Tautology and Natural Selection

I don't actually think that 'survival of the fittest' as
a phrase is tautological unless you assume that the fittest
are the one's that survive -- rather than just treat the phrase
as a summary of an observation.Does that make any sense at all or do I need to lay off the
coffee???

Fitness isn't defined in terms of reproductive success
(at least not in the weltenshaung that presents the
phrase 'survival of the fittest').Fitness is about the ability to survive -- if you are better
able to survive yu are more fit.So 'survival of the fittest' comes down to 'those that survive best
reproduce most'.I don't see any tautology there, only an abservation.Re;Purpose.One cannot use the word 'purpose' unless there is an intelligent
intent behind a function/feature. That's what purpose means.Biological systems (of any order) do NOT have purpose (unless
you are a creationist/believer), they have functions and features
which contribute to their survival.Survival facilitates reproductive success.

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When referring to individual organisms, I don't think it is enough to speak of survival, you also have to refer to fecundity. Taking them together you have reproductive success. I mean one organism can survive for 2 days and have many offspring, and another can live for 2 weeks and have much fewer.

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I've always thought of natural selection as a kind of
'survival filter', but if one individual within a population
was able to bear more young more often because of a heritable trait
I suppose that trait set would flourish even if survival rates
were low.

Wow -- de ja vu -- or however you spell it!!!!I have been having this exact discussion with mark24 in the free
for all.If you define fitness as reproductive success you are OK
so long as reproductive success encompasses reproductive output
and survivability.You cannot say that fitness causes reproductive success or
vice versa if on defines the other -- you would be saying
it's blue because it's colour is blue.If you define fitness in some survival oriented way
then fitness promotes reproductive success and is an after
the fact means of assessing fitness.reproductive success doesn't MAKE something fit, it's the
way that we can see the level of that fitness.

That bit was toward the end of my post -- after I said
'If you describe fitness in some survival oriented way'If you don't ... then I agree with you.

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fitness is not a cause.

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I was commenting on how one defines 'fitness'. Fitness is
not a cause if it is defined as BEING reproductive success
(as mark24 has explained it).IFF fitness is defined in survival terms only, then it can
be a cause of reproductive success (if one is more fit the
one leaves more offspring -- which is how I have always
interpreted natural selection btw).It is never (in either case) approriate to say that reproductive
success causes fitness ... if they are the same thing one cannot
cause the other, and I do not know of another definition of
fitness that would allow it to be caused by reproductive success.Blame Darwin, he's the one who came up with these dangerous
notions ... it's not us laymen's fault that biologists have
redefined everything since then

If you are talking about fitness in any sense or
definition -- mass extinction events aren't relevant.In another topic I referred to the inapproriateness of
looking at endangered species from an evolutionary/natural selection
PoV unless some were bullet-proof ....That said one has to wonder if there are features of
extant critters that would allow them to survive in preference
to other species in different global catastrophies --
like ants and cockroaches surviving nuclear blasts or some such.Were the asteroid impact survivors survivors due to pure chance
or because they were fitter with respect to the radically
modified environment?[Added by edit:: I ... I think I might have changed my mind
halfway through that post -- wow a transitional!!! [This message has been edited by Peter, 07-28-2003]

(2) is what Syamsu seems to have the most trouble with....
apart from general comprehension that is

I think what JustinCy is saying is that natural selection
is operating in a similar way to engineering processes, not
that the evolution of a wing can be viewed to be an engineered
process.S/He says that with an engineering problem you have a function
to be optimised, and feels that natural selection is optimising
reproductive success.I don't agree with JustinCy, but I think your disagreement is with
a different view on what JustinCy is saying.Course I could be the one with the wrong end of the stick....and I'm the one who doesn't see why 'survival of the fittest'
is a problem

I don't disagree with you, but I think what JustinCy is saying
is that natural selection is acting to optimise
reproductive success -- not optimise individual traits.You seem to disagreeing with an engineering analogy, but I think
the analogy is targetted slightly differently to the way
you are looking at it.I still think it's wrong to say that NS optimises anything,
especially reproductive success -- but then I don't think that
reproductive success is a good definition of fitness either,
unless you define repro.succ. to be about survival of offpsring.

What if you take a snapshot of a population where
(for arguments sake) all the offpsring were born in
the same season, and no more offspring will be born until
these ones mature.What determines the extant traits at the beginning of the
reproductive season for the offpsring?Is it how many with trait X were born (reference to numbers
of parents in previous gen.)Or number of trait X offspring that have survived to
the breeding season?It might not be that trait Y individuals have more offspring
so much as more of them survive to maturity.The same holds iteratively for season-on-season survival rates.You may have 100 X's born and 50 Y's but all 50 Y's survive
to breed and only 10 X's.Each X has ten offpsring per season of which one survives
and each Y has one only which survives.

My view is that fitness isn't reproductive success -- someone else
said it was and I disagreed.I veiw it that survival is more important than reprodution,
but that both clearly play a part.All I am saying is that there can be no meanignful concept of
fitness without it being a function of survival (it may also
be a function of reproductive output -- at the same time --
a function of both).

But if some salmon have an adaptation that makes it
more likely for them to make it back to their
breeding pool, then traits from THOSE salmon will
become the norm.The individual selection (survival oriented) has an impact
on the subsequent generations of salmon.

They are well fit , but thet don't contribute to
subsequent generations.Fitness (survival oriented) has an impact in the
allelic frequencies, so does reproductive output.So long as both are represented in a definition of
'reproductive success' I would be happy -- neglecting EITHER
misses the point.My objection is to defining fitness soley as reproductive
success, when reproductive success is understood to be, basically, reproductive output.If that is not the case, and survival is a part of the equation
I don't have a problem.Natural selection is more straightforward to understand if
one views it as cycles of reproduction followed by survival
(it's also a reasonable description of most critters life
cycles).Any living, non-sterile organism can reproduce. The impact
of survival rates for varying trait sets will (in general)
be greater than the impact of rerpoductive output unless
some members of the population have orders of magnitude
more offspring -- even then survival rates could vary enough
to ensure that those that leave the most offspring don't become
the norm (because those offspring don't all survive to
breed).

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You can measure trait frequency at time X and that will tell you what trait etc. is the most predominant at time X.

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Now THAT I can agree with

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This tells you nothing about time Y. If I have ten kids and you have none at time X, I have a higher relative fitness than you...if at time Y all of my kids die and you have one kid then you have a higher relative fitness

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This is the bit I'm still having problems with.If an individual lives for a long time {in relation to
others of the same type) due to heritable characteristics I would consider it 'fit' in a survival sense
whether it bred or not.But I do see that it also needs to be 'fit' in a reproductive
sense.'Reproductive output' isn't 'reproductive success' I suppose,
in which case we may well be in agreement after all.Fitness = Number_of_Offspring * Probability_of_Survival_to_BreedI think 'nature' agrees with me, as those creatures whose young
are most likely to die without issue have the most young.[Added by edit:: I'm not sure but I think I might be mixing
'levels' in my view of fitness][This message has been edited by Peter, 07-31-2003]