Fitness: Hueristic or Fundamental to Biology?

Well, I'm not going to make Quetzal's arguments for him, but if the phenomena that are important to him are best studied with the concept of fitness, then of course any theory that precludes fitness isn't going to be particularly useful to him. If the gene-centered view doesn't allow the concept of fitness, then, yeah, I guess I see Questzal's problem with the gene-centric point of view.If fitness really is important to population biology or population genetics, and if the gene-centered point of view eliminates fitness without any compensatory features, then I would imagine that in these fields the preclusion of "fitness" would be a serious drawback to the concept of gene-centered selection.-

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So maybe, to clarify the issue, i'm asking is fitness fundamental to the concept of natural selection.

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Well, from where I'm sitting (not an expert in population genetics and only knowing as much as Wikipedia has told me), it appears that fitness is a measurement of what natural selecton is doing. I may be biased by my training in the physical sciences, but the ability to measure its effects is what makes a concept useful. Natural selection really only becomes a useful concept if we can see it occurring; "fitness" appears to be one way of measuring whether it is occurring (and, in so doing, gives us an operational definition of what we really mean by natural selection).But maybe I should bow out and let the biologists explain this. Heh. I'm trying to explain a concept of which I'm pretty ignorant about -- sort of like a creationist.

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Actually, if their god makes better pancakes, I'm totally switching sides. -- Charley the Australopithecine

I am having a hard time understanding the question. “Fit” means coming up on the positive side of Natural Selection, doesn’t it? If a specific phenotype or gene (and whether we count one or multiple generations of them in the definition) does not survive its environment to reproduce, does not survive the selective pressures, isn’t this denoted as “unfit?”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?And, IMHO it matters not from what view we look. In an organism-based view “fit” denotes surviving to reproduce (one generation, two generations, 2000 generations, take your pick). In the gene-based view “fit” denotes being passed into other generations (1, 2, 2000, whatever).Are we starting down the road of Semantical Quibbles? Isn’t the real question not “is fitness a concept within NS,” but, “how do we define success (fitness)in NS?”Now we can quibble the number of offspring vs number of generations vs percentage of available alleles vs number of copies of genes...you know...the good stuff.

Let's try to break the recursive cycle ... with a slight change to the "formula"fitness of a genotype = (average fecundity) X (fraction that reproduce).How many offspring the offspring have (their average fecundity) are a measure of the fitness of the offspring and not of the original parent. Thus the fitness of different genes could change with every generation. This is not a problem, rather it is the way it should be.Hope that helps.Edited by RAZD, : added rather

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Naturally, organismal fitness is a useful tool, but it is not an accurate one. It relies on the principle that what is good for the individual (and some number of offspring) is good for the gene, which is usually correct. Certainly for genotypical or organismal fitness, yes. Gene fitness is tied much more closely to how frequencies of alleles shift, and is much more useful to us. It is practically difficult to assess the fitness of a gene simply because of their size - but if it weren't difficult it would provide us with a better picture of what is going on. Since most alleles have more than one copy, the 'average fecundity' of a gene can be much more accurately calculated. I think that gene fitness is an inextricable part in understanding natural seection, and the resulting allele frequency shift known as evolution.How? Those that are fit, will tend to increase in frequency. A fit allele generally gets naturally selected to increase in frequency.

The ability of some of the offspring to themselves reproduce is sufficient if it can result in the total number of offspring in the population being more than the previous generation.Think of ants and termites and bees, where a large proportion of the population is sterile, yet they are successful because the colony as a whole works to make it possible to reproduce the colony from generation to generation -- of the workers and of the queens. The workers contribute in ways that the queens could not and would be vulnerable without, thus increasing her fitness and the fitness of the colony as a whole.

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Another issue with this measure of fitness can be discovered in a very simple population. Imagine a population where all individuals have the same number of offspring, there are no mutation events or any of the other evolutionary mechanisms. Yet still the allele frequencies could still shift.Imagine there are only three genotypes, but there are many copies of them. A, B and C. Since all genotypes have the same number of offspring, population size is unlimited.Genotype A takes one year to grow its phenotype into a reproductive agent. Genotype B takes 10 years and genotype C takes 10 days. Shortly after reproduction comes death.We can easily see from this extreme example that genotype C is going to increase in frequency compared with A and B. The frequency of that genotype (and thus its genes) is going to go sky high. This might be one of the nuances that Quetzal referred to since the simple calculation would render them all equally fit.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.

We run into a slight hitch when calculating the fitness of a sterile insect genotype though. Since it has no offspring - it has a fitness of zero. In the other thread I attempted to include this in there with a fitness definition of 'a genotype that works towards increasing the frequency of its alleles is a fit genotype'. This fitness metric can be applied to the whole hierarchy from gene all the way up to kingdom, and beyond depending on your chosen hierarchy.

But isn't the genotype the same, just whether or not the egg is fertilized or fed a specific nutrient? (thus it is more of a phenotype than genotype difference)I think you have to look at reproductive units rather than individuals in these cases - the female doesn't function without the drones once she's built her reproductive nest, so they are extensions of her reproductive unit. And the fitness of the queen would be low given that most offspring are the sterile drones and only some potential kings and queens, probably less than 0.1 by the above metric, yet they are able to expand and fill new areas easily. If you count the hive ability to produce new hives you get a different picture. Yes, but. To me it has to be a snapshop metric: how is fitness measured today, and then measure it again tomorrow: things change in the environment and fitness changes with it. So if we graph the frequency of alleles then at any time we can take the slope of the curves for each one and judge their relative fitness by their rate of change at that moment. You can also graph the rate of change of the rate of change (second derivative) to see whether fitness is increasing or decreasing.That works for me, and would seem to answer the problem of the hive species as well: it doesn't matter which specific individuals the fitness comes from in the overall population for the selection to work.This can also be applied to observable features within a population, the physical manifestations that breeders use in their selection, that species use for sexual selection, the changes in beak size that match fitness in the Galapagos Finches, and the changes in proportions of light\dark color variations in the Peppered Moths.Thanks.

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Indeed - so how do we calculate the fitness of the genotype? We can't! And therein lies the rub. We have to define fitness from a reproductive unit point of view, which assumingly is a genome that is capable of directly reproducing. A reproductive genome doesn't make exact copies of itself though, only the root reproductive unit - the gene - does that.As I said, thinking of things at this level is usually good enough -don't think me an extremist. Its just that nature is a funny thing, and there end up being exceptions to rules all over the place if you aren't careful. Odd - that unfit entities can spread so well Agreed - it all depends on how much resolution you require. Sometimes, to find out what is happening we need to zoom all the way into the alllele, but oftentimes we can look at how traits change to deduce indirectly how the alleles change.

Or the metric doesn't really measure fitness. You can pick your resolution for the period you find the slope of the curve over. The nice thing about this is that it automatically averages all the individuals and all the {alleles\variations\features}. If you are worried about sudden change causing extinction you can zoom in on that effect.

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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.

It depends on what you mean by 'fitness'. If 'fitness' is the abilty to survive and successfully pass on your genes, then yes.

I'm not sure whether it matters what I mean by "fitness"; I already posted the actual definition of "fitness".

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Actually, if their god makes better pancakes, I'm totally switching sides. -- Charley the Australopithecine

You just replaced "fitness" with the definition of "fitness"
Message 11
redundant not a tautology.Enjoy.Edited by RAZD, : = not -

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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.