|
Register | Sign In |
|
QuickSearch
Thread ▼ Details |
Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
|
Thread Info
|
|
|
Author | Topic: What exactly is natural selection and precisely where does it occur? | |||||||||||||||||||||||||||||||
Modulous Member Posts: 7801 From: Manchester, UK Joined: |
Infertile members cannot be said to be individually subject to the rigors of Natural Selection since they are incapable of breeding. Regardless of what happens to them in life changes nothing in regards to reproductive success, except for the contribution of their work to the success of the reproduction of the whole. Correct. Indeed - my entire point. The whole of what though? The genes. The entities that experience reproductive sucess are genes - not individuals since some individuals are incapable of reproduction.
- I have a difficult time ascribing any concept of “altruism” to members of ant colonies since, with brains the size of pinpoints, controlled by the mind-bending chemicals of that fat drug-pushing bitch down at the bottom of the hole, there are no options but to act in accordance with her will just as surely as your right hand must (usually) obey the dictates of your brain, with no freedom of anything approaching “individual action” let alone any prospect of independent reproduction. Altruism doesn't have to be an act of will or decision. The individual ants aren't being altruistic in the sense we are used to - they are being selfish by making sure that their genes get passed on. They do this by making sure their sisters and brothers are able to protect the reproductive members of the community whose role is to directly replicate the genes.
- There is not even the possibility of any “evolution” of worker generations from any specific queen. (Queen can last 5-7 years while worker lasts from 4-5 weeks.) Only the reproductive progeny can carry the mutation/allele re-combinations necessary for the species as a whole to evolve any/all the phenotypes expressed by the organism (various workers, queen, drone). A Queen cannot improve the phenotypes of her workers. Only her reproductive progeny can create better (or worse) workers. It is again the whole of the single organism, the colony, which is the focus of Natural Selection. 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. The colony is more than just the genes - there are plenty of things that are included in the set {colony} that do not and never will be copied in the next generation - including exact numbers, exact actions, exact phenotypes. These things are not copied. The genes are largely the same from generation to generation, though some increase in frequency, some decrease, and some are lost.
In this view the worker is but an appendage, vital though it may be, to the organism and “individuality” (in a Natural Selection sense) is lost. I understand the metaphor - as I have previously said. And I agree it has its uses. However, smudging the lines on what is and what is not an individual based on reproductive capability is dodgy grounds, for reasons I have already highlighted. However, genes do replicate - that is their defining feature. Individual genes are the true individuals that are the subject to natural selection.
There are further studies that appear to show that in some older colonies on the verge of death some of the new larva are spawned not by the queen but by a worker. But these are exceptions that my argument so I’ll ignore them. The hallmark of a solid theory is right here. The genecentric view doesn't have to ignore these exceptions. These workers don't suddenly become individuals having been limbs or organs or appendages all their life previously. They have the same genome they always did (give or take normal intra-genome mutational events of course) - those genes are working to replicate themselves through the tactic of emergency queen-duty replacement. We don't even have to look at insects - several social mammals exhibit similar quandries to the individualist. Consider individuals that voluntarily decide to not reproduce - perhaps it is a society with an alpha-individual or alpha-group who are permitted to reproduce. An individual that is not permitted should (according to the individualist) attempt to mate anyway...otherwise they will be selected out. However, this doesn't happen nearly as often as the individualist model would predict. The lesser males/females in this group are charged with other duties to the group. Things such as lookouts, childcare, parasite removal etc etc. Are these individuals also 'appendages'? Of course not! They are individuals. They are protecting their genes, and helping them replicate. The genes that are responsible for instructing the individual not to mate are looking out for themselves! If these individuals did mate, there could be overpopulation problems - the group's resources will be pushed to the limit, and more of them will die. That means less genes survive, which the genes do not want to happen since their only goal is to replicate. Those genes that replicate well survive, those that don't get selected out.
|
|||||||||||||||||||||||||||||||
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
|
|||||||||||||||||||||||||||||||
crashfrog Member (Idle past 1498 days) Posts: 19762 From: Silver Spring, MD Joined: |
1. Natural selection selects or selects for groups. How did you get that from what you quoted?
quote: Those were my words, but I don't see where I used the terms "natural selection" or "groups" in any of that. Go back to the classic example - bacteria and antibiotic resistance. Individuals who are resistant survive, individuals who aren't, do not. The subsequent generations are all the descendants of those individuals who survived, which means they're also resistant, and so now you have a population that has evolved resistance by selection of individuals. The things you write are nonsense, because apparently you don't understand what words mean. That's the only explanation I can offer for why you understood what you quoted to be referring to "natural selection of groups," language that does not appear in the quoted section.
Why would Darwin even bring up the idea of natural selection if it didn’t explain how biological evolution works in the active sense? A house has walls and a roof, but does that mean that a roof is a house? Or that a wall is a house? You're confusing the process with the result. Natural selection is one of the processes that result in evolution of populations.
|
|||||||||||||||||||||||||||||||
Percy Member Posts: 22508 From: New Hampshire Joined: Member Rating: 5.4 |
Hoot Mon writes: Thus far, we have established three schools of thought on the operational definition of natural selection... As I said in the very message you're replying to, everyone is just explaining the same thing to you, but in different words and from different perspectives. There are not "three schools of thought" about natural selection. It's a simple concept with only a single school of thought.
I happen to agree with Modolous, mostly, if more emphasis is placed in allele frequencies. I hope Modulous sees this, because it makes clear that you understand natural selection neither in terms of genes nor of individuals.
Individuals don’t get naturally selected, or selected for, not in the Darwinian sense. Darwin didn't know about genes. He described natural selection in terms of selection of individuals. What was it about the analogy of natural selection to artificial selection that you didn't understand?
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? People keep explaining natural selection to you, and you keep asking what it is. I see no evidence that yet another of my explanations is finally going to do the trick, maybe someone else will finally find the right words. --Percy
|
|||||||||||||||||||||||||||||||
Quetzal Member (Idle past 5903 days) Posts: 3228 Joined: |
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. How do you figure? This is precisely the definition of natural selection Darwin and Wallace developed.
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? NO! How many times do you have to be told? You even quoted us in this post on this subject! Evolution is the result of natural selection operating on individual members (or suites of genes if you like Mod's construction better) over generations in a population. Natural selection is (one of) the mechanism(s) of evolution. It is NOT evolution. Populations evolve. Individuals (or genes) are selected. There is no disagreement here.
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. Good grief - you even state it here! It is the agency or mechanism of evolution! Why do you keep repeating the nonsense (and apologies, but that's what it is) about individuals evolving if subject to natural selection?
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? And here again, for some reason, you lose it. I really and truly do not understand what element of the concept you're not grasping, Hoot. I really don't. Setting aside for the moment whatever it is you're trying to convey with the "active context" and "active sense", which, since they aren't terms used in science as far as I know, are inherently meaningless (you'll really need to expand/explain what you're trying to say), Darwin absolutely DID use natural selection as the explanation for biological evolution. In fact, it was his (and Wallace's) key insight into the mechanism of evolution - natural selection - that was so revolutionary. Up until then, various folks from Lamarck to Erasamus Darwin could see that evolution occurred - but nobody until Darwin came up with a how that fit all the facts.
|
|||||||||||||||||||||||||||||||
Chiroptera Inactive Member |
quote: I suggest that right now. you don't worry about whether it is the individual organism or the gene that is being selected. It isn't important to the definition of natural selection. Try to understand the basic concept first; complications and extensions to the basic concept can come later. I will repeat my earlier attempt at a definition:
Populations consist of a number of different individuals. These individuals are different in physical features, some of which are heritable. When some individuals leave more surviving offspring behind than others due to these heritable differences, we call that "natural selection". Note that I made no mention of whether it is the individual or the gene that is being selected. All I have done is define natural selection in terms of observable phenomena, namely that some individuals leave behind more progeny than others, and that this difference be due to inheritable characteristics. Whether the "individual" is the organism or the gene can be put off later, after it is demonstrated that you understand the basic concept. Actually, if their god makes better pancakes, I'm totally switching sides. -- Charley the Australopithecine
|
|||||||||||||||||||||||||||||||
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
|
|||||||||||||||||||||||||||||||
Chiroptera Inactive Member |
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. Both of these are possible as well. Actually, if their god makes better pancakes, I'm totally switching sides. -- Charley the Australopithecine
|
|||||||||||||||||||||||||||||||
crashfrog Member (Idle past 1498 days) Posts: 19762 From: Silver Spring, MD 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. That can't be right, can it? 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?
|
|||||||||||||||||||||||||||||||
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
|
|||||||||||||||||||||||||||||||
Chiroptera Inactive Member |
quote: If you say so. But I think you are again demonstrating how little you know about the subject. Edited to add: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. Edited by Chiroptera, : No reason given. Actually, if their god makes better pancakes, I'm totally switching sides. -- Charley the Australopithecine
|
|||||||||||||||||||||||||||||||
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
|
|||||||||||||||||||||||||||||||
Chiroptera Inactive Member |
As I have been saying, I think it will be more fruitful if we were to focus on the basics first; complications like eusocial species can come later.
I will repeat my attempt at a definition:
Populations consist of a number of different individuals. These individuals are different in physical features, some of which are heritable. When some individuals leave more surviving offspring behind than others due to these heritable differences, we call that "natural selection". First, this definition makes no mention of which is being selected, the organism or the gene. It simply makes a simple observation: some individuals do not reproduce as much as other individuals. Whether the invisible hand of natural selection is actually pointing to the individual that is not reproducing or to its genome isn't yet important. I am merely linking natural selection to the most observable phenomenon. 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. I would suggest one or two fixes myself, now that I think about it, but let's see what the objections to this definition are first. In particular, I am interesting in seeing what your objections are. As far as I know, this definition is or is close to the actual definition actually used by biologists. Actually, if their god makes better pancakes, I'm totally switching sides. -- Charley the Australopithecine
|
|||||||||||||||||||||||||||||||
Modulous Member Posts: 7801 From: Manchester, UK Joined: |
In fact, I suspect that Modulous will basically agree with this definition (although he might, and should, have some reservations about details). Let me step in, and say that this is pretty much bang on! I'll quote Dawkins yet again, since he is the prolific, understandable, modern writer on genecentric selection.
Dawkins writes: Every living creature has ancestors, but only a fraction have descendants. All inherit the genes of an unbroken sequence of successful ancestors, none of whom died young and none of whom failed to reproduce. Genes that program embryos to develop into adults who can successfully reproduce automatically survive in the gene pool, at the expense of genes that fail. This is natural selection at the gene level, and we notice its consequences at the organism level. There has to be an ultimate source of new genetic variation, and it is mutation. Copies of newly mutated genes are reshuffled through the gene pool by sexual reproduction, and selection removes them from the pool in a way that is non-random.
From {New Scientist} I know that copy/pastes from sites are frowned upon and 'own words' are looked for, but I can't resist citing this 'compromise' site.
Obviously, natural selection cannot choose replicators directly, because it does not operate directly on DNA, but rather on the phenotypic effects expressed by genes. Therefore, natural selection does in a sense select at the organism level, because it makes proxy selections based on the adaptation of the phenotypes of various competing organisms. Natural selection operates directly on phenotypic adaptations and thus indirectly on the genes responsible for those phenotypes. Optimons obviously benefit from the survival of their vehicles, so adaptations appear to favor the survival of the individual organism. However, some optimons do not always favor the individual organism - some may confer a measure of "altruistic" behavior toward kin because they are likely to share genes with a given organism. By coding for altruistic behavior, such genes encourage their own survival in the body of the relative benefiting from the behavior. Conversely, an optimon may "prefer" to favor, say, more offspring for a given organism over that individual organism's survival. Thus the optimon ensures its own replication even at the expense of its vehicle when necessary.... Suppose that a female, asexually reproducing insect, such as an aphid, produces a daughter, who in her turn produces a granddaughter, etc. Suppose that the original aphid suffers an injury at some point before reproducing. This injury may persist throughout her lifetime, but will not be passed down to the next generation. Acquired characteristics are not inherited and have no effect on genes, which are passed down. The organism is not a replicator, because a copy of the organism was not made. On the other hand, an error in the insects' genomes will be passed down to all subsequent generations - it is a replicator. Because genes cause phenotypic effects, but phenotypes have no effect on genes, only genes and not phenotypes are replicators. Which basically mirrors what I have been saying. From here. Not really debating your position here. I thought bringing together my thoughts in the often more carefully crafted fashion of professional writers would help clarify my position to any who may have been confused. As an addendum, I'm arguing a specific position heartily, because it is under represented here. This is a genuine debate, a genuine controversy as it were. It's fascinating to hear both sides, but I generally favour the utility of genecentric vision for truly understanding what is going on - but I accept the pragmatics of discussing things at higher levels such as organism /family/colony/race/breed/species/[insert arbitrary grouping, as long as that grouping is done on the basis of common ancestry] level. I just think it is easy to go from the pragmatics of this view, and get a little carried away with it - finding oneself in a position of having difficulty explaining certain things.
|
|||||||||||||||||||||||||||||||
Quetzal Member (Idle past 5903 days) Posts: 3228 Joined: |
Mod's article writes: Obviously, natural selection cannot choose replicators directly, because it does not operate directly on DNA, but rather on the phenotypic effects expressed by genes. Therefore, natural selection does in a sense select at the organism level, because it makes proxy selections based on the adaptation of the phenotypes of various competing organisms. Natural selection operates directly on phenotypic adaptations and thus indirectly on the genes responsible for those phenotypes. Heh, this is what I've been saying all along - although obviously not as well. The last paragraph in your quote also sums up well - the genotype is indeed what gets replicated (outside of clonal species, of course). That is never in question. Throughout I've been talking about what gets selected - not what gets replicated. Perhaps that's where our miscommunication arises?
|
|
|
Do Nothing Button
Copyright 2001-2023 by EvC Forum, All Rights Reserved
Version 4.2
Innovative software from Qwixotic © 2024