A new creature can be created by randomly mutating an existing creature. This can be done by modifying an existing node in some way or by adding a completely new node to the creature. The process continues until enough creatures with sufficiently large fitness values are created. Fitness of a creature is measured differently for each type of movement. Swimming fitness is based on speed.
Straight swimming is rewarded more than swimming in circles.
Walking is also based on speed. Jumping is based on measuring the maximum height above ground of the lowest part of the creature. Several different trails are used for following light sources, and again, speed is the main criteria used for the fitness calculations. It was found that the evolved creatures tended to become homogeneous within a particular experiment but that different experiments often produced completely different sets of creatures for the same task. Because of this, many separate evolutions were performed for 50-100 generations.