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Author Topic:   Tautology and Natural Selection
Quetzal
Member (Idle past 5872 days)
Posts: 3228
Joined: 01-09-2002


Message 91 of 130 (48273)
08-01-2003 2:21 AM
Reply to: Message 89 by Peter
07-31-2003 1:55 PM


[Added by edit:: I'm not sure but I think I might be mixing
'levels' in my view of fitness]
Ya know, I think you're probably right. Not only are there several biological meanings of "fitness" depending on whether you're talking gene or organism or population (or whatever), but several different uses of the term. You can talk in terms of how well adapted ("mean fitness") a population or species is for its particular niche/habitat. You can talk in terms of the fitness of a particular individual (or trait or suite of traits) compared to others in the same population or in relation to the mean fitness of its species or even in relation to other competitive species. Etc. So the problem is quite likely one of both level and useage. Which is why, when we get back to the original discussion of "survival of the fittest" as a tautology, it's extremely easy to conflate or confuse several uses/meanings/levels because of a fixation on the word "fitness".
It's such a bloody useful term tho', when used properly and in context, that I can't think of another way of saying it. It's like the people who want to replace "species" - because it's so squishy and hard to define - with "evolutionarily stable unit" or some such awkward construction.
Still, it makes for interesting discussions...

This message is a reply to:
 Message 89 by Peter, posted 07-31-2003 1:55 PM Peter has replied

Replies to this message:
 Message 92 by Peter, posted 08-01-2003 4:33 AM Quetzal has replied

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


Message 92 of 130 (48280)
08-01-2003 4:33 AM
Reply to: Message 91 by Quetzal
08-01-2003 2:21 AM


quote:
Which is why, when we get back to the original discussion of "survival of the fittest" as a tautology...
Was ... was that a subtle way of saying we're off topic here
I have been unable to see where 'survival of the fittest' is
a tautology, though. It was a phrase coined to summarise what
Darwin originally said about natural selection so maybe it's
just out-dated wrt modern definitions of fitness et al.
Darwin's idea of fitness seems to me to have been an individual
quality that aided survival, and that enhanced survival probability
was considered to increase the chances of high reproductive output.
Saying 'the ones that are fittest stand the best chance of
surviving' is kind of defining 'fitness' for that context.
Personally I'd be interested to see the definition of reproductive
success -- that seems even more vague to me. Syamsu would
say it means to breed or not to breed

This message is a reply to:
 Message 91 by Quetzal, posted 08-01-2003 2:21 AM Quetzal has replied

Replies to this message:
 Message 93 by Quetzal, posted 08-01-2003 7:56 AM Peter has replied

  
Quetzal
Member (Idle past 5872 days)
Posts: 3228
Joined: 01-09-2002


Message 93 of 130 (48292)
08-01-2003 7:56 AM
Reply to: Message 92 by Peter
08-01-2003 4:33 AM


Saying 'the ones that are fittest stand the best chance of
surviving' is kind of defining 'fitness' for that context.
Yep. And therein lies the rub, as it were. The way you used fitness here is only valid in terms of comparing two (or more, I suppose) organisms in a particular population at a specific moment in time. Survival in that case IS the "win" for the individual. However, it is misleading (at the least) for discussion of relative fitness in an evolutionary context. You can use fitness-as-survival as a measure of where a particular critter sits on its fitness landscape, I suppose, in comparison to its conspecifics. However, no matter how long-lived and happily scampering about it is - watching its friends and relations bite the dust around it - if it never reproduces it is evolutionarily unfit. Literally a dead end. Even if it DOES reproduce, it may not necessarily be "fitter" if its traits get swamped - homogenized - by the traits in the rest of the crowd down through the generations. It's all context.

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 Message 92 by Peter, posted 08-01-2003 4:33 AM Peter has replied

Replies to this message:
 Message 94 by Peter, posted 08-01-2003 8:35 AM Quetzal has replied

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


Message 94 of 130 (48294)
08-01-2003 8:35 AM
Reply to: Message 93 by Quetzal
08-01-2003 7:56 AM


Comes back to theory vs. description though.
Are there organisms that are long-lived wrt peers that
leave less offspring?
--apart from humans that is
Just reproducing a lot doesn't make you evolutionarly fit if
all your offpsring die within a week of birth.
Fitness must be a function of both reproductive output and survival.

This message is a reply to:
 Message 93 by Quetzal, posted 08-01-2003 7:56 AM Quetzal has replied

Replies to this message:
 Message 95 by Wounded King, posted 08-01-2003 8:59 AM Peter has replied
 Message 96 by JustinC, posted 08-01-2003 9:08 PM Peter has replied
 Message 101 by Quetzal, posted 08-04-2003 7:15 AM Peter has seen this message but not replied
 Message 102 by Wounded King, posted 08-04-2003 9:24 AM Peter has seen this message but not replied

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


Message 95 of 130 (48298)
08-01-2003 8:59 AM
Reply to: Message 94 by Peter
08-01-2003 8:35 AM


When you say with respect to peers do you mean 'Are there variations of r and K strategy within species?'?

This message is a reply to:
 Message 94 by Peter, posted 08-01-2003 8:35 AM Peter has replied

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JustinC
Member (Idle past 4844 days)
Posts: 624
From: Pittsburgh, PA, USA
Joined: 07-21-2003


Message 96 of 130 (48356)
08-01-2003 9:08 PM
Reply to: Message 94 by Peter
08-01-2003 8:35 AM


quote:
Fitness must be a function of both reproductive output and survival
This is what I think of when I say reproductive success, i.e producing offspring that have a good chance of producing offspring of their own. So individual survival would be a part of it, and reproductive output would be apart of it. In 'survival of the fittest', I would say if you are speaking of individual organisms you would have to interpret survival as reproductive success since their is no selection for just surviving without reproductive output and no selection for reproductive output without survival.
Do you know see how the tautology issue arises?
And I'm sure some organisms in the wild are born sterile and survive along time, although I never observed it.

This message is a reply to:
 Message 94 by Peter, posted 08-01-2003 8:35 AM Peter has replied

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


Message 97 of 130 (48526)
08-04-2003 4:12 AM
Reply to: Message 95 by Wounded King
08-01-2003 8:59 AM


Yes.
Within a species do you get some idividuals that produce
a lot of offspring and die young and others that produce
one or few and die old?

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


Message 98 of 130 (48527)
08-04-2003 4:22 AM
Reply to: Message 90 by JustinC
07-31-2003 3:30 PM


Hi Justin,
Sorry for the late response..I have been writing a paper for publication...and it is really boring ..so I had to do something to spice it up like frying my modem so I had no internet connection for the last 3 days.
quote:
I understand it can homogonize a population, but would you say the populations are competing with each other to a noticable degree? Wouldn't the gene flow just introduce a new allele into the population which would affect competition in that population? I'm not speaking as if I know the answer, I'm just asking.
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.
quote:
The thing I don't like about relative fitness is that it is completely ad hoc. I mean if there is a mudslide that kills a member of a population, is it less relatively fit? If the cause is a trait or traits, wouldn't you be looking for what is better designed for reproductive success?
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.
quote:
I was thinking more along the lines of the first organism to have some sort of photorecepting cells, or the first single-celled organism to have a photorecepting path of pigments. In which case I would think that they would still be able to reproduce, although I can't be a hundred percent sure.
The problem with such a model is that single cell organisms typically reproduce asexually and can transmit traits horizontally by conjugation. Thus a bacteria that has not photoreceptor system could get the entire pathway with one conjugation even in theory. 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...or those with it would consume all the resources available or find the resources more efficiently leaving nothing behind for those without the trait...or the population with the photoreceptor gets to close to a thermal vent and is completely eliminated and only the non-photoreceptor variatns remain..and evolution has to start all over again

This message is a reply to:
 Message 90 by JustinC, posted 07-31-2003 3:30 PM JustinC has replied

Replies to this message:
 Message 108 by JustinC, posted 08-04-2003 9:45 PM Mammuthus has replied

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


Message 99 of 130 (48528)
08-04-2003 4:23 AM
Reply to: Message 96 by JustinC
08-01-2003 9:08 PM


If 'survival' is reproductive success and 'fitness' si reproductive
success I think I can see a tautology.
One of the suggestions I have made before is that it is tautlologous
only with modern conception, and that when phrased it was simply
stating a definition or summary of Darwin's natural selection
observations.
Darwin focussed his attention on survival to reproduce.
Before anyone starts moaning about harping on about Darwin when
ToE has moved on .... 'Survival of the fittest' was coined in
Darwin's time, and used by Darwin as a sub-title in chapters
on natural selection.
Natural selection is still more about survival of the fittest
though.
Extreme PoV example:
Suppose you have a population with 400 variants, all of whom
have indefinite life-span and none of whom breed.
Environmental factors operate such that some individuals have
a reduced survival capacity relative to others and so find it
harder or impossible to survive.
Result, some of the original 400 variants disappear completely,
and the representation of others diminishes significantly.
Allelic frequency in the population has changed over time.
Isn't that a definition of evolution?
In the above the absence of reproduction means there is no
adaptability, so many changes of environment would eventually
wipe out the whole population.
It does not prevent natural selection changing the allelic
frequency of the population.

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 Message 100 by Wounded King, posted 08-04-2003 5:58 AM Peter has replied

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


Message 100 of 130 (48546)
08-04-2003 5:58 AM
Reply to: Message 99 by Peter
08-04-2003 4:23 AM


You really are turning into Syamsu now Peter, you have just started an argument based on a fictional hypothetical population specifically tailored to suit your point but completely divorced from anything which actually exists in the real world.
How can you show that the fitness in your population is related to the genetic variation rather than anything else, given their incapacity to breed?

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 Message 99 by Peter, posted 08-04-2003 4:23 AM Peter has replied

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Quetzal
Member (Idle past 5872 days)
Posts: 3228
Joined: 01-09-2002


Message 101 of 130 (48558)
08-04-2003 7:15 AM
Reply to: Message 94 by Peter
08-01-2003 8:35 AM


Are there organisms that are long-lived wrt peers that
leave less offspring?
I've been wracking my brain to see if there were any examples of this in nature to no avail. The closest I came was a vague memory of differential reproductive success between two populations of neotropical songbirds (and I can't remember what the genus was to save my life) based on acceptance/rejection of cowbird nest parasitism. One population solved the problem of nest parasitism by the simple expedient of booting the cowbird eggs out of the nests as soon as they were laid. The other population tolerated the cowbirds (or at least didn't get rid of them), consequently suffering at least 50% reduction in nest survivorship (i.e., reproductive success).
It turns out that both populations suffer from infestations of parasitic flies which caused staggering infant mortality if not controlled. In the non-tolerant population, the birds had developed a comensual relationship with aggressive wasps which controlled the flies. The tolerant population accepted the cowbirds because they would have lost even MORE infants to the flies. Apparently with a cowbird in the nest pecking away at the flies (which are evidently a cowbird delicacy), fewer infants were lost to cowbird parasites than were lost to fly parasites - making the best of a bad situation and actually increasing reproductive success for the population as a whole.
I don't know whether this relates to your point about survival or not.
Hmm, just realized that this might be speciation in action: a significant behavioral isolating mechanism, maybe. It would be an interesting experiment to pull a switcheroo on the populations and see what happens. Nature is soooo cool.
[Edited for clarity. I had my flies and cowbirds mixed up.]
[This message has been edited by Quetzal, 08-04-2003]

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


Message 102 of 130 (48570)
08-04-2003 9:24 AM
Reply to: Message 94 by Peter
08-01-2003 8:35 AM


There are some interesting studies on the links between longevity and fecundity in drosophila, of course, and some other animals. There was an interesting review of work on guppies in high and low predator environments by a fellow called Reznick and others. Sadly my computer refuses to cut and paste in Mozilla anymore so I cant give you all the details of the reference, but a pubmed search for 'Reznick' and 'guppy' should bring it up.

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


Message 103 of 130 (48579)
08-04-2003 9:58 AM
Reply to: Message 100 by Wounded King
08-04-2003 5:58 AM


quote:
You really are turning into Syamsu now Peter, you have just started an argument based on a fictional hypothetical population specifically tailored to suit your point but completely divorced from anything which actually exists in the real world.
LOL!! Humour me for a couple of posts and we'll see whether
looking at hypothetical limit cases is worth the bother
quote:
How can you show that the fitness in your population is related to the genetic variation rather than anything else, given their incapacity to breed?
The same way you would with a breeding population -- you look
at trait frequencies as a snapshot of the population at some
point.
One assumes (as is the case for real populations) that the
traits which dominate are those which confer a 'fitness'
advantage.
You can apply exactly the same reasoning and analysis via
natural selection to changes in trait frequency in this limit
case, even though there is no reproduction going on.
Removing survival issues and just looking at reproduction we could
have 400 variants who each produce a different number of offspring
during their maximal lifespans.
If all live the same amount of time the one which reproduces
the most dominates traits set.
If they do not -- a survival factor -- this changes.
Survival must be a part of what fitness means.
That's all I'm saying.

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 Message 100 by Wounded King, posted 08-04-2003 5:58 AM Wounded King has not replied

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


Message 104 of 130 (48583)
08-04-2003 10:09 AM
Reply to: Message 103 by Peter
08-04-2003 9:58 AM


quote:
Removing survival issues and just looking at reproduction we could
have 400 variants who each produce a different number of offspring
during their maximal lifespans.
If all live the same amount of time the one which reproduces
the most dominates traits set.
If they do not -- a survival factor -- this changes.
Survival must be a part of what fitness means.
Why do they have to live the same amount of time? If one variant produces 50 offspring in one year and then dies and another produces 3 offspring but lives 100 years the first one that died after one year has a much higher relative fitness though it was relatively lousy at long term survival....produce more offspring..you win

This message is a reply to:
 Message 103 by Peter, posted 08-04-2003 9:58 AM Peter has replied

Replies to this message:
 Message 105 by Peter, posted 08-04-2003 11:41 AM Mammuthus has replied

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


Message 105 of 130 (48605)
08-04-2003 11:41 AM
Reply to: Message 104 by Mammuthus
08-04-2003 10:09 AM


But then you haven't elliminated survival from the
equation -- which is what what I was trying to do
in the same way that I attempted to elliminate reproduction
from the other case.
Assuming the offspring have a similar life-span the sepcies
persistence matters, doesn't it?
Case A: lifespan = 1 year reproductive output = 50
represents 50 organism-years ( in management terms)
Case B: lifespan 100 years reproductive output 3
represents 300 organism years.
Reproductive output alone cannot be used as a fitness measure.
Even if you just look at generation years, A above has to persist
for 100 generations to match B in persistence terms.

This message is a reply to:
 Message 104 by Mammuthus, posted 08-04-2003 10:09 AM Mammuthus has replied

Replies to this message:
 Message 106 by Mammuthus, posted 08-04-2003 12:10 PM Peter has replied
 Message 107 by Wounded King, posted 08-04-2003 12:14 PM Peter has replied

  
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