SimLife: The Genetic Playground was a relatively successful attempt by Maxis to produce an ecosystem simulator, allowing the player to design their own planetary ecosystem based on basic laws of physics which they could control in regards to a planetary climate, such as radiation, gravity, heat, light, and so forth.
The object of the game was to successfully produce a stable Earth-like planetary ecosystem and populate it with plants and animals either provided by the game or created by the players themselves, a task which required great patience and a meticulous nature, as the animals could be tweaked in dozens of ways using slider controls, and would easily perish if conditions for their survival weren't perfect.
Like most of Maxis' early Sim games, many fans simply had more fun destroying theirs and others' creations than building upon them endlessly, and SimLife catered to that crowd as well, giving players the ability to call down devastating disasters such as brush fires, floods, and meteor impacts that would drastically alter the world's topology, climate, and radiation levels, occasionally causing drastic genetic mutations in the offspring of the surviving animals. Additionally, the player was able to produce incredibly voracious, hardy animals with extremely high birth rates, which would quickly multiply beyond control, devouring the biomass of the planet (both animal and plant alike), and would then turn on their own as cannibals, leaving behind nothing but a barren rock of a world from what was once a verdent eden.
It is highly likely that SimLife, SimAnt, and SimEarth's development culminated in the design of Spore, as Spore contains elements of all three titles in its gameplay.