Random Mutations

[FreeThinker]

I understand that most mutations are a disadvantage to the particular organism.

 

I can see how a random mutation (tiger with bigger teeth, faster antelope…)could be of benefit to a particular organism, and how that mutation would populate the entire species over a period of time.

 

Now here is the part I can’t quiet get my head around; with the miscopying of DNA it seems to me as if the number of possible mutations is close to infinite. So how do we get a series of mutations that develops a certain aspect of the body, such as feathers on birds? My process of reasoning takes me through these steps:

 

1. A certain reptile developed skin in between its claws (SBC) making it more air resistant and able to jump of higher rocks (for example).

2. The particular reptile survives to pass the genes for SBC to its offspring. Soon we have a whole population of the particular reptile species with SBC.

3. More miscopying of DNA results in the skin developing to reach the end of the claws. Once again this serves as an advantage… And so on.

 

Even to get the first bit of skin between the claws is to beat the odds against all other possible mutations on the body. To reach the feathered ancestor version (birds) the number of mutations, on the same place of the body (claws), would be enormous. So how did birds develope feathers? Is there a huge amount of mutations ,where almost all mutational possibilities happen? It seems logical that a chance of a mutation happening on one part of the body is just as likely as it happening anywhere else. We would have to go a whole cycle to get back to the additional mutation to the skin between claws. I understand some mutations might occur soon after the previous one, but surely not for the whole development of wings!

 

The only answer I can think of is that if animal A has a mutation for Skin between claws (SBC) those genes are passed down and eventually the whole species has the gene for SBC. Now the odds of the SBC mutation improving are significantly higher because there is so many animals with SBC.

 

How many mutational steps occur during the development of wings? I am guessing an enormous number. How do they all pile up on the same part of the body? Wouldn’t the species go instinct from all the bad mutations before such a high cumulative number of good mutations occur?

 

Looking forward to the discussion

 

Thank you,

 

Freethinking

[ecoli]

a mutation is only passed on if it occurs in the sex cells of an organism. Also, most mutations are corrected by the many enzymes designed for that purpose.

[FreeThinker]

If the enzymes correct mutations, how is it that we get any at all?

 

How many possible mutations could happen within a organism? How many of those would be corrected?

[Mokele]

The answer is that not all mutations are even significant, and not all possibilities exist.

 

For the first point, note that most of DNA is just plain empty space, so mutation there will accomplish precisely nothing. Also, DNA is read in groups of 3, each group (codon) making an amino acid. But each amino acid is coded for by several codons, so even if a mutation occurs in the coding sequence, there's little chance of anything happening. On top of all that, there are four types of amino acid: acidic, basic, polar and uncharged. Replacing an acidic AA with another acidic one will likely do nothing. So, basically, most mutations do nothing (or at least not right away).

 

On top of that, protiens can only do so many things, so you're limited by chemistry.

 

And finally, the hot field of evo-devo: all organisms have developmental pathways, how the zygote becomes an adult. These constrain the possible effects of mutations, which is why you don't get animals with wheels.

 

But developmental genes can *also* cause very rapid alterations in phenotype. In a recent experiment, a single mutant gene caused a mouse to grow enormously elongate fingers, like a bat.

 

So, like all good questions, the answer to yours is "It depends..."

 

Mokele

[imasmartgirl]

 

How many mutational steps occur during the development of wings? I am guessing an enormous number. How do they all pile up on the same part of the body? Wouldn’t the species go instinct from all the bad mutations before such a high cumulative number of good mutations occur?

 

natural selection and survival by taking flight would cause the development of wings a lot more than several mutations.

[Skye]

How many mutational steps occur during the development of wings? I am guessing an enormous number. How do they all pile up on the same part of the body?

All parts of the birds genome and its body are evolving concurrently.

Wouldn’t the species go instinct from all the bad mutations before such a high cumulative number of good mutations occur?

Not necessarily, as a larger proportion of the birds with defective genes should be removed each generation by natural selection, preventing the build up of defective genes. There'll be some equilibrium state depending on how bad the mutation is and how often the mutation occurs.

[LucidDreamer]

Organisms carry an enormous arsenal of inactive genes and residual DNA. I think some of the mutations that we find that have resulted in beneficial phenotypic changes occur when a gene that was once active and beneficial millions of years ago for an ancestor with a different niche becomes active again and provides a new advantage now that the organism has again changed environments.

 

In your example of a reptile that develops skin between its fingers, it could be that the reptile already had genes that coded for webbed fingers from its amphibian ancestors but these genes were turned off because webbed fingers are not an advantage to a land animal. However, this animal may have already become small, light, and have taken to spending it's time in the trees. So when the gene for coding for webbed fingers became active again through a mutation, this individual was not at a disadvantage like its land-scurrying ancestors would have been. In fact, this creature had an advantage with its webbed fingers because it could leap farther distances between trees when it was escaping predators or seeking new sources of prey. This mutation, which has reactivated an old gene that has now become advantageous again in a new environment, spreads throughout the population until its prevalence is almost complete.

 

 

Here is another mutation scenario that would produce a strong advantage from a single mutation. Let’s say that the webbed finger gene only causes a certain amount of skin between the fingers, but does not fully cover the area between the fingers. Lets then imagine a crossing over mutation that results in two copies of this gene in a single chromosome that is separated to a gamete and becomes part of an individual’s genome. This creature now has two copies of the webbed finger gene that causes fully webbed fingers and this mutation quickly spreads to the whole population because of its advantages.

 

As a final scenario, I offer a mutation that occurs in a developmental gene that regulates bone growth. This gene produces a protein that acts as a hormone that induces bone growth for the early stages of the developing animal. When this animal's ancestors were on the ground he needed dense bones to sustain all of the activity of tumbling around on the ground. So this gene was regulated to produce 50 copies of the protein per milliliter of blood to induce the correct density of bone. However, since the animal now leaps from tree to tree he would benefit greatly from having lighter bones. Now when a mutation occurs that causes greater regulation of that gene that produces a protein that regulates bone growth and results in only 30 copies of the protein per milliliter of blood it spreads throughout the population because lighter bones have now become an advantage.

 

The point of all that was to show that small mutations in developmental genes can cause great and sometimes beneficial changes in the phenotype of an animal, animals keep large warehouses of old genes and DNA that can be reactivated for future use, animals often have several copies of genes that can be increased or decreased to need, animals have a variety of steps during development and regulation that are subject to mutations and can cause a range in protein amounts and phenotypic changes, and that variations caused by these mutations already exist within populations and are constantly acted on by natural selection and can work together simultaneously to create a synergistic effect causing an adaptation to a new environment. Evolution does not have to create from scratch and it rarely does.

[MM]

Just a thought on the randomness of mutations. How does central limit theorem apply to evolution in particular to the probability density for random mutations?

[Mokele]

Well, I don't know the math, but I do know that mutations do not occur at all points on the DNA molecule with equal probability, and that there are certain mutational "hotspots" which seem to be much more prone to mutations.

 

Mokele

[MM]

Well' date=' I don't know the math, but I do know that mutations do not occur at all points on the DNA molecule with equal probability, and that there are certain mutational "hotspots" which seem to be much more prone to mutations.

 

Mokele[/quote']

 

My thought is that evolution is based on the most basic form on mathematical principals, the central convergence theorem would then explain the may evolution works together with natural selection but on a more lower level. How to do you respond to that, taking that mutations doesn't occur everywhere with the same probability, I mean natural selection only has the result to play with.

[bascule]

Now here is the part I can’t quiet get my head around; with the miscopying of DNA it seems to me as if the number of possible mutations is close to infinite. So how do we get a series of mutations that develops a certain aspect of the body, such as feathers on birds?

 

Repurposing. For example, a bee's stinger is a modified egg tube. Your inner ear is made out of reptilian jawbones. A fish's swim bladder was originally a primitive lung (and became the lungs of tetrapods). The arms and legs of tetrapods were originally lobe fins for swimming.

 

A mutation might transform something which originally served one particular purpose to be useful for a totally different unrelated purpose. It may be somewhat maladapted to this purpose, but if it affords the carriers with a benefit, then as this mutation spreads throughout the gene pool natural selection will refine it (mostly by finding what alleles already in the gene pool work best in conjunction with it; an important thing to remember with sexual reproduction is that natural selection is constantly pruning the gene pool to contain the most advantageous alleles so not all adaptation need rely upon mutation as its instegator)

 

I'd once again like to recommend The Plausibility of Life which is full of literally hundreds of examples of such repurposing and some very well written explanations of exactly how complex structures can come to be from incremental adaptive stages.

[bascule]

How many mutational steps occur during the development of wings? I am guessing an enormous number. How do they all pile up on the same part of the body? Wouldn’t the species go instinct from all the bad mutations before such a high cumulative number of good mutations occur?

 

A wing is a very complex structure. However, it's quite likely that feathers originally came about for entirely unrelated purposes, most likely insulation. However, through a process of repurposing they were found to be useful for gliding (which was advantageous for the therapods at the time for some reason), and after several generations of becoming better and better gliders the theropods started flapping and developed true flight. An alternative theory suggests that the ancestors of birds flapped their wings to help them run up hills more quickly, and eventually developed true flight from this behavior.

 

Incremental adaptations, repurposing, incremental behavior modifications (mimiced throughout a population) triggering new and different selection events, changing environmental conditions, all leading to incremental change throughout time. That's really what it's about.

 

And some stuff gets left by the wayside. Your appendix is really a caecum, which originally housed the bacteria you need to digest cellulose, or at least, that's what happens in prosimians and New World monkies. In us, it's vestigial. We don't do a whole lot of cellulose eating, so it shrank down into a little itty bitty nothing that can still kill you. Yay.

 

If we have an intelligent designer, he can't be that intelligent becasue the appendix was a really stupid move. Or maybe it's just there to provide God with more ways to smite you. Not to mention our retinas being on backwards. Or hangnails...

[Mokele]

My thought is that evolution is based on the most basic form on mathematical principals, the central convergence theorem would then explain the may evolution works together with natural selection but on a more lower level. How to do you respond to that, taking that mutations doesn't occur everywhere with the same probability, I mean natural selection only has the result to play with.

 

Unfortunately, I don't remember enough about convergence theory to be able to respond. I remember having it in a class a long time ago, but I can't remember what it actually is. Can you refresh me?

 

Mokele

[starbug1]

Unfortunately, I don't remember enough about convergence theory to be able to respond. I remember having it in a class a long time ago, but I can't

 

When two different geographies, or continents, have similar environments, the animals are adapted to parallel evolution, converging similar phenotypes. I checked it out, and the most common example is marsupials and placentals. A placental mole looks very similar to a marsupial mole, but only phenotypically. Otherwise, they are completely different.

 

And some stuff gets left by the wayside. Your appendix is really a caecum' date=' which originally housed the bacteria you need to digest cellulose, or at least, that's what happens in prosimians and New World monkies. In us, it's vestigial. We don't do a whole lot of cellulose eating, so it shrank down into a little itty bitty nothing that can still kill you. Yay.

[/quote']

 

Figuratively, how long does it take to rule out vestigal organs by natural selection? This is one question I can never find the answer to. But, I think, by looking at similar species, such as the monkey's and their evolutionary history, would we then be able to tell how long these organ stay around? In the case of the appendix, and others like wisdom teeth or nipples in males, will they ever be done away with? To my knowledge, I don't know of anything that says they will ever go away, yet by reasoning of natural selection, I think they would, and in the process develop novel characteristics.

 

Also, humans have the remains of a third eyelid by the bridge of the nose, which, in some species of bird, are present to keep their eyes open and still have a protective transparent film to protect them when flying. How is it we came to develop a third eyelid? and how long did this trait take to erase itself from our genome?

[Mokele]

When two different geographies, or continents, have similar environments, the animals are adapted to parallel evolution, converging similar phenotypes. I checked it out, and the most common example is marsupials and placentals. A placental mole looks very similar to a marsupial mole, but only phenotypically. Otherwise, they are completely different.

 

I'm familiar with convergent evolution (which is actually why I named my pet lizard "Darwin", because he's convergent with monitor lizards), but MM was referring to some mathematical theorem.

 

Mokele

[starbug1]

Sorry, I wasn't even aware there was one.

 

 

[aguy2]

an important thing to remember with sexual reproduction is that natural selection is constantly pruning the gene pool to contain the most advantageous alleles so not all adaptation need rely upon mutation as its instegator

 

Good point. Evoluntionists with a capital E seem to have a strong tendency to overstress the role of random mutation and underate the role of selection through the auspices of sexual preferences. Selection through sexual choice can be very specific and very rapid. In the 1400's 30% of europeans had 'round' skulls; by the 20th century 70% displayed the characteristic.

 

aguy2

[MM]

Unfortunately' date=' I don't remember enough about convergence theory to be able to respond. I remember having it in a class a long time ago, but I can't remember what it actually is. Can you refresh me?

 

Mokele[/quote']

 

Sorry I was thinking of convergence when I wrote it. It should of course be central limit theorem. http://en.wikipedia.org/wiki/Central_limit_theorem

 

As the population gets bigger the variations should resemble more and more a normal distribution. Is it wrong to see this as a kind of evolution?

[qed]

I understand that most mutations are a disadvantage to the particular organism.

 

I can see how a random mutation (tiger with bigger teeth' date=' faster antelope…)could be of benefit to a particular organism, and how that mutation would populate the entire species over a period of time.[/quote']

 

I get the impression that some of you look at selection in the wrong way. Natural selection does not mean to increase the frequency of alleles that are somehow advantageous. It means the extinction of genetic constitutions that are unfavorable. I hope you see the difference. Natural selection is always negative, the only exception are mutations that directly affect the rate of reproduction.

 

Remeber the Hardy-Weinber equillibrium. Evolution doesnt occur on the level of genes (of course mutations are the reason of evolution). It doesnt even occur on the level of organisms. Evolution occurs on the level of populations. That is what most people forget when they try to reconsider an evolutionary pathway.

 

there are no mutations that have a general benefit. Genes wont increase in their frequency without selectional pressure. A population that evolves must shrink in order to adapt. in this case the extinction of the species is more likely than an adaptation that results in a new one. that means that for the survival of a population, genetic diversity in the genepool is essential for the capability to adapt. therefore there is no temporal correlation between a random mutation and the adaptation of a species. Its the combination of all genes in interaction with the environment that gives the fitness.

 

Genes do not evolve, genotypes do not evolve either. Only genepools evolve.

I just want you to bear this in mind.

[FreeThinker]

I get the impression that some of you look at selection in the wrong way. Natural selection does not mean to increase the frequency of alleles that are somehow advantageous. It means the extinction of genetic constitutions that are unfavorable. I hope you see the difference. Natural selection is always negative' date=' the only exception are mutations that directly affect the rate of reproduction.

 

Remeber the Hardy-Weinber equillibrium. Evolution doesnt occur on the level of genes (of course mutations are the reason of evolution). It doesnt even occur on the level of organisms. Evolution occurs on the level of populations. That is what most people forget when they try to reconsider an evolutionary pathway.

 

there are no mutations that have a general benefit. Genes wont increase in their frequency without selectional pressure. A population that evolves must shrink in order to adapt. in this case the extinction of the species is more likely than an adaptation that results in a new one. that means that for the survival of a population, genetic diversity in the genepool is essential for the capability to adapt. therefore there is no temporal correlation between a random mutation and the adaptation of a species. Its the combination of all genes in interaction with the environment that gives the fitness.

 

Genes do not evolve, genotypes do not evolve either. Only genepools evolve.

I just want you to bear this in mind.[/quote']

 

I disagree. Since a mutation will occur in an individual, more specifically a particular gene, the group remains invisible to natural selection. If we have a population of see gulls and one of the members is born with a better beak to catch a fish, natural selection will act upon the very gene that gave it this ability. The rest of the species will not play a part in the selection process. Even long after see gulls, natural selection will use that same gene in a future species as a point of selection.

[qed]

If we have a population of see gulls and one of the members is born with a better beak to catch a fish, natural selection will act upon the very gene that gave it this ability.

 

This will not happen as long as the reproductive capacity of the rest of the population is similar to the individual with the new allele. The new sea gull may grow a little faster as the rest, but without selectional pressure on the whole the population, this new gene will not penetrate. This is especially true for large populations, where random genetic drift is low. The gene may persist in the genepool with low frequency unless the "genotype" of its carriers is not unfavorable in any way (that means if they dont die for any reason).

The relative frequency of an allele is increased only by the decrease of other alleles by the death of individuals. Therefore only shrinking populations change their genepool.

 

Believe it or not, evolution does never act on a particular gene. Only genotypes die or survive, and the evolution of a species takes place on the level of the population.

[Milken]

I'd once again like to recommend The Plausibility of Life which is full of literally hundreds of examples of such repurposing and some very well written explanations of exactly how complex structures can come to be from incremental adaptive stages.

 

1 to 10 how do you rate the book? 1 to 10 how well does it disprove Irred Comp?

[Milken]

The thing is mutations are very rare and when they do happen they're not benefical. The good large scale mutations needed for macroevolution don't happen. To be nice I'll say are extremely rare.

 

Scales to feathers via small mutations, is just. . . almost an absurd thing to think about. Mostly because, even if a reptile had bird skin and features, you'd still be very far from the kind of feathers on wings, wings, and flight. Especially when you consider the time frame, does anyone know the time frame?

[jeskill]

I get the impression that some of you look at selection in the wrong way. Natural selection does not mean to increase the frequency of alleles that are somehow advantageous. It means the extinction of genetic constitutions that are unfavorable. I hope you see the difference. Natural selection is always negative' date=' the only exception are mutations that directly affect the rate of reproduction.

 

Remeber the Hardy-Weinber equillibrium. Evolution doesnt occur on the level of genes (of course mutations are the reason of evolution). It doesnt even occur on the level of organisms. Evolution occurs on the level of populations. That is what most people forget when they try to reconsider an evolutionary pathway.

 

there are no mutations that have a general benefit. Genes wont increase in their frequency without selectional pressure. A population that evolves must shrink in order to adapt. in this case the extinction of the species is more likely than an adaptation that results in a new one. that means that for the survival of a population, genetic diversity in the genepool is essential for the capability to adapt. therefore there is no temporal correlation between a random mutation and the adaptation of a species. Its the combination of all genes in interaction with the environment that gives the fitness.

 

Genes do not evolve, genotypes do not evolve either. Only genepools evolve.

I just want you to bear this in mind.[/quote']

 

I both agree and disagree with you. Evolution occurs when there is a gradual shift in the average trait within a population. i.e. The average beak size gradually increases in a population of birds that eat large seeds. However, in order to have evolution, you have to have variability. Hence, the discussion of how mutations affect evolution is very important. Since mutations occur at the genetic level and individuals are selected out, I think it makes more sense to think of evolution happening at the genetic level.

 

Yes, natural selection is represented at the population level. But by saying that evolution occurs at the population level, I feel like you're implying that natural selection is occuring at the population level -- i.e. group selection is occurring. Group selection is not occurring. Evolution doesn't happen for the benefit and detriment of the group, it happens for the benefit or detriment of the gene.

 

Thank you Dawkins.

[qed]

Since mutations occur at the genetic level and individuals are selected out, I think it makes more sense to think of evolution happening at the genetic level.

 

The cause for evolution lies on the genetic level, or changes on the genetic level. I think we all agree about that.

 

Yes, natural selection is represented at the population level. But by saying that evolution occurs at the population level, I feel like you're implying that natural selection is occuring at the population level -- i.e. group selection is occurring. Group selection is not occurring.

 

Yes, group selection is not occuring, as you said, individuals are selected out. Sometimes this selection is mediated by a single gene, thereby deleting itself from the genepool. But that is irrelevant for the further adaption or evolution of the population. The relevant aspect is, what genetic information remains in the pool after selection and what is its frequency and diversity. The manifestation (does that word fit here?) of evolutionary changes can first be seen in the following generations, and here we are on the population level. The individuals that survived didnt change, their genes didnt change. Life has to reproduce in order to change, and this is indeed reflected in the population.

 

Evolution doesn't happen for the benefit and detriment of the group, it happens for the benefit or detriment of the gene.

 

I definitely disagree. Evolution doesnt happen for the benefit and detriment of anything, there are just mechanisms. There are no trends, purposes or final goals or something like that.

Its the genotype of an individual that gives the fitness in a certain environment. But its the genepool of a population that reflects its adaptive capacity and is therefor the more important aspect. An individual cannot adapt either a single gene.