Someone asked the great anthropologist Margaret Mead, "What is the first sign you look for, to tell you of an ancient civilization?"
The interviewer had in mind a tool or article of clothing. Ms. Mead surprised him by answering, "A healed femur."
When someone breaks a femur, they can't survive to hunt, fish, or escape enemies unless they have help from someone else. A healed femur indicates that someone helped that person, rather than abandoning them and saving themselves.