All living things are a marvelous admixture of commonality and uniqueness. While all daisies express the features of “daisiness,” and all pigs display “pigness,” no two are exactly alike. The blueprint for both species' commonality and individuality is carried by the genes, which instruct and regulate the animals in how to develop, grow, and form throughout life. These genes are all sequences of DNA, an amazing molecule that has the ability to carry these instructions in all cells of the body and to self-replicate. Like the language of Morse code, which can carry the most complex messages using only two symbols, dots and dashes, DNA contains only four significatory components, and all genes are thus information-carrying sequences of these components.

Each animal, then, has a genetic program that directs it to develop into a pig, and into Porky, this pig. The genetic program for pigs or other living things undergoes changes through reproduction, when information from two individuals is combined to generate a new individual, and through artificial or natural selection, through which humans or nature determine which genetic programs will fit human or natural needs. When we breed dogs for certain traits, we choose to perpetuate certain genes and suppress others. When natural conditions favor one set of traits in an animal, say protective coloring versus coloring that flags the animal for predators, nature is choosing which genes will survive.