Re: Challenge for Darwinists - Protein Synthesis


Wall Of Sleep wrote:
allanm wrote:
Wall Of Sleep wrote:

<snip>

Statistically, all variation in an initially varying population will be
eliminated (in the absence of mutation) in (4 * population size)
generations.

So looked at either way - the origin of a sequence or the fate of
variants in a derived population - the existence and persistence of
variation proves the historic reality of ongoing mutation.



It would seem to me that the forces of nature are working against random
mutation at every turn then. I'm still totally unconvinced that this
vehicle can be the driving force behind the millions of unique
biological systems we see today.

<snip>

I'm afraid you've missed my point then. What I described is not a
preservative force but part of the inexorable force for *change*. You
assume that mutants will *always* be eliminated. But they have (at
least) the same chance as every other allele of becoming the 'norm'
as variants are lost.

Consider this:

A population of just 4 individuals. A single diploid gene. Lets label
each gene individually, one from each parent:

Aa
Bb
Cc
Dd

If each different gene were a different variant, we would, by the
inexorable loss of variation I described, end up with all A, or all a,
or all B...... etc etc. Each ancestral gene has an exactly equal chance
of becoming the 'norm', and the other 7 will go. The existence of
variants is thus evidence of the historic action of mutation in
*opposition* to the tendency to homogenize.

Lets then take a theoretical future homogeneous population resulting
from this effect - all A, say.

A neutral mutation arises , A*. It too has an exactly equal chance of
becoming the 'norm' further down the line. So 1 in 8 random neutral
mutations will become 'fixed' - the population becomes all A*.

Then from that position, 1 in 8 times, a further mutation, A**, becomes
fixed..... How does a population manage to stay the same against this
backdrop of mutation and elimination of 'competing' variation?

And this is without any natural selection. Stick that in the picture
and we have a means by which a mutational change can buck the stats. It
no longer has to make do with an equal chance. Selection can work both
ways, of course. Good ideas get a bunk up. But equally, bad ones get
their chance knocked below equality - a preservative force, against
change but also against deterioration. (And, this slightly ups the
chances for the other variants that are 'better').

Multiply this argument up over the whole genome, factor in the
continual variation of the fitness 'landscape' due to external
factors, and you may (I hope) see that the combination of mutation,
statistical factors and selection renders stasis highly unlikely. Or at
the least, get some flavour why people who work in this field don't
seem to share your misgivings.

.

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