Challenges to Neo-Darwinism

[pood]

Here are a couple of topics that interest me, which might make separate threads, and I’d specifically like the input of actual biologists here (of which I guess Peez is one).

How much of a role does genetic drift play in evolution vs. natural selection? The biochemist Laurence Moran seems to think, based on his Sandwalk blog, that drift is pre-eminent, which he calls “evolution by accident.”

What, really, can we say about the possibility of life, or complex life, on other worlds? I’ve read that physicists and astronomers are generally optimistic about such life, but biologists not so much. It’s always pointed out that life started pretty quickly on the earth after it cooled, but it’s also noteworthy that it took a LOOOOONG time for eukaryotes to evolve. I am wondering whether that key step might be ridiculously unlikely, almost a one-off, suggesting that perhaps the complex life we see on earth might be unique, at least in the Milky Way?

 

[Politesse]

The huge difference between Eukaryotes and Prokaryotes. One hopes to see, perhaps via fossils, a progression from one form to the next, but Eukaryotes burst into existence leaving no "trail." The gulf between any Prokaryote and any Eukaryote is HUGELY greater than the difference between an amoeba and one cell from a giraffe, or between that giraffe cell and the cell of an apple tree. There are no missing links visible. The chronological ordering of the MANY evolutionary "inventions" which separate Prokaryote from Eukaryote must be guessed or deduced.

I'm no biologist, but this "challenge" does not seem meaningful to me at all, for two reasons:

• We have the scantest of fossil records for the Proterozoic, a handful of useful exposures, no idea of where and only a general guess at when the evolution of the Eukaryotes might have occurred. It's not as though we were looking at a plush library of possible sources of information and finding none where we would reasonably expect to; you're looking for something very specific and very likely to sweep up the evidence of its own occurence within a short period of time, within a canvas of time that is vast beyond ready comprehension. Worse than that, since changes within simple Eukaryota happen blindingly fast from an evolutionary standpoint. The whole mitochondrial structure could have developed in some unknown hidey-hole now lost to time and erosion within a few million years of the half-billion year long range we're looking at. It is probably more likely that we will never find a fossil imprint of the LECA organism than that we would. And if we did, as always, the Creationist line would not change at all except to now posit a new missing link to the proto-Eukaryotes then discovered. Metaphorically, you're saying "if an elephant went through this forest, where's it's trail", but the only piece of evidence you're waving around is a single uncrushed seed from a single pinecone out of the entire forest. Answer? Probably in another pinecone than the one you have. Luckily, we are not dependent solely on the fossil record for information about the distant past, this knowledge is also encoded in all of our genes.
• You're deeply exaggerating the degree of difference between them. What sort of scientific metric are you using to distinguish between "conceivable" and "inconceivable" here? Yes, they function differently. They are still cells, though, and obviously related to one another. They both possess DNA, built from the same base pairs, translated via ribosome. They are both sheathed in a plasma membrane, filled with cytoplasm. They're, you know, cells. How the major cellular families developed are among the hottest topics in all of paleobiology, and there are even some fairly radical theories (like Eukaryotic priority) still technically on the table. But the questions are about how they all diverged and when, not whether they are related in the first place. Take a swab of your cheek and you'll have all the evidence you need on that point.

My two cents.

 

[Swammerdami]

The HUGE gap between bacteria and eukaryotes does NOT threaten the validity of the neo-Darwinian model. I "shoe-horned" its mention here rather than start another thread. Still it is a challenge to guess at the evolutionary path, or even to contemplate possibilities.

The huge difference between Eukaryotes and Prokaryotes. One hopes to see, perhaps via fossils, a progression from one form to the next, but Eukaryotes burst into existence leaving no "trail." The gulf between any Prokaryote and any Eukaryote is HUGELY greater than the difference between an amoeba and one cell from a giraffe, or between that giraffe cell and the cell of an apple tree. There are no missing links visible. The chronological ordering of the MANY evolutionary "inventions" which separate Prokaryote from Eukaryote must be guessed or deduced.

You're deeply exaggerating the degree of difference between them. ... They both possess DNA, built from the same base pairs, translated via ribosome. They are both sheathed in a plasma membrane, filled with cytoplasm....

The difference between prokaryotes and eukaryotes is much huger than you imply.

Just for starters, a typical eukaryote cell has 30,000 times the volume of a typical prokaryote. Indeed the mass of just the DNA in the eukaryote exceeds the TOTAL mass of a prokaryote. This is key to eukaryote's raison d'être: Bacteria CANNOT achieve the high complexity of eukaryotes because they lack the size and energy production to support the large genome needed for complexity. Given linear dimension L, Bacteria are limited to energy production proportional to surface area (L²) while eukaryotes produce energy throughout the cell (L³). This is why bacteria cannot be large: their evolution emphasizes quick reproduction and rapid mutation as opposed to the complexity and sex-based evolution of eukaryotes.

The diversity of both prokaryotes and eukaryotes is huge; so, sure, you can find unusually large bacteria that are larger than unusually small eukaryote cells. But functionally the large bacterium will closely resemble ordinary bacteria, and the small eukaryote (ignoring degenerate cases like spermatozoa or red blood cells) will closely resemble ordinary eukaryotes.

Prokaryotes have a single circular chromosome while eukaryotes have several straight chromosomes usually arranged in pairs. Eukaryotes' genomes engage in mitosis, meiosis, RNA editing, intron snipping while prokaryotes do not. (Archaeotes' fission has some similarities to mitosis, but the fission of true bacteria doesn't.) The cell nucleus, which encloses various organelles in addition to the chromosomes themselves and facilitates mitosis, meiosis, etc. is the defining difference between Pro- and Eu-.

Here is a long list of differences (mostly borrowed from Nick Lane). There may be some seeming exceptions but most are just nits. For example the diverse eukaryotes lacking mitochondria were once thought to represent a "missing link" but are now known to have evolved from ordinary eukaryotes with mitochondria.

• Even within the nucleus, Eu- chromosomes are further protected by special proteins, lacking in Pro-.
• Pro- are kept rigid with cell walls, Eu- are not.
• Pro- cytoplasm is rather simple. Eu- are filled with stacks of membranes, sealed vesicles, and a dynamic internal cell structure, based on the endoplasmic reticulum. These and other membranes use the same underlying chemicals as prokaryote cell membranes, but these membranes are configured very differently.
• Eu- have specialized organelles such as Golgi apparatus, centrosomes and lysosomes. Pro- don't.
• All Eu- have sex. All Pro- do not.
• Many Eu- have phagocytosis. Pro- don't.
• Many bacteria can adapt (via mutation or DNA transfer) to a very wide range of environments or metabolic modes. Most eukaryotes can only survive in a specific metabolic niche.
• Eu- have mitochondria, the important organelle that made the rest of Eu- size and complexity possible. These are like cells within a cell, since mitochondria have their own DNA, RNA and ribosomes.
• While both Eu- and Pro- have ribosomes, bacterial ribosomes are smaller and do not implement all the functions of Eu- ribosomes. Watch this animation all the way: After a minute or so, see a special mechanism attach the ribosome with its still-incomplete protein to the ER (endoplasmic reticulum) so the protein will end up on the other side of a membrane or even outside the cell. Can bacteria do this? Bacteria don't even have an ER.
  
  And there are some (very minor) differences in the genetic codes of Pro- vs Eu-.

This is only a partial list of differences between Eukaryotes and Prokaryotes.

 

[Peez]

Here are a couple of topics that interest me, which might make separate threads, and I’d specifically like the input of actual biologists here (of which I guess Peez is one).

Guilty as charged.

How much of a role does genetic drift play in evolution vs. natural selection? The biochemist Laurence Moran seems to think, based on his Sandwalk blog, that drift is pre-eminent, which he calls “evolution by accident.”

It really depends on how one wishes to measure the roles. In some ways it is a bit like asking which of the legs of a three-legged stool plays a greater role. Genetic drift can be defined as a change in allele (gene) frequency in a population due to chance (accident). Natural selection can be defined as a functional relationship between a trait and average reproductive rate in a population: if variation in the trait has a genetic basis then evolution may result. Evolution may be defined as a change in allele frequency over time. Mutation (genetic mutation) can be defined as changes in genetic material (DNA), especially in alleles, and in the germ line (cells that may ultimately produce gametes such as sperm or eggs). (It can be more complex than this, but these definitions should serve us here.)

I think of mutation, genetic drift, and selection as being the three legs of the evolution stool. Certainly genetic drift happens all the time, though most notably in small populations, and can drive the evolution of various traits. It can even overpower selection. However, it does not drive the evolution of adaptations (traits that help organisms to survive and reproduce). Only selection is expected to accomplish that, but drift can facilitate selection by allowing a population to evolve traits that are initially bad for survival and/or reproduction, but which open the door to traits that favour good survival and/or reproduction. For example, imagine that the best body size (for survival/reproduction) for some organism is 100, the second best is 200, and the worst is 150. If we assume a smooth decrease in ‘fitness’ from 100 to 150, and then a smooth increase from 150 to 200, then just based on selection we would expect a population of these organisms with an average size of 160 will likely evolve up to body size 200 (assuming a genetic basis to body size). However, if the population is small, it is possible (though certainly not guaranteed) that the population with average size 160 might evolve to become smaller, due to drift, and might end up with an average size of 140, and from there selection could bring it down to 100. This is simplistic, but I hope that it explains what I mean.

What, really, can we say about the possibility of life, or complex life, on other worlds? I’ve read that physicists and astronomers are generally optimistic about such life, but biologists not so much. It’s always pointed out that life started pretty quickly on the earth after it cooled, but it’s also noteworthy that it took a LOOOOONG time for eukaryotes to evolve. I am wondering whether that key step might be ridiculously unlikely, almost a one-off, suggesting that perhaps the complex life we see on earth might be unique, at least in the Milky Way?

Every single star system we have explored has had at least one planet with life on it, but our sample size is rather small. Personally, I suspect that “life” is common, the processes that lead to its formation seem common and that formation seems almost inevitable. Of course the characteristics of “life” might be very different elsewhere. In any event I have no special insight, for the moment we can only speculate.

 

[Peez]

The HUGE gap between bacteria and eukaryotes does NOT threaten the validity of the neo-Darwinian model. I "shoe-horned" its mention here rather than start another thread. Still it is a challenge to guess at the evolutionary path, or even to contemplate possibilities.

Fair enough, but then you probably should not have introduced these topis with this:

This has all been off-topic of course. The thread isn't about Challenges to Darwinism in the 19th century, but about Challenges to Neo-Darwinism in the 21st and late 20th centuries.

Two topics I might discuss are

The difference between prokaryotes and eukaryotes is much huger than you imply.

Just for starters, a typical eukaryote cell has 30,000 times the volume of a typical prokaryote. Indeed the mass of just the DNA in the eukaryote exceeds the TOTAL mass of a prokaryote.

That may be true, but if we are discussing the evolution of eukaryotes from prokaryotes then that is less important. In fact the largest living prokaryotes can be 50,000,000 times the volume of the smallest living eukaryotes. Obviously the average difference in the size of modern cells is not a barrier to the evolution of one type from the other.

This is key to eukaryote's raison d'être: Bacteria CANNOT achieve the high complexity of eukaryotes because they lack the size and energy production to support the large genome needed for complexity. Given linear dimension L, Bacteria are limited to energy production proportional to surface area (L2) while eukaryotes produce energy throughout the cell (L3). This is why bacteria cannot be large: their evolution emphasizes quick reproduction and rapid mutation as opposed to the complexity and sex-based evolution of eukaryotes.

While I would agree that the more complex structure and genetics of eukaryotes has facilitated the evolution of larger cells and multicellular organisms, once again it is not clear how this bears upon the evolution of eukaryotes from prokaryotes. There are living prokaryotes with a genome 20 times bigger than that of some living eukaryotes.

The diversity of both prokaryotes and eukaryotes is huge; so, sure, you can find unusually large bacteria that are larger than unusually small eukaryote cells. But functionally the large bacterium will closely resemble ordinary bacteria, and the small eukaryote (ignoring degenerate cases like spermatozoa or red blood cells) will closely resemble ordinary eukaryotes.

It is not clear what point you are trying to make here.

Prokaryotes have a single circular chromosome while eukaryotes have several straight chromosomes usually arranged in pairs. Eukaryotes' genomes engage in mitosis, meiosis, RNA editing, intron snipping while prokaryotes do not. (Archaeotes' fission has some similarities to mitosis, but the fission of true bacteria doesn't.) The cell nucleus, which encloses various organelles in addition to the chromosomes themselves and facilitates mitosis, meiosis, etc. is the defining difference between Pro- and Eu-.

Indeed, eukaryotes have evolved a number of unique traits. Once again I am not clear on how this would provide a challenge to the neo-Darwinian synthesis. The same goes for the following list, but...

Pro- are kept rigid with cell walls, Eu- are not.

Not actually true. Almost all prokaryotes have a cell walls, and many eukaryotic cells do.

Many bacteria can adapt (via mutation or DNA transfer) to a very wide range of environments or metabolic modes. Most eukaryotes can only survive in a specific metabolic niche.

Vague and, I would argue, unsupportable.

In any event, if we are thinking about how an ancestral prokaryote evolved into an ancestral eukaryote, it is more useful to think about the simplest form of the eukaryote. That simple form then evolves more and more differences, over at least two billion years. While there are more differences between baceria and amoebas than between rabbits and oak trees, the same principle applies: enumerating the differences between the lagomorph and the tree will not help, you need to look at the ancestors of each.

 

[pood]

I think of mutation, genetic drift, and selection as being the three legs of the evolution stool. Certainly genetic drift happens all the time, though most notably in small populations, and can drive the evolution of various traits. It can even overpower selection. However, it does not drive the evolution of adaptations (traits that help organisms to survive and reproduce).

My interest in this topic, given my limitations as a layman who nevertheless has some perhaps more-than-basic understanding of evolutionary biology, was piqued by a sometimes acerbic exchange between the biochemist Larry Moran and Richard Dawkins at Moran’s Sandwalk blog. The two butted horns, so to say, over the evolution of rhinoceros horns and blood types, among other subjects. Moran positively stated that the evolution of blood types was a result of drift and seemed to argue, though not as conclusively, for the idea that horn evolution was also an example of drift. In general it seems Moran is arguing that most evolution, not just at the genotypic but also phenotypic level, is likely a result of drift (“evolution by accident,” as he calls it.) Dawkins, by contrast, says that perhaps fifty percent or more of evolution at the molecular level may be due to drift, but far less than that at the phenotypic level. Anyway, the fascinating exchange can be found here.

 

[Swammerdami]

Comments lead me to suspect that some Infidels felt I was trying to argue that the (one-time) evolution of Eukaryotes from Prokaryotes was too big a leap, and therefore unlikely or impossible.

NOT AT ALL! I was ONLY commenting that the huge gap between Prokaryotes and Eukaryotes seems INTERESTING.

This has happened here before. I make comments because something seems interesting, and others think I have some agenda. No. I thought the vast gulf between the simplest known Eukaryote and ALL prokaryotes is INTERESTING. If I thought that this "challenged" the evolutionary model I'd have said so explicitly.

In any event, if we are thinking about how an ancestral prokaryote evolved into an ancestral eukaryote, it is more useful to think about the simplest form of the eukaryote. That simple form then evolves more and more differences, over at least two billion years. While there are more differences between baceria and amoebas than between rabbits and oak trees, the same principle applies: enumerating the differences between the lagomorph and the tree will not help, you need to look at the ancestors of each.

But there is no nice phylogenetic tree to examine in relating eukaryotes to archaeotes. The "simplest [known] form of the eukaryote" already has ALL the differences from prokaryotes I listed above.

The ordering of those changes can only be guessed or deduced. I think it's widely agreed that mitochondria must have come first: They provided the energy density (in particular the L³ vs L² explained above) prerequisite for the increased size and complexity.

 

[Swammerdami]

... In fact the largest living prokaryotes can be 50,000,000 times the volume of the smallest living eukaryotes.

Interesting! Can you give a specific example? (Preferably not something like spermatozoa which are dependent on their multicellular "parent.")

 

[Peez]

Hi Swammerdami,

For the record, I did not get the impression that you are a creationist (though I did draw a parallel between one of your comments and a common creationist idea), and I agree that the issue is interesting.

The simplest known eukaryote in nowhere near as simple as the simplest eukaryote that ever lived. The fact that we do not have detailed information on the simplest eukaryote does not impose any special problems on the evolution of a eukaryote from a prokaryote, but it does make it more difficult for us to work out exactly how it happened. Although we have better information about the evolution of trees and rabbits from a common ancestor, the difference is not all that great: the earliest known ancestors of trees already have fundamental differences from the earliest known ancestors of rabbits.

Actually I don't have any reason to think that mitochondria came first. All the sources I have read put the evolution of the nuclear envelope (with endoplasmic reticulum) first, but I must admit that I have not read widely on this issue.

 

[Swammerdami]

Much or most of the posts in this thread are off-topic. I'm used to that here (and am indeed one of the worst offenders). In a thread about Biden we might veer into a discussion of the electoral college, then Greta Thunberg, be reminded that environmentalists are a "rapture-like cult", and so on!

And here come the most off-topic paragraphs of all! I'll enclose them in a Hide box to reduce my offense.

Spoiler: Off-Topic

An essay should be self-contained with no reference to the title, especially when that title is NOT a complete sentence. Did your High School English Teacher teach you this? Did mine teach me? (I honestly don't remember: Over 99% of everything I've learned was learned via independent reading or thinking.)

Blah blah blah. There are thread(s) for discussing Biden, thread(s) for discussing AOC, and so on. I saw no thread for interesting facts about evolutionary biology but wanted to post an article whose very title had a phrase similar to "Challenges to Neo-Darwinism." STUPID ME.

If someone wants to suggest a different, more general title please tell me and I will attempt to use my super-powers to change the title of this thread.

Meanwhile, please observe the rule Miss McNulty may have taught me 57 years ago. My posts will be self-contained. If I don't mention a "challenge" to "evolution" then ... wait for it ... I am NOT challenging evolution.

The simplest known eukaryote in nowhere near as simple as the simplest eukaryote that ever lived. The fact that we do not have detailed information on the simplest eukaryote does not impose any special problems on the evolution of a eukaryote from a prokaryote,

In my previous post I wrote THREE times that I was NOT challenging the hypothesis that eukaryotes evolved from prokaryotes. I thought that was excessive, but it appears I did not mention it enough!! I'll try once more, and then simply give up.

I am NOT challenging the hypothesis that eukaryotes evolved from prokaryotes.

Actually I don't have any reason to think that mitochondria came first. All the sources I have read put the evolution of the nuclear envelope (with endoplasmic reticulum) first, but I must admit that I have not read widely on this issue.

My information comes from Nick Lane. I've read two of his books (and reviewed some of his on-line papers). They are wonderful, very rich books and report on much recent (21st century) research and thinking. It was foolish of me to think I could or should try to summarize the huge amount of information in these rich books, and I'll try to resist further temptation.

On the matter of Which came first: the mitochondrion or the nucleus, Lane stipulates that this is controversial but offers at least two arguments favoring the mitochondrion. I've already mentioned one: L-cubed versus L-squared energy production (Lane does NOT explain it this way). Another argument may be even more convincing.

Everyone agrees (I think) that eukaryotes are a "chimera" (Lane's word) between an archaeote and a true bacterium: they have lots of DNA from EACH of those two Domains. (Lateral DNA transfer complicates the issue but ... guess what ... I can't summarize Lane's entire book in this post.) The bacterial DNA was presumably introduced when a bacterium was engulfed (into a symbiosis) and became the first mitochondrion. To postulate a pre-existing nucleus would put the cart before the horse.

 

[Peez]

Interesting! Can you give a specific example? (Preferably not something like spermatozoa which are dependent on their multicellular "parent.")

Spermatozoa are functional eukaryotic cells, albeit highly specialized. However, that is not what I was thinking of.

Thiomargarita namibiensis is a roughly spherical bacterial cell that can be up to 300 microns in diameter.

Ostreococcus is a roughly spherical eukaryotic organism about 0.8 microns in diameter.

​

 

[Jokodo]

Here are a couple of topics that interest me, which might make separate threads, and I’d specifically like the input of actual biologists here (of which I guess Peez is one).

Guilty as charged.

How much of a role does genetic drift play in evolution vs. natural selection? The biochemist Laurence Moran seems to think, based on his Sandwalk blog, that drift is pre-eminent, which he calls “evolution by accident.”

It really depends on how one wishes to measure the roles. In some ways it is a bit like asking which of the legs of a three-legged stool plays a greater role. Genetic drift can be defined as a change in allele (gene) frequency in a population due to chance (accident). Natural selection can be defined as a functional relationship between a trait and average reproductive rate in a population: if variation in the trait has a genetic basis then evolution may result. Evolution may be defined as a change in allele frequency over time. Mutation (genetic mutation) can be defined as changes in genetic material (DNA), especially in alleles, and in the germ line (cells that may ultimately produce gametes such as sperm or eggs). (It can be more complex than this, but these definitions should serve us here.)

I think of mutation, genetic drift, and selection as being the three legs of the evolution stool. Certainly genetic drift happens all the time, though most notably in small populations, and can drive the evolution of various traits.

I feel this is an important point - effective population size really has a huge effect on the relative contribution of genetic drift vs. selection. For the more visually inclined among us, I ran a few rounds of simulating evolution in a very simplistic model population of different size, and with mutants with different magnitude of selective advantage. The model has a population of size n that starts out with 5% carriers of a beneficial mutation which affects the average number of offspring but not survival. I.e., each cycle has a procreation phase where each individual spawns a random number of offspring uniformly spread around a mean of 5 with a standard deviation of 3 for the wildtype, and for the beneficial mutations I simply shift the mean - I refer to a mutation with a mean of 5.1 as having a 2% selective advantage. In the culling phase that follows, a random sample of size n of the offspring is selected to survive to the next round.

• Here:s a typical result with an effective population size of 100,000 and a selective advantage of 2%. What we see here is a pretty smooth sigmoid curve with a long tail. As in the next images, x is number of generations since begin of simulation, y is number of wildtype individuals at the end of the generation (n=100000, b=1.02):
  
• Same with a population of just 10,000 - still a discernable sigmoid curve, but more pronounced "teeth" (n=10,000, b=1.02):
• Now with a population of 100, the most typical result actually is that the beneficial mutation hits the closest wall in its random walk pretty soon, i.e. becomes extinct despite being beneficial by hitting a frequency of less than 1 individual through random fluctuations, sometimes pretty instantly, sometimes after making some headway (n=100, b=1.02):
  
  
  
• Even if it does become dominant, the path is much less straightforward (n=100, b=1.02):
• It may even become extinct after initially becoming dominant (n=100, b=1.02):
  
• With a smaller benefit, similar randomness is observed in larger populations. This is with an effective population of 10,000 (remember the fairly smooth curve above?) and a selective advantage of 0.1% (n=10,000, b=1.001, initial frequency=0.02):
  
• We even sometimes observe it going extinct again in the larger population size when the benefit is smaller (n=10,000, b=1.001, initial frequency=0.02 - typical outcome for these parameters!):
  

Of course this is with one mutation. In a real-life scenario with many mutations randomly occurring, a small subset of them will reach fixation in small populations despite being slightly detrimental, much the same way this one beneficial mutation often times failed to become dominant. In the larger populations, they will instead co-exist with the wildtype for many generations but very rarely become dominant.

 

[Gun Nut]

Some Infidels may have overlooked the key point of the research.

Obviously natural selection (in regions where malaria is endemic) will favor propagation of any HbS mutation which arises by chance. But the researchers measured the rate of NEW HbS mutations, i.e. individuals who had HbS even though NEITHER parent had it. That NOVEL mutation, arises randomly in Darwin's model, but was more likely to occur in Africa than in non-malarial regions.

This result, if valid, may be the "opposite side of the coin" posited in this research.

Why would an environment that damages the lungs increase the likelihood of lung cancer, but not prostate cancer? Same reason exposure to an environment that supports malaria might increase the likelihood of an HbS mutation, but not a Glu mutation.

 

[Peez]

I think of mutation, genetic drift, and selection as being the three legs of the evolution stool. Certainly genetic drift happens all the time, though most notably in small populations, and can drive the evolution of various traits. It can even overpower selection. However, it does not drive the evolution of adaptations (traits that help organisms to survive and reproduce).

My interest in this topic, given my limitations as a layman who nevertheless has some perhaps more-than-basic understanding of evolutionary biology, was piqued by a sometimes acerbic exchange between the biochemist Larry Moran and Richard Dawkins at Moran’s Sandwalk blog. The two butted horns, so to say, over the evolution of rhinoceros horns and blood types, among other subjects. Moran positively stated that the evolution of blood types was a result of drift and seemed to argue, though not as conclusively, for the idea that horn evolution was also an example of drift. In general it seems Moran is arguing that most evolution, not just at the genotypic but also phenotypic level, is likely a result of drift (“evolution by accident,” as he calls it.) Dawkins, by contrast, says that perhaps fifty percent or more of evolution at the molecular level may be due to drift, but far less than that at the phenotypic level. Anyway, the fascinating exchange can be found here.

We should certainly avoid assuming that every trait we look at is 'adaptive' and the product of selection. Virtually all traits probably have had drift as a contributor, but I would tend to side with Dawkins here.

 

[Peez]

Much or most of the posts in this thread are off-topic. I'm used to that here (and am indeed one of the worst offenders). In a thread about Biden we might veer into a discussion of the electoral college, then Greta Thunberg, be reminded that environmentalists are a "rapture-like cult", and so on!

And here come the most off-topic paragraphs of all! I'll enclose them in a Hide box to reduce my offense.

Spoiler: Off-Topic

An essay should be self-contained with no reference to the title, especially when that title is NOT a complete sentence. Did your High School English Teacher teach you this? Did mine teach me? (I honestly don't remember: Over 99% of everything I've learned was learned via independent reading or thinking.)

Blah blah blah. There are thread(s) for discussing Biden, thread(s) for discussing AOC, and so on. I saw no thread for interesting facts about evolutionary biology but wanted to post an article whose very title had a phrase similar to "Challenges to Neo-Darwinism." STUPID ME.

If someone wants to suggest a different, more general title please tell me and I will attempt to use my super-powers to change the title of this thread.

Meanwhile, please observe the rule Miss McNulty may have taught me 57 years ago. My posts will be self-contained. If I don't mention a "challenge" to "evolution" then ... wait for it ... I am NOT challenging evolution.

The simplest known eukaryote in nowhere near as simple as the simplest eukaryote that ever lived. The fact that we do not have detailed information on the simplest eukaryote does not impose any special problems on the evolution of a eukaryote from a prokaryote,

In my previous post I wrote THREE times that I was NOT challenging the hypothesis that eukaryotes evolved from prokaryotes. I thought that was excessive, but it appears I did not mention it enough!! I'll try once more, and then simply give up.

I am NOT challenging the hypothesis that eukaryotes evolved from prokaryotes.

Actually I don't have any reason to think that mitochondria came first. All the sources I have read put the evolution of the nuclear envelope (with endoplasmic reticulum) first, but I must admit that I have not read widely on this issue.

My information comes from Nick Lane. I've read two of his books (and reviewed some of his on-line papers). They are wonderful, very rich books and report on much recent (21st century) research and thinking. It was foolish of me to think I could or should try to summarize the huge amount of information in these rich books, and I'll try to resist further temptation.

On the matter of Which came first: the mitochondrion or the nucleus, Lane stipulates that this is controversial but offers at least two arguments favoring the mitochondrion. I've already mentioned one: L-cubed versus L-squared energy production (Lane does NOT explain it this way). Another argument may be even more convincing.

Everyone agrees (I think) that eukaryotes are a "chimera" (Lane's word) between an archaeote and a true bacterium: they have lots of DNA from EACH of those two Domains. (Lateral DNA transfer complicates the issue but ... guess what ... I can't summarize Lane's entire book in this post.) The bacterial DNA was presumably introduced when a bacterium was engulfed (into a symbiosis) and became the first mitochondrion. To postulate a pre-existing nucleus would put the cart before the horse.

I did not think that you were challenging the hypothesis that eukaryotes evolved from prokaryotes (no need to yell). I was merely addressing the fact that you were exaggerating the relevant differences.

 

[pood]

Paper in OP debunked here.

 

[Peez]

Paper in OP debunked here.

Nice commentary. So, the original article is an example of pseudoreplication. <https://en.wikipedia.org/wiki/Pseudoreplication?msclkid=667efbd5cffe11eca821ea4344c41b34>.

 

[Jokodo]

Thiomargarita namibiensis is a roughly spherical bacterial cell that can be up to 300 microns in diameter.

Incidentally, that's also larger than the smallest insects.

 

[Swammerdami]

Paper in OP debunked here.

Thanks, pood!

Further, the genetic evidence referred to above suggests that the HbS variant prevalent in human populations traces its ancestry back to a single ancestral mutation (Shriner and Rotimi, 2018; Laval et al., 2019) , so that there is no reason to believe that a high mutation rate has enabled multiple copies of the mutation to spread.

That is one thing that confused me about the paper's claim. I knew specific mutations were quite rare but the paper's claim would probably be relevant only if new versions of the HbS mutation were being passed on hundreds of times.

It does seem impressive they could test millions of sperm cells. I guess DNA tests have become VERY cheap.