http://www.sfgate.com/science/article/Dynamic-shoulder-key-to-touchdown-passes-6810508.php

About 2 million years ago, humankind’s ancient ancestors developed a shoulder structure that allowed them to throw spears and rocks to hunt prey, scientists say.

That adaption moved modern humans away from shoulders built for climbing and swinging from branches and today gives them the ability to throw, say, a football, UCSF experts said.

“The same physical and mental abilities that evolved to allow us to thrive as a species allowed us to play football,” said Nathan Young, a UCSF evolutionary biologist and orthopedic surgeon who has studied the human shoulder and its evolutionary past for years.

Chimpanzees are humans’ closest living ancestors, Young added, and though they have evolved as well, they aren’t very good throwers.

“Chimpanzees are extremely strong. They are half of our size, but three to four times stronger than us,” he said. “We are relatively weak in comparison, but if you asked a chimpanzee to try to throw something, he would always do it underhanded and couldn’t do it accurately or strongly.”

Those capabilities come down to humankind’s uniquely specialized shoulder that sits more side-facing than chimpanzees’ and allows more energy storage and arm extension, which are both key factors in throwing.

Young said that mobility of the shoulder allows athletes to throw footballs incredibly far and at great speeds, which make for great games, but can also prove dangerous to the athletes.

“The shoulder is a dynamic joint,” he said. “The human arm is kept in the shoulder by muscles and tendons that cross it. Some of that mobility comes with a price, such as an increased chance for disability.”

Young said human throwing performance may benefit from the low, wide stance of shoulders, long legs and extendable wrists, but not all human shoulders are set up to throw footballs like NFL Super Bowl quarterbacks Cam Newton and Peyton Manning.

Each shoulder is unique in its composition, Young said, and though a lot of practice can change a shoulder to be more conducive to throwing, what a human is born with is sort of what he or she is stuck with.

Beyond the shoulder’s mechanism that allows humans to throw powerfully lies the mind’s ability to know to throw at the right place, at the right time and in a very accurate fashion, said Phillip Sabes, a UCSF neuroscientist.

“When you do a simple task such as throwing a ball, you need to produce a set of muscle activations to throw the ball in the correct way. That’s an issue with control,” said Sabes, who studies motor control and the body’s ability to use sensory information to plan and accurately perform movements.

The trick to control, Sabes said, is identifying where you want to throw the ball, being able to see where your target receiver is moving, predicting the future location of that recipient, and combining that with the body’s ability to sense how to get the ball there.

“You need to be able to look out at the field and know where you want to throw the ball,” he said. “Being able to see and know your target and pick it right and pick it quickly is probably what distinguishes a good QB from a great QB.”

Regardless, both scientists said come Sunday, they’d be thinking about the game itself more than the science behind it — with exception.

“I think about all of this more when a quarterback gets hit hard and their shoulder gets driven into the ground,” Young said.