Is there more than one definition of natural selection?

At the risk of jumping in here,

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Modulous, I would venture to challenge your algorithm this way:

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1. What does “variation in a trait” mean? Alleles are variations of genes, of course, and in this way they ARE the traits. The genes themselves are the not the traits, per se; that job goes to the alleles. For example, I don’t call an eye-color gene a “trait.” I call the alleles of the eye-color gene “traits.” So, the first term in your equation actually pertains to different allele frequencies. The Hardy-Weinberg (dis)equilibrium would seem to account for that.

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Eye-color is a trait, the different colors are variations of that trait.

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What does “heritability of that trait” mean here? Do you mean that certain alleles or their frequencies are more heritable than others? Probably. But all it implies to me is that traits can have variation, even in their heritability, which seems already accounted for by the first factor of your algorithm.

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Heritability refers to that proportion of a variation in a trait which is controlled genetically. Environment may have some effect on the expression of the trait by the organism. Consider beak depth in Darwin's Finches. This trait is approximately 85% heritable, with 15% contributed by the environment.A

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Natural Selection is not Evolution-- R.A. Fisher

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In fact many genes exhibit a random effect on phenotype, a phenomenon known in genetics as penetrance.

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Just to be clear, penetrance is actually the degree to which a gene controls its phenotypic expression. Crashfrog's example is of a gene with low penetrance. A gene whose phenotype is always expressed in every individual has high penetrance.

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Natural Selection is not Evolution-- R.A. Fisher

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I'd like to know if I am wrong that a genetic message”the genotype” is expressed in a protein”the phenotype.

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Most geneticists I'm familiar with refer to the protein as the gene's product, not the phenotype. The phenotype is more properly the result of the protein's activity or function. Example: the enzyme beta-galactosidase is the product of the gene;the phenotype is the specific enzymatic activity on the galactose substrate.

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Natural Selection is not Evolution-- R.A. Fisher

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Maybe I'll change my mind when I finally understand what you're saying, but I cannot at this time see how a differential reproductive success of 0 is always the equivalent of no natural selection taking place. For example, imagine two subpopulations which produce equal numbers of offspring, but that during that particular reproductive season leading up to the equal numbers of offspring that many eggs in both subpopulations were eaten by predators. That's natural selection, even though the differential reproductive success was 0.

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Sorry for jumping in again, but this particular passage interested me.If the relative (I prefer ”relative’ to ”differential’, but that’s just me) reproductive success of one subpopulation is identical to that of the other, than the two subpopulations have identical fitness. Having identical fitness does not mean the absence of natural selection. What it does mean is the allelic frequencies of these subpopulations will change relative to each other randomly, entirely due to genetic drift.Consider the Peppered Moth. It undergoes both bat and bird predation. Under bat predation, both the light and dark genotypes have equal fitness, since bats do not discriminate by moth coloration. One would expect, with no bird predation, to see the frequencies of the two genotypes to drift at random. Under bird predation, however, the fitness of the two genotypes depend on the background coloring of the trees, and one genotypic frequency will increase steadily at the expense of the other, even if bat predation is occurring simultaneously.A

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Natural Selection is not Evolution-- R.A. Fisher

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I'm finding this discussion defining natural selection to be an unexpectedly tough slog. We can't seem to get out of our own way. The approach I'm lobbying for is to start with a simple definition from which we elaborate. I proposed that we start with Darwin's definition, but I'm flexible as long as we start simply. I do feel that we're at far too detailed a level since there isn't even agreement that sexual selection is a type of natural selection.

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I get that feeling as well. For what it is worth, I tend to consider sexual selection as merely a certain kind of animal behavior, subject to natural selection like everything else. As an example, consider first a population of deer mice living in an open, grassy field. These mice are nocturnal, so they do all of their foraging under the cover of darkness. Now suppose a behavioral variant arises that forages during the day. Such behavior in an open field during the day exposes these mutant mice to predation from diurnal animals, such as hawks. This behavioral variation will be selected against if it raises the risk of predation significantly, and would not be expected to become common in the population. Now consider other kinds of behavior in the same population. Let’s assume females only choose mates who smell ”right’--those who possess a certain pheromone. If we imagine a variant male being born who does not possess the requisite pheromone, it should be easy to see that such variants will not become common in the population.So, what is the difference between the two scenarios? Why would we consider the behavior that affects predation risk qualitatively different from the other, which affects mating success? In both cases we have behavioral variants (or, more properly, the genes underlying the behavior) competing with each other for replicative success. I would argue both scenarios are examples of natural selection in action.AEdited by Allopatrik, : Spelling

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Natural Selection is not Evolution-- R.A. Fisher

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So, I have another question for you. Back in Message 32 I mentioned this observation of counter-processing by two evolutionary geneticists, Hartl & Jones:

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If a detrimental allele is maintained in a population by mutation pressure alone, so what? Why do we have to invent some arbitrary "process" for this? Isn't knowing that mutation occurs enough?

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I’ve been arguing that all five processes are possible along the course of an evolutionary continuum. What do you think about it?

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I'm just a simple creature.This is all too abstract and cerebral for me.A

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Natural Selection is not Evolution-- R.A. Fisher

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Can you give me an example of non-random mating in a sexual population that would not be considered Sexual Selection?

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The subdivision of a population into local breeding subpopulations, or demes, due to isolation by distance.A

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Natural Selection is not Evolution-- R.A. Fisher

If you want a simple definition of random mating, all you have to say is, random mating is the situation where every individual in a population has an equal chance of mating with any other individual of the opposite sex.Obviously, there are different conditions which prevent random mating from occurring: habitat fragmentation, sexual selection, and isolation by distance being just a few examples.A
Edited by Allopatrik, : No reason given.

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Natural Selection is not Evolution-- R.A. Fisher

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How the (*^#@ does this not count as Sexual Selection? So the population is small and isolated.

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I didn't say that. Let me ask you a question. Consider a population of deer mice, spread over a large, rectangular geographic area several miles square, with no obvious topgraphical features to block gene flow. Now, consider a male mouse living in the northeast corner of the rectangle. Does this mouse have an equal chance of meeting (let alone mating with) a female who lives in the southwest corner, as he does meeting a female living in his corner?

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Natural Selection is not Evolution-- R.A. Fisher

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No he doesn't. I don't know Deer Meeses. Do Deer Meeses have any selection rituals or do they just jump on anything that comes along? If they just jump then random mating is taking place. Or is this considered non-random soley due to geographic constraints? Then by the same token (back to the corn plant) since the pollen cannot reach over into the next county where other corn plants live is this also non-random? I don't think so.

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If a male mouse does not have an equal chance of mating with any female in the population (and vice-versa), no matter what the reason, then the population is not one with random mating in place by the definition I gave you, and by the usage of the term by evolutionary biologists.

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Isn't random mating indiscriminate sampling (Millstein)? Do not non-selective jumping Deer Mice practice random mating regardless of the fact that they do not have such opportunity with everyone in the population equally? If you don't have an equal opportunity with only one female over the next hill is this then non-random? Is this whole subject nothing but a statistical exercise?

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Evolution is a statistical phenomenon.A

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Natural Selection is not Evolution-- R.A. Fisher

Hoot,Your link to the image doesn't work.A

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Natural Selection is not Evolution-- R.A. Fisher

Rats. Edited by Allopatrik, : No reason given.

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Natural Selection is not Evolution-- R.A. Fisher

Bringing in Hardy-Weinberg equilibrium is just confusing, since everything you have listed prevents that equilibrium from being established.A

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Natural Selection is not Evolution-- R.A. Fisher

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Do you have the original reference for this work, rather than the textbook reference?

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Buri P (1956). Gene frequency in small populations of mutant Drosophila. Evolution 10(4): 367-402.AEdited by Allopatrik, : No reason given.

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Natural Selection is not Evolution-- R.A. Fisher

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Wait a second, Hoot. A bottleneck is a result, not a process. It can be the result of sampling error (as in the founder effect), the result of an extinction event, or even the result of genetic drift (in a very small population). It is not, however, a mechanism of genetic drift or natural selection. It simply represents a severe restriction of a population's gene pool. Careful with your terminology.

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At the risk of sounding pedantic (which is truly not my intent), I think we need to lay out how these terms relate to each other so as to enhance mutual understanding (I've seen some idiosyncratic definitions of terms here, which make it very difficult for me to follow at times).A bottleneck is simply a drastic reduction in population size. It is not caused by sampling error, but one of its effects is the resulting population will not possess a representative sample of the genetic variation in the original population. That is, the effect of a bottleneck is genotypic sampling error. Genetic drift is the random drifting of allelic frequencies relative to each other due to sampling error of various kinds (meiosis, isolation by distance, etc). It must always be kept in mind that genetic drift will occur in every finite population, regardless of size, and independently of any selection going on; however, its effects will be greater in smaller populations than in larger ones.A

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Natural Selection is not Evolution-- R.A. Fisher