no sooner did that idea occur to me than the picture Day and Night (Fig. 49)
popped into my mind. "Of course!" I thought, "It is a sort of pictorial crab
canon, with essentially two complementary voices carrying the same theme
both leftwards and rightwards, and harmonizing with each other!" Here
again was the notion of a single "conceptual skeleton" being instantiated in
two different media-in this case, music and art. So I let the Tortoise talk
about Bach, and Achilles talk about Escher, in parallel language; certainly
this slight departure from strict imitation retained the spirit of crab canotls.
At this point, I began realizing that something marvelous was happen-
ing: namely, the Dialogue was becoming self-referential, without my even
having intended it! What's more, it was an indirect self-reference, in that
the characters did not talk directly about the Dialogue they were in, but
rather about structures which were isomorphic to it (on a certain plane of
abstraction). To put it in the terms I have been using, my Dialogue now
shared a "conceptual skeleton" with Godel's G, and could therefore be
mapped onto G in somewhat the way that the Central Dogma was, to create
in this case a "Central Crabmap". This was most exciting to me, since out of
nowhere had come an esthetically pleasing unity of Godel, Escher, and
Bach.
ANAPHASE: The next step was quite startling. I had had Caroline
MacGillavry's monograph on Escher's tesselations for years, but one day, as
I flipped through it, my eye was riveted to Plate 23 (Fig. 42), for I saw it in a
way I had never seen it before: here was a genuine crab canon--crab-like in
both form and content! Escher himself had given the picture no title, and
since he had drawn similar tesselations using many other animal forms, it is
probable that this coincidence of form and content was just something
which I had noticed. But fortuitous or not, this untitled plate was a minia-
ture version of one main idea of my book: to unite form and content. So
with delight I christened it Crab Canon, substituted it for Day and Night, and
modified Achilles' and the Tortoise's remarks accordingly.
Yet this was not all. Having become infatuated with molecular biology,
one day I was perusing Watson's book in the bookstore, and in the index
saw the word "palindrome". When I looked it up, I found a magical thing:
crab-canonical structures in DNA. Soon the Crab's comments had been
suitably modified to include a short remark to the effect that he owed his
predilection for confusing retrograde and forward motion to his genes.
TELOPHASE: The last step came months later, when, as I was talking
about the picture of the crab-canonical section of DNA (Fig. 43), I saw that
the 'A', 'T', 'C' of Adenine, Thymine, Cytosine coincided-mirabile
dictu-with the 'A', 'T', 'C' of Achilles, Tortoise, Crab; moreover, just as
Adenine and Thymine are paired in DNA, so are Achilles and the Tortoise
paired in the Dialogue. I thought for a moment and, in another of those
level-crossings, saw that 'G', the letter paired with 'C' in DNA, could stand
for "Gene". Once again, Ijumped back to the Dialogue, did a little surgery
on the Crab's speech to reflect this new discovery, and now I had a mapping
between the DNA's structure, and the Dialogue's structure. In that sense,
the DNA could be said to be a genotype coding for a phenotype: the
Artificial Intelligence: Prospects 667