The Evolution of Modern Man

Three and a half million years ago two of our ancestors walked across a field of damp volcanic ash, not realizing that they were achieving a kind of immortality. This occurred in East Africa in what is now Tanzania in a place called Laetoli. Although their brains were still small what made them hominids was bipedal locomotion-they walked upright, and thus, were no longer apes.

Why did our ancestors stand up? By 3.5 million years ago the Ice Age had caused a global shift in weather, which precipitated the disappearance of vast forested areas in Africa, eventually replaced by grasslands, the savannah. An upright posture enabled early man to see much greater distances in the new environment. It freed their hands for food gathering, hunting and caring for offspring. Walking is also much more efficient than moving on all fours, certainly over long distances. It may have rendered them more imposing to an enemy or predator. Finally, a vertical posture subjects one to much less heat radiation from the sun than a horizontal one.
Sometime between 5 and 7 million years ago our common ancestor branched off from the apes in an evolutionary divergence. The earliest known biped is Sahelanthropus tchadensis, whose spectacularly preserved cranium was found in Chad and was nicknamed Toumai by its discoverers. Its brain size was 350cc, the same as a chimpanzee (Normal human brains are around 1400cc). The face was flatter and more human like, very unlike a chimpanzee.
Next in line came Orrorin tugenensis, 6 million years ago, from the Tugen Hills of northwestern Kenya, also known as Millennium Man. The main evidence identifying it as hominid was the humanlike way its femur connected to the pelvis, evidence of its ability to walk.
Between 4.5 and 5.8 million years ago Ardipithecus kadabba and ramidus shared a desert region of present day Ethiopia. The toe bone and teeth are similar to humans. There is evidence that this hominid lived in a forest environment.
Australopithecus anamensis consists of nine fossils from Kenya dated 3.9-4.2 mya. They include a very human-like humerus, while the jaw and teeth are still ape-like.
The creature that left the famous footprints was most likely Austalopithecus afarensis, the southern ape of Afar, a region in Ethiopia, where a group of thirteen individuals, 9 adults and 3 children, were discovered at a site where they probably died together. From this “First Family” came the famous Lucy, so named by her discoverer, David Johanson, after the famous Beatles song. They date to between 3-3.9mya. 45% of Lucy’s skeleton was intact-she was tiny, only three and a half feet tall, with long arms, ape-like facial features and a brain size in the 400cc range, but hands quite modern in appearance, and of course, bipedal. Large molars suggest a coarse, gritty diet, typical of a grassland environment.
Around 3 million years ago a different hominid appeared-Australopithecus africanus,. The jaw and teeth are closer to human and the face less prognathous (a forward ape-like thrust), the body longer and taller than Lucy. The smaller teeth suggest more of a meat diet. The original find was made by Raymond Dart in 1925 at the Taung site in South Africa.