The life that we see around us on this planet is the result of 3.5 billion years of natural selection and evolution. The earth formed approximately 4.5 billion years ago and bacterial life appeared within 1 billion years of the earth's formation. Ever since then, natural selection has been occurring, evolutionary changes have accumulated in populations, and new species have arisen. As humans, we are most interested in the evolutionary events that led to the appearance of our own species, Homo sapiens, some 500,000 years ago. This chapter outlines our evolutionary roots and reminds us that the evolution of species did not and does not occur in a vacuum, but under particular environmental and geographical conditions. Our evolutionary heritage includes the ancestors of insectivorous tree shrews, nocturnal prosimian primates with grasping fingers and toes and binocular vision, and apes with opposable thumbs and larger brains. Africa was the cradle of human life. Over 4 million years ago the first hominid, the first of the human line, appeared there. This was a bipedal creature called Australopithecus ramidus. Africa also gave rise to all three species of humans that have lived on earth. Homo habilis appeared approximately 2 million years ago, H. erectus approximately 1.5 million years ago, and H. sapiens approximately 0.5 million years ago. As each species replaced the preceding one, they spread over a larger area and developed more advanced technology and culture.