As usual, I arrive late for the party. Anyway, here's my bottle.zion said:i mean in terms of graduality, was evolution phenomenon not exponential due to some cataclysmic events occuring over a period of time?
Well, I'll try, but it might be better if you just asked questions.zion said:could you please ellaborate a little more for better grasp of the same...?
thank you.
Hmm...I'm replying to myself - is this a first?QuarkHead said:It is not at all obvious, under classical theory, that this process is sufficient to allow the accumulation of enough genetic variation for a sub-population to survive sudden and dramatic evironmental change.
I hope that at least explains the problem.
A couple of points, not as absolutes, but as plausibles.QuarkHead said:That's why I asked the question "where does the genetic diversity come from?"
I suggest that this is rarely the case, and that there are always the opportunities for small changes that provide minor enhancements. In some settings the differences between two options may be so small that neither comes to dominate, yet in a changed environment one or other may deliver a substantial survivial benefit. These cryptovariants then provide a further source for the genetic diversity required for selection pressures to operate on within a changed environment......our population is perfectly adapted
Yes. Mutation occurs at a constant rate (as far as is known), evolution requires phenotypic diversity and evironmental change or migration (plus selection)NeonBlack said:So the rate of mutation and rate of evolution are different. The rate of mutation will be fairly constant.
Hmm...our population is ideal- it is perfectly adapted- so "beneficial" mutations (don't like that term, but we all use it) don't exist. Of course if our population were not perfectly adapted, then beneficial mutaions will confer a survival advantage, and our population will become better adapted.During periods of equilibrium, any beneficial mutations will be mixed into the population and evolution will proceed rather slowly.
You are, but my point was, in a perfectly adapted population, where is the genetic variation required for rapid evolutionary change?But during a period of stress on the population, the beneficial mutations have a strong advantage over the non-mutated and the rate of evolution increases. Am I on the right track here?
Well, either you are stating the obvious - that change in the environment gives rise to selection pressure- or you are indeed being ever so slightly Lamarkian!Ophiolite said:The magnitude of change in organisms seems roughly porportional to the change in environment.
Yes, well. I was being sloppy here. I was using the terms population and species interchangeably. Large-scale population reductions are called a "bottle-neck", and give rise to some quite interesting effects. We Europeans, for example, are almost certainly the result of some sort of bottle-neck. Hmm. I'd like to say more on that, but won't just now.That change is often associated with not only a reduction in species numbers, but seemingly a reduction in population numbers.
Yes, dear boy, that's the standard model..... mutations occuring at the normal rate now have an opportunity to produce a change that is beneficial in this new enviroment.
Yes, my population was hypothetical. The point I was addressing was that, in gradually changing environments, it is possible to imagine that a mutation rate of 4 x 10<sup>-9</sup> is sufficient to keep pace with slow environmental change. But it may not be so when environmental change is abrupt.I suggest that this is rarely the case, and that there are always the opportunities for small changes that provide minor enhancements.
But you haven't explained how these "cryptovariants" (ugh) stably co-exist with the rest of the population.These cryptovariants then provide a further source for the genetic diversity required for selection pressures to operate on within a changed environment.
I was looking to engage in an interesting discussion not in a game of patronisation.QuarkHead said:Yes, dear boy, that's the standard model.
I have to my satisfaction "I suggest that this is rarely the case, and that there are always the opportunities for small changes that provide minor enhancements. In some settings the differences between two options may be so small that neither comes to dominate, yet in a changed environment one or other may deliver a substantial survivial benefit. " You seem to imply that a phenotype of restricted character always reflects an equally restrcited genotype. I await the opportunity to be educated.QuarkHead said:But you haven't explained how these "cryptovariants" (ugh) stably co-exist with the rest of the population.
Let's also assume that a species is perfectly adapted to its ecological niche (that's bold!)
Hey! I'm sorry if you found my "dear boy" offensive. Here in the UK it is regarded as a (rather dated) form of paliness.Ophiolite said:I was looking to engage in an interesting discussion not in a game of patronisation.
And I agreed that I was talking hypothetically, and that in practice, perfect adaptation is unlikely to occur (and not only for the reasons you gave). I'm trying to build a model, not describe the real world!I have to my satisfaction "I suggest that this is rarely the case, and that there are always the opportunities for small changes that provide minor enhancements. In some settings the differences between two options may be so small that neither comes to dominate, yet in a changed environment one or other may deliver a substantial survivial benefit. "
But I'm afraid I don't understand this comment. What is a restricted genotype? Are you in fact saying that in the population genetic homogeneity may not result in a corresponding phenotypic homogeneity? Or maybe that just because a population is phenotypically homogeneous that doesn't mean it is genetically homogeneous? Yes, that looks better. And if so, you are right, of course. But I don't see how it helps. Remember that selection acts on the phenotype, and it's only affect on genotypes is to change allele frequencies in the population.You seem to imply that a phenotype of restricted character always reflects an equally restrcited genotype.
Depends what you mean by "very long". Remember a population (mine here is, at least) is always in Hardy-Weinberg equilibrium, even when the recessive homozygote is lethal (or strongly selected against - it amounts to the same thing). This pushes the allele frequency down rather rapidly, in evolutionary terms.CharonZ said:That's bold indeed. But even if we assume that such a perfect state exists, one mustn't forget that even detrimental mutations are unlikely to be eliminated completely, if the given pehnotype is recessive.
That is, the detrimental allel might survive very long, even if it is selected against.
Look, I'm not trying to be controversial, I am simply trying to point out that yes, punctuated equilibria are the name of the game, but they are not that easy to accomodate in the standard neo-Darwinian model.Thus diversity in the gene pool is likely to exist even in the perfect state,possibly providing the basis of rapid adaptive radiation.