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Can a computer or a robot be alive? Can an entity which only exists as a digital simulation be "alive"? If it looks like a duck, quacks like a duck, waddles like a duck, but it in fact takes the form of pixels on a supercomputer screen -- is it a duck? And if it's not a duck, then what on earth is it? What exactly does a thing have to do and be before we say it's "alive"?
It's surprisingly difficult to decide when something is "alive." There's never been a definition of "life," whether scientific, metaphysical, or theological, that has ever really worked. Life is not a clean either/or proposition. Life comes on a kind of scale, apparently, a kind of continuum -- maybe even, potentially, *several different kinds of continuum.*
One might take a pragmatic, laundry-list approach to defining life. To be "living," a thing must grow. Move. Reproduce. React to its environment. Take in energy, excrete waste. Nourish itself, die, and decay. Have a genetic code, perhaps, or be the result of a process of evolution. But there are grave problems with all of these concepts. All these things can be done today by machines or programs. And the concepts themselves are weak and subject to contradiction and paradox.
Are viruses "alive"? Viruses can thrive and reproduce, but not by themselves -- they have to use a victim cell in order to manufacture copies of themselves. Some dormant viruses can crystallize into a kind of organic slag that's dead for all practical purposes, and can stay that way indefinitely -- until the virus gets another chance at infection, and then the virus comes seething back.
How about a frozen human embryo? It can be just as dormant as a dormant virus, and certainly can't survive without a host, but it can become a living human being. Some people who were once frozen embryos may be reading this magazine right now! Is a frozen embryo "alive" -- or is it just the *potential* for life, a genetic life- program halted in mid-execution?
Bacteria are simple, as living things go. Most people however would agree that germs are "alive." But there are many other entities in our world today that act in lifelike fashion and are easily as complex as germs, and yet we don't call them "alive" -- except "metaphorically" (whatever *that* means).
How about a national government, for instance? A government can grow and adapt and evolve. It's certainly a very powerful entity that consumes resources and affects its environment and uses enormous amounts of information. When people say "Long Live France," what do they mean by that? Is the Soviet Union now "dead"?
Amoebas aren't "mortal" and don't age -- they just go right on splitting in half indefinitely. Does that mean that all amoebas are actually pieces of one super-amoeba that's three billion years old?
And where's the "life" in an ant-swarm? Most ants in a swarm never reproduce; they're sterile workers -- tools, peripherals, hardware. All the individual ants in a nest, even the queen, can die off one by one, but as long as new ants and new queens take their place, the swarm itself can go on "living" for years without a hitch or a stutter.
Questioning "life" in this way may seem so much nit-picking and verbal sophistry. After all, one may think, people can easily tell the difference between something living and dead just by having a good long look at it. And in point of fact, this seems to be the single strongest suit of "Artificial Life." It is very hard to look at a good Artificial Life program in action without perceiving it as, somehow, "alive."
Only living creatures perform the behavior known as "flocking." A gigantic wheeling flock of cranes or flamingos is one of the most impressive sights that the living world has to offer.
But the "logical form" of flocking can be abstracted from its "material manifestation" in a flocking group of actual living birds. "Flocking" can be turned into rules implemented on a computer. The rules look like this:
1. Stay with the flock -- try to move toward where it seems thickest.
2. Try to move at the same speed as the other local birds.
3. Don't bump into things, especially the ground or other birds.
In 1987, Craig Reynolds, who works for a computer-graphics company called Symbolics, implemented these rules for abstract graphic entities called "bird-oids" or "boids." After a bit of fine- tuning, the result was, and is, unca
They meander around in an unmistakeably lifelike, lively, organic fashion. There's nothing "mechanical" or "programmed- looking" about their actions. They bumble and swarm. The boids in the middle shimmy along contentedly, and the ones on the fringes tag along anxiously jockeying for position, and the whole squadron hangs together, and wheels and swoops and maneuvers, with amazing grace. (Actually they're neither "anxious" nor "contented," but when you see the boids behaving in this lifelike fashion, you can scarcely help but project lifelike motives and intentions onto them.)
You might say that the boids simulate flocking perfectly -- but according to the hard-dogma position of A-Life enthusiasts, it's not "simulation" at all. This is real "flocking" pure and simple -- this is exactly what birds actually do. Flocking is flocking -- it doesn't matter if it's done by a whooping crane or a little computer-sprite.
Clearly the birdoids themselves aren't "alive" -- but it can be argued, and is argued, that they're actually doing something that is a genuine piece of the life process. In the words of scientist Christopher Langton, perhaps the premier guru of A-Life: "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."
The great thing about studying flocking with boids, as opposed to say whooping cranes, is that the Artificial Life version can be experimented upon, in controlled and repeatable conditions. Instead of just *observing* flocking, a life-scientist can now *do* flocking. And not just flocks -- with a change in the parameters, you can study "schooling" and "herding" as well.
The great hope of Artificial Life studies is that Artificial Life will reveal previously unknown principles that directly govern life itself -- the principles that give life its mysterious complexity and power, its seeming ability to defy probability and entropy. Some of these principles, while still tentative, are hotly discussed in the field.
For instance: the principle of *bottom-up* initiative rather than *top-down* orders. Flocking demonstrates this principle well. Flamingos do not have blueprints. There is no squadron-leader flamingo barking orders to all the other flamingos. Each flamingo makes up its own mind. The extremely complex motion of a flock of flamingos arises naturally from the interactions of hundreds of independent birds. "Flocking" consists of many thousands of simple actions and simple decisions, all repeated again and again, each action and decision affecting the next in sequence, in an endless systematic feedback.
This involves a second A-Life principle: *local* control rather than *global* control. Each flamingo has only a vague notion of the behavior of the flock as a whole. A flamingo simply isn't smart enough to keep track of the entire "big picture," and in fact this isn't even necessary. It's only necessary to avoid bumping the guys right at your wingtips; you can safely ignore the rest.
Another principle: *simple* rules rather than *complex* ones. The complexity of flocking, while real, takes place entirely outside of the flamingo's brain. The individual flamingo has no mental conception of the vast impressive aerial ballet in which it happens to be taking part. The flamingo makes only simple decisions; it is never required to make complex decisions requiring a lot of memory or pla