Evolution is a term that has been used, in the broad sense, to denote many different kinds of change, usually gradual change. Stars evolve, life evolved from nonliving molecules, one form of life evolves into another, societies evolve, ideas evolve. This broad-sense meaning, referring even to the evolution of London, is used in the book by evolutionary scientist A. C. Fabian. The term has been used in so many ways that scientists have imposed a narrow-sense meaning to prevent misunderstandings. A similar problem occurs with the concept of adaptation. In the narrow sense, evolution refers to genetic changes over time in populations of organisms. In this narrow sense, neither stars nor ideas evolve; the process of evolution did not exist until life-forms existed; and individual organisms can change but cannot evolve.

One fundamental distinction between evolution and other processes of change involves directionality, or teleology--that is, movement toward a goal. The original word evolvere in Latin refers to an unfolding of a predetermined set of events. However, most scientists use the word evolution, even in the broad sense, to refer to changes that have no predetermined direction or destination. Many natural processes are largely predetermined: For example, the development of an embryo from a fertilized egg is determined by genetic instructions, and the development of a star, from nebula to nova, follows the laws of physics. Even in these processes there is a random element: Two identical eggs can develop in different ways, depending on events and environmental conditions. Their overall predetermined directionality prevents these processes from being legitimately described as evolution. In contrast, the evolution of humans was not inevitable. Had different mutations occurred in ancestral populations, whether of microbes or the earliest vertebrates or of primates; or had environmental conditions, events, or opportunities been different, something other than Homo sapiens in the modern form would have evolved. Some evolutionary scientists such as Simon Conway Morris point out that natural selection would inevitably have produced something similar to human beings. This would have resulted from natural selection happening at each step, and not from change predetermined within ancestral DNA. Therefore humans evolved, but embryos and stars do not. . .

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