When you watch a pitcher wind up and throw a fastball down the middle, or a quarterback step out of the pocket and make a successful long pass, you’re seeing millions of years of human evolution and adaptations in action.

Or so say researchers Daniel Lieberman and Neil Roach. Their study, published today in Nature, determines that this uniquely human trait—high speed and high accuracy throwing—originated with our ancestors Homo erectus, two million years ago.

Darwin speculated that by freeing up the arms, bipedalism may have enabled our hominin ancestors to hunt effectively using projectiles. But scientists had been unable to pinpoint the exact time throwing became viable.

“When we started this research,” Roach says, “we asked: How do we do it? What is it about our body that enables this behavior, and can we identify those changes in the fossil record?”

The researchers began by creating a complex model that incorporated current research about the biomechanics of throwing. Using that model, they were able to explore how morphological changes to the body—wider shoulders, arms that are higher or lower on the body, the ability to twist the upper body independently of the hips and legs, and the anatomy of the humerus—affect throwing performance.

They also studied 20 experienced human throwers during overhand baseball pitching, demonstrating that several derived anatomical features that enable elastic energy storage and release at the shoulder are central to our ability to throw powerfully and accurately. (Video is available of these mechanics on Harvard’s website.)

“We try to push these bits of anatomy back in time, if you will, to see how that affects performance,” Roach says. “The important thing about our experiments is that they went beyond just being able to measure how the restriction affects someone’s ability to throw fast and accurately—they allowed us to figure out the underlying physics. For example, when a thrower’s velocity dropped by 10 percent, we could trace that change back to where it occurred.

“In order to test our evolutionary hypotheses, we needed to link the changes we’d seen in the fossil record to performance in terms of throwing,” he continues. “This type of analysis allowed us to do that.”

This throwing ability was incredibly important for our ancestors, the researchers say. It helped them become more successful hunters and carnivores, paving the way for a host of later adaptations, including increases in brain size and migration out of Africa.

However, while speed and accuracy proved a crucial development for early hunters, the study’s authors warn that repeated use of this motion can result in serious injuries in modern throwers, especially in young baseball players, who often suffer from laxity and tearing in the ligaments and tendons of their shoulders.

“I think it’s really a case of what we evolved to do being superseded by what we’re now asking athletes to do,” Roach says. “Athletes are overusing this capability that gave early humans an evolutionary advantage, and they’re overusing it to the point that injuries are common.”

Image: Rick Dikeman/Wikipedia

Why are humans so crazy about sports?

Well, according to some Belgian researchers, it’s due to evolution. In an article they published last year in Perspectives in Biology and Medicine, cultural evolution plays a part in our love of sports, but if you get down to the brass tacks of it, sports is all about sexual selection.

According to the article, “From a Darwinian perspective, sports may be seen as one of the cultural activities invented to promote the acquisition of status. And acquiring status is—on average, in the long run, and in the ancestral environment to which our species is adapted—beneficial to an individual’s reproductive success.”

Nick Paumgartner of the New Yorker knows this is true. In an article he wrote earlier this month, he talks briefly about the behind-the-scenes sexual successes of athletes during the Olympics. But it’s how he feels as an amateur athlete that we all understand: “I suspect that skiing is, in some respects, an act of vanity. You want to be seen doing it. You make a mark in the snow and ask others to take note.” Sounds a little like a parading male peacock, huh?

In a recent Scientific American blog discussing this matter, Jesse Bering points out that the status is transferred from athlete to fan. “Sports that allow athletes to clearly showcase their most evolutionarily important attributes—strength, intelligence, endurance, speed and litheness, for example—attract the biggest following.” Basketball, check, but how do you explain the popularity of curling at last month’s Olympics?

As a fan, we take on the athletic ideals of the members of our team. Bering sites another study that found that following a World Cup soccer match, “Mean testosterone levels increased in the fans of winning teams and decreased in the fans of losing teams.”

So, your sports fanaticism? Thank evolution. But be careful, it can also be life-threatening. Heart attack rates have been shown to rise during the Super Bowl and World Cup. Go team, but take it easy.

(Update: more recent articles on dangerous sports-watching were published this week here and here.)

Image: Mahanga/Wikimedia