Center for the Advanced Study of Hominid Paleobiology

Neil Thomas Roach

The Evolution of Throwing

We studied the mechanics and evolution of throwing in talented collegiate throwers including many members of the Harvard baseball team. (Image credit: Harvard Athletic Communications).

Summary

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?

Our team, led by Neil Roach, has 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)

Highlights

-       Humans are remarkable throwers, and the only species that can throw objects fast and accurately.

-       Chimpanzees, our closest relatives, throw very poorly, despite being incredibly strong and athletic.

-       We have shown that humans produce high-speed throws by storing elastic energy in the tendons, ligaments, and muscles crossing the shoulder.

-       When this energy is released, it powers the rapid acceleration of the arm and the projectile, including the fastest motion the human body produces.

-       Three changes to the anatomy of the torso, shoulder, and arm that occurred during human evolution make this elastic energy storage possible.

-       These morphological changes are first seen together 2 million years ago in Homo erectus.

-       Concurrent with these changes, archaeological evidence of more intensified hunting behavior suggests that throwing may have played a vital role in early hunting.

-       Hunting had profound effects on our biology. For example, by improving diet quality our ancestors were able to grow larger brains leading to cognitive changes such as the origins of language.

-       Today, most throwing athletes throw much more frequently than our hominin ancestors did and, accordingly, frequently suffer from overuse injuries.

Citation

Roach, N.T., Venkadesan, M., Rainbow, M.J., Lieberman, D.E. (in press) Elastic energy storage in the shoulder and the evolution of high-speed throwing in Homo. Nature. 498. 483-486.

Why throwing?

Humans are amazing throwers. We are unique among all animals in our ability to throw projectiles at high speeds and with incredible accuracy. Professional baseball pitchers and cricket bowlers are capable of throwing a ball more than 90 miles-per-hour, over and over again throughout the course of a game. Even 12-13 year old Little League pitchers routinely throw 60-70 mph!

Our ability to produce high-speed throws is even more impressive when compared to the throwing ability of our closest relatives, chimpanzees. Despite being incredibly strong and very athletic, an adult male chimp that has been trained to throw can only throw a ball approximately 20 mph.

Today, our unique throwing ability is used almost exclusively during sports. However, that was not always the case. Until only a few thousand years ago, most humans hunted and gathered their food from the natural environment around them. There are many accounts in historic times of human hunter-gatherers throwing projectiles to hunt and to defend themselves. We think that it is in these contexts that our remarkable throwing ability evolved.

Our study

This image shows one of our subjects wearing a brace that limits the rotation of the arm. You can also see the reflective markers used to collect the bodies’ movements. (Image credit: Neil Roach)

We started our study with two basic questions: How do humans throw so well? When and why did this throwing ability evolve? To answer these questions we conducted a series of experiments designed to uncover the mechanics of how humans produce powerful throws and how changes to our upper bodies that occurred during human evolution would affect those mechanics.

To study these questions, we brought collegiate baseball players into Dan Lieberman’s Skeletal Biology lab at Harvard and the Wyss Institute Motion Capture lab at Harvard Medical School. Here we collected body size measurements, attached reflective markers to each segment in their upper body, and recorded the movement of those markers in 3D using an infrared motion capture system as they threw baseballs. This camera system is similar to those used to make video games and animate movie characters (eg. Gollum in the Lord of the Rings).

Using those 3D movement data, we then constructed a computer model of the throwing motion and analyzed each throw using inverse dynamics analysis. This analysis uses simple physics to break down complex movements into the individual motions occurring at each joint and estimates the forces needed to create those motions.

In addition to recording and studying normal throwing, we also used therapeutic braces to limit our throwers’ movements. These braces allowed us to mimic our ancestral anatomy in modern throwers, giving us the opportunity to see how anatomical changes that occurred during our evolutionary past would have affected our ability to throw.

How do humans throw so well?

We found that humans are able to throw with such velocity by storing elastic energy in their shoulders. This is accomplished by positioning the arm in such a way that the arm’s mass resists motions generated at the torso and shoulder and rotates backwards away from the target. This “cocking” of the arm stretches the tendons, ligaments, and muscles crossing the shoulder and stores elastic energy (like a slingshot). When this energy is then released, it powers the very rapid rotation of the upper arm, which is the fastest motion the human body produces – up to 9,000 degrees-per-second in professional pitchers! This rapid rotation also causes the elbow to quickly straighten and the projectile to be released at very high speeds.

Former MLB pitcher Billy Wagner shows tremendous rotation of the arm during the “cocking” phase when elastic energy is stored. (Image credit: sportsofboston.com)

We further found that three key anatomical changes that occurred during human evolution made this novel energy storage mechanism possible: expansion of the waist, lowering of the shoulders, and low humeral torsion. The expansion of the waist allows the torso to rotate independently from the hips. This torso rotation generates large forces needed to stretch the elastic tendons and ligaments in the shoulder. The lowering of the shoulder changes the orientation of many shoulder muscles, including the pectoralis major (the large chest muscle), which is crucial to storing energy. Finally, we found that low humeral torsion (the twisting of the upper arm bone) allows us to store more energy and thus, throw faster.

What is elastic energy?

Elastic energy is potential mechanical energy that animals store in tendons, ligaments, and muscles. When these structures are stretched they elongate like an elastic band. When the forces pulling on these elements are then reduced, they return to their original shape, releasing the energy that was used to stretch them. This elastic energy can be used to power forceful movements (such as a frog’s jump) or to make movement more energetically efficient (such as the human Achilles tendon during running). Our study is the first to demonstrate the use of elastic energy in the human arm.

When and why did this throwing ability evolve?

A !Kung San man hunting with a thrown spear in the early 1960s. (Image credit: Neil Roach/Getty Images)

The three anatomical shifts in the upper body that we found affected throwing performance are first seen together nearly 2 million years ago in the species Homo erectus. At this same time, we see evidence of intensified hunting activity by our hominin ancestors (butchered fossil bones, simple stone tools). We propose that the ability to throw with speed and accuracy evolved as an adaptation that helped our ancestors become more successful hunters. Without any advanced weapons or technology such as bows or snares (which were not invented for more than 1.5 million years), our ancestors were likely hunting with little more than rocks and sharpened wooden spears. The ability to throw such simple weapons fast and accurately would have been a huge advantage, allowing hominins to hunt dangerous prey from a safe distance.

Hunting, and by extension throwing, had profound effects on our ancestors biology and way of life. The inclusion of high-protein meat and calorie-rich fat dramatically improved the quality of our ancestors’ diet. These additional calories allowed our hominin ancestors to grow large bodies, larger brains, and have more children. Each of these changes had very profound effects on our biology and are crucial to making humans who we are today. For example, a larger brain is thought to be critical to our cognitive abilities, including the development of language.

We think that hunting also probably changed the way our ancestors interacted with the world around them. For the first time, male and females likely divided their labor differently and shared food-getting tasks. Surpluses of meat from a large kill could be shared or eaten over a number of days, freeing time for other activities. As our ancestors became more reliant on hunting they would also have been free to move into new environments (such as deserts and mountainous areas) that previously would not have had enough fruits and vegetables to sustain them. This ability to move into new environments and thrive would have been crucial as our ancestors migrated out of Africa and spread throughout the world.

If we are evolved to throw, why do throwers get injured so frequently?

While throwing may have been a crucial part of our hunting behavior until very recently, today most throwing is done in the context of sports. Modern athletes use the same energy storage mechanism to now throw balls instead of spears. Yet, modern throwing athletes often suffer from injuries to their shoulders and elbows caused by the high forces our unique throwing ability enables. This is likely caused by the increased frequency with which modern athletes throw. For example, a professional baseball pitcher can easily throw more than 100 very fast pitches over a 2-3 hour period. This is considerably more than our hominin ancestors would have thrown when practicing and using this behavior to hunt. We think that despite being evolved to throw, the overuse of our ability to throw projectiles at high speeds is causing excessive wear and tear to our bodies and making injuries common.

Hall of fame pitcher Sandy Koufax, whose career was cut short at age 30 due to serious injuries. (Image credit: Herald de Paris)

Contact information

Neil Roach
Center for the Advanced Study of Hominid Paleobiology
The George Washington University
2110 G Street NW
Washington, DC 20052
Email: ntroach@email.gwu.edu

Madhusudhan Venkadesan
National Centre for Biological Sciences
GKVK Campus, Bellamy Road
Bangalore 560065, Karnataka, India
Email: mv@ncbs.res.in

Michael Rainbow
Department of Physical Medicine and Rehabilitation
Harvard Medical School
1575 Cambridge Street
Cambridge, MA 02138
Email: mikejrainbow@gmail.com

Daniel Lieberman
Department of Human Evolutionary Biology
Harvard University
11 Divinity Avenue
Cambridge, MA 02138
Email: danlieb@fas.harvard.edu

Funding Information

We are grateful to the National Science Foundation, American School for Prehistoric Research, Wellcome Trust/DBT India Alliance, and Harvard University without whose support this research would not have been possible.

Department of Anthropology
The George Washington University
2110 G Street NW, Washington, DC 20052