|
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? | |||||||||||||||||||||||||||
AZPaul3 Member Posts: 8564 From: Phoenix Joined: Member Rating: 5.1 |
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.
Because of my genome, my complete phenotype is unbearably attractive to the female of my species. I am 6 foot 6, 200 lbs, with muscles that ripple like waves over a stormy sea. I have the chiseled features of the Greek gods I am descended from and my intellect is beyond all known limits. I am not just sexually selected for, I am wanted, I am needed. I can have my way with any woman and I will father an extensive clan assuring my genes are passed on to the next generation by the dozen. I am selected for by the powers of Natural Selection. Assuming, of course, that I am not crippled in a football game, run over by a drunk driver, hit by a falling comet or that I can somehow survive the pandemic of typhus rolling over the continent and find shelter from the mini-ice age that has gripped my world, otherwise I’m just a dead wannabe who leaves nothing behind having been selected against instead of for by all those other elements of Natural Selection. Now that is a most wonderful run-on sentence. But if the point is made then it works so I don’t care. Fantasy is such fun.
|
|||||||||||||||||||||||||||
PaulK Member Posts: 17828 Joined: Member Rating: 2.5 |
quote: I think that your reply is poorly worded and could do with a rewrite - it isn't clear what you mean. Natural selection is the process that produces changes in allele frequencies. Preferential mating is an example of that as Crashfrog said, and as you seem to agree, despite the "No, it's not". However you are also wrong to state that preferential mating cannot be subject to selection. Mate choice is clearly linked to reproductive success and obviously could have an impact on the quantity and quality of offspring. Where it has an overall positive impact it certainly could be selected for.
|
|||||||||||||||||||||||||||
Quetzal Member (Idle past 5903 days) Posts: 3228 Joined: |
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 bolded the part I have a quibble with. Although my points here may serve to confuse the issue more for those unfamiliar with it, I'm afraid I have to disagree with this characterization of natural selection. Setting aside for the moment the "genes'-eye-view" argument, selection is a filter that affects organisms based on their phenotype. I would argue that catastrophic natural disasters - either global or local - are not really subsumed under "natural selection". There has been a great deal of discussion over the years concerning the "whys and wherefors" of differential survival of specific taxa following large-scale extinctions. My personal opinion is that this survival owes more to luck than genetics. IOW, there is no true selective filter in operation. Meaning the frog whose stream dries up due to the beaver, or the continental fauna devastated by an asteroid are not being selected for or against. Their genotype/phenotype has absolutely no bearing on whether they survive or not (well, maybe in the case of the frog if there are individuals in the population more tolerant of a xeric environment, say). I don't know if you get the chance to read much popsci, but one interesting book on this subject is David Raup's Extinction: Bad Genes or Bad Luck? (WW Norton 1992). Although I strongly disagree with many of Raup's contentions (including especially the "Nemesis Hypothesis"), he makes a good case for genetics having diddly to do with survival of taxa following a mass extinction. Asteroids, in short, are not a selective filter acting on a genotype. They represent a field of bullets where the survival of any given taxa is due more to chance than selection. Yon butterfly may have the most perfect genotype/phenotype on the planet with all kinds of wonderful adaptations, but if a bird eats it before it reproduces, its genotype had nothing to do with it, and it is an evolutionary dead end.
|
|||||||||||||||||||||||||||
Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
JustinC wrote:
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. and in Message 32 Quetzal wrote:
In essence, then, anything that affects the fitness of an individual organism is "natural" selection.
and in Message 18 AZPaul3 wrote:
The individual is, of course, the one unit that is affected by Natural Selection pressures.
Does natural selection select for traits, or does it merely select for individuals possessing those traits? In the case of the handicap principle (Message 44), you could say that natural selection may not actually select for mate-desirable individuals, but instead against them. I don’t see how natural selection could act on individuals. Wouldn’t that mean that the individual, somewhere in its ephemeral lifetime, might actually experience natural selection? No, I don’t think so. Individuals come and go. They are as expendable as Kleenex””pull one out and up pops another.’ They only serve to make the gametes and put them where they need to go. No individual ever experiences natural selection. I haver never heard of any human individual say: “Hey, hold on a second, I think I’m experiencing a natural selection!” ”HM
|
|||||||||||||||||||||||||||
crashfrog Member (Idle past 1498 days) Posts: 19762 From: Silver Spring, MD Joined: |
No individual ever experiences natural selection. You introduce an antibiotic into a lawn of E. coli. Resistant individuals live but nonresistant individuals die. How didn't those nonresistant individuals not just experience natural selection? That's the textbook example of natural selection operating on individuals.
|
|||||||||||||||||||||||||||
AZPaul3 Member Posts: 8564 From: Phoenix Joined: Member Rating: 5.1 |
IOW, there is no true selective filter in operation. Meaning the frog whose stream dries up due to the beaver, or the continental fauna devastated by an asteroid are not being selected for or against. Their genotype/phenotype has absolutely no bearing on whether they survive or not (well, maybe in the case of the frog if there are individuals in the population more tolerant of a xeric environment, say). Except a space rock caused such devastation as to exacerbate the extinction of Dinosaurs while, due to its phenotype, some small furry mouse survived. It passed right through this filter of Natural Selection without too much of a problem. I submit its phenotype was the reason why. As you alluded, some frogs survive drought. Some bury themselves in the mud before it dries and, in effect, hibernate until moisture is again present. I submit their phenotype allowed this capability and those species of frog, or even individuals of this species of frog, without such capabilities in their genes, in this instance, did not pass through this filter of Natural Selection. They were "selected" out. Now to the butterfly. This touches on where this discussion wants to go. After, hopefully, establishing the mechanism of Natural Selection operates on the level of the transient individual, now we can look at what this crucible has left us. Why do more than half of the cousins of your poor eaten butterfly survive? Why did this differ from the meager 20% of survivals for this other butterfly population? Different coloration? Different feeding habits? Different types of predators? What is similar about them? What is different? What is different/similar in the phenotype? And, ultimately where this discussion wants to go, what is different/similar in the genotype and why? But first we need to take a step back. I submit that everything that impacts an individual’s reproductive success is an element of Natural Selection from beaver dams to space rocks and all in between including just dumb luck. The interesting stuff is what comes out the other end. Edited by AZPaul3, : Re-phrase.
|
|||||||||||||||||||||||||||
PaulK Member Posts: 17828 Joined: Member Rating: 2.5 |
To start with the most obvious case, luck is surely not an example of natural selection. Yes, it contributes to evolution (in the form of genetic drift) but it isn't an aspect of the phenotype, it isn't heritable - it's just stuff that happens. So I don't see any selective element in luck at all.
|
|||||||||||||||||||||||||||
PaulK Member Posts: 17828 Joined: Member Rating: 2.5 |
You may find Message 38 clears up some of your questions.
In the case of The Handicap Principle there are competing selection pressures. There is negative selection from the handicap itself balanced against a positive sexual selection. Any species is likely to find a balance point between these two pressures.
|
|||||||||||||||||||||||||||
Percy Member Posts: 22508 From: New Hampshire Joined: Member Rating: 5.4 |
Hoot Mon writes: I don’t see how natural selection could act on individuals. Wouldn’t that mean that the individual, somewhere in its ephemeral lifetime, might actually experience natural selection? No, I don’t think so. Individuals come and go. They are as expendable as Kleenex””pull one out and up pops another.’ They only serve to make the gametes and put them where they need to go. No individual ever experiences natural selection. I hope we can address this misunderstanding quickly and not spend much time on it. One oft-cited example of natural selection is the peppered moth of Great Britain during the industrial revolution. As tree trunks became darker due to industrial soot, the peppered moth population went from predominantly light to predominantly dark. The explanation for this change was natural selection. Light colored moths on dark tree trunks were easy targets for birds, so light coloration was selected against, and dark coloration was selected for. As Great Britain's industries became gradually more environmentally responsible, peppered moth coloration again changed with the light color returning to dominance. Because it is individual moth coloration that governs how visible it is to birds that prey upon it, selection occurs at the individual moth level according to coloration. I cite this example not to argue about the validity of Kettlewell's peppered moth experiments, but because this is a familiar topic in creation/evolution debates. In discussions of this topic creationists and evolutionists agree that selection occurs at the level of individuals. Where they disagree concerns whether Kettlewell's experiments uncovered actual natural selection occurring in the wild. They don't disagree on the definition of natural selection. In other words, your understanding of natural selection differs from both creationists and evolutionists. You might want to rethink things. --Percy
|
|||||||||||||||||||||||||||
Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
Quetzal wrote:
Qeutzal, let ask you this: Did NS occur in a individual frog so that, during its lifetime, it evolved into a reptile? Or did 'Eve', during her lifetime, evolve by way of NS from an ape into a human? Therefore, probably from my own biases and experience, I find the use of the individual organism as the "target" of the selective filter to be the most relevant. I think you are others here are placing too much emphasis on what an individual can do in the course of biological evolution. Since no individual survives long enough to actually experience NS, then the operational site of NS must be somewhere or something else. ”HM
|
|||||||||||||||||||||||||||
AZPaul3 Member Posts: 8564 From: Phoenix Joined: Member Rating: 5.1 |
Qeutzal, let ask you this: Did NS occur in a individual frog so that, during its lifetime, it evolved into a reptile? Or did 'Eve', during her lifetime, evolve by way of NS from an ape into a human? You are confusing the mechanism of Natural Selection with the result of Natural Selection. The mechanism is upon the individual, the result is upon the population. The former is life or death, the latter is Evolution.
|
|||||||||||||||||||||||||||
Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
Percy wrote:
Percy, I'm in real bad shape if neither the creationists nor the evolutionists agree wth me. Please tell me what I'm missing here. I see five different ways that biological evolution can take place: In other words, your understanding of natural selection differs from both creationists and evolutionists. You might want to rethink things. 1. random genetic drift”population size drops below crfitical level, altering allele frequencies (NON-SELECTIVE). 2. 'gene flow'”alleles sufficiently imported or exported from of population to alter their frequencies (NON-SELECTIVE). 3. random mutation”nucleotide rearrangement, sufficiently to cause a gene to express a different amino acid in a protein sequence (NON-SELECTIVE). 4. Differential mating”non-random mating, sufficiently to alter allele frequencies (NON-SELCTIVE). 5. Differential reproductive success”otherwsie known as natural selction (SELECTIVE, of course). If any one or more of these conditions are met then biological evolution may occur. NS does not always play a part, but it may eventually have a role in selecting for changes in the allele frequencies resulting from the consequences of the other evolutionary 'forces'. Don't you agree? ”HM
|
|||||||||||||||||||||||||||
Fosdick  Suspended Member (Idle past 5531 days) Posts: 1793 From: Upper Slobovia Joined: |
crashfrog wrote:
I try to keep the E. coli off my lawn. Don't you have indoor plumbing? You introduce an antibiotic into a lawn of E. coli. Resistant individuals live but nonresistant individuals die. ”HM
|
|||||||||||||||||||||||||||
AZPaul3 Member Posts: 8564 From: Phoenix Joined: Member Rating: 5.1 |
I try to keep the E. coli off my lawn. Don't you have indoor plumbing? I like that, Hoot. I could use all the checkles I can get. Thanks. But, to the Frog's point: is his example not Natural Selection? Is its mechanism not operating on the individual?
|
|||||||||||||||||||||||||||
crashfrog Member (Idle past 1498 days) Posts: 19762 From: Silver Spring, MD Joined: |
Once again I've underestimated your enthusiasm for substituting glibness for actual debate. I apologize.
|
|
|
Do Nothing Button
Copyright 2001-2023 by EvC Forum, All Rights Reserved
Version 4.2
Innovative software from Qwixotic © 2024