Creatures

First game of the series, Creatures is a biological simulation where you start with six eggs of Norns, which you need to raise, give them knowledge about the world they live in, teach them how to speak, how to use toys, an elevator, how to eat etc.
They will eventually grow older, reproduce themselves and die.

The game uses its own genetics system, as well as biochemical and neurological calculations to determine the evolution of Norns and the way their DNA would develop in their descendants.