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Re: Rapid Lizard Evo
The majority of random mutations are niether harmful nor beneficial, most
do not impact survival and reproductive success at all.
Exactly. Most are neutral at best (at least initially - lots of small
'neutral' changes can eventually accumulate to actually 'do something'). Of
those mutations that have an immediate impact, most will probably be
maladaptive. Hence why I refered only to *beneficial* random mutations,
which have a better chance of having an immediate selective advantage.
... organisms that use sexual reproduction certainly
leverage genetic recombination to increase the degree of phenotypic
variation in a population.
Bacteria also benefit from recombination by exchanging genes with each
other, so it's certainly not restricted to sexual reproduction.
Also true that organisms with complex central nervous
systems can buffer themselves against selection on their genomes by
altering behavior, and this is especially succesful in organisms that can
transmit learned behaviours.
It should be noted, however, that the vast majority of organisms cannot
utilize one or both of these buffers, so the accumulation of random
genetic variation into the genome still provides the majority of variation
that is acted upon by selection in the history of life.
Certainly this may be the case for *most* transmitted learned behaviour, but
how many organisms don't benefit from recombination? Surely genes can 'cross
over' (nothing to do with John Edwards) during asexual cell division just as
much as during meiosis?
I suppose it depends on how you define 'random mutation'. I tend to restrict
it's use to random changes in gene structure due to outside influences
(radiation, mutagenic chemicals, etc), whereby genetic damage is inflicted
that isn't completely repaired by the cell. I suppose some people might use
the term more broadly to encompass any process that alters a gene sequence
(which would include recombination). The difference I see between 'random
mutations' and other gene-altering processes is that the former tends to
occur in adult cells (which obviously will only be passed on if it occurs in
the gonads), while the latter tends to occur during cell division.
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