Each letter begins as empty space. Then, with each generation, a random mutation occurs: a randomly sized ellipse, rectangle, or triangle is added to the canvas.
Fitness is measured by taking the pixel-difference between the letterform and the "ideal letter" (pictured on the left). The "most fit" letterform survives. The remainder are culled.
The process begins again. The "most fit" parent (in 2nd column) letterform is cloned, but each of its children get a random mutation (columns 3-5). Some will be better, some worse than the parent. Again, fitness is measured and only the most fit go onto the next generation.
Over many generations, the letterform begins to resemble the "most fit letter".
The image is substituted into Darwin's Origin of Species.