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Member (Idle past 4843 days) Posts: 624 From: Pittsburgh, PA, USA Joined: |
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Author | Topic: Tautology and Natural Selection | |||||||||||||||||||||||
Mammuthus Member (Idle past 6475 days) Posts: 3085 From: Munich, Germany Joined: |
Yes..if you look at generation years you see that the reproductive output of A is much higher than B and thus the relative fitness is higher for A regardless of how long A or B survived...that is why fitness is not a measure of survivability of an individual...you are measuring the frequency of a trait in a given generation...that trait got to the generation via the reproductive effort of the preceding generation...the frequency in the current generation is a measure of the success of the previous generation in passing their traits to this one...the same thing when the current generation tries to reproduce.
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Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined: |
But who is trying to eliminate survival? We all know, I should hope, that fitness can have a number of measures all of which are applicable in different situations.
There is a page on the university of Indiana's bio web site that has a good list of a number of factors which 'multiply' together to give total fitness. They include number of offspring per mating/ season, number of matings which might produce offspring, survival in each season, lifespan and other possible factors which aren't covered, but basically anything contributing to reproductive success for the lifetime of the organism.
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JustinC Member (Idle past 4843 days) Posts: 624 From: Pittsburgh, PA, USA Joined: |
No problem on the lateness. I broke some handbones and wrist in car accidenct recently, so my responses may be pithy.
quote:Ok, I thought you were saying that population A on the one side of the mountain and population B on the other were in significant competition. quote:How is it not tautologous if you factor in genetic drift in fitness. It seems like the theory is 'survivors survive'. How would you describe the theory? And as for the deletion, 'Less is More' as Mies van der Roe would say.
quote:What is this selection pressure? Aren't we just looking for the better designed system for reproduction in a certain environment{being all its surroundings)?
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Mammuthus Member (Idle past 6475 days) Posts: 3085 From: Munich, Germany Joined: |
Hi Justin..sounds like a nasty injury...I busted up my hand about a year and a half ago and it was really miserable working on the computer.
quote: Natural selection is only a part of the theory of evolution..and the theory of evolution is not that survivors survive. However, it is not that survivors survive that is of interest to fitness primarly. It is that traits conferring benefits be it food gathering, more accurate transcription, etc. tend to increase in the population and some case become fixed in the population. This is much different than saying survivors survive. Lot's of organisms of different potential fitness are born in each generation..in each generation some will reproduce more than others and will have a higher representation in the next generation i.e. higher fitness. As this is genetically/epigenetically based, alleles will change in frequency over time (evolution) due to some alleles conferrring an advantage on their host. But you can't leave out drift either..some traits/alleles become fixed in populations without conferring a benefit i.e. they are not selected for...they become fixed due to genetic drift.
quote: Why "designed"? As I have pointed out in other examples, there can be situations that are ultimately destructive to the host or its reproductive capacity but propagate anyway because of some other advantage....what is the "design" difference in a family that has 14 children versus a family that has 1 child. The family with 14 kids has a much higher fitness...what is "designed" for reproduction in that family that is not present in the family with 1? Here is an example of conflicting selection pressures as well taken from this weeks Science and Biomednet.com New type of evolutionary conflict demonstrated31 July 2003 2:00 EST by Helen Dell [Caption]Geneticists have uncovered a new type of evolutionary conflict that acts in human testes. There seems to be a clash between what's good for the organism and what's good for the sperm-producing cells, they say. The researchers study Apert syndrome, a developmental disorder characterized by distortions of the face and head and webbed hands and feet. The condition is usually caused by a newly generated mutation, inherited from an unaffected father. What interested the researchers was how often the syndrome-causing mutations seemed to be cropping up - between 200- and 800-times more frequently than background mutations. "Basically, if everywhere [in the genome] was mutating at that sort of level, then none of us would be alive because the genetic burden would be too high," said Andrew Wilkie, Nuffield Professor of Pathology at the University of Oxford, who led the research. Apert syndrome is linked to paternal age, so the older the father is, the more likely he is to have an affected child. The usual explanation for such age effects is that the older a man is, the more cell divisions his sperm-producing stem cells (spermatogonial stem cells) will have gone through. "Not only are you accumulating mutations [with age], but your ability to repair them will get worse," explained Wilkie. So he and his colleagues looked at the most-common Apert mutation in sperm samples from men of different ages. Their results, published today in Science, show that the mutation did indeed appear more often with age, mirroring the incidence of the syndrome. But, when they looked closer at the DNA context that the mutation was found in, it seemed as though the mutation was occurring only rarely. Essentially, the observed rise in mutations is not because of more mutation events, but rather because there are an increasing number of copies arising from one (or a few) events, they suggest. "We propose that the mutation events are infrequent, but when they occur they give a selective advantage to the cells in which they've occurred," said Wilkie. "This is really a radically different explanation for the paternal age effect." When spermatogonial stem cells divide, they usually produce one cell that will go on to be sperm and one cell that remains as a stem cell for the next generation. Wilkie speculates that the Apert mutation might bias this somehow so that occasionally two stem cells would be produced (with no cells becoming sperm). So over time, the numbers of mutated stem cells would gradually increase, while the number of unmutated stem cells would remain the same. That is, the mutated stem cells have a selective advantage over their unmutated neighbours. The idea of strong selection on mutant spermatogonia is very unorthodox, says James Crow, emeritus professor of genetics and medical genetics at the University of Wisconsin, but he is reluctantly impressed. "When I first read the paper, I tried to think of alternative explanations, and I came up blank. This evidence is pretty good...very good. Unless there's a glitch somewhere, I think he's proved his case." Wilkie is intrigued by the evolutionary implications of the findings - that a mutation could be devastating to the organism as a whole while being advantageous to germ cells (any cells that produce sperm or eggs), so that two selective pressures act in opposite directions. "You could imagine a situation where there are much subtler selective effects at the level of the germ cell where the balance is the other way round where the organism is maintained in a sub-optimal state," he said. "[In such a case] the selective disadvantage to the organism from the mutation is less high than the selective advantage that it confers in the germ cell, so that the organism would be better off if it had a slightly different genotype, but it can never get there because the selection in the germ cell is always pushing it in the other direction."
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Peter Member (Idle past 1479 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
That's OK then ... that's all I've been saying.
fitness is a function of reproductive output and survival.
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Peter Member (Idle past 1479 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
But at which point during the life-time of that
generation? That was partly my point of proposing a hypotheticalimmortal population. They can kill each other, or starve to death, or such, but not die of old age. Take snapshots through time and the trait frequencieswould still be changing. For me that means that fitness/reproductive success must havesurvival as one of its variables (or paramaters maybe). WoundedKing says we all knew that all along -- which makes mewonder why this thread has gone on this long -- mind you all the creationists DO seem to disappear in the summer
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Peter Member (Idle past 1479 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
quote: Ouch!! I sympathise, I broke my left wrist and a bone in my righthand a couple years ago when I came off my motorbike!!! quote: It's not that survivors survive so much as those who are fitterhave a greater chance of surviving. Some very fit individuals will still die and some less fit will still survive to breed. 'Survival of the fittest' means 'Those better adapted to theirenvironment are more likely to survive.' The longer one survives the more opportunity one has to breed -- I mean look at Michael Douglas
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Mammuthus Member (Idle past 6475 days) Posts: 3085 From: Munich, Germany Joined: |
and wounded king was right...however, you have been making it sound like survival is the key aspect to fitness above all others which is wrong....you are right about the creationists...other than buzsaw and Symansu they seem to have all gone on creationist vacation
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Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined: |
A lot of definitions refer to changes in allele frequency over generations, why don't you just use that instead of 'over time'. In fact in most evolutionary genetic analysis the time is measured in generations, therefore your immortal population, how ever long lived, would only constitute one point on the time axis.
[This message has been edited by Wounded King, 08-05-2003]
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Peter Member (Idle past 1479 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
But when do you measure/assess the allelic frequency of
the generation? 1 year into the life-span, 2, 10, 20 ... ? Will the allelic frequency be the same in year 0-2 as itis in years 10-15?
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Peter Member (Idle past 1479 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
I have said a few times that I view fitness to be a function
of survival and reproductive output. I do think that survival has much more of an impact thanreproductive output though (in individual and evolutionary terms). Especially in response to environmental change.
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Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined: |
Well as long as you are consistent it shouldn't really matter.
This would only really become a problem with animals with many breeding cycles, or like humans where there is no seasonality to mating. The older population members have to die out some time anyway, except in your hypothetical immortal population of course. The best time to assess would probably be just prior to or subsequent to the first mating season of that generation, when the offspring have reached sexual maturity. [This message has been edited by Wounded King, 08-05-2003]
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Mammuthus Member (Idle past 6475 days) Posts: 3085 From: Munich, Germany Joined: |
A good question really. You do not expect the allele frequency to stay the same always...if it did there would be no evolution i.e. change in allele frequency over time in a population. That is why I keep saying you take a snapshot of a specific moment in time..not with the expectation that it will always remain the same. Most pop gen studies do not have the luxury of timing the breeding cycles of the organism being analyzed. One simply collects as many samples as one can, genotypes them and measures how diverse the samples are and what loci seem to be under selective constraints i.e. are specific loci/alleles at a higher frequency than expected under Hardy Weinberg equilibrium for example.
To do more refined measures of fitness i.e. individual contributions or individual loci would likely require a lab setup with Drosophila...for species with longer generation times it would be much harder to do controlled experiments i.e. you die long before the experiment is concluded...and somebody much later finds out you set it up wrong and it needs to be repeated
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Peter Member (Idle past 1479 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
I suppose in a real population you could take a large
sample and determine allelic or trait frequencies within different age ranges. You could then perhaps make some comment on the 'life-cycle'of traits. These are the things that make me feel that 'survival' isa necessary part of any definition of 'fitness' though.
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Peter Member (Idle past 1479 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
So you would only look at the individuals who are
breeding for the first time?
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