Fitness: Hueristic or Fundamental to Biology?

The purpose of this thread is to state some of my objections to fitness and hopefully clear up some of my misconceptions about the concept.I'd like to start with Quetzl's response to me in another thread, and go from there. Let me isolate his definition and Though it is simplistic it's a good starting point to state my objection.For the opening post, i'll just state that this definition seems to be recursive in nature. In other words fitness is the ability to produce individuals that have the propensity to to produce individuals that have the propensity, etc.(Fitness of a genotype)= (Average Fecundity)X(Fitness of offspring's genotypes)The ability of the offspring to themselves produce offspring would have to be in the definition, or else we come to the absurd conclusion that producing a large number of sterile offspring is the "fit" thing to do.

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Sure. And your objection is?

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By that definition, the fitness of the offsprings genotype would be determined by their offsprings genotype which would be determined by their offsprings genotype, ad infinitim.The equation would be incalculable even in principle.

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recursive equations sometimes can have solutions.

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Yes, but in this case the solution to the function fitness F(x) is depending on the function F(x+1), which is dependent on F(x+2), etc. [added by edit]does anyone know is these type of equations have solutions. My "common sense" mathematical intuition says no, but mathematical concepts are very counterintuitive. I still have troube with a zero volume polyhedron.If F(x+1) was dependent on F(x) then you would simply need to ground it and we'd be on our way.

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But simpler then that is to introduce an arbitrary cutoff at some point.

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I don't disagree with this, but if there was an arbitrary cutoff then I'd call it a good hueristic device; I don't think it could be labled as a fundamental truth of evolutionary theory as it would be be based on the arbitariness of the subject using it. Edited by JustinC, : No reason given.

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In the above scenario of course - we know that bad luck tainted our calculation, but if we have to go on are the numbers, we'd conclude that the genotype was unfit for its environment (assuming mistakenly that the environment was average). By luck, we realize that father snuggle has an identical twin brother - with exactly the same genotype. Uncle snuggles has an absolute fitness of 8, and lives in an average environnment. Even with this amazing stroke of luck, we would deduce this genotype's fitness wildly incorrectly.

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This is kindof my point. 'Fitness' is a tool we use to calculate populational changes, i.e, it isn't intrinsic to organisms or to evolution. Two different genotypes can have wildy different fitnesses and that's ok, as long as we know what the numbers mean and what their use is.To act like organisms have an intrinsic property called fitness and this is the reason they have reproductive success seems just plain wrong.Fitness is just our ability to extrapolate from past results to future results. That is, if the environment is relatively stable we can say that, on average, the genotypes which had increased fecundity in the past will have them in the future. Also, since there is a strong hereditary tendency the offspring will likely have the same genotype, and in the same environment, will have increased fecundity.

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From here could deduce, approximately, how allele frequencies will change in the gene pool of the next generation.

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So would you agree that fitness is just a tool we use to make predictions about the relative frequencies of traits or genes in future generations, and isn't a profound insight of evolutionary theory.What I mean by 'isn't a profound insight' is that it has no explanatory power. Organisms don't survive and reproduce because they are 'fit.' To understand their survival and reproduction you have to look at the complex interaction of the phenotype and environment. Since this is a monumental task if done from scratch, we can just take a short cut and say that those that did well in the past will, ceteris paribus, do well in the future.[edit]Clarification question: Do you think that fitness is an inextricable part in understanding natural selection and evolution?Edited by JustinC, : No reason given.

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May be you're being too ambitious...

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Yeah, that wording did seem a little extreme. I just meant that 'fitness' isn't necessary for understanding natural selection or evolution, i.e, it has no explanatory power.

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Anyway, it seems odd that an entire field of biology would use a technical term if it weren't important.

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I would agree. To reiterate the spirit of this thread: My objections aren't necessarily well-thought out or held with any strong convictions. I'm just throwing some problems out there I have with the concept hoping to get vindicated or corrected. Edited by JustinC, : No reason given.

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I really looked up the word because I wan't certain whether fitness actually had a technical meaning or whether it was a vaguely defined concept used more as an heuristic aid to making a simple explanation and to avoid a forbiddingly technical discussion.

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Well, I do think the concept is more vague than the wiki article let's on. Dawkin's writes in The Ancestors Tales: So I think there is room for some discussion about the concept and how best to define what we are talking about.A reason this is on my mind is because in another thread Quetzl made it seem like it was a failing of the gene-centric view of natural selection because they couldn't define fitness (i'm not agreeing with that, but I think those were the sentiments he conveyed).But, if its not fundamental to a discription of natural selection then it seems like a moot point wrt the gene- or individualist- centric viewpoint.So maybe, to clarify the issue, i'm asking is fitness fundamental to the concept of natural selection. I'm not disputing its an important practical concept. Edited by JustinC, : No reason given.

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I cannot see “fitness” and Natural Selection being separate things. One is not a “fundamental concept” of the other. As far as fundamental concepts, Natural Selection is a fundamental concept (a separate operative mechanism) of Evolution. The same relationship does not exist between Natural Selection and “fitness.” Being “fit” is not a mechanism working within the paradigm of Natural Selection, it is nothing more than shorthand to denote success. Survival of the successful, anyone?

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See, I think I can describe NS fine without invoking the concept of 'fitness.'Individualistic view: differential reproductive success of the individual due to heritiable traits of the individual

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Gene-centric view: differential replicative success of the gene due to heritiable traits produced or intrinsic to the geneI think these two defintions basically get to the essence of natural selection. Adding fitness seems superfluous. For example, take the second definition, and add fitnessGene-centric view: differential replicative success of the gene due to its differential fitness, with differential fitness meaning its differential tendency to replicate itself. It just seems to damn close to a tautology to be actually useful, whereas the first version (of the second definition) doesn't seem to have this failing.As an analogy, let's consider the differential W/L records of chess players. We can either say:1.) Attaining the highest ratio of W/L due to strategy, tactics, attacking schemes, pawn structure, etc. or we can say2.) Attaining the highest ratio of W/L due to being the better player, with better player being defined as having a tendency towards a higher W/L record. The one's explanatory and informative; the other pretty much vacuous.Now I can understand using previous records of the player to extrapolate into the future his chances of success. That is, we can produce a quantity (the W/L ratio in this case) from which we can extrapolate future success, but (and I think this is my point) this quantity doesn't explain his success or failure.In the same way, fitness doesn't explain why organisms have reproductive success; its just a measurement of their likelihood to have reproductive success.So maybe I'm saying its a complementary description of NS, but not necessary for understanding the concept.[edit]I kindof wrote this without reading your entire quote, i just zoomed in on 'survival of the successful.'I believe what I wrote may be in agreement with your main point. You can decide that though. Edited by JustinC, : Format problemsEdited by JustinC, : No reason given.

Well, those are the definitions I use for natural selection.Natural selection is a process. Fitness, on the other hand, is a property of an organism. So I don't see how they can be the same thing; I understand they are related though.Can you give me a definition of NS using fitness that doesn't fall into redundancy?Would it be: genes/individuals have differential fitnessesEdited by JustinC, : No reason given.

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You can argue until the next ice age over whether or not the currently accepted metric is valid. Those who find it useful (I don't particularly - I don't deal with those kinds of questions) will continue to use it and/or seek for a better one. Those who don't find it useful will continue to argue against it.

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So can I mark you down for the "Fitness: Not Necessary for Understanding Natural Selection" column?

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An allelic fitness measurement could be defined as the rate of change of an allele's frequency. This then ties fitness directly and inextricably to the concept of evolution.

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So is this purely a semantic quibble i'm starting? I understand that the tendency for an allele/trait to increase/decrease in frequency at a certain rate is an essential part of understanding NS, and if that is fitness then I see nothing wrong with using the term for convenience (as stating, "tendency for.." would get a bit tedioius).As I asked RAZD, are there two equivalent ways to describe natural selection.1.)Alleles have different tendencies to increase or decrease in frequency per generation (or whatever time frame one uses) due to heritable traitsand2.) Alleles have different fitnessesThat is fine with me.Though one problem I have with fitness is that it seems inextricably intertwined with "survival of the fittest" in most of the populace's mind, and I don't think that phrase is accurate at all wrt to explaining natural selection. This is a different concern, though, than my OP's.

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"Have you stopped beating your wife yet?"

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Come now, the question wasn't that loaded

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It is not "necessary", but it can be useful for understanding some questions under the rubric of natural selection.

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'Can be useful but not necessary'- agreed

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The current definition of fitness refers to a metric measuring the outcome of NS. The unit of time used is one generation. Any other questions?

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If fitness is just a defined metric then I'd say its just a hueristic device designed to measure something more fundamental, i.e., adaptiveness.