In biology, evolution is the change in the characteristics of a species over several generations and relies on the process of natural selection. In a population which affects the physical characteristics (phenotype) of an organism. Evolution is the biological change of a species over a span of time. The process of evolution keeps a species alive and thriving and allows organisms to successfully pass down their genes. Understanding evolution is important. Understanding evolution helps us solve biological problems that impact our lives. To control hereditary diseases in people, researchers study the evolutionary histories of the disease-causing genes. In these ways, a knowledge of evolution can improve the quality of human life. Biological evolution is the change in inherited traits over successive generations in populations of organisms. The environment acts to promote evolutionary change through changes in development, but little is known about the underlying mechanisms.