With the knowledge of how to express genetic information comes the ability to alter that expression for useful purposes. In one sense, humans have done this since the agricultural revolution. For example, early North Americans learned how to breed varieties of the grass teosinte so that the offspring would produce seeds that were less hard and simultaneously more plentiful. The result was maize. More selective breeding for yield and disease resistance has led to hybrid corn varieties today. Similarly, humans has bred animals for desirable properties, such as horses for speed or power, or dogs for gentle temperament, strength, and so on. DNA‐based genetics is a continuation of that same sort of breeding with two differences: first, the DNA is manipulated biochemically rather than in a genetic mating, and second, DNA can be exchanged between different species (which happens only rarely in nature, although it does occur)