Animal Weapons

by Douglas J. Emlen

  This is not true for cultural evolution. Consider the rifle. Rifles are manufactured in shops or factories, rather than wombs. Instructions for their manufacture are copied and transmitted from one person to the next, but they are recorded in documents rather than DNA. Most important of all, whether a lot of copies are made or a few has little to do with numbers of offspring. Success of one rifle type over another is not linked to the reproductive success of the people who make and use it, and the population of rifles—all rifles in existence at any point in time—is not the same as the population of people.

  Cultural evolution thus unfolds on a different plane from biological evolution. Occasionally the events in these two layers intersect—the annihilation of Lachish certainly affected the reproductive success of its inhabitants, for example—but most of the time, the processes unfold in isolation. Humans evolve, and our weapons evolve, but these events unfold independently. As long as this distinction is clear, there’s no reason we can’t compare the evolution of animal weapons to the evolution of weapons we build.

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  By the end of WWI, it was clear that infantry needed a new weapon. Engineers endeavored to combine the portability of a rifle with the rapid-fire capabilities of existing machine guns.33 The first of what would become the “assault” rifle, the Russian Fedorov Avtomat, never went into mass production because the cartridges it used, pistol ammunition, were too low-powered to be accurate beyond a few hundred feet. The French Chauchat fared better, with roughly 250,000 rifles produced by the end of the war. But this gun used ammunition that was too powerful, making the recoil uncontrollable during automatic fire. The French Ribeyrolle 1918, the Danish Weibel M/1932, and the Greek EPK soon followed, all using newly developed intermediate-caliber ammunition and thus balancing the need for accuracy at several hundred yards with the need for minimal recoil and control. But these weapons were cumbersome and heavy, as was the American M1918 Browning Automatic Rifle (BAR). By 1942 the Germans introduced the MKb 42 (H) and the Stg 44. Three years later the United States had modified the M1, adding a twenty-round detachable magazine to the rifle and giving it both selective and automatic fire options, but the ammunition for these rifles was still too powerful (the United States later scaled this down to the M16, which uses intermediate-caliber ammunition).

  In 1949, the Russian Avtomat Kalashnikova, or AK-47, entered this mix of competing assault rifles. It combined the best of these other models into a frame that was virtually indestructible. The AK-47 used intermediate-caliber cartridges and had a curved, detachable magazine for smooth firing. The barrel was shorter than those of earlier assault rifles, and it was significantly lighter. Best of all, this rifle could be produced rapidly and cheaply. Simple to build, simple to use, and reliable under even the most extreme conditions, the AK-47 swept the field. Now, more than sixty years after its introduction, the AK-47 has spawned a family of related assault rifles that together are the most recognizable and abundant firearms on earth, with an estimated one hundred million units manufactured—one assault rifle for every seventy people on the planet.34

  Even at a glance, it’s apparent that the history of assault rifles has all of the elements of an evolutionary process. Although the information relevant to rifle construction is transmitted through documents and computers, rather than DNA, the result is faithful copying of the design from rifle to rifle. Rifles coming off of an AK-47 assembly line are all AK-47s and not M16s or Stg 44s. Yet, through accident or design, engineers are constantly adjusting rifle design, probing possibilities, and testing variations on the theme. Most of these experiments fail, but every now and then new design features work, and are rapidly incorporated into newer models. Most important of all, the realities of markets and battlefields act like agents of selection, culling assault rifles that are too expensive to produce, that jam or misfire, or that are more cumbersome or awkward than other available alternatives. The conditions of modern warfare shape the evolution of assault rifles in much the same way that natural agents of selection, such as battles between rival males, shape the evolution of elk antlers.

  As long as we focus on the weapons—antlers and rifles—rather than the animals or humans using them, comparison of their respective evolutionary paths is relevant and informative. It’s only when we start confounding rifle evolution with human evolution that things get murky. Assault rifles clearly affect the survival of humans. After all, they’re used to kill people. Dead people don’t have babies, so rifles also affect reproductive success. But these are not the metrics that matter for rifle evolution. What matters for the success or failure of a specific type of rifle is how well it performs relative to the other rifle models in existence at the same time. The same can be said for ships, castles, and catapults. Designs that work are copied and spread; those that fail are abandoned. It’s the conditions conducive to weapon evolution that I compare between animals and ourselves; these conditions, I’m suggesting, are essentially the same.

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  My first encounter with Mayan fortifications happened by accident. In 1990, I spent two weeks in a tent in the Belize jungle, part of Princeton’s tropical ecology course. It rained incessantly both weeks, and the trenches we dug around our tents couldn’t divert the water fast enough. Mud plastered our faces, our clothes, our sleeping bags, and all of our equipment as we sloshed and slurped about in rubber gum boots. A tarp stretched between trees sheltered the “kitchen,” and another thrown together from thatched palm fronds made up the “lab.” This was my first stint in a tropical forest and, aside from almost slicing my thumb off with a machete and getting stung by a scorpion one night through the floor of my tent, the trip was a success. I was hooked. Our task for the class was to design and conduct an experiment tackling a biological topic of our choice. But on my first day exploring I stumbled into a tangled wonderland that blew my mind, and I convinced my professors to let me do something very different instead.

  Hidden deep in the forest a mile from our camp was a lost Mayan city. Looming up from the dark floor of the forest were fifty-foot-tall pyramids—lots of them—all buried in detritus. Centuries of tropical growth and decay blanketed each pyramid; they sprawled like earthen hills covered with roots and vines, trees sprouting up from their sides. A thousand years earlier this had been the center of a thriving metropolis, the courtyard at the heart of an ancient city. Now, it was enshrouded in forest and forgotten.

  For my project I was going to map this Mayan city. Utterly inexperienced in cartography, I set out with a compass and a sketchbook and started pacing. Each day I marched through the forest, sketching the towering mounds that rose before me, pulling aside jungle tangles, scrambling through branches, and slipping in the mud and rain. I could tell from holes dug into their sides that some of the mounds had been looted. Here and there stood a lone stone tablet—a signpost, or stela—rising from the soil in front of a pyramid, proclaiming deeds of some long-dead leader. By the end of my trip I’d found more than twenty-five pyramids nestled in that patch of Belize forest.

  Author’s 1990 sketch of La Milpa

  The Mayan city is called La Milpa (I wasn’t the first to discover it), and, two years after I wandered through its plazas, formal excavations began. It now appears that La Milpa was inhabited from 400 BCE to 850 CE, peaking with a population of roughly seventeen thousand.35 The city perched atop a steep-sided escarpment so that, like Lachish, it sat above the surrounding plain. Aside from its location, however, La Milpa wasn’t very heavily protected. Even the much larger, neighboring city of Tikal was protected only by a deep ditch and low wall. These two cities reflect the pinnacle of one of the world’s most impressive ancient civilizations, a people whose society revolved around warfare. Why weren’t they better defended?

  The history of human fortifications is a boring one in most regions, marked by relatively little change. Most armies could not sustain the cost and logistics required for mounting effective siege attacks in far-off lands and, even when armies were large e
nough, the landscape sometimes got in the way. Thousand-foot precipices and spectacular gorges made approaches to Andean cities impractical, while swamps and vast tropical forests hindered movements in Mesoamerica. Wheeled towers and catapults weren’t practical in these environs and, despite having the requisite wealth, forces, and political organization, the Incan, Olmec, Mayan, and Aztec empires never incorporated siege weapons into their military strategies.36

  Without the threat of siege weapons, there was no need to enlarge defensive walls. Simple walls sufficed, and little evolution of fortification design occurred. From the earliest traces of civilization, pre-Incan villages dating to 5000 BCE, until the arrival of the Spaniards in the 1500s, fortifications in Central and South America consisted of ditches, earthen mounds, and stick or stone palisades.37 Most cities were walled and a few, like Tenochtitlan, were surrounded by water, but basic fortifications held against the types of threats they encountered. The same holds true for much of Asia, Africa, and North America; ditches and timber palisades look almost the same in eighteenth- and nineteenth-century Iroquois and Maori villages as they did in the Fertile Crescent and the Andes more than seven thousand years ago.38

  Only in the Middle East, Europe, and parts of Asia did siege warfare escalate, and it’s here that fortresses evolved to their greatest size and complexity.39 The protruding towers and balconies we saw in Lachish selected for a means to breach walls at a distance, and by the time of the Hellenistic Greeks artillery was added to siege repertoires.40 Ballistas, wheeled contraptions with a spring-loaded giant sling or wooden spoon, hurled rocks several hundred yards. Giant, multiperson catapults fired iron-tipped spear-sized missiles. Boulders punched holes into walls and snapped battlements. The best hits were on towers, since the corners were more fragile than the rest. Hitting a corner just right could rip away chunks of the tower, and often the walls above the gash then collapsed.41

  The devastating impacts of artillery, in turn, selected for ways to keep these catapults out of range, beyond the reach of the flying stones. New walls were thrown up outside of the original walls. Outer walls were very expensive, since they encircled a much larger area than inner walls, and many were several miles long. Simple barriers wouldn’t suffice, since they’d be smashed or undermined. So outer walls had to be equipped with full suites of defensive paraphernalia, including crenellated bastions, protruding balconies, and towers at regular intervals. For a while, these new walls worked. But the ability to hold siege weapons at greater distances only led to the design of bigger and bigger artillery. By the time of the Romans, onagers were hurling hundred-pound stones more than a thousand yards.42

  Over time, fortress walls got thicker and taller, and siege towers and battering rams bigger. Early Assyrian siege towers had two or three stories, carrying rams handled by several dozen men. Later models got taller and wider, and, in their heyday, towers stood more than ten stories high, pushed by more than two thousand men. Battering rams reached lengths of 150 feet, crewed by a thousand men apiece.43

  On and on the race continued as walls, towers, rams, and catapults grew. By the Middle Ages a new style of catapult was invented, the counterweight trebuchet. Trebuchets used gravity and leverage to hurl stones from a sling, and they surpassed all artillery weapons of their day. More accurate and powerful than ballistas, trebuchets could launch 350-pound boulders far enough to reach the inner fortress towers of most castles. Square corners once again proved vulnerable, and they all but disappeared. Round, cylindrical towers were less prone to collapse if they were struck directly. Even better, they were almost never hit directly, since their rounded edges deflected missile boulders to the sides.44

  Artillery evolved in tandem with fortress size and design, hurling bigger stones farther distances. Greek ballista (left) and medieval trebuchet (right).

  By the thirteenth century every self-respecting nobleman in the Middle East and Europe had erected a castle, and more than thirty thousand dotted the landscape.45 Castles quickly evolved into the extravagant structures most of us are familiar with today. They had concentric outer and inner walls punctuated at regular intervals with round towers; battlements and arrow slits throughout; protruding balconies with floor holes for dropping incendiaries onto attackers; giant side-by-side gatehouses restricting access to narrow, heavily guarded, tunnel-like entryways; and massive portcullises—wrought iron gates—dropped as needed to block passage. Castles were almost always situated strategically to lie above the surrounding countryside and to be as inaccessible as possible. Often they straddled rock cliffs or were surrounded by water. If no cliffs or lakes were available, moats were built. In their day, castles ranked among the most resplendent and expensive structures ever built by the hands of man.

  Everything changed with the invention of gunpowder. The destructive power of cannons rendered even the most impressive castle walls obsolete, and by the end of the fifteenth century the benefits of castle-style fortifications weren’t worth their exorbitant costs. The arms race was over. The cannon had won, and thousands of castles across England, France, Spain, Germany, and Belgium were abandoned.46

  From the ashes of this arms race grew a new style of fortifications, the “star fort.” Utterly transformed, this new breed of fortress was designed to defeat cannon fire. Gone were high walls and imposing towers. These fortresses hunkered low, surrounded by shock-absorbing earthen berms, and their walls jutted outward in long, angled points—like the points of a star.47 The logic behind the new design was to avoid presenting any broad surfaces to incoming cannonballs, since the sloping, pointed “bastions” could deflect cannonballs fired from any direction. Fort Bourtange in the Netherlands, for example, is a maze of low angled walls alternating with earthen mounds and moats. From the ground, nothing sticks up high enough to hit with a cannon; from the air, the fortress looks like a snowflake.

  Star forts sprang up across Europe and in colonial settlements, including the New World. In a classic illustration of the ever-present balance between costs and benefits, British and Dutch colonies invested in earthworks and stone star forts only in locations where they were likely to encounter cannons. Forts Crown Point, Ligonier, Ontario, and Frederick, for example, all overlooked harbors or inland waterways, locations well within reach of the broadsides of warships from the major naval powers.48 Fortifications erected inland protected settlers from natives rather than navies, and returned to the timeless tradition of inexpensive, simple wooden palisades, punctuated occasionally by protruding towers or balconies.49

  Even star forts became obsolete with the spread of exploding artillery. Much as they spelled the end for wind-powered warships, rifled cannons with deep-penetrating exploding shells proved more than star fortresses could handle. Bombs dropped from planes soon followed, and by the time of the strategic bombing initiatives of WWII, no aboveground structure was safe from attack. Security lay deeper and deeper belowground, and the new norm became dispersed networks of tunnels and bunkers.50

  During the Battle of Britain in 1940, the safest shelters were the deepest ones, and because they were in short supply, as many as 150,000 Londoners huddled in a labyrinth of subway tunnels each night. The Maginot Line, an inordinately expensive, thousand-mile-long string of fortifications built by the French to stall and divert the advancing Germans, was almost entirely belowground. The Japanese carved elaborate networks of tunnels, gun ports, and barracks into the volcanic rock of the Pacific Islands.51 Shielded by solid stone, these positions withstood repeated bombardment from battleship artillery and bombs dropped by planes, and in the end most had to be cleared by brutal hand-to-hand combat. Even Gibraltar, Eisenhower’s command post for the Allied invasion of north Africa, was buried deep beneath a mountain.

  Once the age of aboveground fortifications ended, it didn’t return. To this day, rogue organizations such as al-Qaeda and the Taliban hide in mazes of caves buried deep inside mountains,52 and our own government maintains multibillion-dollar bunkers, such as Cheyenne Mountain, lurking hundred
s of feet below the surface, shielded by millions of tons of solid rock.

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  Artillery and fortifications are manufactured structures, yet they evolve just like the weapons of animals do. Advances in the effectiveness of artillery select for new and better designs of fortresses, and vice versa, in a back-and-forth cycle that can spiral into an arms race. Because fortresses are fixed in place, rivals in these races have defined roles as attackers and defenders, much like animal predators and prey. The final examples pit attacker against attacker, in matched contests more reminiscent of battles between beetles or elk.

  13. Ships, Planes, and States

  We weren’t supposed to do it, but every once in a while I’d take a canoe across Gatun Lake into the main channel of the Panama Canal. At night I could paddle right up to the container ships as they chugged past. This was the folly of youth, counting coup with sideways floating skyscrapers. The challenge was to get as close as possible. If I slid in really close, within, say, six feet or so, I could tap the side with my paddle and ride the big wave peeling off from the bow.

  There’s no way anyone on the ships ever saw me, in part because I did this under cover of darkness, but also because the people steering were more than a city block away. These were big boats. The decks alone could house three football fields end to end, if they weren’t piled high with thousands of semitruck-sized boxes, and the “cabins”—hundred-foot-tall buildings ringed with glowing windows on the top floor—perched all the way back at the stern. From where the bow sliced into the water, the pilot was almost a quarter mile away.