In spite of its vast importance to all fields of biology, evolution is often misunderstood and misinterpreted. In our society, the term evolution frequently refers to any type of change. However, evolution, in the biological sense, refers only to a specific type of change: genetic change taking place in a group of organisms. Two aspects of this definition should be emphasized. First, biological evolution includes genetic change only. Many nongenetic changes take place in living organisms, such as the development of a complex intelligent person from a single-celled zygote. Although remarkable, this change is not evolution because it does not include changes in genes. Second, biological evolution takes place in groups of organisms. An individual organism does not evolve; what evolves is the gene pool common to a group of organisms.