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[Social Life] "More time to grow -- Beginning 500,000–160,000 years ago -- By this time, early humans had evolved much larger brains. Infants were born with small brains, enabling the head to pass through the birth canal. The brain continued to grow throughout a long childhood. During adolescence, youngsters continued to prepare for the challenges of adulthood." "Two Roads to Adulthood -- Humans are unique among primates in having long, distinct periods of childhood and adolescence. These stages enable us to learn, play, socialize, and absorb important experiences prior to adulthood. During childhood, human children depend on adults for food and care. During adolescence, a growth spurt occurs, and male and female body features develop."