This is Conway's game of life. This grid of cells evolves over time. At the end of each period, each live cell with fewer than 2 neighbors or more than 2 disappears. And a live cell appears if it has exactly 3 live neighbors. In this implementation you can click on the grid to toggle cells, launch the model and see how your pattern evolves. See also: Jan Willem Tulp's version as a d3 tutorial. See also the wikipedia page for examples of patterns to try out.