About 1.8 million years ago, a boy died. An abcessed tooth suggests an infection may have killed him, although the cause is not certain. His bones were fossilized, and they lay undetected until 1985, when they were discovered by paleoanthropologist Richard Leakey.
The Nariokotome boy's skeleton has been called the fossil find of the century. Because it was so complete, it revealed a great deal not only about the anatomy of his species, Homo erectus (sometimes called Homo ergaster), but also clues about their life history and even social structure.
He was only about 10 years old when he died, revealed by the fact that his molar teeth were still emerging, yet he was already about five feet tall and would have been over six feet at maturity. His legs were relatively long in proportion to his body compared to earlier hominids like Lucy. With his tall, slender build, he was well adapted to staying cool in hot, dry climates. His ribcage and shoulder girdle indicate that he could swing his arms when walking or running, as we do, something that earlier hominids were incapable of. Combined with his relatively slender waist, which gave him more flexibility, this suggests an adaptation to greater speed or endurance, or both.
His face, molar teeth, and chewing muscles are smaller than those of earlier hominids, suggesting a softer, high-quality diet, which he would have needed to nourish his relatively large brain. (With a volume of about 880 cubic centimeters, his cranium was larger than an australopithecine's, but smaller than a modern human's.) The brain is a very costly organ metabolically, and needs a reliable source of both calories and protein to sustain it.
The proportions of skull to pelvis indicates that his sisters would have had to give birth to relatively immature infants, to allow the baby's skull to fit through the pelvic opening. These immature infants, much more helpless than, say, a newborn chimp, would have needed an extended period of care, more like a modern human baby. This in turn suggests that his species must have been able to provide the necessary support for a mother and her child, whether in the form of monogamous pair bonding or some other social system.
With the appearance Homo erectus/ergaster in the fossil record we also see the first use of fire, the first appearance of more systematic toolmaking, and the first migration of hominids outside Africa. The Nariokotome boy and his kind represent the beginning of a new phase of human prehistory.