<i>
Harnad, S. (1997) "Lively Flights of Fancy." Book review of
M. Boden (ed.) "The Philosophy of Artificial Life."
Blackwell. Times Higher Education Supplement. January 31, 1997
</i>
<p>
<h3>
<center>
LIVELY FLIGHTS OF FANCY
</h3>
<p>
Stevan Harnad
<br>
Department of Psychology
<br>
University of Southampton
<br>
Highfield, Southampton
<br>
SO17 1BJ UNITED KINGDOM
<br>
harnad@cogsci.soton.ac.uk
</center>
<p>
Suppose Boeing 747s grew on trees. They would first sprout as embryonic
planes, the size of an acorn. Then they would grow until they reached
full size, when they would plop off the trees, ready to fly. Suppose
also that we knew how to feed and care for them, how to make minor
repairs, and of course how to fly them. But let us suppose that all of
this transpired at a very early stage in our scientific history, when
we did not yet understand the physics or the engineering of flight: Hence
the phenomenon was a complete mystery to us. (To keep things simple, let
us suppose that no other entity on earth could fly, only 747s.) And for
the last ingredient in this fantasy world, suppose that computers
likewise grew on trees, and we knew how to use and fix them too.
<p>
Being the inquiring species we are, we would not settle very long for
leaving flight a mystery. We would try to discover its design
principles. In doing so, we would be doing a kind of
reverse-engineering: In ordinary forward-engineering, known physical
and engineering principles are applied so as to build things that are
useful to us (bridges, carriages, catapults, ovens) -- much the way
that 747s were built in our real world. But in this fantasy world, the
747s are built by Mother Nature, so our task is instead to discover how
they work: how they are able to perform the remarkable feat of flying.
<p>
Some of us would no doubt make a cult of flight, believing that it was
a God-given gift. Others would say that flight was an emergent
phenomenon, not explicable in terrestrial terms. Still others would set
to work trying to explain flight in the same way that everything else
(bridges, carriages, catapults, and ovens) was explained. And
philosophers would become involved too, trying to define flight, and to
argue that it can be subsumed under ordinary earthly principles (or
not, depending on the philosopher's school of thought).
<p>
Now those who aspired to reverse-engineer flight might go about it in
two ways: They could (based on the limited knowledge that they already
had about how to fly, fuel, and do minor repairs on the planes)
attempt to build one from scratch. Let us suppose that this research
programme was going extremely slowly: they had not yet even found a way
to build something that could taxi along on the ground, let alone
get off it. Let us call this bottom-up approach to understanding flight
"artificial flight" (a-flight), because of course the planes that grew
on trees would be cases of natural flight.
<p>
Now recall that there was another unlikely entity of arboreal
provenance in this fantasy: the computer. Suppose that the second kind
of a-flight researcher tried to come to an understanding of the
principles of flight, not by trying to build a plane, but by trying to
simulate one computationally. As both of these approaches are examples
of a-flight, let us call the first "synthetic flight" and the second
"virtual flight." These two approaches to a-flight could be seen as
competing with one another to be the first to successfully
reverse-engineer flight. S-flighters would be laboriously trying to
build artificial planes based on observing and tinkering with natural
planes, whereas v-flighters would try to do it by tinkering with
computational simulations of both the plane and its earthly and aerial
environment: a virtual plane in a virtual world.
<p>
Now let us suppose that the v-flighters beat the s-flighters to it:
They manage to get their virtual 747 aloft while the s-flighters are
still working on getting theirs to back onto a runway. And suppose
the v-flight community gets very excited about what they have done:
"It flies! Its aloft!" The press is called in, along with the general
public. A curtain is parted to reveal a huge computer screen;
portentous music is played as the image of the 747 appears, its jet
motors getting louder and louder as it picks up speed on the runway,
until it becomes airborne and climbs to 40,000 feet where it proceeds
to do aerial tricks to the delight of the children before descending in
graceful circles to make a # stately, 3-point landing to a roar of
applause -- until a child cries out: "But that was just a cartoon
plane!" -- at which the audience gasps and begins to murmur "He's
right! There's no plane there! Its all just a hoax!"
<p>
Who would in fact be right? If the v-flighters claimed that their
plane really flew, then of course we would all agree that that was not
true: Flying only happens in a real sky. It's obvious that the
computer is not flying; the images merely look as if they were flying.
But what if the v-flighters said: "Fine; if you don't believe our
simulation has really captured the principles of flight, then watch!"
And they set about building a 747 by applying the principles that had
successfully generated virtual flight, and the first synthetic plane
they build according to those principles indeed manages to take to the
air, just as the virtual plane had done.
<p>
Would there be a volume on "The Philosophy of Artificial Flight" in order
to sort these things out? I think not, and the reason is quite
simple: Flight is observable, so we are perfectly capable of
distinguishing veridical flight from virtual flight. Life, in contrast,
is not observable. (You can observe living things, but not the property
of being alive.) So we are free to fancy that virtual creatures are
really alive.
<p>
Chris Langton's and Thomas Ray's chapters give inspiring and
impassioned accounts of progress in v-life, a field to which they are
active contributors. They describe their remarkable simulations of
little virtual creatures that feed, mate, compete, mutate and reproduce
for generation after generation. But Langton and Ray insist that it
cannot be ruled out that these computational creatures are really
alive.
<p>
Now it is conceivable that the real scenario for life will be like the
fantasy scenario for flight, in that v-life manages to discover the
vital principles more quickly than s-life does. Will that also serve to
quicken its virtual creatures? Philosopher Elliot Sober's Chapter gives
the same negative answer that is implicit in my little allegory about
flight. And philosopher Maggie Boden, a seasoned exegete of artificial
intelligence, does an admirable job of integrating the diverse views of
her contributors. But otherwise I must say that one learns considerably
less from the chapters by philosophers than from those by the
nonphilosophers: The philosophers tell us about Aristotle's views on
life, which are interesting although their relevance is unclear; even
less edifying are the views of Spencer and Dewey on life. Some of the
contemporary philosophers venture their own views on life, but one does
feel that these are fussy and ad hoc and very much following rather
than leading the thought on the subject. And the three chapters in
which nonphilosophers philosophise are both speculative and vague, one
invoking Heidegger, one Ernst Nagel, and the third passing the buck to
quantum mechanics.
<p>
There is also a chapter on something even more immaterial than virtual
life: possible life (p-life, of which real life is merely a subset) and
the very general constraints on it that are suggested by the
theoretical work of Stuart Kauffman on complexity, order and evolution.
A refreshing breath of real life is felt in the short and only chapter
on what we might call "n-life" in this context: Biologist John Maynard
Smith reminds us that studying natural selection and real organisms may
still reveal more than a-life, whether synthetic or virtual. Then
biologist David McFarland turns this admonition on its head, suggesting
that real organisms may be better understood as cost-based robots.
<p>
All in all, the topic is fascinating and the volume thought-provoking.
It leaves one eager to hear who will ultimately win in this game of
reverse-engineering life: the computationalists, the roboticists or the
naturalists.
<p>