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Member (Idle past 4875 days) Posts: 624 From: Pittsburgh, PA, USA Joined: |
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Author | Topic: Tautology and Natural Selection | |||||||||||||||||||||||||||||||
Peter Member (Idle past 1510 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
quote: Was ... was that a subtle way of saying we're off topic here I have been unable to see where 'survival of the fittest' isa 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 individualquality 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 ofsurviving' is kind of defining 'fitness' for that context. Personally I'd be interested to see the definition of reproductivesuccess -- that seems even more vague to me. Syamsu would say it means to breed or not to breed
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Peter Member (Idle past 1510 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
Comes back to theory vs. description though.
Are there organisms that are long-lived wrt peers thatleave less offspring? --apart from humans that is Just reproducing a lot doesn't make you evolutionarly fit ifall your offpsring die within a week of birth. Fitness must be a function of both reproductive output and survival.
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Peter Member (Idle past 1510 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
Yes.
Within a species do you get some idividuals that producea lot of offspring and die young and others that produce one or few and die old?
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Peter Member (Idle past 1510 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
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 tautlologousonly 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 whenToE 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 fittestthough. Extreme PoV example: Suppose you have a population with 400 variants, all of whomhave indefinite life-span and none of whom breed. Environmental factors operate such that some individuals havea 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 noadaptability, so many changes of environment would eventually wipe out the whole population. It does not prevent natural selection changing the allelicfrequency of the population.
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Peter Member (Idle past 1510 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
quote: LOL!! Humour me for a couple of posts and we'll see whetherlooking at hypothetical limit cases is worth the bother quote: The same way you would with a breeding population -- you lookat trait frequencies as a snapshot of the population at some point. One assumes (as is the case for real populations) that thetraits which dominate are those which confer a 'fitness' advantage. You can apply exactly the same reasoning and analysis vianatural 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 couldhave 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 reproducesthe 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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Peter Member (Idle past 1510 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
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 sepciespersistence 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 persistfor 100 generations to match B in persistence terms.
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Peter Member (Idle past 1510 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 1510 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 1510 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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Peter Member (Idle past 1510 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 1510 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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Peter Member (Idle past 1510 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 1510 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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Peter Member (Idle past 1510 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
But you could only do that for females since you won't
necessarily know which males have bred? Or would you look at all individuals that have come tomating age?
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Peter Member (Idle past 1510 days) Posts: 2161 From: Cambridgeshire, UK. Joined: |
The reason I asked was to see whether or not I agree
with your definition of 'fitness'. The way you have suggested measuring it agrees with the wayI view fitness -- which is what I thought. By looking at which 'trait sets' have survived to maturityyou are assessing the reproductive fitness of those 'trait sets' from the previous generation. If you were only looking at which first-timers have bredyou would be looking at reproductive output only. I think the former is a means of assessing fitness, and itcombines reproductive output and survival -- which makes me happy.
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