Related Clues:

• Steps in human evolution
• Sacks
• Choppers
• Earth rulers in a 1968 film
• Extras in the opening of '2001: A Space Odyssey'
• X and Y, maybe
• Chops down
• Monkeys' uncles?
• Bronx Zoo houseful
• Siamangs, e.g.
• Gorillas and chimps
• Real swingers?
• Quadrant separators
• 'Great' beasts
• Follows suit