https://github.com/alkoclick/miniLifeSim to play with this and to read more!
This is a barebones evolution simulator that I made for fun. The little balls running around are organisms. The organisms survive on nutrition (the squares), of which there are several types. When they have more than a threshold (double their starting life, by default), they produce an offspring. The organisms return nutrients back to the environment in a different form when they have processed it. On the explorer to the left you can see the currently living organisms. Their name also displays what they ingest and what they egest.