Part 6, Chapter 28 Summary and Analysis

Our understanding of the origins of humanity continues to evolve. Humans share 98.4 percent of their DNA with chimpanzees. The two were very closely related until seven million years ago, when a new being emerged from the tropical forests of Africa onto the open savannah.

Creatures who walk on two legs, known as bipeds, present unique structural challenges. The pelvis must become load bearing, narrowing in the process. This makes childbirth painful and often fatal. Because of the narrow pelvis, infants are born small and helpless, necessitating male-female bonding. Much of the development of young human children takes place before birth in other complex animals.

Apparently, five million years ago the dominant hominid Australopithecines, walked upright. The most famous example of this species is the partial skeleton known as Lucy, discovered in Ethiopia in 1974. Lucy is 3.5 feet tall and while...