In this applet one can simulate evolution of bugs in which you play the role of natural selection. This is an idea described in Richard Dawkins' book `The blind watch maker'. Each frame of the applet contains the picture of some critterlike object. It is grown by a fixed set of instructions together with some input parameters which may vary. As the parameters change the picture changes. So we can view the parameters as a genotype of the critter, while the picture represents the phenotype.
By pushing a zap-button, six arbitrary parameter sets are generated and the corresponding pictures drawn. The select-button leaves the critter concerned fixed, while small random variations in its parameters are applied to grow the critters in the other frames. By expressing a preference for big critters, or small ones, or colorful ones, or any preference one might have, you can indeed shape the critter according to this preference. However, it will usually turn out that new surprising life forms show up whose traits are far more striking than what one originally intended.
To have a good look at the critters you can mouse drag them within their frame, or enlarge the frame. Have fun! For more Richard Dawkins related information, see the beautiful site The world of Richard Dawkins.