Put another way, what exactly does the term :"requsite" in the term requisite variety mean?
"Requisite" is likely referring to Ashby's "ultrastability" [1].
As long as the system can maintain itself within it's
operating parameters it has no requirement for
additional states.
Any superfluous additional states may require overhead
for their maintainance so the spontaneous generation of
many superfluous states by a system may be detrimental
(cancerous).
If the system is already capable of ultrastability, the
spontaneous generation of additional states may seem to be
superfluous and wasteful, but if the right combination
of such additional states can yield a different field
of stability than the original system obeyed, and which is
also capable of ultrastability, then the new set of
states may be acceptable and become the minimal or
requisite set of a new "evolved" system. It may
even be that this new system will find the old set of
requisite states as less economical than the new set
and these old states will become vestigial and perhaps
disappear altogether at some later point at which point
we may say the metamorphosis of the old system into the
new system is complete, and perhaps irreversible ?
The need for additional states (variety) may be imposed
by environment. But the requisite number is probably
the most economically minimal number needed for
ultrastability in terms of those states.
For instance, the electrons states of various elements
is not a smooth progression and contains what Ashby
would probably call "step functions" governed by
Pauli's exclusion principle ?
[1] Design for a Brain, 1952
