Wesley R. Elsberry wrote:
>> ... But the process of
>> reproduction in humans is not simply a matter of drawing a set
>> of alleles, like cards from two decks, from each parent, even
>> when one excludes the usual potential for point mutations to
>> occur. Recombination does not respect reading-frame
>> boundaries. This means that information *different* from that
>> seen in the parent providing the gamete is possible. Whether
>> that information change also marks a *novelty* is another
>> matter, but one which is a possible outcome.
David replied:
> Are you referring to the phenotype? [In which case, I agree]. Or
> are you referring to the genotype? [In which case, I do not "see"
> an information change].
I think the real difficulty here is knowing what is meant by
"information change" in this particular context. I'm also confused
here because we know that recombination affects the genotype
directly and the phenotype secondarily. So whatever information
has changed, it is first manifested at the level of DNA.
> When you use the words "possible outcome", are you making a deductive
> statement, or can this be justified by empirical evidence?
This is definitely empirical evidence. Look up the molecular mechanisms
of recombination in any of the _Genes_ textbook series by Benjamin Lewin.
Recombination can generate novel variation and new alleles.
> I am not just quibbling over words. The vast majority [if not all]
> of the variation in living things noted by Darwin related to
> phenotypic expression rather than genotypic changes. Those who
> extrapolate plant and animal variations due to artificial breeding
> and argue for "macroevolutionary" change are making the same
> category mistake.
Recombination can generate expressed variation. So I don't see this
as a "category mistake" problem. Also, remember what started this
discussion: contrasting recombination vs. spontaneous mutation as
generators of variation. The genotype/phenotype issue -- which is
new to this thread --- applies equally to variation produced by
recombination or spontaneous mutation. Bringing it up here will not
resolve the original topic.
>> Theretically, in the presence of sufficient base-pair
>> diversity, a series of recombination events can produce the
>> same result as a series of point mutations, or a single point
>> mutation.
>
> Theoretically, I will concede this point. But I will suggest that
> it is not particularly helpful, as it does not convey the reality of
> what is going on with either recombination or mutation.
I believe the original proposition was that the variation generated
by point mutation was distinct from that generated by recombination.
Further, it was implied that spontaneous point mutations were somehow
"bad or defective processes" whereas recombination was a "good
process" for generating variation. The bottom line is that they are
both processes which can generate heritable variation. Whether that
variation is "good" or "bad" is independent of the source.
>> There is no theoretical basis upon which to divide
>> recombination and point mutation as possible information
>> sources.
>
> I suspect this conclusion is highly controversial amongst
> evolutionary biologists. The only way I can agree with it is to
> add that neither recombination nor mutation are possible information
> sources and so the two processes cannot be divided on this account.
I would hesitate to add that last comment. This sounds like a leading
reference to "Spetnerian information" that was discussed here in
September and October. I haven't seen any way of measuring biological
"information" that simultaneously makes such a statement true while
retaining much use for evaluating evolution.
Regards,
Tim Ikeda
tikeda@sprintmail.hormel.com (despam address before use)