Researchers say ability to throw played a key role in human evolution

Jun 26, 2013
Dr. Neil Roach, a postdoctoral scientist in GW's Center for the Advanced Study of Hominid Paleobiology in the Columbian College of Arts and Sciences at the George Washington University, is the lead researcher for a study published on the cover of the June 27 edition of the journal Nature. By examining evolutionary anatomy and conducting an experiment with baseball players, Dr. Roach and colleagues found that certain anatomical features allow humans to store and release energy in the shoulders-- features that first appeared 2 million years ago when man began to hunt. Credit: William Atkins

It's easy to marvel at the athleticism required to throw a 90-mile-per-hour fastball, but when Neil Roach watches baseball, he sees something else at work – evolution.

That ability – to throw an object with great speed and accuracy – is a uniquely human adaptation, one that Roach believes was crucial in our evolutionary past. How, when and why humans evolved the ability to throw so well is the subject of a study published today (June 26) in the journal Nature. The study was led by Roach, who recently received his Ph.D. from Harvard's Graduate School of Arts and Sciences and is now a postdoctoral researcher at George Washington University, with Madhusudhan Venkadesan of NCBS at the Tata Institute of Fundamental Research, Michael Rainbow of the Spaulding National Running Center, and Daniel Lieberman, the Edwin M. Lerner II Professor of Biological Sciences at Harvard. They found that a suite of changes to our shoulders and arms allowed early humans to more efficiently hunt by throwing projectiles, helping our ancestors become part-time carnivores and paving the way for a host of later adaptations, including increases in brain size and migration out of Africa.

"When we started this research, there were essentially two questions we asked – one of them was why are humans so uniquely good at throwing, while all other creatures including our chimpanzee cousins are not," said Roach. "The other question was: 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?"

What they found, Roach said, were a suite of physical changes - such as the lowering and widening of the shoulders, an expansion of the waist, and a twisting of the humerus – that make humans especially good at throwing.

While some of those changes occurred earlier during human evolution, Lieberman said it wasn't until the appearance of Homo erectus, approximately 2 million years ago, that they all appeared together. The same period is also marked by some of the earliest signs of effective hunting, suggesting that the ability to throw an object very fast and very accurately played a critical role in human's ability to rise to the top of the food chain.

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"The ability to throw was one of a handful of changes that enabled us to become carnivores, which then triggered a host of changes that occurred later in our evolution," Lieberman said. "If we were not good at throwing and running and a few other things, we would not have been able to evolve our large brains, and all the cognitive abilities such as language that come with it. If it were not for our ability to throw, we would not be who we are today."

To start unpacking the evolutionary origins of throwing, Roach began not by studying how humans throw, but how our closest relatives – chimpanzees – do.

Though they're known to throw objects (often feces) underhand, chimps, on rare occasions, do throw overhand, but those throws are far less accurate and powerful than those of the average Little League pitcher, Roach said. Additionally, chimps throw as a part of display behavior and never when hunting.

Part of the reason for chimpanzee's poor throwing performance, Lieberman said, is tied to their technique, which in turn is limited by their anatomy. "Chimps throw overhand using either a dart throwing motion, where the elbow is extended, or much like a cricket bowler, where their elbow is kept straight and they generate force by swinging their shoulder", Lieberman said.

"That led us to studying cricket bowlers and trying to understand what happens when you keep your arm straight, and why that diminishes your throwing ability," Roach said. "Eventually, we began to think that changes in the way the shoulder is oriented with regards to the rest of the body could change the way you generate force when you're throwing."

To explore those physical changes, Roach and colleagues 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 – effect throwing performance.

In addition to the modeling, Roach performed a series of real-world experiments in Lieberman's Skeletal Biology Lab using members of the Harvard Baseball team and a host of braces designed to limit their movements.

The idea, Roach explained, was that by restricting certain motions, the players would be forced into a more primitive condition, giving him the opportunity to see how different anatomical shifts contribute to the mechanics of modern throwing.

Armed with a method known as inverse dynamics, Roach and colleagues were able to not only quantify how much restricting certain types of movements affected throwing performance, but were able to trace the effect to specific changes in the mechanics of each player.

"We try to push these bits of anatomy back in time, if you will, to see how that affects performance," Roach said. "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 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 continued. "This type of analysis allowed us to do that."

What they found were three key physical changes that helped to make fast, accurate throwing possible.

Evolutionary changes in the shoulder show that, as a pitcher cocks their arm back, "what they're doing is stretching the ligaments and tendons that run across their shoulder," Roach said. "Those tendons and ligaments get loaded up like the elastic bands on a slingshot, and late in the throw they release that energy rapidly and forcefully to rotate the upper arm with extraordinary speed and force." That rotation is the fastest motion the human body can produce. "The rotation of the humerus can reach up to 9,000 degrees-per-second, which generates an incredible amount of energy, causing you to rapidly extend your elbow, producing a very fast throw", Roach said.

Among the evolutionary changes that proved key to generating a powerful throwing motions, he said, was a twist in the bone of the upper arm and an expanded, mobile waist, which both gave early humans the ability to store up and then release more of this elastic energy

"The linchpin is really what's going on with the shoulder," Roach said. "When you see the shift from a chimpanzee shoulder to a more relaxed human-like shoulder, that enables this massive energy storage. Many of the evolutionary changes we studied, whether in the torso or the wrist, may predate Homo erectus, but when we see that final change in the shoulder, that's what brings it all together."

While the findings help shed light on a critical phase of human evolution, they also hint at a possible solution to a hotly debated question in sports: When it comes to young players, how much throwing is too much?

"It's a tough question to answer," Roach said. "The real difference, from an evolutionary perspective, is the frequency with which some folks throw now. To successfully learn to throw and use that ability to hunt, our ancestors would need to throw often, but nothing like the 100 or more high speed throws that some baseball pitchers throw now in the span of a couple of hours."

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

Ultimately, Lieberman said, the evidence points to one clear conclusion – the ability to throw with speed and accuracy is a uniquely human adaptation, one that played an immeasurably important role in human development.

"Recent research indicates that stone points – the oldest kind of spear point – are about 500,000 years old," he said. "But people have been killing animals for at least 2 million years, and eating animals for about 2.6 million years."

"That means that for about 1.5 million years, when people hunted, they basically had nothing more lethal to throw than a pointed wooden stick," he continued. "If you want to kill something with that, you have to be able to throw that pretty hard, and you have to be accurate. Imagine how important it must have been to our ancestors to throw hard and fast."

Explore further: Woolly mammoth skeleton sold at UK auction

More information: Paper: dx.doi.org/10.1038/nature12267

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User comments : 11

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flashgordon
1 / 5 (6) Jun 26, 2013
This makes sense; it's almost a "why didn't I/we think of this before." Many people have hit on the idea of using fire to defend oneself from much more athletic animals. Why not throw things to fend off Leopards, cave bears and maybe even birds?
axemaster
not rated yet Jun 26, 2013
The main question in my mind after reading the article is this: why are (a majority of?) women so bad at throwing? Is it a cultural thing? Anatomical? It seems strange that such an apparently vital physical skill would be largely absent in 50% of the species...
Bog_Mire
3 / 5 (2) Jun 26, 2013
Axe master, you refer to modern day women, or to Neolithic women? I would imagine that the ability to throw is inherent in all human beings, regardless of sex. It is a skill that can be learned with practice like any other. We all have the anatomical structure to become an expert thrower.
orti
1 / 5 (8) Jun 26, 2013
Flashgordon is right. It's so obvious how unique (to humans) and how important it is (was) ... once someone points it out.
Shitead
1 / 5 (3) Jun 27, 2013
Dr. Roach should go further back in time than homo erectus. Ardi (Ardipithecus ramidus) lived about 4 million years ago and had surprisingly "modern" arms, wrists, and shoulders. She, yes she, was dumb as a chimp and could barely walk upright, but lordy could she fire a fastball. The pointed stick wouldn't be invented for at least another million years but with an infinite supply of rounded river rocks, who needs sticks?
Mandan
not rated yet Jun 27, 2013
It would be interesting to see a similar comparison of these differences in human and chimp shoulder structure to efficiency of climbing. Is there, in other words, a trade-off being made in terms of less reliance on canopy exploitation for fruits and other sources of nutrition by humans in exchange for increased accuracy and power in throwing/hunting?

Also, the point (no pun) about the timing of stone projectile appearance in the record should be re-considered given the ubiquity of pebbles and rocks in nearly any environment available to be picked up and thrown by themselves with lethal effect.

I also wonder if the mechanics of fist fighting are related to the mechanics of throwing as well. Losing canine size while at the same time increasing the accuracy and power of arm extension/fist position abilities would suggest transition to new ways of engaging in social hierarchy establishment as well as hunting technique-- killing two birds with one stone, as it were.
axemaster
5 / 5 (1) Jun 27, 2013
Axe master, you refer to modern day women, or to Neolithic women? I would imagine that the ability to throw is inherent in all human beings, regardless of sex. It is a skill that can be learned with practice like any other. We all have the anatomical structure to become an expert thrower.

That's probably true, but I'm sure you've noticed that many women simply can't throw properly. The phrase "you throw like a girl" exists for a reason. I'm simply wondering why there seems to be a difference between males and females in this regard.
JohnGee
1 / 5 (8) Jun 27, 2013
The phrase "you throw like a girl" exists for a reason.

Correct, the phrase exists because of men that throw that way.
Mandan
not rated yet Jun 27, 2013
These "girls" can throw:

NJCAA National Women's Softball Championship
http://www.youtub...BO95_nEQ

Now certainly they don't bring the "heat" that male ball players can, but I'd hate to get hit in the head by an apple thrown by any of those fielders.
Bog_Mire
1 / 5 (1) Jun 27, 2013
Neolithic women would have been expert throwers by need. But we suppose that gradually women became defined as infant careers/food gatherers/home carers, while men became hunters and defenders.

Until eventually Modern women have no need, mostly. So they do not learn this skill by repetitive training. Throwing based sports and activities are male gender heavily biased - hence boys generally learn this skill by repetitive training more so than girls

TheGhostofOtto1923
1 / 5 (3) Jun 30, 2013
You brainiacs must know thatthe question would have been asked before -?

"...the "throwing gap," as it's called, is one of the biggest differences between the genders. It's not just the largest gap in physical activities--although it's the largest gap in that field--it's possibly the most salient gap. Period."

"Thomas pegs evolution for that, hypothesizing that throwing was the most important trait for hunting, and that the best (male) hunter was more likely to pass on his genes with the woman of his choosing. There's no way to test that theory, of course..."

-Neolithic women would have had their arms full with babies. Men would have been selected for their ability to hunt the predators which were hunting them, be they animal or human. Securing food is much less critical than avoiding BEING food.

Once the animal predators were effectively eliminated, humans began hunting each other. Chronic tribal war ensued. The puzzle is why researchers consistently fail to acknowledge this.

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