Evolution is one of the most fundamental of biological processes. Physical anthropology-concerned with all aspects of how humans came to be and how we adapt physiologically to the external environment. Charles darwin was the first person to explain the basic mechanics of the evolutionary process. Natural selection-the most critical mechanism of evolutionary change, refers to genetic frequencies of certain traits in populations due to differential reproductive success between individuals. Darwin and wallace to independently develop the theory of evolution by natural selection. Fixity of species-the notion that species, once created, can never change; an idea diametrically opposed to theories of biological evolution. Aristotle->earth circled by the sun, mood, and stars was the centre of the universe. John ray->developed the concept of species, first person to recognize that groups of plants and animals could be distinguished from other groups by their ability to mate with one another and produce offspring, genus-shared similarities with other species.