The document discusses early evidence of human origins in Africa, including 3.6 million year old footprints that showed upright walking, and the 1974 discovery of the fossilized remains of "Lucy" dating to 3.2 million years ago which also exhibited upright walking. It notes the advantages of upright walking include freeing the hands while walking and increased energy efficiency, though it makes childbirth more difficult. Later hominid skulls and brains increased in size over time, with Australopithecus having a brain size of around 500 cubic cm compared to modern humans' 1400 cubic cm, showing the importance of brain development to human dominance.

1. Human Origins in Africa

2. About 3.6 million years ago, a couple of hominids of the species we call Australopithecine went strolling through some volcanic ash. Their footprints were found in 1978.

9. The top ones are female and male modern humans. The bottom one is a chimpanzee pelvis.

16. Man, gorilla, chimpanzee, orangutan, gibbon