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Member (Idle past 2728 days) Posts: 2843 From: You couldn't pronounce it with your mouthparts Joined: |
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Author | Topic: Stasis and Evolution | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Blue Jay Member (Idle past 2728 days) Posts: 2843 From: You couldn't pronounce it with your mouthparts Joined:
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Near the end of Calypsis4's "Living fossils" thread, Arphy expressed an interest in debating the importance of stasis in evolutionary biology (Source: Arphy's Summation).
It is his contention that the ToE should not allow the long bouts of stasis that we see in the fossil record. Elsewhere, other creationists (including Kaichos Man) have brought up issues related to the rate of change and the quantity of change. I think the topic deserves some special attention, so I propose a thread to discuss stasis in evolution. My perspective is that Arphy’s contention is a misunderstanding of evolution that stems mainly from the format of discourse in the biological sciences. Biologists talk about mutation and natural selection, and often characterize them as mechanisms, which creationists find troubling because of the apparent circularity or vague, story-like feel to the definition. In a post in the free-for-all Lossy Adaptation via..., I gave a description of the actual mechanisms behind mutation and natural selection (AChristianDarkly used a three-part, A-B-C model to link a source, a mechanism and an outcome, and that’s the motif I used in that post). The problem is that neither mutation nor natural selection really refers to anything mechanistic. Biology has hundreds, probably thousands of actual mechanisms at play, and these can be collected into two groups based on the effects they have on organisms:
With this in mind, one should remember that, when a biologist says, Natural selection favors the fit, he is not referring to an actual force or entity that is causing some things to die, while allowing others to live. Rather, he is referring to a collection of mechanisms (or a subset of mechanisms from that collection) that are unrelated, but relatively similar in outcome. Examples of mechanisms include predation, pathogens, resource fluctuations, sparring for dominance, mate preferences, etc. They are all different, and each has varying shades of influence on fitness depending on the effectiveness of the predator, the severity and character of the resource flux, the lethality of the pathogen, the rules of the sparring contest, or the personality of the choosy mate. Since all of these mechanisms are part of evolution, and since they don’t all have the same influence in all scenarios, we should expect to see a variety of responses (in terms of quantity, direction, rate and form of the response) in different animals. And, organisms will have to deal with multiple mechanisms over time, so sequence will also come into play. So, there are literally millions of ways these different mechanisms can interact to shape evolution of life on Earth, and that’s why there are literally millions of different types of organisms, each responding to a different set of pressures that act on different time scales, with different intensities, and different fluctuations. Here is a tabular representation, with a number of pressures, or mechanisms, listed across the top, and the characteristics of the response along the side:
(Don’t get hung up on the numbers: they’re just fillers). This is just for one organism. It is conceivable, (and probable, under the evolutionary model), with so many different possible ways to respond to so many different mechanisms, which act on so many different temporal and spatial scales, that there would be great variety in the outcome of selection on different lineages of organisms. So, in summary, my position is that Arphy’s view (that stasis should not happen if things evolve) comes from an oversimplified understanding of evolution, and of the processes and functions of life. Forum recommendation: Biological Evolution" Edited by Bluejay, : column missing from table Edited by Bluejay, : Better formatting and a couple additions around the table Edited by Bluejay, : I swear I fixed this twice already! Thanks, Perdition. Edited by Bluejay, : Table caption and mechanism categories -Bluejay (a.k.a. Mantis, Thylacosmilus) Darwin loves you.
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AdminNosy Administrator Posts: 4754 From: Vancouver, BC, Canada Joined: |
Thread copied here from the Stasis and Evolution thread in the Proposed New Topics forum.
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Perdition Member (Idle past 3269 days) Posts: 1593 From: Wisconsin Joined: |
Very good post, I think, but you may want to look at the formatting of your table. The information in it is confusing (to me at least) and the fact that every row but the first is pushed one cell to the right makes it even harder to understand.
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RAZD Member (Idle past 1436 days) Posts: 20714 From: the other end of the sidewalk Joined:
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Hi Bluejay,
Interesting topic, and I hope you get some creationist responses. Another interesting part of the "missing fossil" equation is how fast can the punctuation occur. For some idea of that, see Differential Dispersal Of Introduced Species - An Aspect of Punctuated Equilibrium where certain introduced species serve as surrogates for the founder populations. In each case the founding population was small. In each case the species spread was determined by how well it was pre-adapted to the ecology. In each case there are similar species in the ecology that are being displaced in different degrees by the invaders, but existing populations are not necessarily wiped out. This shows that a pocket population that evolves independently of a parent population does not have to be large to initiate a punctuation event, it just needs the right conditions of adaptation and reasonable fitness to the ecology that it is spreading into. So if anyone wants to discuss the punctuation aspect instead of the stasis aspect, then you can direct them to the Differential Dispersal Of Introduced Species - An Aspect of Punctuated Equilibrium thread.
It is his contention that the ToE should not allow the long bouts of stasis that we see in the fossil record. Elsewhere, other creationists (including Kaichos Man) have brought up issues related to the rate of change and the quantity of change. Except (as has already been pointed out to him) that evolution selects for adaptation to the ecology - it's a response mechanism, with feedback for fitness. Thus if the ecology does not change, then natural selection operates to cause stasis, as all mutations that would alter the fitness to a lower level are selected against rather than allowed. To change away from a fit phenotype would be contrary to evolution. 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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Blue Jay Member (Idle past 2728 days) Posts: 2843 From: You couldn't pronounce it with your mouthparts Joined:
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Hi, Perdition.
Meh. The table was just there to show how many different factors there can be contributing to evolution. And, I kind of wanted something to break up all the text. I guess I could have explained it better, though. The values in the cells are supposed to represent some fictitional measurement of various parameters of the response (along the side) to a selection mechanism/pressure (across the top). These could be measurements of an accumulated total change since some arbitrary point in the past, or they could be all the pressures that the population is being exposed to and is having to deal with concurrently. Each cell thus represents one evolutionary pathway or event. So, each one is one way in which the evolution of two different species might diverge. Admittedly, it probably isn't the best way to present it, but it did give me the chance to practice HTML tables. If it causes too much trouble with the creationists, I'll just take it down and focus on text for my arguments. Thanks, Perdition. -Bluejay (a.k.a. Mantis, Thylacosmilus) Darwin loves you.
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Perdition Member (Idle past 3269 days) Posts: 1593 From: Wisconsin Joined:
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I think it's an interesting concept, and maybe it could be expanded and detailed more. For example, what units of measurement are we using for the change: Mutational rate, phenological differences, survival rate? I understand it was just thrown out there, but I think it could be developed if someone wanted to spend the time to do it (meaning not me )
Once we have that, we could, perhaps, show some actual numbers for the changes between, say, Archaeopteryx and an Ostrich, versus an extinct land mammal and the whale, etc.
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RAZD Member (Idle past 1436 days) Posts: 20714 From: the other end of the sidewalk Joined:
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Hi Perdition & Bluejay,
For some off the cuff measurements of the differences in living animals and in skeletons see Dogs will be Dogs will be ??? Notice that measurements of bones and establishing their proportions is one of those things that paleontologists actually due to determine species and changes. 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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Blue Jay Member (Idle past 2728 days) Posts: 2843 From: You couldn't pronounce it with your mouthparts Joined:
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Hi, RAZD.
Glad I could provide you a place to plug all your past threads at EvC! Now, if only some creationists would come and read it, maybe our efforts won't have been in vain... -Bluejay (a.k.a. Mantis, Thylacosmilus) Darwin loves you.
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Blue Jay Member (Idle past 2728 days) Posts: 2843 From: You couldn't pronounce it with your mouthparts Joined:
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Hi, Arphy.
If you would like to discuss stasis in evolution, I've provided this thread as an opportunity to do so. I look forward to reading your arguments. -Bluejay (a.k.a. Mantis, Thylacosmilus) Darwin loves you.
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Arphy Member (Idle past 4463 days) Posts: 185 From: New Zealand Joined: |
Ah, just read this, sorry a bit short on time at the moment, but hopefully will reply in the next few days.
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CosmicChimp Member Posts: 311 From: Muenchen Bayern Deutschland Joined: |
Greets RAZD,
You need to fix this bit.
... as all mutations that would alter the fitness to a lower level are selected against rather than allowed. This is generally true as a cause for the opposite as well as what you are trying to show a cause for.
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RAZD Member (Idle past 1436 days) Posts: 20714 From: the other end of the sidewalk Joined:
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Hi CosmicChimp
This is generally true as a cause for the opposite as well as what you are trying to show a cause for. I don't follow. If you have a population in ecology {A}, natural selection will select for fitness to ecology {A}. If the ecology changes to {B}, then natural selection will select for fitness to ecology {B}, rejecting mutations that move the population away from fitness for ecology {B}. However, if ecology doesn't change, then natural selection will continue to select for fitness to ecology {A}, rejecting mutations that move the population away from fitness for ecology {A}. 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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CosmicChimp Member Posts: 311 From: Muenchen Bayern Deutschland Joined:
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I think it is true what you have stated in both of you posts, but my concern is that you have given as reason or causation for stasis (of the phenotype of a population) the exact same reason/cause that is true for change (of the phenotype). The cause as I think you may be stating it is Natural Selection. But I think the true cause is that the probability of achieving a beneficial mutation has been reduced to near zero in the case of stasis in an unchanging ecology; whereas in a new changed ecology a mutation surely has a higher chance of being beneficial compared to the other case.
You have in effect said, Natural Selection is the cause for staying the same and the cause for changing, I don't see the distinction that has to be drawn in order show what causes the one over the other event. Edited by CosmicChimp, : clarity Edited by CosmicChimp, : clarity, last edit
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RAZD Member (Idle past 1436 days) Posts: 20714 From: the other end of the sidewalk Joined:
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Hi CosmicChimp, let's see if we can clear this up.
You have in effect said, Natural Selection is the cause for staying the same and the cause for changing, I don't see the distinction that has to be drawn in order show what causes the one over the other event. Evolution in general, and natural selection in specific, is a response mechanism, it doesn't cause anything, but it reacts to everything that affects survival and breeding. The cause of the change or the stasis is the ecology -- how the population fits in with the rest of the biology around it. If it changes then the population will adapt or perish, but if it stays the same then the population will stay the same or perish. Mutations still occur, and natural selection still benefits the more fit over the less fit, whether the ecology changes or the ecology is in stasis.
But I think the true cause is that the probability of achieving a beneficial mutation has been reduced to near zero in the case of stasis in an unchanging ecology; Whether a mutation is beneficial or deleterious is related to how it affects the fitness of individuals in the population, it isn't inherent in a mutation to be one or the other. So yes, the probability of a new mutation increasing fitness decreases as the population nears "absolute fitness" when the ecology is static, but it is still measured for fitness to that ecology by natural selection.
whereas in a new changed ecology a mutation surely has a higher chance of being beneficial compared to the other case. Which is why you have population explosions and rapid speciation after extinction events. 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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caffeine Member (Idle past 1055 days) Posts: 1800 From: Prague, Czech Republic Joined:
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Something that Bluejay said when writing about rats made me think about evolutionary stasis in omnivorous animals capable of surviving on a variety of foodstuffs, that are very behaviourally adaptable already. In such a species, wouldn't it be a stable, unchanging environment that actually selected for change?
Imagine a population living in an environment that changes rapidly from generation to generation - such as those humans create, perhaps. If things are very changeable, there'll be little sustained selective pressure in any particular direction. Bigger animals may be favoured in one particular generation, and then smaller ones again a generation or two down the line as conditions change. We'd see slight variations around a point, but little major change. Too much specialisation in any one direction would be penalised by selection, as a specialisation which is useful for a couple of generations may turn out to be deeply counterproductive shortly afterwards. The most highly adaptable animals - those who will readily alter their behaviour in new conditions and can move to new food sources easily, will consistently pass on their genes generation after generation. The changing environment is selecting for the adaptable individuals, maintaining stasis in an already adaptable species. If we imagine that one population got isolated somewhere remote, however, where the environment is very stable over long periods of time - it would be this that prompted change in the population. There would be no selective pressure to retain the ability to metabolise unavailable sources of food, and if more efficient metabolism of whatever is available is possible at the expense of being able to digest almost anything, specialisation will be selected for. Equally, a mind and body designed for behavioural adaptability might not be as successful as one more narrowly focused on exploiting the resources of the new environment, assuming these to be constant, and specialisation would again be selected for. If this idle speculation has any merit then, it's a changeable and uncertain environment that would select for relative stasis in the most adaptable organisms; while stabilising that environment would prompt evolutionary change (at least until the organism's as specialised as it's going to get for while).
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