Re: Evolution: A few questions

D. F. Siemens, Jr. wrote:

>On Wed, 16 Jun 2004 17:01:43 +0200 Peter Ruest
><pruest@mail-ms.sunrise.ch> writes:
>
>>Dick Fischer wrote:
>> >Peter Ruest, wrote:
>> >>The spontaneous generation of information by means of natural
>>selection
>> >>of random mutations does occur, but each such step of selection
>>is just
>> >>a yes/no "answer" of the environment to the "question", "Is this
>>ok?" of
>> >>the organism.
>> >
>> >I believe it is entirely possible that environment factors play an
>>active
>> >role in eliciting change in the genetic mix upon which selection
>>can act.
>>
>>The influences of environmental factors on the evolutionary processes
>>are more complex than simple mutation and selection, as can be seen in
>>what follows. What I formulated above is just the simple basics of
>>evolution. But whatever these more complex processes contribute to the
>>phenotypes in a population, the environment's "answer" remains at most
>>one bit - yes/no for each phenotypic result. The increased complexity of
>>the "question" may be expected to slow down the fixation of any mutation
>>(usually pleiotropic - having various effects) possibly selected, if
>>any. Such more complex evolutionary steps hardly speed up the
>>acquisition of information usable to build novel systems. Environmental
>>factors tend to make evolution more difficult, not easier.
>>
><snip>
>I don't get the yes/no answer. If we have a dominant lethal or a neutral
>mutation, it seems XOR fits. But most mutations are more graded in their
>effect. I recall a study many years back that noted that the sickling
>mutation distribution was slowly decreasing in the United States among
>persons of African descent with the absence of endemic malaria compared
>to those remaining in Africa. I don't recall the figures, but it was
>given as a slow process. I suspect that there is also data on the
>incidence of the various forms of thalassemia (same gene but various
>mutations) which affect other populations. One may also imagine a highly
>beneficial mutation or other genetic change, one which could sweep
>through the population, whose bearer encounters a predator or a virulent
>pathogen before reproducing. At the other end of possibility there is
>genetic drift. Isn't the situation much more complex and subtle than a
>binary response?

I wrote "...the environment's 'answer' remains at most one bit - yes/no
for each phenotypic result." Notice that "at most one bit" means
anything between zero and one. In fact, usually it's much less than one
bit. Each time a new (or just slightly changed) phenotypic feature of an
organism occurs, it interacts with the environment, in that the changed
feature is more or less "fit" than the original one - with respect to
the current environment. By definition, this fitness difference results
in a different number of progeny (or is defined by this result). To be
somewhat more precise, this effect happens to the first individual
organism changed, but the outcome is of course modified by a very large
stochastic uncertainty. But in the long run, it happens to the species
as a whole - if the change doesn't disappear (by negative selection or
random drift) before it is fixed in the gene pool of the species. But in
any case, the "response" of the environment is at most "yes, this is a
very good change, we keep that" - which corresponds to one bit of
information.

For a neutral mutation, no information is gained at all. A dominant
lethal one in a diploid organism survives only if there is a
heterozygote advantage (you call it "XOR", but in fact it amounts to,
e.g., 0.2 bit of information for one allele and 0.6 bit for the other,
in each case at most 1 bit), and such is only possible if the mutation
has a pleiotropic effect, i.e. more than one phenotypic effect. Yet,
even in this case, all the environment provides is at most one yes-or-no
"response" for a given individual, and an intermediate response (less
than one bit) for the population (may be different for different
populations with a different genetic and/or environmental background).

Your last example with the highly advantageous change, which happens to
be eliminated, just shows the importance of the stochastic uncertainty
for the individual case. For the population as a whole, the gain of
information is zero, in this case. The population's gain of information
can only be evaluated when the change has been fixed (no old alleles
left), or a state of stable polymorphism has been attained (as with
sickle cell anemia).

>I also don't get the assumption that mutations are the determinative
>factor. There are various forms of duplication of genes and chromosomes
>and their control areas, along with recombinations. Color vision
>apparently began with the duplication of a somatic gene for
>photosensitivity to the X chromosome, followed by duplication of that
>gene. I understand that some people have more than the two genes on their
>Xs. Also, I recall reading of a New World monkey where some females have
>different genes for visual pigments on their paired Xs, while males can
>have only one kind of pigment. Despite the fact that I don't know much
>about genetics and the mechanisms of evolution, it looks to me that the
>situation is much more complicated.
>Dave

Mutations are the determinative factor because duplications and
recombinations don't produce any new information, in the sense of just
repeating what has been here before: "grass is green, grass is green"
doesn't give any more information than "grass is green". To be slightly
more precise, we may consider a recombination of a polynucleotide of 600
bases with one of 900 as one change, just as a mutation of one
nucleotide is one change. Color vision depends on two or three
photopigments whose spectral characteristics must be different. If they
evolved from duplicates of the same original pigment, they require
subsequent mutations to become different.

I also indicated that in real life, the situation is more complex than
the general answer I gave in my first post, but that these complexities
just slow down the acquisition, by a species, of new information from
the environment.

Peter

-- 
Dr. Peter Ruest, CH-3148 Lanzenhaeusern, Switzerland
<pruest@dplanet.ch> - Biochemistry - Creation and evolution
"..the work which God created to evolve it" (Genesis 2:3)