In article <9109052236.AA17124 at bambi.ccs.fau.edu>, tomh at BAMBI.CCS.FAU.EDU (Tom Holroyd) writes:
> Systems that behave this way show power law scaling of the bursts with
> respect to time. The cute way of saying this is "an order of magnitude
> more bursts, an order of magnitude less often." This means that the bursts
> of change happen on all time scales, or, that there is no characteristic
> time for change in such systems. This would correspond to the "rate"
> of evolution, if it existed, but these arguments suggest that the rate,
> or characteristic time, is undefined: a power law scaling would be the
> more appropriate description.
Bursts of evolution may reflect, among other things, fluctuations in the
effective population size of a species.
>> Another avenue of attack is that the genetic structure of an organism
> is hierarchical. If you start with the assumption that point mutations
> are equally probably anywhere along the genome (a perhaps not too safe
> assumption, but it would only help my argument if it was false), then you
> can examine each point on the genome and ask the question "would a
> mutation here produce a viable creature?" If the answer is "no",
> then you can ask "would an additional mutation somewhere else help?"
> What I'm driving at is that some points are going to need mutations
> at other points first, if the creature is to survive. In fact, there
> may be a large cascade of changes necessary before a single mutation
> can be viable.
Perhaps not quite true, especially for higher organisms where the diploid
structure (or even more complex duplication events) can allow an unfavourable
(even lethal) mutation to achieve a significant frequency (with the death of
only a few homozygous individuals). Then, a further mutation which may confer
a selective advantage over the existing gene can occur at any time.
Peter Stockwell
Biochemistry Department,
Otago University,
New Zealand.
