Tautology and Natural Selection

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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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Ok..I finally see where the problem is and why we are talking past each other. Measurement of fitness comes at a specific time point...you can measure trait frequency at time X and that will tell you what trait etc. is the most predominant at time X. 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...you could measure relative fitness over a few generations (well in fruit flies or shorter lived organisms) as well to add a temporal component...but you cannot measure events that have not happened yet...maybe humans go extinct...then we ultimately have fitness = 0. Evolution is not static....however, taking a measurement is a mere snapshot in an ongoing process of unknown trajectory.

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.

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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.

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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.

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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?

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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.

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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.

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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

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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.

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If all live the same amount of time the one which reproduces
the most dominates traits set.

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If they do not -- a survival factor -- this changes.

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Survival must be a part of what fitness means.

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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

Yes..if you look at generation years you see that the reproductive output of A is much higher than B and thus the relative fitness is higher for A regardless of how long A or B survived...that is why fitness is not a measure of survivability of an individual...you are measuring the frequency of a trait in a given generation...that trait got to the generation via the reproductive effort of the preceding generation...the frequency in the current generation is a measure of the success of the previous generation in passing their traits to this one...the same thing when the current generation tries to reproduce.

Hi Justin..sounds like a nasty injury...I busted up my hand about a year and a half ago and it was really miserable working on the computer.

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How is it not tautologous if you factor in genetic drift in fitness. It seems like the theory is 'survivors survive'. How would you describe the theory?
And as for the deletion, 'Less is More' as Mies van der Roe would say.

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Natural selection is only a part of the theory of evolution..and the theory of evolution is not that survivors survive. However, it is not that survivors survive that is of interest to fitness primarly. It is that traits conferring benefits be it food gathering, more accurate transcription, etc. tend to increase in the population and some case become fixed in the population. This is much different than saying survivors survive. Lot's of organisms of different potential fitness are born in each generation..in each generation some will reproduce more than others and will have a higher representation in the next generation i.e. higher fitness. As this is genetically/epigenetically based, alleles will change in frequency over time (evolution) due to some alleles conferrring an advantage on their host. But you can't leave out drift either..some traits/alleles become fixed in populations without conferring a benefit i.e. they are not selected for...they become fixed due to genetic drift.

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What is this selection pressure? Aren't we just looking for the better designed system for reproduction in a certain environment{being all its surroundings)?

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Why "designed"? As I have pointed out in other examples, there can be situations that are ultimately destructive to the host or its reproductive capacity but propagate anyway because of some other advantage....what is the "design" difference in a family that has 14 children versus a family that has 1 child. The family with 14 kids has a much higher fitness...what is "designed" for reproduction in that family that is not present in the family with 1?Here is an example of conflicting selection pressures as well taken from this weeks Science and Biomednet.comNew type of evolutionary conflict demonstrated
31 July 2003 2:00 EST
by Helen Dell[Caption]
Geneticists have uncovered a new type of evolutionary conflict that acts in human testes. There seems to be a clash between what's good for the organism and what's good for the sperm-producing cells, they say.
The researchers study Apert syndrome, a developmental disorder characterized by distortions of the face and head and webbed hands and feet. The condition is usually caused by a newly generated mutation, inherited from an unaffected father. What interested the researchers was how often the syndrome-causing mutations seemed to be cropping up - between 200- and 800-times more frequently than background mutations."Basically, if everywhere [in the genome] was mutating at that sort of level, then none of us would be alive because the genetic burden would be too high," said Andrew Wilkie, Nuffield Professor of Pathology at the University of Oxford, who led the research.Apert syndrome is linked to paternal age, so the older the father is, the more likely he is to have an affected child. The usual explanation for such age effects is that the older a man is, the more cell divisions his sperm-producing stem cells (spermatogonial stem cells) will have gone through. "Not only are you accumulating mutations [with age], but your ability to repair them will get worse," explained Wilkie.So he and his colleagues looked at the most-common Apert mutation in sperm samples from men of different ages. Their results, published today in Science, show that the mutation did indeed appear more often with age, mirroring the incidence of the syndrome.But, when they looked closer at the DNA context that the mutation was found in, it seemed as though the mutation was occurring only rarely. Essentially, the observed rise in mutations is not because of more mutation events, but rather because there are an increasing number of copies arising from one (or a few) events, they suggest."We propose that the mutation events are infrequent, but when they occur they give a selective advantage to the cells in which they've occurred," said Wilkie. "This is really a radically different explanation for the paternal age effect."When spermatogonial stem cells divide, they usually produce one cell that will go on to be sperm and one cell that remains as a stem cell for the next generation. Wilkie speculates that the Apert mutation might bias this somehow so that occasionally two stem cells would be produced (with no cells becoming sperm). So over time, the numbers of mutated stem cells would gradually increase, while the number of unmutated stem cells would remain the same. That is, the mutated stem cells have a selective advantage over their unmutated neighbours.The idea of strong selection on mutant spermatogonia is very unorthodox, says James Crow, emeritus professor of genetics and medical genetics at the University of Wisconsin, but he is reluctantly impressed. "When I first read the paper, I tried to think of alternative explanations, and I came up blank. This evidence is pretty good...very good. Unless there's a glitch somewhere, I think he's proved his case."Wilkie is intrigued by the evolutionary implications of the findings - that a mutation could be devastating to the organism as a whole while being advantageous to germ cells (any cells that produce sperm or eggs), so that two selective pressures act in opposite directions."You could imagine a situation where there are much subtler selective effects at the level of the germ cell where the balance is the other way round where the organism is maintained in a sub-optimal state," he said. "[In such a case] the selective disadvantage to the organism from the mutation is less high than the selective advantage that it confers in the germ cell, so that the organism would be better off if it had a slightly different genotype, but it can never get there because the selection in the germ cell is always pushing it in the other direction."

and wounded king was right...however, you have been making it sound like survival is the key aspect to fitness above all others which is wrong....you are right about the creationists...other than buzsaw and Symansu they seem to have all gone on creationist vacation

A good question really. You do not expect the allele frequency to stay the same always...if it did there would be no evolution i.e. change in allele frequency over time in a population. That is why I keep saying you take a snapshot of a specific moment in time..not with the expectation that it will always remain the same. Most pop gen studies do not have the luxury of timing the breeding cycles of the organism being analyzed. One simply collects as many samples as one can, genotypes them and measures how diverse the samples are and what loci seem to be under selective constraints i.e. are specific loci/alleles at a higher frequency than expected under Hardy Weinberg equilibrium for example.To do more refined measures of fitness i.e. individual contributions or individual loci would likely require a lab setup with Drosophila...for species with longer generation times it would be much harder to do controlled experiments i.e. you die long before the experiment is concluded...and somebody much later finds out you set it up wrong and it needs to be repeated

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Yeah, it's pretty pathetic. I'm forced to type with my nose :-)....or my left hand.

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As a right hander..I rather type with my nose than left hand

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It doesn't seem like reproductive success should be the definition of fitness. Say an asteroid hits the earth and incinerates the surrounding animals, is it fair to say they were less fit? Shouldn't it be that on average if an animal is more adapted for reproductive success in a certain environment it will have reproductive success? I understand genetic drift has a major role in evolution, but for this I'm talking about a specific selection process...industrial melanism possibly.

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The incinerated animals were less fit..they contributed nothing to the next generation. However, in that case, you know exactly what the source of the reproductive differential was unlike the more subtle effects of competition.

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Was the differential reproductive success caused by inheritable traits? If not then I wouldn't say they are more fit, just they had more offspring in a generation than another.

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If they leave behind more offspring they are more fit i.e. they produced more offspring. If it is not heritable the trait will not be passed on and the next generation will not have this advantage and thus will not evolve....as a dumb example, I can't pass on a penile implant but it could potentially allow me to produce more offspring and thus increase my relative fitness.

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I just can't tear myself away from design. Why not design? Design doesn't imply 100% efficiency.

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...but design does imply purpose and pre-adapatation.

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In NS, it just has to be better at reproductive success than another design in an inheritable way. It can still have sub-optimal qualities about it as in your Apert syndrome example. It also depends on what level you are looking on. From the sperm cell's perspective, it is becoming better at reproductive success than other sperm cells, though this may be horribly disadvantagous to the organism as a whole.

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I think the problem here is that within a species or population even there will be no way to say what the design is. Some individuals may benefit from something while others from something else thus they are not coalescing on any one "design". Arctic char for example have morphotypes that are enormous and some that are small that live in the same population and occupy a slightly different niche...however, they interbreed as their genetics show no differentiation between types...what is the "design" of char? I prefer the concept of local optima or adaptive peaks. You have many possible solutions to a particular challenge and whichever works slightly better than the others becomes fixed or frequent. Mutations constantly occur that can move the group up or down the peak or even to a new and better one (or a worse one). The process is thus random i.e. mutation driven with each generation re-starting the competition to increase its representation in the next generation...this also allows for genetic drift and allows for catastrophic accidents which if not causing extinction can start the population at a completely different area in the fitness landscape.cheers,
M

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Sorry for the lateness, I just got back from an Alaskan vacation.

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Lucky lucky ...see any interesting animals?

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What is the point of having that definition of fitness if it is merely defined by post hoc analysis? Aren't you just saying that some animals survive and some don't? How does that factor into natural selection? Aren't we looking for why on average some animals survive due to traits they possess? (Sorry for all the questions)

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The observation is not that some animals survive and some do not...some variants be it morphological or genetic occur at higher frequency than others. The why is a different issue. You can make the observation without knowing what the underlying reason for the differential is...and it is one of the main subjects of evolutionary study to find out why. Such an observation is post hoc because you are observing an event that has occurred i.e. you see which traits in the current generation. However, you can track variants through generations in both lab and natural studies (though in the field it is a real pain in the butt depending on the animal you study). This can go a long way to helping find out what the source of the differential success might be.

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So if they leave behind more offspring they leave behind more offspring? In natural selection doesn't the trait have to be heritable(genetically or culturally) in order for an animal to be considered fit because of it?

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What you say in your second sentence is true to an extent...however, by definition since you asked if on your way to work you are hit by a car and never have kids your fitness is zero...a population that is incinerated by a meteor has a fitness of zero. That is the measure of that population at that specific time. Non heritable circumstances can contribute to your fitness though you cannot pass the advantage on to your offspring. For example, one of the chimp males Jane Goodall studied (forgot which one he was) was a smaller weaker and older male who would normally never have reached the dominant position in the group that he did..but dumb luck had it that he got hold of oil drums (I believe...read this ages ago) which made a hell of a lot of noise and scared the other males...he thus became the dominant male with greater access to the females and probably sired more young as a result..thus his fitness was increased though he cannot pass the advantage on to his young.

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Maybe purpose or function, I don't know about pre-adaptation. Can you expound a bit?

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It means that mutations do not anticipate what the environment will do and then Lamarkian like the organism magically fits...the environment applies pressure to the natural variation in a given population and as a consequence some variants will be more successful than others...how is this design where you go into a sitation, determine what the solution should be, and then design something to fit intentionally?

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I'm not sure you can generalize about the design of char, I do think you can theoretically look at the individual and determine its chances of reproductive success in a certain environment.
Why would a certain trait be better? What standard do you use for 'better'....better designed for reproductive success perhaps ;-)[edit: non homosexual wink, not that there's anything wrong with that]

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If you want some surreal debates on homosexuaity check out the Faith and Belief forum and the Free for All My standard for better is that the trait when put in competition with other variants is able to achieve a higher representation in the population...the individual does not matter to me in such a case. If I can determine that a trait provides a competitive advantage to the organism on average...I can make predictions about the potential fitness of organisms bearing that trait...in the lab, I could then refine the analysis by altering the environment to see more precisely why the trait is advantageous.

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Species may be able to move to a worse area on an adaptive landscape, but not in a selection event...right?

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It is possible but it is difficult to move from one adaptive peak to another incrementally since selection will work against individuals that are going down the peak eliminating them before they can go up another higher peak....you usually need the population to fragment and rare alleles to get fixed by drift such that the population can proceed along another trajectory.welcome back.cheers,
M