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Member (Idle past 1669 days) Posts: 53 From: Reno, Nevada, USA Joined: |
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Author | Topic: Small Steps---how small can they be? | |||||||||||||||||||||||||||
InGodITrust Member (Idle past 1669 days) Posts: 53 From: Reno, Nevada, USA Joined: |
How small can evolutionary steps be?
The mutation of a single gene is responsible for the change from dichromatic to full color vision. A single genetic mutation can shut down the immune system of a human. These seem like large leaps. If you have a dimmer switch on a light, you might think of a resistor with an infinite number of settings. But a 3-way bulb in a lamp has only 3 settings. As a hollow viper fang developes in the embryo, it starts out solid, and then becomes increasingly more deeply grooved. Finally enamel wraps around the front of the groove and encloses it. If this is also the way the fang evolved, how many steps would it take? Could it be done in 3, like the 3-way bulb? And would each step take a new genetic mutation? The reason I'm curious about this is because it would affect the speed of evolution. The more genetic mutations needed the slower evolution would proceed. I hope this question isn't too basic, and the answer is "do your homework". But if that's the case, the moderator probably wouldn't allow it to clutter the forum. Thanks---IGIT Edited by InGodITrust, : No reason given. Edited by InGodITrust, : No reason given. Edited by InGodITrust, : No reason given.
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Adminnemooseus Administrator Posts: 3974 Joined: |
Thread copied here from the Small Steps---how small can they be? thread in the Proposed New Topics forum.
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RAZD Member (Idle past 1405 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Hi InGodITrust,
The mutation of a single gene is responsible for the change from dichromatic to full color vision. A single genetic mutation can shut down the immune system of a human. These seem like large leaps. ... etc. So using some "large leaps" means micro steps are not possible? The smallest "leap" would be neutral mutations - ones that offer neither benefit nor hindrance to breeding or survival in the current selection environment. You could call that a "null" step.
The reason I'm curious about this is because it would affect the speed of evolution. The more genetic mutations needed the slower evolution would proceed. Yet several of your examples could co-evolve with continued adaptation by mutation and selection over many generations - other snakes don't stop evolving while waiting for a fang to be developed, so the poison snake is not dependent on it to evolve.
If you have a dimmer switch on a light, you might think of a resistor with an infinite number of settings. But a 3-way bulb in a lamp has only 3 settings. And individual mutations have a discrete number of changes rather than a blended transformation. This leads to the conclusion that any apparently blended transformation, such as the poison viper fang, would be the result of several mutations.
And would each step take a new genetic mutation? Think of evolution as being opportunistic rather than deterministic: organisms take advantage of the opportunities provided by their inherited variations to gain an advantage over other organisms for breeding or survival in the ecology they inhabit - which may be a new ecology, due to those variations, that they now have the opportunity to inhabit and adapt to. Also, while we can identify several steps that may have occurred in the development of a single feature, that does not mean that the development is a linear progression. Evolution does not move from point A to point B - it's more like the flight of a butterfly landing on a flower at random in a field.
The reason I'm curious about this is because it would affect the speed of evolution. The more genetic mutations needed the slower evolution would proceed. How much speed does a butterfly need to cross a field? The known rates of mutation are vastly higher than the rate needed to develop any feature known in the time frame we know was available. Enjoy. Edited by RAZD, : No reason given. by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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Dr Adequate Member (Idle past 284 days) Posts: 16113 Joined: |
In principle, the smallest change possible is a single nucleotide substitution: the change of one base of DNA into another. Or, similarly, the insertion or deletion of a single base.
The reason I'm curious about this is because it would affect the speed of evolution. The more genetic mutations needed the slower evolution would proceed. It is possible to measure the rate of mutation, and to show that this accounts for the amount of evolution that's happened in the available time. But you're talking about significant and useful mutations. That's harder to quantify. Our ability to read genomes is fairly recent. People are still trying to figure out what were the significant mutations that make, for example, humans different from chimps. If you're still posting on these forums in twenty years, bump this thread.
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greentwiga Member (Idle past 3427 days) Posts: 213 From: Santa Joined: |
The problem is that there are a variety of completely different genetic activities that are lumped into evolution. You mentioned creation of a totally new gene. This is typically quite slow. When a child inherits genes from its parents, it is not an simple inheritance. If the mother has two gene # 5s, say 5a and 5b, the child does not just inherit one or the other. These genes can cross and the child inherit part of 5a and part of 5b. Sometimes transcription errors occur and the child inherits a gene 5 that is too big or too small, or even some genes installed backwards. This "evolution" is quicker than the new gene evolution. Then there is the timing. If you look at dawn horse, eohippus I believe, and compare it to modern horses, most of the changes are due to timing changes. The gene does not have to be changed. Only the amount of time that the gene is active changes. This is a very fast change. Even in your lifetime, a gene can change its timing and cause cancer. These timing changes can be very small and very fast. This type of change is like your dimmer switch example. For Example, the 17 year cicadas can mutate into 13 year cicadas, probably by a timing change. The two groups would not interbreed except rarely because they hatch in different years.
Remember, that some animals remain very constant over millions of years. Gators and Crocs are a good example. Their type is so well adapted to their niche, that most changes are weeded out. When an environmental disaster occurs and many niches are now empty, then, many changes that would have been weeded out now survive. During these times, evolution seems to go into overdrive as other animals fill the empty niches. This is why the timing changes are so important.
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InGodITrust Member (Idle past 1669 days) Posts: 53 From: Reno, Nevada, USA Joined: |
Thanks everyone.
You can probably see what I'm up to: trying to see if there is a way to run natural selection out of time. The timing (dimmer switch) changes probably make this approach to disproving natural selection less likely than it already was. Edited by InGodITrust, : No reason given.
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Dr Adequate Member (Idle past 284 days) Posts: 16113 Joined: |
You can probably see what I'm up to: trying to see if there is a way to run natural selection out of time. You mean a creationist asked a quantitative question about genetics? We ought to give you some sort of a medal. Sarcasm apart, no, you can't "run natural selection out of time" according to the data we have, and in fact the data we have shows that the time one would estimate according to mutation rates is pretty darn consistent with the time one gets from measuring the ages of fossils. In short, biologists win again. Damn, why do they keep doing that? Could it be that ... biologists are right about biology?
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RAZD Member (Idle past 1405 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Hi Dr Adequate, we should be careful not to oversimplify and understate the issue.
It is possible to measure the rate of mutation, and to show that this accounts for the amount of evolution that's happened in the available time. First off, the rate of mutation may be relatively steady in mature populations, but they have been shown to increase when the individuals are under stress. This is due to the relationship between development and ecology. Hormones affect development and stress affects hormones, where the stress comes from the ecology (hot, dry, predator dominated, etc). Second, the ability of a population to fix mutations (ie pass them on to following generations) is related to the level of selection pressure: when selection pressure is low, more marginal mutations pass muster (survive long enough to breed), and resulting in more variety of mutations within the population, while under high selection pressure these individuals fail to meet the mark and the number of mutations available to the next generation is reduced.
It is possible to measure the rate of mutation, ... This has been done, and the results show that the rate of mutations can vary in specific populations. When we try to apply that knowledge to the historical perspective, what we are really measuring is the rate of fixed mutations. The number of fixed mutations is necessarily smaller than the number of mutations, and the proportion is variable (as noted above), so they cannot be used to extrapolate a rate of mutation for the population in general.
... and to show that this accounts for the amount of evolution that's happened in the available time. Curiously, we get a kind of cart and horse situation here. We take, for example, the genomes of human and chimpanzee and bonobo and gorilla, and from this family tree we can see that the rates of fixed mutations in these different populations occurred at different rates, and this is generally reported as an average rate of mutation for each population - there is no way to find max and min rates within those periods. We can compare those to the known rates of mutations today and see that they are within the range of fixed mutations in populations from the known highs to the known lows. Many times we also find that even the low rates of known mutations are much more than sufficient for evolution to have occurred in some populations -- in other words that evolution can be lazy in getting from one place to another -- but have yet to find an instance where the amount of fixed mutations cannot be explained by known rates of mutation and the fixing of mutations in a population.
If you're still posting on these forums in twenty years, bump this thread. I agree that his aspect of the field of genetics is still in the infancy stage, an exciting place where discoveries are waiting to be made. But I predict it will take much less than 20 years ... Enjoy. by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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greentwiga Member (Idle past 3427 days) Posts: 213 From: Santa Joined: |
It is so hard to comprehend 4+ billion years. For example, continents move at the rate fingernails grow. This slow movement has allowed the continents to crash together and break apart a number of times. This is so much time that during times of stability, animals and plants remain fairly constant and still there is more than enough time for evolution to occur at the rather slow rate of mutation of genes. After mass extinctions, such as the Permian, life, using this mutation rate, fairly quickly fills the empty ecological niches.
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Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined: |
This is due to the relationship between development and ecology. Hormones affect development and stress affects hormones, where the stress comes from the ecology (hot, dry, predator dominated, etc). I'm not sure where this ties in to the rate of mutation. Are you saying that differing hormone levels give rise to higher rates of mutation in the germ line cells? Or are you thinking of something like assimilation where the environmental interaction with development can influence the direction of an evolving population to fix a phenotype? There are obviously environmental factors which have directly mutagenic properties, such as ionising radiation and many chemical compounds, I'm just not quite sure what sort of thing you are thinking of. There is certainly plenty of evidence for 'mutator' systems in bacteria which act in response to environmental stress/ genetic damage but I'm not sure how what evidence there is of this sort of thing in multicellular organisms driven by hormone levels. TTFN, WK
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Percy Member Posts: 22391 From: New Hampshire Joined: Member Rating: 5.2 |
It's worth mentioning that small amounts of evolutionary change do not require mutations. Genes and alleles are remixed and reordered during sexual reproduction, and their interactions can produce differences beyond what one might expect from a simple combining of the parental haploid genes and alleles. And I'm going to speculate that during asexual reproduction that gene order on chromosomes can change, and that this is not without impact.
--Percy
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RAZD Member (Idle past 1405 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Hi Wounded King, correct me if I'm wrong, but it seems to me that there are a number of processes going on, which make it difficult to determine an accurate mutation rate outside the lab.
I'm not sure where this ties in to the rate of mutation. Are you saying that differing hormone levels give rise to higher rates of mutation in the germ line cells? Or are you thinking of something like assimilation where the environmental interaction with development can influence the direction of an evolving population to fix a phenotype? Yes, that is part of it - organisms produce different hormones at different levels while under stress, and this affects both the ability to reproduce and the resulting development. Salamanders when exposed to dry conditions can divert from normal growth to early ability to reproduce, and when this happens their normal development is arrested, such that the larval stage gills are not lost. When normal conditions return the salamanders revert to development along the normal lines, with the gills being lost. The mudpuppy salamander has evolved to reach reproductive ability while retaining the gills and some other juvenile traits (see pedomorphosis). This developmental interruption likely has become fixed in the population through subsequent mutations and selection -- because the opportunity occurred for this to happen as a result of the environmental stress response. A similar thing occurs during speciation, where an existing population has an opportunity to branch out into a secondary environment, which then allows more new mutations to be fixed in the parent population before it divides into the daughter populations that specialize in the different environments. This relates more to the rate of mutation fixing than to mutations per se, however, when we compare genomes of populations we are also comparing fixed mutation rates. Mutations that don't make it past the first generation are not measured.
There is certainly plenty of evidence for 'mutator' systems in bacteria which act in response to environmental stress/ genetic damage My understanding here, is that the (normal? evolved?) repair (control) mechanism/s break down, allowing more dodgy division to occur. I thought I saw a reference to similar in a multicellular life form, but can't find it at the moment. by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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CDevoclast Junior Member (Idle past 5266 days) Posts: 1 Joined: |
IGIT:
You have asked THE seminal question upon which all "extrapolations" of evolutionary biology rest, one that is seldom asked. Mark Ridley's book "EVOLUTION" contains the following which essentially speaks for the field: "Darwin's "gradualist" requirement is a fundamental property of biological evolution theory." (page (260) Ridley then states: "The Darwinian should be able to show for any organ that it could, at least in principle, have evolved in many small steps---" Jerry Coyne's recent best seller "Why Evolution is True" depends heavily on the "small steps" that create "new traits" from "pre-existing traits" in the process of species splitting. Coyne never explains what constitutes a small step, which also speaks for the evolutionary biology field. The point is to explain and demonstrate the FUNCTIONAL INTERACTIONS and SEQUENCE OF ORIGIN of all the components that make up a small step---references to "mutations" and the like are not explanationa of a process. For an assessment of the reasion Coyne does not define NOR ILLUSTRATE a small step, see this blog: Blog not found and in particular see Episodes 7, 8, and 9. or search for CDevoclast. Edited by CDevoclast, : No reason given. Edited by CDevoclast, : No reason given. Edited by CDevoclast, : No reason given. Edited by CDevoclast, : Text omission
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Dr Jack Member Posts: 3514 From: Immigrant in the land of Deutsch Joined: Member Rating: 8.7 |
In principle, the smallest change possible is a single nucleotide substitution: the change of one base of DNA into another. Or, similarly, the insertion or deletion of a single base. At the genetic level this is true; but natural selection can only act on phenotypes (and I think that is what the OP was talking about). Point mutations can have quite large effects, or almost no effect; larger changes can also have large effects, or almost no effect. Look at the plants and animals around you, InGodITrust, and consider the range of individual variation you can see; consider the smallest difference that might be possible between two such individuals - evolution can work with that; whether it's fur a millimetre longer, or a slightly enlarged leg muscle, or a tiny difference in the light wavelengths that are best percieved. (Although, as should be noted, a decent portion of individual variation is environmentally influenced)
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