Imagine a small drop of water. Inside that drop is a world of little critters living their lives, looking for food, and making other little critters.
Well, now you can actually see this (and take part in altering the enviroment) www.swimbots.com offers a cool little game/simulator where you can watch some virtual organisms live, reproduce and evolve right on your desktop.
Do you feel bad for the hungry litle pink squiggly guy over there? Well, grab a speck of food and drop it into his tiny mouth.Do you feel that there isn't enough food for all the animals? You can adjust the settings making it a friendlier place (or tougher, depending on how you want this little world to proceed).
The first session I opened, which I didn't manipulate too much, lasted about 2 hours before everything had died. Everything. So, for the second try, I made food more plentiful and actually "hand" fed some of the animals. That was 4 days ago, and although the population is a little thinner, a balance has been reached where everything is going along smoothly. Some of the original variations have gone extinct, but that seems to be the point. Survival of the fittest.