The Creature Creator, the first piece of Electronic Arts' highly anticipated evolution game Spore, launched Tuesday. Created by Will Wright, who's known for the video games SimCity and The Sims, Spore begins with a player controlling a single-celled organism and progresses through various evolutionary stages until the player controls an entire space-faring race. The Creature Creator part of the game consists of a modeling interface that lets players build their own organisms from a set of highly customizable and flexible parts.

When Wright first began talking about Spore in 2005, he expressed a vision of extreme player control. Rather than having game designers build thousands of 3-D models of creatures in advance and program their behavior, he had the staff develop algorithms to animate the creatures that players built, using a technique called procedural generation. While using the Creature Creator, each choice that a player makes to design the look of her organism affects how it moves or interacts with others. The game is entirely populated with creatures created by players, but it's not a multiplayer game. Secondary creatures are controlled by artificially intelligent software, not by other players.

The Creature Creator's free trial edition is available today. A full version is available for $9.99 on the PC, with a Mac version to follow. The full version of Spore will launch in North America on September 7.

On the eve of the Creature Creator's launch, Technology Review's assistant editor, Erica Naone, talked with Spore's executive producer, Lucy Bradshaw, about the effects of procedural generation on Spore's game play.

Technology Review: Procedural generation was commonly used in games in the earlier days of computers, when they didn't have the memory to store lots of details about creatures and terrain. Designers relied on processing power to build up game worlds from a small set of instructions when they had no other choice, but that technique fell out of favor when computers began to store large quantities of data easily. What made you take another look at procedural generation?

Lucy Bradshaw: Will [Wright] wanted to use procedural generation because he wanted to put as much creativity into the hands of the player as we possibly could. In most games, [developers] create a set of predetermined skeletons and predetermined textures. What we wanted was for players to be able to construct anything they could imagine. Doing the content procedurally allowed us to do that, and to create a game dynamic that gives meaning to each of the players' creations by giving them game purpose.

TR: Can you offer an example of how procedural generation gives meaning to the design choices that a player makes when building a creature?

LB: The creatures' abilities come from the parts that players choose to put on them. Socializing parts, for example, give you the ability to charm other creatures, to dance, to sing, or to pose. With the Creature Creator, you can put these things on. For instance, a charm part might be a little flower, or some sort of antenna might give you the charm ability. There's AI in the game, and creatures will behave based on the parts that you've added to them. So, if I'm going to decide I want to socialize with a number of other species, I'm probably going to opt to put on more socializing parts and create my possibilities there. If I want to attack and win by brute force, then I'm probably going to invest more in the combat parts. There are also movement parts that give creatures the ability to sneak and jump and glide. All of these things together create the kind of strategies that you get to play out once you get the game.