If you are looking for a game where you simulate or interact with alien life, there are several popular and highly-rated titles (though most are paid, not "free download" in a legal sense):
A great place for free, experimental indie simulation games. alien-life-simulator-pc-game-free-download
A relaxing ecosystem simulator where you can breed and evolve various life forms. If you are looking for a game where
Focuses on breeding and evolving your own animal tribe to survive in different biomes. 2. You're looking for a Research Paper or Article alien-life-simulator-pc-game-free-download