Artaios, the First Father, had six children with his wife, Branwen, the First Mother. They grew up to be gods and guardians of the biosphere. The siblings loved each other very much. They were strong of build and sharp of mind. Whatever they attempted, they succeeded with ease, and faultlessly. When the young gods had grown to adulthood, Artaois and Branwen bade them each create something to add it to their creation, so that it would enrich the world and populate it. And thus, the gods created six very different types.
Time passed and the creations of the gods multiplied and spread without restraint across the biosphere. And so it came to pass that Artaios and Branwen bade their children bring order to their creation. Whoever would be the first to bring their population into accord with the biological order would be called “Lord of Creation” from thereon.
In Biosphere, the player siblings each control groups of different populations (dubbed “types” in game terms). In each round, a percentage of the types goes extinct, then players receive and spend evolutionary points to make their types either larger or smaller, and more versatile or more dedicated depending on what they think is appropriate for the landscape (which is scaled based on the number of players) and the current state of the game. Reproduction, movement, and lifespan can all be modified by players during the game. If a player meets the right conditions, they can play one development card from hand, gaining benefits from this. Players then move across the landscape, reproduce, and fill the different terrains based on their positions relative to other players.
How do the siblings prove their worth to Artaios and Branwen? By fulfilling assignments revealed at the start of play. One assignment is drawn from each of seven categories, and once a player completes an assignment, they mark it, with others still being able to mark it later. Whoever first fulfills five assignments wins the game.