|
At the workshop Langton
began with his quest for a definition of life. Existing ones seemed inadequate. As more research was started over the years following the first conference, physicist Doyne Farmer proposed a list of traits that defined life. Life, he said, has:
- Patterns in space and time
- Self-reproduction
- Information storage of its self-representation (genes)
- Metabolism, to keep the pattern persisting
- Functional interactions -- it does stuff
- Interdependence of parts, or the ability to die
- Stability under perturbations
- Ability to evolve.
The list provokes. For although we do not consider computer viruses
alive, computer viruses satisfy most of the qualifications above. They
are a pattern that reproduce; they include a copy of their own
representation; they capture computer metabolistic (CPU) cycles; they
can die; and they can evolve. We could say that computer viruses are the
first examples of emergent artificial life.
On the other hand, we all know of a few things whose aliveness we don't
doubt yet are exceptions to this list. A mule can not self-reproduce,
and a herpes virus has no metabolism. Langton's success in creating a
self-reproducing entity made him skeptical of arriving at a consensus:
"Every time we succeed in synthetically satisfying the definition of
life, the definition is lengthened or changed. For instance if we take
Gerald Joyce's definition of life -- a self-sustaining chemical system
capable of undergoing Darwinian evolution -- I believe that by the year
2000 one lab somewhere in the world will make a system satisfying this
definition. But then biologists will merely redefine life."
Langton had better luck defining artificial life. Artificial life, or
"a-life" in short hand, is, he said, "the attempt to abstract the logic
of life in different material forms." His thesis was that life is a
process -- a behavior that is not bound to a specific material
manifestation. What counts about life is not the stuff it is made of,
but what it does. Life is a verb not a noun. Farmer's list of
qualifications for life represent actions and behaviors. It is not hard
for computer scientists to think of the list of life's qualities as
varieties of processing. Steen Rasmussen, a colleague of Langton who was
also interested in artificial life, once dropped a pencil onto the desk
and sighed, "In the West we think a pencil is more real than its
motion."
If the pencil's motion is the essence -- the real part -- then "artificial" is
a deceptive word. At the first Artificial Life Conference, when Craig
Reynolds showed how he was able to use three simple rules to get dozens
of computer-animated birds to flock in the computer autonomously,
everyone could see that the flocking was real. Here were artificial
birds really flocking. Langton summarized the lesson: "The most
important thing to remember about a-life is that the part that is
artificial is not the life, but the materials. Real things happen. We
observe real phenomena. It is real life in an artificial medium."
Biology -- the study of life's general principles -- is undergoing an
upheaval. Langton says biology faces "the fundamental obstacle that it
is impossible to derive general principles from single examples." Since
we have only a single collective example of life on Earth, it is
pointless to try to distinguish its essential and universal properties
from those incidental properties due to life's common descent on the
planet. For instance, how much of what we think life is, is due to its
being based on carbon chains? We can't know without at least a second
example of life not based on carbon chains. To derive general principles
and theories of life -- that is, to identify properties that would be
shared by any vivisystem or any life -- Langton argues that "we need an
ensemble of instances to generalize over. Since it is quite unlikely
that alien life-forms will present themselves to us for study in the
near future, our only option is to try to create alternative life-forms
ourselves." This is Langton's mission -- to create an alternative life, or
maybe even several alternative "lifes," as a basis for a true biology, a
true logic of Bios. Since these other lifes are artifacts of humans
rather than nature, we call them artificial life; but they are as real
as we are.
The nature of this ambitious challenge initially sets the science of
artificial life apart from the science of biology. Biology seeks to
understand the living by taking it apart and reducing it to it pieces.
Artificial life, on the other hand, has nothing to dissect, so it can
only make progress by putting the living together and assembling it from
pieces. Rather than analyze life, synthesize it. For this reason,
Langton says, "Artificial life amounts to the practice of synthetic
biology."
continue...
|