Possible Clues:

• Some of our ancestors, needing exercise, agreed to box
• Extinct human ancestors
• Our ancestors, hypothetically
• Old relatives occasionally upset inside? So be it
• Knuckle-draggers
• The hypothetical humanzees, e.g
• Ancestors revealing the last word in exercise? Other way round
• Tarzan wannabes
• Tarzan's ilk
• Brawny fellers