That is the field of molecular biology and genetics and biochemistry which has totally changed our perceptions of how life on Earth is actually organized. Much of the biology to which you may have been exposed until now has been a highly descriptive science. That is you may have had courses in high school where you had to memorize the names of different organisms, where you had to understand how evolutionary phylogenies were organized, where you had to learn the names of different organelles, and that biology was, for you, a field of memorization.