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The Evolution of High-Speed Throwing
Neil T. Roach, Harvard
Humans are the only species that can throw objects both incredibly fast and with great accuracy. This unique throwing ability may have been critical to the survival and success of our hominin ancestors, helping them to hunt and protect themselves. Our research asks: How are humans able to throw so well? When did this behavior evolve? Was throwing important in our evolutionary past?
We found that humans are able to throw projectiles at incredible speeds by storing and releasing energy in the tendons and ligaments crossing the shoulder. This energy is used to catapult the arm forward, creating the fastest motion the human body can produce, and resulting in very rapid throws. We show that this ability to store energy in the shoulder is made possible by three critical changes in our upper bodies that occurred during human evolution: 1. the expansion of the waist, 2. a lower positioning of the shoulders on the torso, and 3. the twisting of the humerus (bone in the upper arm). All of these key evolutionary changes first appear together nearly 2 million years ago in the species Homo erectus.
We propose that this ability to produce powerful throws was crucial to the intensification of hunting that we see in the archaeological record at this time. Success at hunting allowed our ancestors to become part-time carnivores, eating more calorie-rich meat and fat and dramatically improving the quality of their diet. This dietary change led to seismic shifts in our ancestors’ biology, allowing them to grow larger bodies, larger brains, and to have more children.
Armed with nothing but sharpened wooden spears, the ability to throw fast and accurately would have made our ancestors formidable hunters and provided critical distance between themselves and dangerous prey.
This image shows differences in the position of the shoulder between chimpanzees (left) and humans (right). These differences can be seen in both the muscular anatomy and in the bony anatomy of the scapula (shoulder blade). (Image credit: Brian Roach/Neil Roach)