Stone Age Kalashnikov

New Scientist
15 May 1999
By Kurt Kleiner

WILLIAM ROBERT PERKINS notches the long, flexible spear onto a spur on the end of the stick in his hand. He draws back his arm, and throws. The spear flies away from the stick, an atlatl, towards the hay bales 30 metres away and thunks into the flattened cardboard beer carton that serves as a target.

Never mind that a few of the missiles miss the target and sail off into the Arizona desert beyond; everyone agrees that the atlatl can be tricky to use. Besides, Perkins, a former competition winner, has been so busy making and selling atlatls that he hasn't had much time lately to practise. The reason he's so busy is that the atlatl—a weapon that most hunters abandoned 10,000 years ago—is enjoying a renaissance. Thousands of people in America and Europe are making atlatls, competing in international tournaments, and even hunting with them.

Perkins, or Atlatl Bob as he's known, is no ordinary craftsman. Trained as an engineer, he is one of a group of people who have been studying the mechanics of this primitive weapon and found it to be surprisingly sophisticated. Using modern engineering concepts and experimental techniques, they are rediscovering ancient construction methods that make subtle but important improvements to the weapon's performance.

Armour piercing

"The physics and math is all in here," Perkins says, weighing an atlatl in his hand at a recent workshop on primitive technology held near Phoenix, Arizona. "It really impresses me, the ability of these ancient people to be able to do this. They certainly didn't have calculus. Wave mechanics, they didn't know that. But they knew intuitively."

Atlatl is an Aztec word for what's also called a throwing board or spear thrower. But most enthusiasts object to the term "spear", since it suggests a rigid shaft. An atlatl actually throws a flexible shaft that's more like a 150-centimetre-long arrow and is properly called a dart. The atlatl itself is about 60 centimetres long, with a handle at one end and the small, sharp spur at the other. A dart thrown with an atlatl can kill a deer at 40 metres and will fly more than 200 metres. For comparison, the world record for throwing the javelin is just under 100 metres.

According to archaeological evidence, the atlatl first made its appearance between 25,000 and 40,000 years ago in the region that today encompasses Algeria, Morocco and Tunisia. From here, it radiated outwards to Europe, Australia, Asia, and eventually the New World. Then, about 15,000 years ago, the bow and arrow began to displace the atlatl. The power and range of the two weapons are comparable but the bow and arrow is easier to aim. The atlatl's extravagant throwing action makes it more prone to wild shots, and can startle the prey. Still, in some places atlatls survived until more modern times. Aztec warriors greeted the invasion by Cortes in the 16th century with atlatl darts capable of penetrating Spanish armour, and Australian Aborigines still use them.

Today, many other people are rediscovering the atlatl, thanks largely to the trend for archaeologists to try to recreate the artefacts they find. Some modern enthusiasts also seem to stumble across the atlatl for themselves. "People call up and say, `I didn't know anyone knew about atlatls but me. I've been making these since I was eight years old'," says Leni Clubb, president of the World Atlatl Association, which is based in Ocotillo, California, and sponsors contests and demonstrations.

Perkins discovered the atlatl while studying engineering at Montana State University. He took a course in replicative archaeology and decided to make it the focus of his study.

Kickdown

One reason Perkins objects to the term "spear thrower" is that it gets in the way of understanding how the atlatl really works. Some of the first archaeologists to experiment with atlatls tried to throw rigid spears, and managed only poorly aimed shots that flew just 45 metres. They concluded that only constant practice from childhood would have allowed anyone to use the weapon effectively. In fact, a beginner can start to hit targets, large ones at least, after just an hour's practice.

So how does the atlatl work? The thrower holds the atlatl and dart parallel to one another and horizontal, with elbow bent and the hand just beside the ear. There's an initial forward motion with the shoulder, then the elbow straightens and finally the wrist flicks the atlatl forward with an action not unlike that of an overexuberant fly fisherman trying to lure a trout. The atlatl accelerates the rear of the dart through an arc, with a movement similar to that of an ancient ballista flinging boulders against the enemy.

That's the obvious part. What isn't so obvious is how the projectile springs away from the tip of the atlatl. In the early tests, the rigid spears were reluctant to part company with the atlatl. So, all too often, at the end of the throw, as the atlatl tip began to move downwards it would drag the back end of the spear down too, ruining accuracy—an effect called kickdown. (Some Inuits use atlatl-like sticks to launch rigid harpoons. But these are launched downward from boats, and the kickdown effect doesn't make much difference.)

A flexible dart, by comparison, springs away from the atlatl tip. You can think of the dart as a spring, which is compressed by the initial force of the throw. The dart releases this stored energy at the end of the throw by pushing off the atlatl tip before the tip begins moving downwards.

Perkins also analyses the dart in terms of wave mechanics At the start of the throw, the dart bends as the acceleration pushes against the mass of the stone tip. A wave propagates from the rear of the dart to its tip. When the wave reaches the tip, it is reflected back again. At the rear, the force generated by the still-accelerating atlatl reinforces this wave and sends it once more towards the dart tip, where it reflects again.

When the wave reaches the rear this time, however, the atlatl has stopped accelerating, and the wave's energy strikes the atlatl tip and propels the dart forward. "The wave goes through a cycle of harmonic oscillations, gaining a tremendous amount of energy as the dart's speed is increased," Perkins explains. It's this energy, he argues, that makes most of the difference between the 45 metres that a rigid spear will travel and the 200-metre flight of a flexible dart.

But energy is not stored just in the dart. Atlatls also bend, and release their stored energy just as the dart launches. The atlatl's stored energy is more modest in size than that stored in the dart, and can probably account for increases in distance of about 10 per cent, reckons Perkins.

Looked at this way, the atlatl works very much like a bow and arrow. When an archer draws back the bowstring, the bow stores up energy which it releases very quickly to push the arrow forward. "This is really the same weapon system as a bow and arrow," says Perkins. "It's a flexible shaft accelerator. The only difference is that a bow is a linear accelerator. It's accelerating a flexible shaft in a straight line. And the atlatl is doing it in an arc."

For an ideal combination, the dart and atlatl have to be the right lengths, with the atlatl about one third as long as the dart. They also need to be made of the right stuff. Atlatls can be made from the same strong, springy wood that bows are made from, says Perkins. He uses an American hardwood called osage orange. Authentic darts he usually makes from red osier dogwood, but if you want a modern dart he supplies them in aluminium. The dart also has to be properly tuned. It must have the proper amount of flexibility for its mass, and needs a mass at the tip of the dart to aid compression. Perkins finds that a 7-gram stone point optimises his 100-gram wooden darts.

Perkins also thinks he has solved the mystery of atlatl weights—small, shaped stones which were often attached to North American atlatls. One suggestion was that they served a ritual purpose. But Perkins thinks the weights have a function. Mounted about halfway down the rear of the atlatl shaft, the weight helps to tune the flex of the atlatl. "The atlatl weight improves the performance of the system in terms of efficiency," he argues. "Smoother, more controlled and powerful launches make for better accuracy."

He also thinks a specific type of oddly shaped weight, called a banner stone, served as a kind of silencer, stopping a hunter's prey from being startled by the sound of the throw. Normally, an atlatl makes a distinctive "zip" sound when the dart is thrown. But a banner stone, extending sideways like wings on an aeroplane, again about halfway down the atlatl, seems to muffle this sound. To test his theory, Perkins threw a number of darts over the head of a very brave engineer who measured the noise made by the launches. He found that, sure enough, atlatls with a banner stone made less noise than those without.

But could primitive atlatl makers really have taken advantage of all of these subtleties? Perkins believes they did. If the atlatl weights and banner stones aren't convincing enough evidence, there's also the mass of the stone points. For any dart, there is an optimum weight for the stone tip, and the tolerance is fairly narrow.

One day while at the Smithsonian Institution examining weapons left by native Americans from North and South Dakota, Perkins found three stone heads from the same site that had never been used. Two were made from chert, the third from much denser flint. All were made in the same way, but the one made of the denser stone was a centimetre shorter than the others. They weighed 7.6, 7.7 and 7.8 grams. If the maker had designed them by size alone, the denser point would have weighed much more. Perkins argues that this shows the maker had a standard weight which worked best with the darts.

Perkins hasn't proved his ideas, but archaeologists take them seriously. "There's considerable difference of opinion among professional archaeologists. Folks like Bob are doing a real service by engaging in the actualistic research of these weapons," says Leslie B. Davis, an archaeologist and curator at the Museum of the Rockies in Bozeman, Montana.

Others are more critical. Dick Baugh, another engineer turned atlatl maker, published a paper in Lithic Technology (Spring 1998) to counter the "extravagant claims [that] have been made regarding the increased dart velocity achieved with a flexible atlatl". Baugh created a computer model of a person using an atlatl, then changed the length and flexibility of the atlatl and removed the atlatl weights. He concludes that atlatl flexibility makes little difference to performance, and atlatl weights make even less. He also argues that while the dart's flexibility is important for launching it off the atlatl, it makes little impact on the distance the dart actually flies.

Ray Strischek of Athens, Ohio, who tied last year for best shot in the world, thinks the flex in the atlatl does make a difference. But rather than increasing velocity, he thinks it acts as a sort of shock absorber, buffering the jerkiness of the throw and creating a smoother, more accurate launch. "The debate goes on," says Strischek. "No one has been able to quite pin it down."

Until a machine with a perfect throwing action reveals the importance of all the various parameters, the experiments and controversy will continue as people continue to be fascinated by the atlatl. "What separates us from other predators is our ability to throw a projectile at a prey," says Perkins. "No other animal on Earth can do that. This is just our supreme expression of using that natural ability."