[From Bruce Abbott (941228.1150 EST)]
Bill Powers (941227.1145 MST) --
This is probably the core of our semantic difficulties. In your program,
behavior determines a consequence, which happens in this case to be
death. This consequence, however, does not determine anything without
the help of another part of the model: the part that detects death and
takes it as the occasion for creating a new organism. The behavior of
the new organism (in the given environment) then determines whether
death will occur or not, and so forth. This active system is designed to
replace dead organisms with live ones, and clearly it (or its
programmer) prefers live ones.
"Semantic difficulties" is, I think, the problem, and not any lack of
understanding on my part as to how the program operates. Selection, as I said
in my post (941227.1000 EST), is done by the program (in the IF DEAD
statement) and not by the consequences. Yet it is important to keep in mind
what those consequences are, and how they enter into the decision function. I
referred to "death" as error; error can only come from comparison. Thus there
is an implicit reference of "survival." Given that reference, the
consequences determine what will happen on the next loop of the program. This
is all that I mean by "selection by consequences" in this example, and I still
hold that there is nothing semantically or logically incorrect about it.
However, in the interest of clarity in communication, I'll try to refrain from
using this phrase in the future (except, of course, to annoy Rick). (;->
Do I perceive correctly that you and Rick now agree with me that this
simulation DOES provide an analog of the reorganization process?
Regarding your interesting discussion of control in evolution:
What I am suggesting is that some time very early in the evolution of
life, the principle of blind variation and _purposive_ selection
evolved. Purposive selection entails detecting some variable, comparing
it with a reference level, and instituting a blind variation in a
particular relation to the difference: sooner for large differences, and
later for small ones. The mechanism for doing this is called "mutation,"
and is generally attributed to cosmic rays or thermal noise; I am
attributing it to a capacity that organisms have evolved. Organisms that
have remained the same for several hundred million years (like that tree
they've found in Australia, or coelocanths, or cockroaches) have not
become immune to cosmic rays; they have attained a state in which the
perceived values of fundamental variables match their reference states,
so that no mutation is called for.
A few years back I was thinking about the problem that evolution seems to
"run" at different speeds at different times. In the geological record, some
organisms appear to move virtually unchanged through the eons and then, bam!,
rapid evolution occurs. I came up with the hypothesis that unfavorable
changes in the environment might place an existing group of organisms under
considerable stress (poorly corrected disturbances), and that under the
resulting changes in the organism's internal environment, the physiological
mechanisms of reproduction might work less "faithfully," producing more
uncorrected transcription errors, crossovers, and so on. This would of course
increase the genetic variability of the offspring, thus providing a wider
range of options to test in the unfavorable environment. As seems to be the
case with most of my "original" ideas, someone else was already thinking along
the same lines and soon published it (I don't remember who, but the person is
now somewhat famous for having thought of it).
Your conception is very close to mine, except that in your version the
mechanism is a control system, whereas I had not thought of the mechanism
explicitly in those terms. It did occur to me that, if this "loosening" of
control over reproductive fidelity were in fact adaptive, then by definition
it would have been "selected" for and thus mechanisms would have evolved with
the correct relationship between stress and fidelity. However, in my
conception the relationship was a simple byproduct of a FAILURE of control
rather than the product of a control system. Thus there are no perceptual
signals being detected, no references, no error signals in any explicit sense,
other than those of the usual physiological control systems.
If such a mechanism exists (yours or mine), then the stability of creatures
like the clam and the cockroach would imply either that these creatures'
control systems are superbly adapted to cope with a wide variety of
environmental disturbances, or that they function in an environment that is
especially stable. Either way, the "variation" mechanism would not be brought
into play.
Regards,
Bruce