Thoeries of Evolution Evolution is the process by which living organisms originated on earth and have changed their forms to adapt to the changing environment. The earliest known fossil organisms are the single-celled forms resembling modern bacteria; they date from about 3.4 billion years ago. Evolution has resulted in successive radiations of new types of organisms, many of which have become extinct, but some of which have developed into the present fauna and flora of the world (Wilson 17). Evolution has been studied for nearly two centuries. One of the earliest evolutionists was Jean Baptiste de Lamarck, who argued that the patterns of r