Recently, Rieffel and Sayles [50] evolved circular 2-D
shapes where each design was fabricated on a 3-D printer
before assigning fitness values. Interactive evolution was
undertaken wherein the fitness for each printed shape was
scored subjectively. Each individual’s genotype consisted of 20
linear instructions which directed the printer to perform discrete
movements and extrude the material. As a consequence
of performing embodied fitness evaluations the system as a
whole can exhibit epigenetic traits, where phenotypic characteristics
arise from the mechanics of assembly. One such
example was found when selecting shapes that most closely
resembled the letter “A.” In certain individuals, the cross of the
pattern was produced from the print head dragging a thread of
material as it moved between different print regions and was
not explicitly instructed to do so by the genotype.