6. Out of Africa I, 1.8 million years ago Multi-Regional Theory Out of Africa II, ca. 150,000 b.c.e.

8. FOCUS ON: Homo ergaster WHEN: 1.9 to 1.4 million years ago WHERE: Africa BRAIN SIZE: around 850 cubic centimeters, around twice the brain size of a chimpanzee but about two-thirds that of a modern human DIET: probably mostly plants with some meat AVERAGE ADULT HEIGHT: females: 1.6 meters (5 feet, 3 inches) males: 1.8 meters (5 feet, 11 inches) AVERAGE ADULT WEIGHT: females: 56 kg (123 pounds) males: 68 kg (150 pounds) WHAT DID EARLY HOMINIDS EAT? By two million years ago, our ancient relatives had added meat to their diet. How do we know? Animal bones from around this time have been found with cut marks made by stone tools, a clear indication that early hominids cut up animal carcasses to eat the meat. Firm evidence for the domestication of fire is only occasional at best before 400,000 years ago, so early hominids such as Homo ergaster probably ate their meat raw. GROUP LIVING? Gorillas and many other modern primates live in groups of more than 20. Scientists are not sure exactly how large early hominid groups were, or how these groups were organized. But there is no question that these ancient primates, too, were social animals. An adult male and female Homo ergaster are shown as a pair in the diorama, but the scene is not intended to suggest a nuclear family. TALL AND SLENDER Homo ergaster's tall body, long legs and relatively short arms look remarkably similar to those of modern humans. What genetic changes caused this sudden transformation? Researchers can only guess—a huge variety of genes affect skeletal growth. But geneticists have learned that even small changes in DNA can have a big impact. For example, "regulatory" genes control the timing and expression of other genes. Altering one of them can have cascading effects throughout an individual's development. In this way, a change in a single gene might have reshaped Homo ergaster. Some modern human peoples, such as the Samburu of northern Kenya, tend to have especially long, slender limbs, a feature that allows the body to cool efficiently. A similar trait may have helped Homo ergaster survive in the hot, dry climate of eastern Africa.

10. FOCUS ON: Homo erectus WHEN: 1.8 million to 40,000 years ago WHERE: East and Southeast Asia BRAIN SIZE: around 850-1,250 cubic centimeters, compared to the average of 1,400 for modern humans DIET: probably plants with some meat AVERAGE ADULT HEIGHT: females: 1.5 meters (4 feet, 11 inches) males: 1.7 meters (5 feet, 7 inches) AVERAGE ADULT WEIGHT: females: 52 kg (115 pounds) males: 58 kg (128 pounds) ANCIENT HYENA DENS Hyenas typically bring parts of their prey back to their dens, where they eat many of the bones along with the flesh. This behavior has made prehistoric hyena dens an important source of hominid remains. Fossilized fragments of up to 40 members of the species Homo erectus have been found in what appears to have been an ancient hyena den in eastern China. Scientists once held two competing views about the relationship between modern humans and Homo erectus. Some maintained our species, Homo sapiens, evolved from populations of Homo erectus in many regions of the world between one and two million years ago. Others argued we evolved from an African ancestor less than 200,000 years ago, then expanded out of Africa, replacing Homo erectus and other species. Recently, studies of DNA from living humans have helped resolve this debate. Researchers estimate that the common ancestral population of all humans alive today lived roughly 150,000 years ago, a date that favors the "out of Africa" model.

24. FOCUS ON: Homo neanderthalensis WHEN: 200,000 to 30,000 years ago WHERE: Europe and western Asia BRAIN SIZE: up to about 1,700 cubic centimeters, at least as large as a modern human brain DIET: mainly meat, with some plants AVERAGE ADULT HEIGHT: females: 1.6 meters (5 feet, 3 inches) males: 1.7 meters (5 feet, 7 inches) AVERAGE ADULT WEIGHT: females: 50 kg (110 pounds) males: 64 kg (140 pounds) CHANGING VIEWS Our understanding of the Neanderthals has shifted over time. A 1919 image depicts a primitive brute; one from 1983 shows a mother engaged in animated conversation, with her hair coiffed and her skirt neatly sewn. Today, scientists think Neanderthals lived in complex social groups, controlled fire and were fairly proficient hunters. Yet they did not create art or possess language as we know it. They did bury their dead, but probably not with an elaborate ritual as modern humans do.

25. NEANDERTHALS: long, low braincase and double-arched browridge flaring, funnel-shaped chest flaring pelvis robust fingers and toes MODERN HUMANS: tall, rounded braincase and small, divided browridge cylindrical, barrel-shaped chest narrow pelvis slender fingers and toes SKELETON STAFF

26. Homo sapiens WHEN: around 150,000 years ago to present WHERE: around the world BRAIN SIZE: around 1,400 cubic centimeters DIET: plants, meat and other animal products and processed foods AVERAGE ADULT HEIGHT: females: 1.6 meters (5 feet, 3 inches) males: 1.7 meters (5 feet, 7 inches) AVERAGE ADULT WEIGHT: females: 54 kg (119 pounds) males: 65 kg (143 pounds)