Darwin's Dangerous Idea - Evolution and the Meaning of Life

172 PRIMING DARWIN'S PUMP The Laws of the Game of Life 173
in 1957. Francis Crick and James Watson had discovered DNA in 1953, but
how it worked was a mystery for many years. Von Neumann had imagined
in some detail a sort of floating robot that picked up pieces of flotsam and
jetsam that could be used to build a duplicate of itself that would then be
able to repeat the process. His description (posthumously published, 1966)
of how an automaton would read its own blueprint and then copy it into its
new creation anticipated in impressive detail many of the later discoveries
about the mechanisms of DNA expression and replication, but in order to
make his proof of die possibility of a self-reproducing automaton mathematically
rigorous and tractable, von Neumann had switched to simple, twodimensional
abstractions, now known as cellular automata. Conway's Lifeworld
cells are a particularly agreeable example of cellular automata.
Conway and his students wanted to confirm von Neumann's proof in
detail by actually constructing a two-dimensional world with a simple physics
in which such a self-replicating construction would be a stable, working
structure. Like von Neumann, they wanted their answer to be as general as
possible, and hence as independent as possible of actual (Earthly? local?)
physics and chemistry. They wanted something dead simple, easy to visualize
and easy to calculate, so they not only dropped from three dimensions
to two; they also "digitized" both space and time—all times and distances,
as we saw, are in whole numbers of "instants" and "cells." It was von
Neumann who had taken Alan Turing's abstract conception of a mechanical
computer (now called a "Turing machine") and engineered it into the
specification for a general-purpose stored-program serial-processing
computer (now called a "von Neumann machine"); in his brilliant
explorations of the spatial and structural requirements for such a computer,
he had realized—and proved—that a Universal Turing machine (a Turing
machine that can compute any computable function at all) could in principle
be "built" in a two-dimensional world. 6 Conway and his students also set out
to confirm this with their own exercise in two-dimensional engineering. 7
It was far from easy, but they showed how they could "build" a working
computer out of simpler Life forms. Glider streams can provide the inputoutput
"tape," for instance, and the tape-reader can be some huge assembly
of eaters, gliders, and other bits and pieces. What does this machine look
like? Poundstone calculates that the whole construction would be on the
order of 10 13 cells or pads.
6. See Dennett 1987b, ch. 9, for more on the theoretical implications of this trade-off in
space and time.
7. For a completely different perspective on two-dimensional physics and engineering,
see A. K. Dewdney's The Plantverse (1984 ), a vast improvement over Abbott's Flatland
(1884).
Displaying a 10 13 -pixel pattern would require a video screen about 3
million pixels across at least. Assume the pixels are 1 millimeter square
(which is very high resolution by the standards of home computers ). Then
the screen would have to be 3 kilometers (about two miles) across. It
would have an area about six times that of Monaco.
Perspective would shrink the pixels of a self-reproducing pattern to
invisibility. If you got far enough away from the screen so that the entire
pattern was comfortably in view, the pixels (and even the gliders, eaters
and guns) would be too tiny to make out. A self-reproducing pattern
would be a hazy glow, like a galaxy. [Poundstone 1985, pp. 227-28.]
In other words, by the time you have built up enough pieces into something
that can reproduce itself (in a two-dimensional world), it is roughly as
much larger than its smallest bits as an organism is larger than its atoms. You
probably can't do it with anything much less complicated, though this has not
been strictly proven. The hunch with which we began this chapter gets
dramatic support: it takes a lot of design work (the work done by Conway
and his students) to turn available bits and pieces into a self-replicating
thing; self-replicators don't just fall together in cosmic coincidences; they are
too large and expensive.
The Game of Life illustrates many important principles, and can be used to
construct many different arguments or thought experiments, but I will
content myself here with just two points that are particularly relevant to this
stage in our argument, before turning to my main point. (For further
reflections on Life and its implications, see Dennett 1991b.)
First, notice how the distinction between Order and Design gets blurred
here, just as it did for Hume. Conway designed the whole Life world—that is,
he set out to articulate an Order that would function in a certain way. But do
gliders, for instance, count as designed things, or as just natural objects—
like atoms or molecules? Surely the tape-reader Conway and his students cobbled
together out of gliders and the like is a designed object, but the simplest
glider would seem just to fall out of the basic physics of the Life world "automatically"—nobody
had to design or invent the glider; it just was discovered
to be implied by the physics of the Life world. But that, of course, is
actually true of everything in the Life world. Nothing happens in the Life
world that isn't strictly implied—logically deducible by straightforward
theorem-proving—by the physics and the initial configuration of cells. Some
of the things in the Life world are just more marvelous and unanticipated ( by
us, with our puny intellects) than others. There is a sense in which the Conway
self-reproducing pixel-galaxy is "just" one more Life macromolecule
with a very long and complicated periodicity in its behavior.
What if we set in motion a huge herd of these self-reproducers, and let
them compete for resources. And suppose they then evolved—that is, their
descendants were not exact duplicates of them. Would these descendants