Tautology and Natural Selection

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You were okay up to here, I think. As Mammuthus pointed out, the engineering analogy falls flat as the only way we can call an organism "fit" is by the post hoc analysis: if it survived, it was fit enough to do so. Merely an observation, and somewhat trivial to boot.

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I still wouldn't say "only by the post hoc analysis." In Mammuthus E.coli example, you didn't need a post hoc analysis. I'd say its analogous to testing wings in a wind tunnel. You can figure out before hand what will be a good wing for lift, but the best way and most pragmatic way is to just place it in the tunnel and see how it performs.

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In addition, the idea of "best engineered" doesn't work when you take into consideration evolutionary anachronisms like Persea (avocado), Gleditsia triacanthos (honey locust), etc. They reproduce in the wild, more or less, but do so veeerry inefficiently, since their reproductive strategies rely on seed dispersal by critters that have been extinct for 10,000 years. They are "fit" in the sense that they have persisted as a lineage even in the absence of a well-engineered reproductive strategy. They are "good enough" (barely), but not necessarily fitter than other plants in their various habitats.

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If a mutation arises which increases reproductive success in those organisms, then the mutants would certainly overtake them as they are today. It manifestly hasn't. Them being "good enough" is consistent. What are they good enough for? Reproductive success. So they are better than all their ancestors for reproductive success. Why does changing the curvature of wing increase it's lift? An explanation is given about pressures and forces. And then a person would ask why again? And you'd be forced to say, "because that increases lift". "Increased lift by the best engineered wing" seems like a good description. It just seems like all things with a function can be described as tautologous.Any thoughts?JustinC[This message has been edited by JustinCy, 07-28-2003]

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I agree in these cases. However, the critical distinction here is that with experiments such as you reference, you know every aspect of the fitness landscape - in fact, you control it - in advance so it's fairly easy to make a reasonable prediction as to potential outcomes. When examining a population in locus, however, the only way you can determined fitness is by a detailed examination of the fitness landscape in which the population resides. An a posteriori analysis. Sometimes you can get enough of the natural history of the organism to state that a given characteristic or suite of characteristics provides "better" fitness. Most of the time, however, you have to extrapolate from questions such as why this organism rather than that one occupies a given niche. IOW, what traits are possessed that makes the organism "fitter".

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I agree with all of that....I think. Do you think I don't? I'm just wondering so I can articulate what I am saying better in the future.

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What the E. coli experiments and others of the same type provide is unequivocal (well, to anyone but a creationist) evidence of the creative power of natural selection acting on statistical variation within a population. As to the wind tunnel, of course you can occasionally take a given design and determine whether it is "better engineered" than another. However, translating that better wing shape into population mean fitness - or even relative fitness - is misleading without, as Mr. Hambre pointed out, taking into consideration the rest of the fitness landscape.

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I'm not using the wing in terms of how it functions on an organism and the fitness it will induce. I'll explain below.

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There are documented cases where certain obvious traits in natural populations have been isolated to the point where we can say "this trait increases the statistical probability of survival and/or reproduction in this organism". I'm thinking primarily of beak size in the Grants' Geospiza studies where .5 mm difference spelled a statistical difference in survival (!!) and the one with the guppies (I'll have to look up the specifics, I don't have my books here at the office) where variation in spot patterns, color, and size spelled the difference in predator-selected survival. There were fairly significant and key (read easily identifiable) selective pressures on both of these populations that would tend to swamp or overwhelm potentially countervailing or reinforcing selective pressures. However, these are relatively rare occurances and it has been extraordinarily difficult to document many other examples.

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Agreed.

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Then again, evolutionary ecology is still a very young science. I have high hopes that much refinement and many more examples will be forthcoming - to the point where we may be able to get an accurate picture of what's going on.

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Just out of curiousity, is anyone here an evolutionary biologist or know anybody in the field? I'm majoring in Biology right now, but I want to specifically go into Evolutionary Biology, and even more specifically Paleoanthropology. I'm going to be a sophomore, so either way classes for my specific major haven't been taken yet.

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Hypothetically speaking, that would be true. However, I mentioned specific organisms which are "holding on" with significantly reduced ranges (in the wild), which are not occupying many potential habitats, and/or which rely on secondary or even tertiary dispersers for bare replacement. There's a whole flipping list of plants - especially in the neotropics - which aren't "better than all their ancestors".

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Maybe I wasn't specific enough. I mean better than their immediate ancestors, again barring genetic drift.

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These guys are evolutionary relicts - fading memories of the distant past (forgive the lyricism). If I might speculate for a moment, I would say that these organisms are living examples of species exchange - caught in the act, as it were. Further, I'd speculate that - absent your hypothetical mutation that allows adaptation - these species would be doomed in the wild if left to their own devices. Or they'll end up like Wollemia nobilis - a microscopic remnant of a once widely spread species hidden away in some remote, inaccessible habitat where they cling to a precarious existence in the absence of competition from other, hardier and more adaptable organisms.

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I'm still not sure how this is objectionable to my statements. They'd have to be better engineered for reproductive success than their immediate ancestors for them to be here at all, even if they are now in a state of decline due to environmental changes or because of variant populations.Out of curiosity, what do you mean by species exchange? Do you mean being replaced by a closely related species that they share a common ancestor with?

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Again, taking the wing out of its context, it really does make it a tautology. Most definitions are. However, just because a particular wing shape gives it better lift than some other similar shape doesn't translate into fitness for the organism possessing that wing shape. Better lift might be counterproductive in a case where flying increases the chances of predation or being blown out to see. I understand what you're trying to say. I'm merely attempting to point out that the "best engineered" concept is misleading without taking into consideration the remainder of the adaptive pressures operating on the organism/population.

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I wasn't referring to the wing in context of an organism, I was actually thinking about jetplanes when I wrote it. I was analogizing the wing situation with the organism situation, i.e. wing=organism, lift=reproductive success, and air=environment. Wings lift and organisms reproduce. So you'd factor in everything that effects lifting or reproduction. In the case of reproduction, wings lift may or may not affect reproduction; that wasn't my point though.[This message has been edited by JustinCy, 07-29-2003]

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Actually this is not completely true. You can stack the odds in favor of a desired outcome, however, perhaps a bacteria that deletes part of your insert has a fitness advantage or knocks everything out except the promoter and the amp resistance gene has an advantage...then you end up with an unexpected and undesireable result. This actually happens in most of these experiments i.e. there is a substantial fraction of surviving bacteria that do not have what you wanted in or selected for. This will happen under almost any circumstances i.e. fairly homogeneous populations can produce novel variants as well that fall somewhere else in the fitness landscape, better, worse, the same...

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I did say with all other factors being equal, so I'm not sure the novel variant scenerio is necessarily a criticism. Also, I've stated before that it should be 'The probable reproductive success of the best engineered for reproductive success', so I'm not saying that reproductive success is definative.

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I would not concede that surival of the fittest is unuseful only that as moose pointed out, due to chance events i.e. boloid collisions etc. less fit organisms can survive and reproduce. Again, it is a probability. The observations is that some alleles, variants, are more predominant than others...that is something you can go out and test. The explanation is that said variants have come to predominate by having more offspring i.e. higher fitness.....

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I wouldn't say its an explanation of why they predominate. Isn't reproductive success and predomination essentially the same thing? That is one variant leaves the most offspring, then it will predominate by definition. I think predomination and reproductive success are basically referring to the same thing.

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where survival of the fittest goes a bit astray is that it is a bit all or nothing...a certain trait can be at a high frequency without driving all other variants to extinction. The tough part is to figure out why certain variants predominate in natural populations.

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Why would all other variants not be driven to extinction, out of curiousity? Is it because that some variants would be due to recessive traits and because of genetic drift? Why would bacteria have different variations living together besides those variants produced by mutations in the previous generation?

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My problem with using the term engineering is that implies intent i.e. purpose. If you just have an increase in representation of variants that produce more offspring regardless of whether it makes them better or worse from an engineering perpective it is the opposite of engineering. Remember, you can have variants arise that say see worse than other variants but are so fecund that they come to dominate..from an engineering perspective this is crazy..but from natures point of view it makes sense.

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An engineering perspective is only relevant to enhancing a process or function. It wouldn't be opposite an engineering perspective to say that if the function is reproductive success then certain features will be conducive for reproductive success while not being conducive towards another function, like optimal vision.I can sympathize with your objections about using 'function' and 'purpose'. I stated before that they shouldn't be used, but I don't know. When can we say something has a function and does not? Do only human artifacts have functions? Do the wings of an airplane have function but not the wings of an eagle?Any thoughts about words like function and purpose?JustinC

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Maybe you could take a moment to explain exactly what you're getting at (another dangle) and why you find the engineering analogy so compelling. THEN we can disagree on something substantive that doesn't rest on mutual misunderstanding

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I think that natural selection is essentially like engineering. In engineering you have a purpose, for consistency lets say to maximize a wings lift. In natural selection, it's reproductive success. In the wing scenerio, lets say every time a better wing was designed it would replace all other wings. And then they'd modify that wing until they got something better and so on. It would be like natural selection, except surviving would be non sequitir. But if the function is reproductive success, then the organisms will by definition have a higher chance of reproductive success. Also, better engineered for other features may or may not be conducive to this broad function, so they could be expected as well.I also like the way that they both have the "tautology" problem when describing the principles in general. 'Reproductive success of the better engineered for reproductive success' and 'Better lift by the wing better engineered for better lift'.I don't know if that is coherent, I pulled an alnighter and have to go to work in the fields in 10 min.Let the disagreeing begin.

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Again I re-iterate, an engineer has an explicit a priori goal or desired outcome. Natural selection and evolution do not..so how are they comparable.

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I think it's perfectly reasonable to talk about reproductive success as the 'goal' of natural selection, more specifically a self optimizing goal. Maybe you can say I'm falling into the "Modeler's Fallacy."

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And natural selection is not optimizing reproductive success...how is it that when a trait becomes more frequent it is "optimized"...what is optimal?

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The trait is only considered optimal because it confers reproductive success upon the organism that has it. Some traits might not confer any fitness (or negligable fitness) and get passed along also.

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Not a single biological system is optimal. Reproductive success can be the difference between producing 10 offpring or 1 in a small population..is this optimized if the related group or species the next mountain range over has a population size of millions? Which one is optimized? How has natural selection optimized reproductive success? Some phenotypes are more abundant because of advantages in transmitting their heritable material from one generation to the next...not because they are the optimized reproducers....

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I think it can only be considered optimal in relation to its direct environment, i.e its optimized in relation to the organism that produced 1 offspring. As for the organisms over the mountain range, you can't make the comparison because they are not competing.To clear things up I'm using 'optimal' to loosely. I'm thinking about optimal in terms of a a progression from 0 optimality to infinite optimality.JustinC

Would it be wrong to say the purpose of an eagles wing is to aid in flying and then to say an eagle has no purpose? Or purpose should never ever be used? Just random questions.JustinC

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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.

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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).

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When you say survival do you mean 'Individual Survival'? If so I'd have to disagree. 'IS' is only pertinent in context of reproduction. Why do you think salmon swim all the way up stream to reproduce, and then die? Because there is no 'selecting' for mere survival unless it is in context of reproductive success. I guess you could say the summum bonum of the process is reproductive success.

This is pretty sweet getting responses so quick.

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Now you have switched from engineering to "goal" which compounds the problem. You don't have the environment pushing individuals to produce...those that happen to produce more offspring in a generation have higher relative fitness because of some quality that has nothing to do with refining the process of reproduction...

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But it must have some relation to reproduction if it causes the organsims to be reproductively successful.

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those indiviudals and whatever trait that conferred the benefit may in the next generation be a detriment and some very rare variant may come to predominate...how is this goal oriented?..goal implies a priori knowledge i.e. pre-determined outcome just like engineering does.

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I know 'goal' is probably a bad word to use, but I would still say that a goal could be better designed systems for reproduction.

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So what if there are 20 variants that are at equal frequency but are highly selected for such that all other variants but the 20 are quickly eliminated..which of the 20 is optimal?

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Equal optimality.

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actually the individual the produced 10 offpring has a higher relative fitness. I should have better clarified that there can be gene flow between the two populations though not frequent...thus, they are still competing.

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If it's not frequent I'd say it is probably negligable.

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How would an optimal of 0 to infinity be descriptive? That is why there are terms such as relative fitness because it does not imply that something is better "designed, engineered, reaching a goal"..it just means that for some reason there are more of one type of variant than another in a given generation...

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Wierd, but I think terms like relative fitness are useless. But I guess that can be because I'm thinking about 0 to infinite fitness (optimality is to confusing).What does it mean to be relatively fit? To go back to the eye examples, you'd say that 1 percent vision is fit relative to 0 percent vision. How can you compare the two systems? Don't you have to have a reference to the environment, and the better designed (adapted if you like) will survive?[This message has been edited by JustinCy, 07-30-2003]

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Tautologies don't make predictions. Definitions don't predict. They just identify. That is all that is going on when you say that 'survivors survive' -- you are pointing out the relevant subset of creatures. Why this subset? The reason is reproduction. Dead creatures don't reproduce and are hence irrelevant to evolution.

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Survial in 'survival of the fittest' would be synonomous to reproductive success. If it is defined by the post hoc, then you would get 'survivors survive' or 'reproductive success of the reproductive successful'. How is that supposed to explain evolution? They're just definitions, as we agree.

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What direction?

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If you mean that 'survivors survive' doesn't tell us which adaptations lead to higher survival rates, then of course it doesn't. You have to examine the survivors to find out. I think you are trying to drag way too much out of the first step of the analysis.

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I'm not sure I disagree with the above. Can you tell me where you think i do?

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Well, if it is always true, it is a very good place to start. Then you ask, "Why?" "Is there a reason some survive and others do not?"

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It's always true based on logical necessity. Yes, the 'why' question is what natural selection tries to explain. Again, if fitness is defined by the post hoc analysis, then it would explain nothing. No more than my ground breaking theory of "people that walk, walk."

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One hundred critters are born. You tag them and release them. A year later, you find all the tags but only 25 are attached to living animals. This is not observation?

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You observed that some animals survived. They are the survivors, by definition. You did not observe survivors surviving. If I stare at a blank wall I can assert that survivors survive without observation, because its a logical necessity. It's no more of an observation than saying, "x=y because y=x". Is that an observation?

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I dare you to do science without definitions. Hell, I dare you to think about anything without starting with definitions. Why are you downplaying this? Consider. We want to study light. What is light? Well, you have to define it somehow, otherwise you can't move on to further study. "Light is what illuminates the Earth during the day." "Light is what candles emit." All very circular definitions really. It is unavoidable. You seem to object to this step.

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I think you know exactly what I mean, and it's not that definitions aren't useful for science. They are needed to communicate.What I meant is that they are not scientific theories.[This message has been edited by JustinCy, 07-30-2003]

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Why? That is only true if you think that every trait of an organism is directly involved with the reproductive system. Do you think that flight is directly involved in gonadal development for example?

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We are referring to traits that will cause reproductive success if selection, right? I don't think I said every trait will. I don't think its involved in gonadal development, but it will more than likely have an affect on the organisms reproductive success (atleast at one time if the trait is completely homogonized).

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Since it is an inappropriate word to use why use it? Fitness advantage, higher relative fitness, even higher frequency describe the same thing without adding a goal directed connotation.

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Then maybe I'll just stop using it then, huh? What about that?

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That is why optimal is a useless term...equal optimality does not help...so if a new group of variants are produce in the next generation some of which are slightly better adapted are they more equal optimal..or hundreds of opitmal variants...optimal fails then to describe the relative advantage

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If they are better adapted, why would I say they are 'more equal optimal (fit)? Wouldn't I just say they are more fit?

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Unfortunately genetics is against you here...very small levels of migration/immigration i.e. gene flow can homogenize populations over long distances over long periods of time...it is hardly negligible.

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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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Relative fitness means that an individual, species, allele produces more offspring, population members, copies of itself than another individual, species, allele...that simple. The cause of this relative advantage of passing this information from one generation to the next is what evolutionary biologists are interested in.

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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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Your vision example misses the point. The vision trait itself is not fit...if those with 1% vision leave more offspring behind than those with 0%, then the 1% are relatively more fit.

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This is what I don't like about relative fitness. Is something only more fit when compared to another in the population? Shouldn't fitness be determined by the environment, and the fittest will survive?

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If they leave equal number of offspring behind then they have equal relative fitness...which over time comes to predominate in the population will be dictated by chance and not by selection...any kind of refinements to the vision system as you are interested will only come when variants appear which then have a higher relative fitness to those that already exist for example a mutation occurs in the 1% vision system that allows for a new light wavelength to be distinguished and gives those individuals an advantage in locating food. They eat more, live longer, produce more offspring and voila..a few generations down the road, that variant is predominant...and it can turn around just like that...a new pollutant is added to the atmosphere and that wavelength of light is now longer visible..individuals of the original 1% vision group don't expend energy making the protein that allowed the new variant to see the now blocked wavelength..so the original variant a few generations later it is again at high frequency...no goals, no direction, no pre-determined path, not optimized...more like a never ending lottery.

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I understand in the long run there is alot of chance, but aren't we talking about natural selection, which won't factor in genetic drift?

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Comparing species with no vision system to those with a vision system is similar in concept but the parameters are very different as you are then comparing individuals that do not reproduce with one another...and it is much more difficult to determine the relative fitness of species i.e. predator species such as wolves will almost always have a smaller population density than their prey species...if the wolves increased their number dramatically it would actually be a disadvantage long term....but this is where an ecologist like Quetzal would have better input...

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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.JustinC

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Fitness must be a function of both reproductive output and survival

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This is what I think of when I say reproductive success, i.e producing offspring that have a good chance of producing offspring of their own. So individual survival would be a part of it, and reproductive output would be apart of it. In 'survival of the fittest', I would say if you are speaking of individual organisms you would have to interpret survival as reproductive success since their is no selection for just surviving without reproductive output and no selection for reproductive output without survival.Do you know see how the tautology issue arises?And I'm sure some organisms in the wild are born sterile and survive along time, although I never observed it.

No problem on the lateness. I broke some handbones and wrist in car accidenct recently, so my responses may be pithy.

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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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Ok, I thought you were saying that population A on the one side of the mountain and population B on the other were in significant competition.

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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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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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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

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

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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.

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Yeah, I agree. I wasn't very coherent. I'm referring to the phrase "Survival of the Fittest". I forget, you may of answered this already. Do you think the phrase is (or can be with some interpolation)an accurate description of NS and if so how would you interpret it to make it more accurate.

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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.

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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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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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Yeah, I agree. I'm referring specifically to NS though, not evolution is general.

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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?

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

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

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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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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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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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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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but design does imply purpose and pre-adapatation

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

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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

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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]Species may be able to move to a worse area on an adaptive landscape, but not in a selection event...right?JustinC[This message has been edited by JustinCy, 08-20-2003]