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The Making of Bob's Backgammon

Bob’s Backgammon provides a set of several computerized opponents, or agents, which can play backgammon against a human or against another agent. The skill of Bob’s Backgammon's agents is not a result of probability theory, expert systems, recursive look-ahead algorithms, or even programming genius. (Not entirely, anyway.) The strategies used by the agents are their own invention--or would it be more accurate to say they were born knowing how to play?

Instead of analyzing the game of backgammon and attempting to program in winning strategies, the Silicon Highlands design team only programmed in the rules of backgammon. Given any position and roll of the dice, the program can generate a list of all legal moves (and only legal moves). The agent then chooses which move to make.

But isn't this just begging the question? Surely the agent is just another program, or part of the program? Yes, but the intelligence of the agent wasn't "programmed in" by a programmer--the intelligence of each agent spontaneously grew out of an environment which allowed evolution to take place, leading to some degree of mastery over the laws of nature. The designers provided only the environment and a representation of the laws of nature--in this case, the rules of backgammon--but not the mastery.

Dozens of agents were created using a template, or genetic structure, created by the design team, but with the actual content of the genes based entirely on chance. (Agent is our acronym for Artificial GENetic Template.) The structure was designed to give some sort of value to any backgammon position, and to "look at" many features of the board which might be useful in coming up with a value. As might be expected, these first agents did not play very good backgammon--they were as likely, for instance, to reward a position containing a blot which the opponent could capture with a very high score as they were to penalize it with a very low score.

But then, a very interesting event occurred. The agents played a tournament against each other. Although none of them were any good, some were worse than others. The very worst were weeded out. To replace them, new agents were "born", using genetic material from two parents chosen from the surviving agents, plus some random mutations. Another tournament was played, and again the worst agents were weeded out and replaced. No evaluation of the agents' play was made by human backgammon experts or programmers to decide which agents would survive; only the results of the tournaments between agents determined which lived and which died.

After a few generations of agents had come and gone, many of the new agents were clearly better than any of the original agents had been. The process was allowed to continue--day and night for several months--on the fastest computers available at the time. In each generation dozens of agents would play as many as 100 games each, until many millions of games and thousands of generations had passed--more generations, in fact, than separate us from the time of the Neanderthals. The latest agents can easily beat those of earlier generations, and the best are beginning to beat the best human players at Silicon Highlands with depressing regularity.

Interestingly enough, they still seem to be improving.

The genetic algorithms used in Bob’s Backgammon are a branch of a field of study called Artificial Life. Despite the pretentious name, genetic algorithms and other branches of Artificial Life are among the hottest research areas today and may greatly alter the way we interact with computers in coming decades.

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