of genetic diversity. This is observable, repeatable science.

Sure, selection pressures regulate diversity.
But as I explained in a previous post, diversity in that sense is quite different from variation.