Eye on evolution: Churchill, with casts of fossil forebears looking on, oversees BB gun experiment. Chris Hildreth
Eye on evolution: Churchill, with casts of fossil forebears looking on, oversees BB gun experiment. Chris Hildreth

Shot Clock

When did early humans come up with the weaponry that made them the world's dominant predators? A Duke paleontologist goes on the hunt.
January 31, 2011
 

In a basement laboratory with walls lined with casts of human skulls, paleontologist Steven Churchill watches his student assistant pick up a BB gun and get ready to start pumping.

“All right, let’s do it,” Churchill says, stepping behind the line of fire.

“One, two, three, four, five, six, seven,” junior Paul Salem counts before locking his air gun into a rifle stand. Then, with all the ease of the U.S. Marine Corps sniper he once was, he fires.

The BB pellet flies through a chronometer set up on a lab table to measure its speed. In a flash, it lodges in a big brick of ballistics gelatin Salem had mixed for the occasion and floats suspended like a tiny copper pearl in bleached amber.

“That’s good, that’s very good,” Churchill says, hustling over to the block with Salem and another student, junior Kelly Ostrofsky, who is assisting Salem with the experiments. Ostrofsky records how deep the pellet penetrated.

The firing is the first stage of a small experiment that may help answer a very big question. Churchill, the only paleontologist at Duke studying human evolution, wants to estimate more precisely the time when Stone Age people started using projectile weapons—most likely, mini spears flung using handmade throwers. Their innovation freed humans from the limitations of an earlier technology, heavier handheld thrusting spears, which could be thrown but not that far or with much force.

To Churchill, weapons are about much more in human history than hunting game or waging war. They are the tools that were pivotal to the success of our species at colonizing an entire planet over a surprisingly brief time. Weapons helped transform people into dominant predators wherever they settled and protected them from dangerous carnivores such as lions and leopards. They even gave them an edge against their rivals (and close cousins), the Neanderthals. Perhaps most important, projectile weapons produced enough stability to allow people to live in larger bands, forge more cooperation within groups, and create more specialization—the sort of stuff that makes the best of civilization possible, then and now.

With no peephole into the past, Churchill pursues how and when prehistoric people expanded their arsenals by studying fossils and surviving stone points for clues. When they don’t explain enough, he experiments with proxies. Hence the air gun, the ballistics gel, and those BB pellets.

“We appreciate Steve because he is a big-picture guy,” says Anne Pusey, chair of Duke’s evolutionary anthropology department, where Churchill is based. But as anyone who has tried to fill in blanks in big pictures knows, the work takes an awfully long time. And progress doesn’t always follow a straight line.

Ballistics gelatin

Weapons watch: ballistics gelatin
Chris Hildreth

As a kid growing up in northern Virginia, Churchill, who is fifty-one, imagined becoming a paleontologist. He liked the idea of finding and studying fossils to try to piece together what life was like in the deep past. But he pictured himself studying grade-school favorites: dinosaurs such as Tyrannosaurus rex or Triceratops, animals that went extinct 65 million years ago. “I didn’t think humans were that interesting,” he recalls.

At Virginia Polytechnic Institute and State University, where he enrolled in 1977, Churchill changed his mind. In the anthropology classes he took, teachers were excited about the fossil remains of a hominid named Lucy, which had been discovered only three years earlier in Africa, the cradle of human development. Lucy was, at the time, the oldest known member of our evolutionary clan, dating to 3.2 million years ago. (Older traces of our earliest human-like or “hominid” lineage, fossilized skeletal remains that paleontologists nicknamed Ardi, were reported in the scientific literature in 2009.)

By studying fossils such as Lucy (and now Ardi)—as well as clues embedded in our DNA—scientists have concluded that humans and chimpanzees, our closest living relatives, branched off from a common ancestor 5 to 7 million years ago. Churchill entered graduate school at the University of New Mexico eager to learn more.

In Albuquerque, Churchill studied with Erik Trinkaus, a researcher known widely in paleontological circles for his studies of Neanderthals (pronounced nee-AN-der-tals). Our closest human ancestors, Neanderthals emerged in Europe and the Near East but went extinct about 28,000 years ago. In the 1970s, a lot of scientists focused solely on Neanderthals’ possible kinship to modern Europeans. Trinkaus, the first to conclude that Neanderthals walked upright just as Homo sapiens do, instead encouraged his students to concentrate on how Neanderthals adapted to their very specific environments. That’s an approach Churchill adheres to today when studying all prehistoric hominids.

Most scientists studying ancient peoples have to work with a cast of the fossil or relic. But Trinkaus had an actual Neanderthal fossil in his laboratory: one of the skeletons recovered from Shanidar Cave in Iraq in the 1950s, on loan from the Smithsonian Institution. When graduate students worked in the lab into the night, Churchill recalls, they would sometimes take out the fossil—carefully—to get a good look. “You’d be holding a fossilized bone from a person who lived 75,000 years ago, and it was a real Neanderthal,” he says. “Yes, there was a certain coolness.”

But he got a much bigger charge during his second year in Albuquerque. An archaeology professor invited him to look at some Neanderthal stone tools that had been discovered in the Dordogne region of France. The professor was rifling through a drawer for a particular object to show Churchill and pulled out what archaeologists call a scraper tool. It was a milky-white piece of flint that a Neanderthal had shaped in just the right way so it would have a sharp edge and a good grip. It was probably used to scrape animal hides or strip branches.

“He said, ‘Hold this,’ ” Churchill says, clearly still stirred by the memory. “It fit so well in my hand. Not only did a Neanderthal make it, a Neanderthal used it. When you hold a tool, you are interacting with their behavior in a way you are not when holding a bone.”

To this day, Churchill makes a point of passing around a hand ax made by a much older hominid, Homo erectus, when he teaches his human evolution class at Duke. “Just in case one of the students makes the same kind of connection,” he says.

Photograph of projectiles


Weapons watch: projectiles
Chris Hildreth

Graduate school inspired Churchill to study all hominids, including Neanderthals, dating from about 500,000 to 10,000 years ago. That is when our species started transitioning from a migratory way of life to one involving more permanent settlements. But if you’ve ever heard of Churchill, chances are it was in connection with a Neanderthal.

In 2009, the international media lapped up news of his detective work into what might have been a very cold case: a possible Neanderthal homicide. At issue was an unusual wound to the ribcage of a Neanderthal skeleton that is at least 50,000 years old, dug up half a century ago in the same cave in northeastern Iraq that yielded the fossil Trinkaus had shared with his students. The injury was a clean cut to one bone instead of the more common crushing damage to multiple bones caused by animal attacks.

So Churchill developed an experiment. On the secluded grounds of a bed-andbreakfast outside Chapel Hill that was closed for repair, he and students assaulted a pig carcass with a stone-tipped thrusting weapon—the kind dug up near Neanderthal remains. They also attacked the gutted animal with stone-tipped arrows of the kind that Homo sapiens were believed to have hurled with throwers when they and Neanderthals were both in the Near East some 50,000 years ago. After precisely evaluating the position, angle, and shape of the damage done to the carcass’ ribs, Churchill concluded that the injury more likely was done with the flung weapon.

Some journalists interpreted Churchill’s findings to mean that people drove Neanderthals to extinction. But Churchill envisions no prehistoric genocide, with Homo sapiens executing every Neanderthal they saw. Such assaults, if they happened at all, were more likely one factor of many contributing to the disappearance of our close relatives. “Neanderthals were an endangered species before modern humans ever set foot on the continent,” Churchill says.

His efforts to look beyond bones to try to piece together the lives of Stone Age peoples grab the attention of other researchers, says archaeologist John Shea of Stony Brook University in New York, who also researches prehistoric weapons. At scientific meetings on prehistoric people, Churchill’s work has appeal to both paleontologists, who tend to focus on bones, and archaeologists, who are more likely to focus on tools, Shea says.

“Some people get up and read a paper on why this Neanderthal has a bump on its head, and the archaeologists yawn, get up, and go to the bathroom,” Shea says. “The archaeologists start going on about this and that stone tool type, and the paleontologists get up and go to the bar. When Steve gets up and says this change reflects on this behavior, people stay. That’s where the fun is.”

Neanderthals remain of interest to Churchill for multiple reasons. For one, Neanderthal fossils are more abundant from the period when they and our species were both roaming the Earth. Because they appear to have begun burying their dead before Homo sapiens did, more of their remains were untouched by hungry carnivores, which frequently scattered human bones.

Line of fire: Sharpshooter Salem takes aim

Line of fire: Sharpshooter Salem takes aim
Chris Hildreth

But Neanderthals also interest Churchill because they were not us. Their physical qualities, tools, and cultures serve as handy contrasts to ours, providing insight into why our species has flourished over these many millennia when they did not. Churchill has delved deep into that topic.

Neanderthals and modern humans may have descended from the same archaic humans—the tool-making and possibly language-using Homo heidelbergensis. But Neanderthals may have evolved from a subset of the species that left Africa for what today is western Asia and Europe. Glacial climates cut them off from their southern kin. In time, the northern branch of the family developed the shorter stature and bigger muscles that distinguished the cold-weather-ready Homo neanderthalensis.

With Andrew Froehle of the University of California at San Diego, Churchill has calculated the fuel needs of a bigger-bodied Neanderthal making a living in a relatively cold climate, based on studies of a global sample of modern people living in different climates. The result: Neanderthals probably needed more food, on the order of 100 to 350 calories per day. “That’s the difference between driving a Cadillac and a Honda Civic,” Churchill says.

In a 400-page book manuscript he has been working on for eight years, Churchill expands the comparison. Living in a colder climate before agriculture was invented, Neanderthals probably didn’t have much access to plant food, he says. That means they likely hunted for a good share of their meals, which could not have been easy. Their hunting gear appears to have been primarily those heavy spears used for short throws and thrusting. Consequently, Neanderthals probably were not the top predators in their day. In fact, they were underdogs to large-bodied carnivores that roamed the same territories, including lions, leopards, saber-toothed cats, wolves, dholes (Asiatic wild dogs), and hyenas.

Churchill suspects that a lack of food at times suppressed their ability to reproduce. Collections of fossilized remains and the size of the rock shelters where Neanderthals lived strongly suggest they lived in small bands of only about ten people. Analysis of Neanderthal DNA indicates that small bands of Neanderthals were isolated from others, meaning that social groups had a limited ability to help each other with communal hunts, to build up their meat stores for the long winters, or to drive packs of carnivores from their territories.

Homo sapiens, who reached Europe from Africa about 43,000 years ago, came much better equipped, Churchill is convinced. He believes that our ancestors carried dart or arrow throwers during their migration. Part of the evidence comes from studies of modern athletes who regularly throw in competition—javelins or baseballs, for example. These athletes develop changes in their humerus, the arm bone connected to the shoulder. The stress produces miniscule fractures, which stimulate increased growth. Skeletons of prehistoric humans that Churchill and Jill Rhodes, a biological anthropologist at Bryn Mawr College, examined don’t show the same extent of changes observed in today’s athletes, but collectively do show differences in one arm over another, suggesting one was indeed a throwing arm.

“Throwing produces large forces on the upper limbs—large torque forces,” Churchill says.

This is key because projectile weapons allowed people to kill at a distance. While a handheld spear’s reach is only about six meters, darts can reach forty meters. Churchill knows this because nearly twenty years ago, he studied all published research based on observations on how contemporary hunters and gatherers use such projectile weapons in real life.

Rather than trying to trap or ambush prey, prehistoric hunters with throwers could launch them from a distance into open country. Not only could they throw at what they wanted to eat, they could also aim at other carnivores competing for the same prey. In fact, Churchill has concluded that while they can be tools of war, projectile weapons very likely encouraged cooperation among prehistoric people, who would likely work together on hunts.

It wasn’t that long after Homo sapiens reached what is now Europe and Asia that they became the top predators there. That’s a pattern that distinguishes humans’ occupancy—some would say conquest—of nearly every habitat in the world. “Modern humans get to Europe 43,000 years ago, and Neanderthals are gone by 28,000 years ago,” Churchill says. “Cave lions and sabertooth cats are gone by 18,000 years ago. By 15,000 years ago, almost all the large-body carnivores are gone.”

As people enjoyed more reliable food supplies and faced fewer threats from other animal predators, such as lions and leopards, they had more children, started living in larger bands, and started cultivating some of the specialization that allowed more modern cultures to flower. Today specialization yields everything from clever computer programs to classical ballet. But much earlier, one person might have focused on making tools, another on hunting, and another on producing clothes.

“We are ecological dominators,” says Churchill. “We walk into an ecosystem and crowd out everything else. Agriculture is the last step of that. We crowd out the herbivores, the bison, and horses, and we plow up their grassland so we can grow our own domesticated plants.”

 
Line of fire: Sharpshooter Salem takes aim

Churchill, Salem, and Ostrofsky examine the results of their test.
Chris Hildreth

It's important to note that no dart or arrow shafts have been found from 43,000 years ago, the time when our ancestors are believed to have reached Europe and western Asia after their migration out of Africa. That is not a surprise, says Churchill. Wooden shafts disintegrate pretty quickly. But he sees evidence beyond the damage to the Neanderthal rib that people had the weapons before they left Africa: a collection of small stone tips found in Botswana that date back some 75,000 years stored today in that country’s National Museum in Gaborone.

Churchill, along with one group of archaeologists with expertise in this area, says the tips, which are too small for handheld spears, are the oldest darts or flung spear tips yet found. Churchill’s efforts to shore up that theory explains why Paul Salem was firing BB pellets into ballistics gel this fall. Churchill met Salem when he was a sophomore enrolled in Churchill’s forensics class. Salem recalls he was told that the material was tough, but the teacher was great.

One day in class, Churchill talked about the different ways that bullets move through space, depending on the shooter’s distance from the target. When fired from a long distance, he told his students, bullets tumble through the air. Salem told Churchill that, from his Marine Corps experience, he was certain such tumbling did not occur. Instead of getting defensive, Salem recalls, Churchill smiled and extended an invitation.

“He said, ‘If you’re interested in ballistics, I have a project for you,’ ” Salem says.

Churchill briefed Salem on those points discovered in Botswana that are dated to 75,000 years old. One of the puzzling things about them is their shape. Most points hafted onto shafts for projectile weapons approximate symmetrical triangles—much like the pre-colonial-era arrowheads North Americans still find in riverbeds and fields. The Botswana points are asymmetrical. Churchill thinks that’s because the people who manufactured them had a distinctive chipping process that produced points with unequal masses on each side. He theorizes that they made the odd asymmetrical shape to compensate for the off-balance weighting when they were propelled through the air.

To test his theory, he, Salem, and Ostrofsky, the undergraduate assistant, are performing comparative studies of different point shapes.

The first test, firing the BB pellets into the ballistics gel, established that the gel was properly prepared to respond to a shot in the same way an animal muscle might. The response they were looking for was penetration at a depth of about 8.5 centimeters when fired at 590 feet per second.

A couple of weeks after confirming that the gel was properly made, Salem, Ostrofsky, and Churchill are back in the basement lab. This time, Salem carries in a plastic toy crossbow he purchased online. “Let’s fire this a few times to see what it does,” Churchill says.

In this session, the team needs to make certain that the toy crossbow can be fired accurately enough to hit the gelatin and that the chronometer, which captured the speed of the BB pellet, would record the arrow shaft’s speed, too. Salem sets the crossbow in the same rifle stand he used for the BB gun. “Okay, bottom left corner,” he says and squeezes the trigger. The chronograph, placed once more on the table, records the speed of the arrow shaft as it whizzes by, and the shaft plunges into the gel. This experiment is beginning to look feasible.

In the next stage of the experiment, Salem will attach differently shaped arrowheads to the plastic shafts that come with the crossbow. Alex Steenhuyse, an experienced flint knapper at the University of Pennsylvania, will make some of the points. Salem will try to compare their performance to the flint points with the more traditional shape.

Salem, who is leading the project, is thrilled with the opportunity that Churchill has given him. “He’s taken research that is important to him and said, ‘Okay, Paul, do this. Come up with the best way and make it happen,’ ” Salem says.

Over the past two years, Churchill has learned a lot himself about just how dynamic research can be. Since 1995, he has worked in South Africa with other scientists, looking for hominid fossil remains dating from 10,000 to 500,000 years ago, in a region north of Johannesburg. A World Heritage Site, it’s called the Cradle of Humankind because so many hominid fossils have been unearthed there.

Two years ago, a collaborator, a paleoanthropologist at the University of the Witwatersrand in Johannesburg, took a walk at the site with his nine-year-old son to look for fossils. The boy found pieces of what looked like human bones embedded in rock outside a cave. They turned out to be parts of a 2 million-year-old fossilized partial skeleton and a new species of hominid. Since then, scientists have found more fossils like it nearby.

Because of his expertise with hominid arms and other major moving parts, Churchill is helping lead the analysis of the fossils, even though he usually focuses on more recent hominids. This past summer, he spent six weeks in a laboratory at the University of the Witwatersrand, where he has a faculty appointment, and he planned to return there over winter break. Methodically, he is measuring one fossil bone after another and comparing them with other hominid fossils and with the skeletons of chimpanzees, bonobos, and us modern humans.

In October, Churchill stood before more than two dozen graduate students and faculty members from his own department with big news: The fossils appear to be an important transitional species in our evolutionary lineage. They have chimpanzeelike features associated with extremely old hominids, including the long arms associated
with tree-climbing, primitive feet, and a small brain. But they also have features associated with modern humans, such as long legs that allowed them to walk upright and human-like hips and pelvises.

In fact, he said, these remains might change our understanding of Lucy, whose discovery in northern Ethiopia in 1974 helped lure Churchill to his field to begin with. The newly found fossils may be closer relatives to us than Lucy was.

Of course, Churchill acknowledges, loads of work will be needed for them to make a scientific case for that. Which is okay, he says. “That’s why I got into this stuff—so I’d be challenged and learn new things all the time.”

And, apparently, to show a thing or two to the rest of us.

Clabby is a science journalist and the associate editor of American Scientist magazine.