Destroying Darwinism

No one, apart from you, suggests that natural selection would not be occurring in a population of uniformly white pepper moths, all they are saying is that the melanic trait could not be being selected for if it was not already present. Similarly gravity will not affect a body which is non existent.

What part did you not understand?

I cant believe this thread is still on the same issue of white and black moths. How can there be both white and black moths in the population without variation Syamsu?Are you suggesting that there should be some particular standard used as a measure of fitness for individuals in isolation in a population without variation i.e. one individual in an effectively clonal population? I would have thought that reproductive success would be the obvious one. But if all the members of such a population seem to be similarly fit, as the model most of us adhere to would predict, then where does the natural selection come in? Especially in a clonal population where there is nothing to select?

You can have reproduction without encroachment, as long as the environment has spare carrying capacity.As for your copy machine example, if you consider the original ream of blank paper plus your original to be copied as the full carrying capacity of the environment then yes, when all the blank pages have been copied to then the blank page will be extinct in that environment. But a copy machine is a ridiculous analogy for population genetics.How does the spread of a specific allele through a population not represent a form of encroachment, assuming that the proportion of the encroaching allele in the population increases even if the alternative allele is still increasing in copy number due to reproduction? This still assumes there is no limit to the carrying capacity of the environment. Is a change from 25% to 50% not encroaching?

How many examples of genetically clonal populations do you really think there are? There are variations even in asexually reproducing organisms. Your best bet is probably highly inbred lab strains of drodophila or mice. It may be that there can be homogeneity of one trait in a population, but that does not make the population homogeneous.You seem to want to change natural selection into a simple measure of reproductive success. But this doesnt inform us as to the propagation of an allele in a population, and therefore the evolution of that population, unless it is looked at in comparison to the reproductive success of other alleles.

But unless you combine your observations of the reproductive rates you will not know how the traits are spreading through the population.You have no cutdown theory of natural selection, all you have is the concept of reproductive success which you seem to think is all there is to natural selection.You had better hope your clonal populations dont have much variation, if they do then your midi preps are going to be pretty worthless.

You havent produced a short version of darwinism though, all you have done is rename reproductive fitness as natural selection.I cant see why you think we should have difficulty in comparing the relative fitness of populations in different environments provided you allow us to look at the proportional spread of alleles in the population. If the different alleles interact differently with the two environments then this should be reflected, unless the new environment is just generally more permissive in which case the allele frequencies may not change at all.Obviously if you are thinking of your theoretical genetically homogenous population again then it makes no difference however much reproduction goes on as nothing is ever going to happen in evolutionary terms in a homogenetic population with no capacity for variation. You seem to have decided that population dynamics rather than population genetics should be the focus of evolutionary biology.Your photosynthetic and non photosynthetic organisms would still be competing for many of the same resources if they reamined in the same environment. If your photosynthetic organism can colonise new environments then obviously it will have managed to avoid the pressure of competition from the previous non photosynthetic form.If the original environment has a limited carrying capacity in any of a number of limiting factors, such as space, other than food then natural selection will still operate on the proportions of the population showing photosynthetic and non photosynthetic traits.[This message has been edited by Wounded King, 06-10-2003]

Dear Syamsu,Looking at two populations in completely different environments is very different from looking at two populations or sub populations in the same environment. Once again you ignore the concept of a carrying capacity. The upper limits of the two populations probably is relatively stable within a limited environment due to one of any number of limiting factors. It is the presence of both populations within this limited environment which leads to competition for space/raw materials etc..Obviously any competition between two populations one of which is located in the photic layers of the sea and one which is restricted to deep see caves without light, is going to be of the most indirect kind imaginable if there is any at all. But your model presumed the photosynthetic arise from the non photosynthetic, presumably this was not in the environment of a lightless cave as if it was then the development of photosynthesis would not be much advantage. The original population from which the photosynthetic strain arose probably would be wiped out, that doesnt mean that some spooky action at a distance wipes out similar strains in completely different environments.If you made the initial assumptions of your model a bit more explicit it might help.

It shouldnt be neccesary for me to mention natural selection every second line for you to grasp the point. Since we were discussing a hypothetical example that you came up with I would suggest any irrelevance to natural selection was rather your doing.You stated that NS only applies to variants to the extent they use the same resources, which is fair enough. But you seem to fail to see that if there is no limit to the resources then such a permissive environment will produce very little selective pressure. Such permissive environments are very rare except perhaps in instances where a new environment is colonised and one or more limiting factors are thereby alleviated, such as rabbits on introduction to Australia.You then gave the example of the evolution of photosynthesis. Even allowing your non gradual evolution of photosynthesis there is still no rationale behind your apparent belief that the gaining of photosynthesis would mean the two variants were not competing for the same resources. They might not both be competing for one specific resource but there are a lot of other limiting factors they would need to compete for IF they are in the same environment. If the photosynthetic variant had such a reproductive advantage as to take up all of one of those shared resources then it could drive the non photosynthetic variant to extinction.

I ignored most of those types of relationship as they are much more often interspecies rather than intraspecies relationships. Most predator prey relationships are not seen within species and symbiosis almost invariably refers to an interspecies relationship.We dont have a theory of natural symbiosis as natural selection is sufficient to explain the origin of symbiotic relationships.You have yet to say anything about the idea of carrying capacity. If we assume a population at carrying capacity then your +/+ and +/0 relationships are obviously impossible.

This is also biology Sysamu and as any biologist knows it is a complex and messy sort of science. If you want hard and fast formulas then stick with physics.Your environmental argument seems highly dubious given your previous claims that most populations show effectively no variation, could you try for a bit of consistency?I believe that most populations do contain variation and the point of mainting that variation is so that the populations are not susceptible to either inbreeding or being wiped out suddenly by disease as is common in clonal populations.If these populations are at carrying capacity I would certainly not say they were above it a population can be at other things though especially populations below a lower limit where recessive genetic factors become very obvious. This certainly doesnt show that +/+ relationships exist within a population as you suggest. Obviously heterogeneity is advantageous for a population but the heterogeneity does not neccessarily favour all alleles equally, that would be dependent on natural selection, it also doesnt neccessarily allow expansion beyond the carrying capacity, unless that is it opens up a new environment/niche to be exploited.Look at it in the more common evolutionary way as changes in the frequency of a trait. Assuming a single on/off trait, such as your hypothetical photosynthesis, the proportion of the population displaying that trait can never be more than 100% and the proportions obviously vary in direct relation to each other. The actual numbers of organisms are not as important as the frequency of the trait, in terms of evolutionary genetics.And since you thought up these relationships doesn't it rather fall on your shoulders to show that they exist? Although given your predator/prey, symbiosis terminology +/0 might be termed commensalism. Almost any relatively stable heterogenous population should be a good example of a -/- population, that simply being a representation of competition. The +/- one is harder, can you think of an example? All I can think of off hand is non poisonous forms which mimic poisonous, but these are likely to be from different species.[This message has been edited by Wounded King, 06-11-2003]

I never said that biology was a soft science, I simply said that it did not have as many examples of the same sort of clear cut, straightforward apparently universal rules that physics does, Biology is much more contingent than that, mainly as a result of evolution.My requirement for variation is not at all duplicit. Variation is not required for a population to exist, but most natural populations do show variation. Even if variation in one trait is completely wiped out then further variation in that trait can arise through mutation. This is looking at things incredibly simplistically of course, a recessive variant of a gene may be present in a population which all have the one dominant phenotype and therefore no variation in terms of NS.As to the richness of nature, I may not know everything that is out there but then neither do you. It rather devolves to you to show evidence for rather than demanding that I prove the non existence of something. Your hypothetical examples dont really show anything, why should the glutters ever rise to a level where they could deplete the environment if they use their resources inefficiently, they should therefore be at a reproductive disadvantage to the modest variants. You are not showing either the glut trait to be negative to the modest trait, except in as much as the variants compete for resources, nor the modest trait to be beneficial to the glut trait. If you want these hypothetical populations to serve any purpose you need to make your initial assumptions much clearer, if all other things apart from their efficiency in using resources were equal then the glutters would almost certainly die off except perhaps as a recessive trait.You have still to address how your different relationships relate to allele frequency, the usual standard for evolutionary genetics.

If you dont think that allele frequncy is fundamental to evolution then you obviously have no idea of any evolutionary concepts produced since the 'rediscovery' of Mendel's work and the formulation of neo-darwinian theory.Of course in a homogenetic population natural selection would be limited by the mutation rate, if all the members of the population are genetically identical then what is there to select for?A black population could give arise to white moths if the white trait was recessive and NS could then act on that white moth.If your glutters and modest users have seperate niches then what resources are they supposed to be competing for and how do they constitute one population? Do you understand the concept of a niche? So the glutters have an increased reproductive rate to compensate for their extra resource uptake, a point that it might have been useful to mention when you first made this example. To be a useful thought experiment these populations should only vary in one trait, all other factors should be equal surely since it is the effect of the variation in that one trait we are examining.Please give me a reference for an environmental group claiming that variation is beneficial to declining populations of endagered animals because different variants of alleles have a symbiotic relationship. It is much more likely that they say it is important, as I did, because otherwise the populations will be susceptible to problems associated with inbreeding and also more susceptible to all being struck by one disease.

We can talk about mutations if you like, or alleles. But when there are two distinct phenotypes in the same population you have to call them something, even if you just call them 'distinct phenotypes'you don't change the fact that they vary from each other. Obviously in a theoretical homogenetic population there would be no variation and hence no variants. Interest in the 'preservation' of the photosynthetic trait is no more important than interest in the 'preservation' of the non-photosynthetic trait, what is interesting is the way a specific trait may be selected for by the environment. Why should we treat members of one population as if they were members of two? Do you think species should diverge at the nucleotide polymorphism level?

Dear Syamsu,I thought we had covered this before. Of course natural selection applies to cells, if you look at a cancers development it is an obvious example of a heritable adaptation which improves the relative reproductive success of the cancerous cells compared to their neighbouring cells. This is only relevant to the cells in the body though, the cells are not independent living things under normal circumstances. Of course unicellular organisms are just one cell each and natural selection certainly applies to them. What was your point supposed to be? Not everything NS applies to has to be in the definiton, should the definition list all the different species it applies to? It is generally applicable.As to the Earths gravitational field, surely that is simply a property of its composition and dimensions, a better analogy would be the Earths orbit in which all of the various bodies in the solar system and beyond would play their own small part.As to the photo and non-photo example, they must originally arise within the same population, therefore until the respective traits reach fixation in any specific environment they should be treated as one population, unless their photosynthetic trait somehow makes them reproductively isolated. You cant start off with them in different environments if one is supposed to have developed from the other.