The ability to throw objects fast and accurately helped to turn humans from a second-rate primate into one of the most successful species on the planet, a study suggests.
Throwing enabled the ancestors of modern humans to defend themselves against dangerous predators, hunt big game, expand their diet, boost brain power and colonise almost every corner of the globe, scientists said.
The skills that today enable top-class bowlers to deliver cricket balls at up to 100 mph are the result of key evolutionary adaptations to the torso, shoulders and arms which began nearly 2 million years ago, the researchers said.
“We think that throwing was probably most important early on in terms of hunting behaviour, enabling our ancestors to effectively and safely kill big game,” said Neil Roach of George Washington University in Washington DC.
“Eating more calorie-rich meat and fat would have allowed our ancestors to grow larger brains and bodies and expand into new regions of the world—all of which helped make us who we are today,” said Dr Roach, the lead author of the study published in the journal Nature.
The researchers tracked the upper-body movements of American college baseball pitchers using 3-D cameras and computer animations. This revealed how the human shoulder acts much like a slingshot during a throw by storing and then suddenly released large amounts of energy.
They found that compared to a chimpanzee, which can only throw objects at less than a third of the speed of a 12-year-old child, the human anatomy is finely tuned for the act of throwing.
Dr Roach and his colleagues found that three crucial adaptations – a wide waist, a lower position of the shoulders on the torso and the ability to twist the upper arm bone – all occurred as early as nearly 2 million years ago, during the time of Homo erectus, our hominin ancestor.
These three changes to the human anatomy enabled our early relatives to throw projectiles, such as rocks or wooden spears, 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,” Dr Roach said.
“When humans throw, we first rotate our arms backwards away from the target. It is during this ‘arm-cocking’ phase that humans stretch the tendons and ligaments crossing their shoulder and store elastic energy,” he said.
“When this energy is released, it accelerates the arm forward, generating the fastest motion the human body produces, resulting in a very fast throw,” he added.
The scientists believe that these evolutionary changes, which occurred long after the human and chimpanzee lineage diverged from the last common ancestor about 7.5 million years ago, were crucial to the subsequent development of humans into a large-brained creature with language and advanced tool-making skills.
“Humans are remarkable throwers, and the only species that can throw objects fast and accurately. Chimpanzees, our closest living relatives, throw very poorly, despite being incredible strong and athletic,” Dr Roach said.
“Adult male chimps for instance can only throw objects at about 20 mph, one third of the speed of a 12-year-old little league pitcher,” he said.
Homo erectus most likely used his new throwing skills to hunt big game and defend valuable carcasses against other predators. This expansion of diet enabled humans to build bigger brains, develop language and expand their geographic ranges.
“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,” Dr Roach said.
“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 labour differently and shared food-getting tasks,” he said.
“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 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,” Dr Roach added.
However, our innate throwing prowess is not to be abused. Premier league cricketers and baseball players throw far more frequently than our ancestor would ever have done during hunting and practising.
This can lead to stretching and strains the human body is not able to cope with, Dr Roach explained.
“At the end of the day, despite the fact that we evolved to throw, when we overuse this ability it can end up injuring us,” he said.