side of the coin: "What is the original?" This can best be explained by
referring to some examples:
(1) a program which, when interpreted by some interpreter
running on some computFr, prints itself out;
(2) a program which, when interpreted by some interpreter
running on some computer, prints itself out along with a
complete copy of the interpreter (which, after all, is also a
program);
(3) a program which, when interpreted by some interpreter
running on some computer, not only prints itself out along
with a complete copy of the interpreter, but also directs a
mechanical assembly process in which a second computer,
identical to the one on which the interpreter and program
are running, is put together.It is clear that in (1), the program is t.he self-rep. But in (3), is it the program
which is the self-rep, or the compound system of program plus interpreter,
or the union of program, interpreter, and processor?
Clearly, a self-rep can involve more than just printing itself out. In fact,
most of the rest of this Chapter is a discussion of self-reps in which data,
program, interpreter, and processor are all extremely intertwined, and in
which self-replication involves replicating all of them at once.TypogeneticsWe are now about to broach one of the most fascinating and profound
topics of the twentieth century: the study of "the molecular logic of the
living state", to borrow Albert Lehninger's richly evocative phrase. And
logic it is, too-but of a sort more complex and beautiful than any a human
mind ever imagined. We will come at it from a slightly novel angle: via an
artificial solitaire game which I call Typogenetics-short for "Typographical
Genetics". In Typogenetics I have tried to capture some ideas of molecular
genetics in a typographical system which, on first sight, resembles very
much the formal systems exemplified by the MIU-system. Of course, Ty-
pogenetics involves many simplifications, and therefore is useful primarily
for didactic purposes.
I should explain immediately that the field of molecular biology is a
field in which phenomena on several levels interact, and that Typogenetics
is only trying to illustrate phenomena from one or two levels. In particular,
purely chemical aspects have been completely avoided-they belong to a
level lower than is here dealt with; similarly, all aspects of classical genetics
(viz., nonmolecular genetics) have also been avoided-they belong to a level
higher than is here dealt with. I have intended in Typogenetics only to give
an intuition for those processes centered on the celebrated Central Dogma of
(^504) Self-Ref and Self-Rep