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Author Topic:   Tautology and Natural Selection
Mammuthus
Member (Idle past 6475 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002


Message 106 of 130 (48613)
08-04-2003 12:10 PM
Reply to: Message 105 by Peter
08-04-2003 11:41 AM


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.

This message is a reply to:
 Message 105 by Peter, posted 08-04-2003 11:41 AM Peter has replied

Replies to this message:
 Message 111 by Peter, posted 08-05-2003 6:04 AM Mammuthus has replied

  
Wounded King
Member
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 107 of 130 (48615)
08-04-2003 12:14 PM
Reply to: Message 105 by Peter
08-04-2003 11:41 AM


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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 Message 105 by Peter, posted 08-04-2003 11:41 AM Peter has replied

Replies to this message:
 Message 110 by Peter, posted 08-05-2003 5:59 AM Wounded King has not replied

  
JustinC
Member (Idle past 4843 days)
Posts: 624
From: Pittsburgh, PA, USA
Joined: 07-21-2003


Message 108 of 130 (48697)
08-04-2003 9:45 PM
Reply to: Message 98 by Mammuthus
08-04-2003 4:22 AM


No problem on the lateness. I broke some handbones and wrist in car accidenct recently, so my responses may be pithy.
quote:
Yes, the new introduced variation would be in competition...it is a new allele or trait that can spread in the population and will either be more or less relatively good at spreading itself.
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:
If a mudslide kills the member of the population before it reproduces it has a fitness of zero. Chance plays a huge role in all of this. Drift is important, freak accidents, all of this must be factored into determination of relative fitness. If the cause is an accident you don't look for traits invovled in the fitness differential. If it is traits you don't look for design..as it could be as simple as the deletion of a cell surface receptor i.e. in principle a detrimental mutation that causes the fitness advantage like with individuals naturally resistant to HIV infection. It is also complicated since it is often quantitative i.e. lots of small effects accumulated bestow the fitness advantage and it can be a real pain to tease out the individual contribution of each trait..similar problem with quantitative genetics.
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:
But the ultimate effect in such a population is selection pressure was high tfor have such a system would be to drive it to fixation in the population as the individuals without it would not produce viable offspring
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)?

This message is a reply to:
 Message 98 by Mammuthus, posted 08-04-2003 4:22 AM Mammuthus has replied

Replies to this message:
 Message 109 by Mammuthus, posted 08-05-2003 4:25 AM JustinC has replied
 Message 112 by Peter, posted 08-05-2003 6:10 AM JustinC has not replied

  
Mammuthus
Member (Idle past 6475 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002


Message 109 of 130 (48731)
08-05-2003 4:25 AM
Reply to: Message 108 by JustinC
08-04-2003 9:45 PM


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:
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.
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:
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)?
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 demonstrated
31 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."

This message is a reply to:
 Message 108 by JustinC, posted 08-04-2003 9:45 PM JustinC has replied

Replies to this message:
 Message 125 by JustinC, posted 08-06-2003 8:40 PM Mammuthus has replied

  
Peter
Member (Idle past 1479 days)
Posts: 2161
From: Cambridgeshire, UK.
Joined: 02-05-2002


Message 110 of 130 (48744)
08-05-2003 5:59 AM
Reply to: Message 107 by Wounded King
08-04-2003 12:14 PM


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: 02-05-2002


Message 111 of 130 (48745)
08-05-2003 6:04 AM
Reply to: Message 106 by Mammuthus
08-04-2003 12:10 PM


But at which point during the life-time of that
generation?
That was partly my point of proposing a hypothetical
immortal 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 frequencies
would still be changing.
For me that means that fitness/reproductive success must have
survival as one of its variables (or paramaters maybe).
WoundedKing says we all knew that all along -- which makes me
wonder why this thread has gone on this long -- mind you
all the creationists DO seem to disappear in the summer

This message is a reply to:
 Message 106 by Mammuthus, posted 08-04-2003 12:10 PM Mammuthus has replied

Replies to this message:
 Message 113 by Mammuthus, posted 08-05-2003 6:23 AM Peter has replied
 Message 114 by Wounded King, posted 08-05-2003 7:03 AM Peter has replied

  
Peter
Member (Idle past 1479 days)
Posts: 2161
From: Cambridgeshire, UK.
Joined: 02-05-2002


Message 112 of 130 (48746)
08-05-2003 6:10 AM
Reply to: Message 108 by JustinC
08-04-2003 9:45 PM


quote:
No problem on the lateness. I broke some handbones and wrist in car accidenct recently, so my responses may be pithy.
Ouch!! I sympathise, I broke my left wrist and a bone in my right
hand a couple years ago when I came off my motorbike!!!
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?
It's not that survivors survive so much as those who are fitter
have 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 their
environment 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: 08-09-2002


Message 113 of 130 (48748)
08-05-2003 6:23 AM
Reply to: Message 111 by Peter
08-05-2003 6:04 AM


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

This message is a reply to:
 Message 111 by Peter, posted 08-05-2003 6:04 AM Peter has replied

Replies to this message:
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Wounded King
Member
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 114 of 130 (48752)
08-05-2003 7:03 AM
Reply to: Message 111 by Peter
08-05-2003 6:04 AM


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]

This message is a reply to:
 Message 111 by Peter, posted 08-05-2003 6:04 AM Peter has replied

Replies to this message:
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Peter
Member (Idle past 1479 days)
Posts: 2161
From: Cambridgeshire, UK.
Joined: 02-05-2002


Message 115 of 130 (48798)
08-05-2003 12:00 PM
Reply to: Message 114 by Wounded King
08-05-2003 7:03 AM


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 it
is in years 10-15?

This message is a reply to:
 Message 114 by Wounded King, posted 08-05-2003 7:03 AM Wounded King has replied

Replies to this message:
 Message 117 by Wounded King, posted 08-05-2003 12:21 PM Peter has replied
 Message 118 by Mammuthus, posted 08-06-2003 4:04 AM Peter has replied

  
Peter
Member (Idle past 1479 days)
Posts: 2161
From: Cambridgeshire, UK.
Joined: 02-05-2002


Message 116 of 130 (48801)
08-05-2003 12:09 PM
Reply to: Message 113 by Mammuthus
08-05-2003 6:23 AM


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 than
reproductive 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: 04-09-2003


Message 117 of 130 (48804)
08-05-2003 12:21 PM
Reply to: Message 115 by Peter
08-05-2003 12:00 PM


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]

This message is a reply to:
 Message 115 by Peter, posted 08-05-2003 12:00 PM Peter has replied

Replies to this message:
 Message 120 by Peter, posted 08-06-2003 7:09 AM Wounded King has replied

  
Mammuthus
Member (Idle past 6475 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002


Message 118 of 130 (48869)
08-06-2003 4:04 AM
Reply to: Message 115 by Peter
08-05-2003 12:00 PM


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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 Message 115 by Peter, posted 08-05-2003 12:00 PM Peter has replied

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Peter
Member (Idle past 1479 days)
Posts: 2161
From: Cambridgeshire, UK.
Joined: 02-05-2002


Message 119 of 130 (48881)
08-06-2003 7:05 AM
Reply to: Message 118 by Mammuthus
08-06-2003 4:04 AM


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' is
a necessary part of any definition of 'fitness' though.

This message is a reply to:
 Message 118 by Mammuthus, posted 08-06-2003 4:04 AM Mammuthus has not replied

  
Peter
Member (Idle past 1479 days)
Posts: 2161
From: Cambridgeshire, UK.
Joined: 02-05-2002


Message 120 of 130 (48882)
08-06-2003 7:09 AM
Reply to: Message 117 by Wounded King
08-05-2003 12:21 PM


So you would only look at the individuals who are
breeding for the first time?

This message is a reply to:
 Message 117 by Wounded King, posted 08-05-2003 12:21 PM Wounded King has replied

Replies to this message:
 Message 121 by Wounded King, posted 08-06-2003 7:31 AM Peter has replied

  
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