The previous page shows a set of steps evolved by the system. The design was defined to be symmetrical about the plane z=0 and was evolved from an initial population of entirely random shapes.
A portable set of steps was desired, suitable for use in a small library. The desired function of the steps was defined by five reusable 'evaluation modules'. These specified that a good set of steps should be a certain size, should have a low mass, be unfragmented (i.e., no part should be unconnected and 'float free' of the design), have three flat surfaces at certain heights and with certain areas, and should be capable of supporting a heavy object on the edges of each of its three flat surfaces without toppling over.
The design has a number of very intricate features that allow it to perform the desired function. The two side supports hold the steps rigidly and with great stability. These side supports are actually thicker (and thus more massive) at the front of the design, to counter-balance any excessive weight placed on the top step. The bottom of the first step is level with the bottom of the side supports, forming part of the base, and ensuring that weight placed on the first step can never cause the design to topple. If you rotate the design around to the back, you will also see that the top step is supported by a rear column which also reaches the ground and forms part of the base. This means that this design is capable of supporting huge amounts of mass on all three steps without any danger of toppling over.