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Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
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Author | Topic: What exactly is natural selection and precisely where does it occur? | |||||||||||||||||||||||||||||||
Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
Percy, I'll respond to this one specifically:
Percy in Message 62: Natural selection means that individuals best suited for their environment have the best chance of surviving to produce offspring. Any organism that produces offspring in the wild has been naturally selected.
Should I then adopt this definition of NS? Does this mean that humans have to go out into the wild to be naturally selected? Can't they get selected at home in the comfort and privacy of their own bedrooms? Does this mean that every reproducing organism is naturally selected? I have children. Does this mean that I have been naturally selected? And what about gay individuals who put their sperm into the mouths and rectums of other gay individuals? Does this mean they are being naturally selected against? I certainly do agree that unless individuals mate and have offspring there is no role for natural selection to play in the course of biological evolution. I'm just having trouble seeing how the individual gets naturally selected. By your definition, then, if the individual has offspring it has been "selected," in the Darwinian sense, to undergo biological evolution (since selection = evolution). This seems to concur with what AZPaul3 who wrote in Message 46:
Natural Selection is all elements of an environment that impact an organism’s reproductive success. From changes in climate to big space rocks smashing into the planet, from the beaver’s dam that dries up the stream for the frogs 3 miles downstream to the brilliance or lack thereof of the peacock’s tail. All factors, even luck, good or bad, that impact an organisms reproductive success are naturally occurring, without purpose, guidance or forethought and have what we call a “selective” effect. Sexual selection is but one of these natural selective elements.
I do not agree that sexual selection is an "element" of natural selection, but I'll defer on that issue. I suppose, then, that everything that reproduces is evolving. Makes me wonder how there are any species at all. But wait, doesn't natural selection, in Darwinian terms, amount to evolution? And is there something other than individuals, per se, that get "selected for," rather than individuals being merely "selected" by nature to evolve? Maybe "selected for"”as in "selected for traits"”is a better perspective. JustinC wrote in Message 37:
Does the distinction "selected for" and "selected of" help the situation? That is, there is selection of genotypes for for phenotypes. And the genes that can work well with the most assortments of genes get selected (the genes that are incorperated in the most number of successful genotypes), but their success is rooted in the sum of the effects of the entire genotype on the phenotype, that is the individual.
But of course we know that individuals die in relatively short order, so maybe we need to look at the extant genes, traits, or lineages as those biological thingies that get naturally selected and evolve, since they don't die with the ephemeral individuals. I suppose you could say they live on in their homologies, but that seems self-evident. ”HM
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Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
Percy wrote:
Percy, I simply don't agree with you, and furthermore I don't write "nonsensical ramblings." (Your attitude causes me to think that you have not read very much of S. J. Gould.) You have not yet convinced me that, even with cartoon characterization for a colorful spin, all reproducing individuals experience natural selction. HM wrote: ...(since selection = evolution). I'm extremely perplexed that you're still saying this. Pardon my loss of patience, but how many times and how many people are going to have to tell you that selection is not evolution before it sinks in?
I do not agree that sexual selection is an "element" of natural selection,... That's because you still don't understand what natural selection is. When you finally figure it out you're going to make like Homer Simpson in a major way! I'm not going to address the rest of your post as it descends into nonsensical ramblings. Thus far, we have established three schools of thought on the operational definition of natural selection: 1. Natural selection selects or selects for groups. For example, crashfrog wrote in Message 3:
Even in a population undergoing no appreciable selection, genetic drift is causing changes to the allele distribution of the population. 2. Natural selection selects or selects for individuals. For example, Quetzal wrote in Message 67:
Evolution . operates at the level of population, not individuals. Natural selection, on the other hand, is an individual selective filter. Evolution operates ONLY over generations. Selection operates during the individual's lifetime.
And Percy wrote in Message 66:
The gene is the unit of heredity, not the unit of selection. Genes can only be selected in entire collective bunches because natural selection operates on individuals.
3. Natural selection selects or selects for for genes (or kin). For example, Modolous wrote in Message 63 Natural selection does not affect the frequencies of individuals, it selects which genes survive in the population...it affects gene frequencies [or allele frequencies] . Selection is about selecting for things that make more copies of themselves that can survive to make more copies of themselves, not about selecting individuals that die since they all will. I happen to agree with Modolous, mostly, if more emphasis is placed in allele frequencies. Individuals don’t get naturally selected, or selected for, not in the Darwinian sense. But there is another issue here: Does natural selection, in and of itself, amount to evolution? Or does natural selection only lead to eventual evolution? I’ll think Darwin saw natural selection as the actual evolutionary event, or as its cause, because he explained it (standing on Malthus’s shoulders) as an active mechanism or agency of evolution. While I agree that evolution can happen without natural selection”via random genetic drift, for example, as crashfrog points out”I don’t agree that natural selection and evolution are NOT the same thing. Indeed they are, if one views NS in an active context. Why would Darwin even bring up the idea of natural selection if it didn’t explain how biological evolution works in the active sense? To me, the Darwinian meaning of natural selection is best seen in the active context. You however prefer to view natural selection is the passive context. Which one of us is right? ”HM
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Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
All right, thank you, everyone. My education is coming along nicely. You teachers have been so kind and polite about my corrective surgery. Just to be sure I have things right, though, maybe you could critique these two statements about the agencies of evolution:
1. The allele frequencies of population A over time t remain unchanged, owing to the absence of selective pressure and/or random genetic drift. 2. The allele frequencies of population B over time t change, owning to the presence of selective pressure and/or random genetic drift. More nonsense? ”HM
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Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
Chiro wrote:
I'm going with #5, then, because allele frequencies must have nothing to do with selection pressure and/or random genetic drift. Hmm, I wonder what accounts for them. Morphogenic fields? Parallel convergences? And we can add another: 3. The allele frequencies of population C over time t remain unchanged despite the presence of selective pressure. 4. The allele frequencies of population D over time t change despite the absence of selective pressure and/or random genetic drift. ”HM
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Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
Chiro wrote:
Thank you. It is a good one, but a wet one here in the Puget Sound region. I still think you should be concentrating on understanding the basic concepts before trying to add complications. Oh, and happy birthday. I hope you have a good one. I take it, then, that you disagree with Modulous, who wrote in Message 136:
I agree that natural selection cannot happen on the individual members, nor can it happen on the Queen. Individual ants don't get selected. Their genes get selected to replicate into the next generation (or not). It is not the colony that gets selected to replicate, it is the colonies genes.
To explain NS and other agencies of evolution, I think you have to focus on the replicators, which are the genes and their alleles. Replicators are the biological entities that get selected and evolve. Individual organisms are not replicators. They do not replicate themselves, not as unique individuals. They only reproduce more unique individuals. And what about the worker ant individuals (re: Modulous's discussion) that don't reproduce at all? Would you say they get naturally selected against? (Are eunuchs and homosexuals naturally selected against?) ”HM
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Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
Chiroptera wrote: When some individuals leave more surviving offspring behind than others due to these heritable differences, we call that "natural selection"...In fact, I suspect that Modulous will basically agree with this definition (although he might, and should, have some reservations about details). Neither he, nor anyone else, has objected to this since I have proposed it twice, so I am assuming that most of us are in broad agreement that it is a useable definition...As far as I know, this definition is or is close to the actual definition actually used by biologists. Just curious: Do you think that 'individuals selected to reproduce' is different from 'replicators selected to replicate'? I do agree that Darwinian evolution by "natural selection" is Malthusian in principle, andI think I understand it: A population may grow faster than its supply of food and resources, possibly causing differential reproduction success amongst it members. And I do understand that individuals succeeding in reproduction may be seen as “being selected”” in the sense of “selected to reproduce.” But I still don’t see this as Darwinian "natural selection." I agree that natural selection can be correctly defined as differential reproductive success of individuals across a population. But you confuse me when you imply in Message 143 that natural selection occurs even in populations whose members enjoy effectively equal reproductive success:
3. The allele frequencies of population C over time t remain unchanged despite the presence of selective pressure.
Selective pressure with no change in allele frequecies? How could that be? If there is no change in alllele frequencies how else would you measure selection pressure? And just because an organism successfully reproduces doesn’t mean it has been “naturally selected." (I think natural selection operates on the relative favorability of genetic traits inherited generationally”I'll call them "allele frequencies"”not on the ephemeral individuals who bear them temporarily.) ”HM
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Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
But, Chiro, you haven't yet explained how natural selection occurs in a population with unchanging allele frequencies, owing to effectively equal reproductive success amongst its individuals. You're just saying that any individual that reproduces successfuly is naturally selected. I'm still confused. I thought Darwinian natural selection happens, or can happen, when the individuals of a populations have differential reproductive success.
”HM
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Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
1. The allele frequencies of population A over time t remain unchanged, owing to the absence of selective pressure and/or random genetic drift.
Even the maximally simple population, the Hardy-Weinberg population, moves towards equilibrium, doesn't it? And wouldn't mutation also cause changes in allele frequencies? ”HM
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Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
I've been told that I am being confusing, so I am going to bow out of this conversation.
I suppose you can go hang upside down in your cave, Chiroptera, if you want to. Does this mean, then, that you have abandoned your position that natural selection happens even in populations experiencing no differential reproductive success amongst its individuals? ”HM
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Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
I don't think that Hoot Mon was trying to be rude.
No, I wasn't trying to be rude. I was only trying to understand how natural selection happens when there is no natural selection. If natural selection happens even when there is no differential reproductive success, as you claim, then how do you explain it? ”HM
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Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
I could not possibly put it any better than Modulous has done here in Message 166. His view of NS is precisely consistent with my view of it.
”HM
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Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
Hoot Mon writes:
I would explain this differently than Chiroptera, but please realize it is only the approach to explanation that is different, not the underlying concept being explained. If natural selection happens even when there is no differential reproductive success, as you claim, then how do you explain it? Say you have two first-year brown rabbits that have never reproduced that have wandered a bit too far north and find themselves in a snow covered landscape in the spring. While seeking food they are both eaten by foxes. They have both been deselected by natural selection. The difference in their reproductive success is zero, but natural selection has occurred. Whatever it was in their phenotype that caused them to place themselves in a vulnerable position will not be passed on to the next generation. ”HM
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Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
Now...please remember that I am NOT talking about evolution, only natural selection. Since we both agree that evolution occurs at the level of population, then I assume we have no disagreement that talking of the change in allele frequencies - the result of natural selection (among other things) - in a population is evolution.
Quetzal, I am pretty clear about the way you differentiate natural selection from evolution. I'll have to agree with you, mostly, but I have a few more questions. Are you saying that evolution cannot happen at other levels besides the population? Do you mean only speciation? Why can't traits (even a single phenotype/genotype) evolve, as is claimed to be the case in microevolution? Ah, but you will probably say that it takes a population to do that. I wouldn't disagree, but there is still a rumple on my bed of understanding. Maybe it's the idea that natural selection can occur without evolution, even microevolution, taking place. So, is it correct to say that natural selection is something that manifests in a population having differential reproductive success amongst its individuals, causing evolutionary effects ranging from zero to speciation? Are you saying that the action of NS may have no effect on the evolution of a population? Are you saying that natural selection sort of lurks in almost every population, causing evolution to occur only on occasion when the selection pressure gets too high? I guess I'd have to agree. I agree that evolution can happen without natural selection. There are other agencies, such as random genetic drift. But I will have to adjust my perspective a little, as you convince me that differential reproductive success does not necessarily make evolution happen every time. Of course it does not. So your point is well taken. Two things still bother me: 1. Doesn't your view of natural selection obviate the "selected for" aspect of the concept? That is, nothing could be "selected for" when natural selection is merely the occasion of differential reproductive success (with its evolutionary effects ranging from zero to speciation). 2. This absurd idea, not yours but Chiro's, that natural selection happens even when there is no differential reproductive success. What? This one is hard for me to swallow. ”HM
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Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
The population is the fundamental element of evolution . However, it is quite useful to talk about gene lineages evolving.
Kinda fickle, aren’t we? Actually. I see it mostly your way:
. It makes no sense to talk about evolving individuals, or for that matter the arbitrary groupings we call species, genera, etc, except in the abstract...However, when describing the effects of selection as it pertains to evolution, the gene's-eye-view is the more relevant - because it describes the result of selection over evolutionary timescales .
And Modulous’s way, too. But I still have a quibble with this:
Natural selection is basically just a seive that "sorts" individual organisms based on some trait or characteristic (or suites of traits or characteristics). This sorting may affect the individual's survival, reproduction, reproductive rate, etc. In other words, the trait or whatever impacts the individual's fitness in its current environment. That's all.
This is troublesome for me, because the agreed-upon definition of natural selection is: ”differential reproductive success amongst individuals across a population’. This definition does NOT take into account: individual survival, sexual selection, “ . or whatever impacts the individual’s fitness in the current environment.” If natural selection is, by definition, ”differential reproductive success across a population’ then natural selection can only impact a relatively even distribution of reproductive success across of population.But I still get a confusing response from your when I mention: This absurd idea, not yours but Chiro's, that natural selection happens even when there is no differential reproductive success. What? This one is hard for me to swallow.
What do you mean, "absurd"? ...Again, it seems to boil down to "selection" vs. "response to selection", n'est-ce pas? Understand the difference? only the filtering that natural selection is a sieve . The seive is always operating. The "sorting machine" of natural selection is always "on". ”HM Edited by Hoot Mon, : No reason given.
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Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
Natural selection is the term people use when speaking of evolution. Evolution according to Darwin is natural selection and descent with modification, and natural selection does not seem a particularly confusing term...While I think the discussion you're having with Quetzal is very useful and informative, I think it is also confusing the heck out of Hoot Mon.
Percy, Quetzal, Chiroptera, et al, I think I understand your problem with the specific meaning of natural selection. You think natural selection is anything that affects the survivability and general wellbeing of individuals or genes in a population, while not necessarily affecting the evenness of reproductive success amongst its individuals. If, for example, a mutation occurs that affects certain individuals by making them shorter, then that, in and of itself, by your reasoning, would be a form of natural selection”nevermind if it helps or hurts their reproductive success. But it's good to remember that natural selection it is not the only mechanism of evolution. Let me point out, as I did earlier, the five known causes, drivers, or mechanisms of evolution: 1. Random genetic drift”change in allele frequencies owing to decrease in population size (non-selective) 2. Gene flow”genes/alleles entering or leaving a gene pool (non-selective) 3. Mutation”heritable nucleotide sequence alteration (non-selective) 4. Sexual selection”differential mating success (non-selective) 5. Natural selection”differential reproductive success (selective) Evolution can happen without natural selection. There are four other “drivers.” Sure, any one or more of them may affect the evenness of reproductive success in a population (i.e., natural selection), but any one or more of these mechanisms may bypass natural selection altogether en route to an evolutionary event. You seem to be saying, if I understand you correctly, that natural selection is all five of the above, whether or not they cause differential reproductive success in a population. You might be saying that mutation, for example, serves the cause of natural selection. I would not necessarily agree, because evolution can happen apart from natural selection. Random genetic drift is as valid a mechanism of evolution as natural selection is. ”HM
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