sir_toejam
Posts: 846
Joined: April 2005
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"The Darwinian theory of evolution is based on the idea of slow steady changes arising from accumulated mutations. It is slow because, according to the theory, mutation is disadvantageous. The only mutations occur as a result of unavoidable errors in transcribing genetic information."
this is not actually precise.
1. the idea of slow and steady is a bit of an oversimplification that is based on what darwin himself thought without the benefit of the genetic information we have available. it doesn't correctly translate to modern evolutionary theory.
2. there is no assumption in modern theory as to the relative advantage/disadvantage of any specific mutation event. relative selective pressures determine this, not any a-priori assumption.
3. mutations can occur by a variety of mechanisms other than the one you list. Moreover, errors are not "unavoidable" in any specific sense with regards to transcription itself. there are actually very good mechanisms in place to prevent transcription errors, which make them typically quite rare. hence, the sources of mutation don't always arise strictly from transcription "errors", but could arise pre-transcription from any of a number of sources; oncogenes, for example.
"The correct value for mutation is obtained by considering all possible mutations and assigning them a probability and a cost (or benefit). The net cost (benefit) of mutation is the sum of the costs (benefits) multiplied by the probability that they will individually occur."
Funny you should mention this; one of the leading evolutionary theorists of all time, Robert Trivers, is attempting to do just that: attempting to produce equations that balance the absolute inclusive fitness of a trait. the reason i point this out is that there are so many variables to calculate in real-world examples of inclusive fitness that calculating the "value" for any specific trait would be extremely difficult.
for example, you could have multiple, competing selective pressures on any given trait. how would you be able to determine ALL the relevant selective pressures in the field? Moreover, at the genetic level, traits can be linked. While there might be significant pressure against one trait, it might be linked to another trait that is even more "favored". Just two small examples, but you can see how complicated this can get.
You can't even correctly determine the "probability that they will individually occur" without more detailed knowledge of what factors into that. even in its most simplistic form you propose, that of simple 'translation errors', it would take a phenomenal effort to calculate what the factors and frequency of translation errors occur within an individual population in the field, which is all that really matters.
"Of more importance, a beneficial mutation increases the long term probability of an organism having descendants and is limited by the impossibility that the probability can exceed one; similarly a deleterious mutation decreases the long term probability of an organism having descendants and is limited by the impossibility of the probability being less than zero"
congratulations, you essentially just reworded what amounts to the theory of inclusive fitness.
"At any point where the reproduction ratio drops sufficiently to virtually ensure extinction the long term probability of the organism having descendants is essentially zero. Consequently, the cost of deleterious mutations, as a fraction of this must also be zero."
the cost to whom? individuals do not "divine" the relative value of deleterious mutations, nor do they consider the value of maintaining the "species".
On the contrary, it really depends on what specific selective pressure you are talking about as to what strategy actually makes sense under those pressures.
you can't generalize "environment" as a selection pressure per say. There are numerous selective pressures that could conflict with each other and still come under the heading "environment". Even if you restrict the selective pressures to purely physical ones. However, restriction to purely physical selection pressures is very unrealistic.
you are mistaking something general (environment) with something very specific (a specific selective agent) when you use the example of a colony of bacteria "threatened" by an antibiotic.
look, essentially what the argument proposes is that generalists are favored under some conditions, specialists under others. However, this has little to do with genetic mutation rates. Selection could just as easily act on the variablity already extant in a population. under such circumstances, it would simply favor those individuals with offspring already more compatible with whatever the primary selective pressure is. In fact, it predicts the exact opposite of increased mutation. I would expect to see those individuals with the greatest fitness under the restricted circumstances to be those with less variability in their offspring, but whose traits are more compatible with whatever the most prevalent selective pressure at the time is. these individuals would have the most surviving offspring, not the ones with increased variability.
aside from all of that, what you are proposing is essentially that environmental bottlenecks end up producing most species, through a genetic mutation mechanism. the problem with that is you can more easily explain it through standard evolutionary theory.
once you have an extreme bottlneck, afterwards you have a whole buch of blank niches to fill. intrapsecies competion would then be a far greater selective pressure than interpsecies ones, which would then favor individuals to move into new niches.
no need to propose massive genetic mutation as a response to bottleneck-level selective pressures.
see?
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