Animal Weapons The Evolution of Battle by Doug Emlen

Excerpt from Animal Weapons by Doug Emlen


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For as long as I can remember I’ve been obsessed with big weapons, which is rather surprising given that I descend from a long line of Quakers. On field trips to the natural history museum it wasn’t birds or zebras that caught my eye; it was mastodons with curling tusks, or triceratops with five-foot-long horns. In every room, it seemed, loomed another species with a crazy protrusion jutting from its head, or from between the shoulder blades, or from the end of its tail. Gallic moose wielded twelve-foot-wide antlers, and arsinotheres had horns six feet long and a foot wide at the base. I couldn’t peel my eyes from these creatures. Why were their weapons so big?

As I grew and, in particular, as I learned more about biology, I realized that “big” had little to do with absolute size. Extreme weapons were all about proportion. Some of the most magnificent structures are borne by tiny creatures. Hiding in drawer after drawer of dried, pinned specimens in museum archives, for example, are uncountable numbers of oddball species: beetles with front legs so long they have to be folded awkwardly around the animal in order to shut the lid on the case, or horns so big the animals have to be mounted in the drawer sideways. Many species are so small that their weapons become apparent only with a microscope: twisted tusks protruding from the faces of West African wasps, for example, or broad, branched antlers adorning the faces of flies.

I began my career determined to study extreme weapons, so I set out to find the craziest, most bizarre animals that I could. I also wanted my research to take me someplace exotic. In my case, this meant the tropics, so I narrowed my search. My study animals needed to be easy to find in large numbers, to observe in the wild, and to rear in captivity. As fate would have it, the animals that best fit this bill were dung beetles. I resisted at first. After all, dung beetles lack the panache of elk or moose and, well, they eat dung. Dung beetles were also a tough sell whenever I tried to explain what I did to anyone outside of biology. My father-in-law springs to mind—he’s a retired U.S. Air Force colonel—and I’ll never forget breaking it to him that I wanted to take his daughter with me to a remote field station in the thick of a tropical rainforest so I could watch dung beetles.

But dung beetles really were the best animals for testing the ideas I wanted to test, and there were lots of them in the tropics. Squat like little tortoises, these beetles were armed to the teeth with spectacular horns. Better yet, almost nothing was known about how these weapons were used, why they were so big, or why species differed so incredibly in the numbers and shapes of horns that they produced. To a biologist, that kind of unknown is intoxicating. Like exploring the depths of the ocean or outer space, I was going to plunge into the abyss of the biological void, and I was going to learn about extreme weapons in the process.

Two decades later, I remain just as awestruck by beetle weapons as I was that first year in the tropics. I’ve followed their stories to Africa, Australia, and throughout Central and South America. I’ve also had a chance now to step back from beetles, to consolidate the lessons learned by biologists studying a plethora of extreme weapons in animals ranging from moose flies and fiddler crabs to elephants and elk. These are the stories I set out to tell in these pages, weaving together for the first time the narratives of nature’s most extravagant creatures.

In the process of weaving their histories together, it became clear that there was another species that belonged in the mix: humans. The more I sought common threads—themes uniting the stories of diverse animal species—the more apparent it became that these threads applied to our own weapons, too. In the end, my book about animal weapons evolved into a book about extreme weapons everywhere. I pored deeper into the literature surrounding our past, searching for the environments and circumstances in which our most elaborate weapons evolved. To my amazement, these circumstances truly were the same, and I realized I couldn’t tell one story without telling the other. Back and forth I went, as the biology of animal weapons and our weapons fused, inextricably woven into a single tale. This is a book about extreme weapons. Let’s just leave it at that.


It was a cold, clear mountain night. The Milky Way streaked across the sky; jagged peaks loomed black against the starlight. A college buddy of mine and I were camping in Rocky Mountain National Park. It was early fall—peak of the rut for elk. I’d insisted we take the most remote campsite possible, and we’d pitched our tent as far away from the rest as we thought we could get away with. I wanted to be surrounded by aspen and cottonwood, not other people.

Somewhere around two a.m. I jolted awake, sleep still spinning in my head. A gunshot? I sat there in the silence listening. It came again—crack! In an instant I knew what was happening, and it was no gunshot. I shook Scott awake and we bolted from the tent. Almost a ton of testosterone-driven rage exploded beside us in the blackness not twenty feet away. Mature bull elk easily weigh in at eight hundred pounds apiece, and the two bulls locked in combat before us wouldn’t even notice if they trampled a tent or its occupants in the scuffle.

There we stood, shivering, bare feet burning in the new frost, squinting in awe at the shadowy beasts clashing beside us. The bulls circled, assessing each other, and then lowered their heads and slammed. Antlers clacked as they locked heads, gigantic silhouettes straining, grunting, gouging divots from the earth each time they lunged. Hindquarters whirled by our tent as they quickstepped their ancient dance, oblivious to the world around them. In the end, we didn’t get trampled, and our tent survived unscathed. But images from that September night fifteen years ago stay etched in my mind. I still remember steam rising from their breath in swirling clouds against the dark shadows. I even remember the smell, thick and musky, from the oil glands on the bulls’ faces.

By any account, elk are magnificent beasts, icons of power and beauty. But most of what impresses us sticks out from the tops of their heads. It’s the antlers that inspire our wonder. The weapons. The racks of elk, red deer, moose, and caribou have added regal splendor to the walls of royal halls for centuries. Indeed, no self-respecting chateau or castle would be complete without them. Antler-wielding stags are one of the most pervasive symbols in heraldic coats of arms, and mounted heads with antlers or horns grace the fireplaces of innumerable hunters’ dens, sporting goods stores, restaurants, and bars, reflecting silent glory upon the ones who slayed them.

Obsession with animal weapons is nothing new. The earliest known paintings attributable to our species, inked onto the smoky walls of caves more than thirty thousand years ago, feature the branching antlers of stags, curved mastodon tusks, and rhinoceros and buffalo horns. Today, antlers and horns are embedded into the brand strategies of corporations ranging from single malt scotch (Glenfiddich, The Dalmore) and other spirits (Jägermeister, Moosehead Lager), to farm equipment (John Deere), firearms (Browning), automobiles (Porsche, Dodge), clothing (Abercrombie & Fitch), mountaineering gear (Mammut), sports franchises (Manitoba Moose, St. Louis Rams, Milwaukee Bucks, Texas Longhorns), and even pharmaceutical companies (Janssen) and investment firms (The Hartford, Merrill Lynch). No matter how you stack it, we love antlers and horns.

But why are antlers so impressive? What is it that captures our imagination and awe? It’s not just that they’re weapons—most animals have weapons of one sort or another. Tigers and lions have claws, eagles have talons, snakes have fangs, wasps have stingers, and even our household dogs have a respectable set of teeth. What strikes us about antlers is that they are big. The rack on a bull elk is forty pounds of bone erupting from the head in two curved beams, each adorned with as many as seven sharp tines. In the largest bulls, antlers tower four feet above the male and arch backward over half the length of the rest of his body. That’s massive. And, although most of us never stop to think about it, we all know at some level that anything that big must also be expensive. In fact, the price bulls pay for their antlers is extraordinary, and they pay this price again and again since they shed and regrow their antlers anew each year.

Unlike the rest of the body, which takes years to grow to adult size, antlers in even the largest bulls go from nothing to full size in just a few months. Antlers grow faster than any other bone in any animal, and this record speed racks up record energetic costs. Estimates from antlers of a related species, fallow deer, show that while males are growing antlers they more than double their daily energetic needs. In addition, growing antlers suck up so much calcium and phosphorus—minerals that make up the bone—that the males cannot possibly get enough from their food. Instead, they leach these vital minerals out of other bones and shunt them to the antlers, depleting the rest of their skeleton so severely that they experience a seasonal form of osteoporosis. Their bones get weak and brittle at precisely the time of the year—the rut—when they must hurl themselves against eight-hundred-pound rivals in incessant battles for access to females. By the end of the rut, the males will have fought so often and so hard that they’ve lost a quarter of their body weight, and they emerge from this season battered, starved, and brittle boned. If they cannot replenish their reserves in the few short weeks before winter, they’ll starve.

Such is the reality of extreme animal weapons. Brutal and beautiful, extreme weapons have cropped up repeatedly during the unfolding of the history of life. All told, some three thousand species now wield them. That’s a drop in the bucket considering there are 1.3 million described types of animal, but it’s a collection packed with remarkable creatures. Early champions include the horns of triceratops, titanotheres, and trilobites, the tusks of mammoths and dolphins, and the racks of Irish elk. Today, extreme weapons are wielded by walruses, antelope, whales, crabs, shrimp, beetles, earwigs, plant bugs, and flies, to name just a few. The weapons themselves can be matted hair, bone, teeth, or chitin, and they take any number of different forms. Some, for example, are overgrown versions of an existing structure, like a tooth or a leg. Others appear to have arisen de novo, as new bumps or knobs that became so large they formed their own distinct structure. In absolute size, they run the gamut from quarter-inch “antlers” on a New Guinean fly to sixteen-foot tusks on a mastodon. Yet, relative to the size of the individuals who carry them, all of these weapons are massive.

This is a book about extreme weapons, structures so gargantuan and bizarre they look like they shouldn’t be possible—so awkward that the animals who bear them ought to tip over, or trip, or get tangled each time they attempt to move. Why are these weapons so big? What happens to animals once their weapons get this big? And is there such a thing as too big? To answer these questions, we’ll delve into the murky forests and mountainsides where animals do battle, immersing ourselves in the details of their lives in order to identify patterns: things these wildly different species all share in common, and things that illuminate the logic behind such extraordinary animal forms.

We humans are animals, too, and no book on extreme weapons would be complete without an examination of our own arsenals. We’ll see that the parallels between animal weapons and manufactured weapons run deep. In both cases, the vast majority of weapons are relatively unimpressive and small. But, here and there, circumstances arise that shatter the norm, sparking bursts of rapid escalation in weapon size called “arms races.” Very specific factors must fall into place before weapon evolution launches into one of these races, and it turns out that the same special circumstances triggering arms races in animals also prompt humans to manufacture bigger and bigger weapons.

Once started, both sorts of races quickly lead to extreme weapon forms—staggering in both size and cost—and along the way they each progress through the same sequence of recognizable stages. Analogous circumstances even bring about their collapse, as huge weapons come crashing down and the race dissolves. Ultimately, we’ll see that our animal counterparts can teach us a surprising amount about ourselves.

• • •

Animal Weapons is necessarily a book about evolution: the gradual turnover within populations that leads to changes in animal form over time. At its most basic, this evolutionary process is a simple one. Entities exist in multiple forms—they vary from individual to individual—and their individual characteristics are transmitted from one generation to the next. The transmission of this information is efficient but it’s not perfect, and mistakes get made along the way. Errors in the transmission of information lead to new characteristics—novel variations that crop up in the population from time to time. New variants now exist side by side with earlier forms, competing with them for resources and reproduction, and only some of them will persist.

Whenever individuals differ in how successful they are at propagating their kind, evolution occurs. This can be due to chance—random deviations in the reproductive success of types—or it can result from selection; individuals with some characteristics perform better than individuals with other characteristics, and as a result they leave behind more copies of their kind. Such a process, iterated over generations, results in the eventual replacement of inefficient with more efficient forms. The population evolves as the least effective types are culled and replaced by more effective types. As transmission errors yield new types of individuals, they inject fresh forms into the mix. If the new individuals do worse than the rest, they gradually disappear. If they do better, then the new forms can spread, replacing earlier forms in the process. This turnover is evolution.

Huge animal weapons look too awkward to be favored by selection, and in the vast majority of cases, this appearance isn’t misleading. Big weapons are ungainly, and most individuals fare poorly with them. For most weapons in most species, selection favors modest size and minimal cost—enough tooth to bite or grab prey, for example, but not enough to slow you down or impair your ability to maneuver. What this actually means is that selection on weapons is balanced: bigger weapons may be better for stabbing or biting, but they are also more expensive to produce and more difficult to carry. The result is a tenuous balance, much like a game of tug-of-war, which accounts for the multitude of unimpressive weapons adorning the vast majority of animal species.

Yet, every so often this balance is tipped. Here and there, sprinkled across the tree of life, are animal lineages where modesty of proportion was cast aside. The evolution of weapons in these species surged forward unencumbered. Gone were the shackles of balancing selection, and all that remained was selection favoring bigger and bigger weapon sizes. Here, individuals with the most grotesque or extreme armaments beat opponents with smaller weapons. In so doing, they secured opportunities to breed. Their progeny, as impressive in their weapons as their parents, quickly replaced earlier forms and advanced the population another notch in weapon size. As soon as the next new innovation arose—an even larger or more complex variant of the existing design—the process repeated itself. Again and again, individuals with the newest and biggest weapons won, replacing those with earlier and smaller forms, and this process pushed the population still further on the path to extreme. In short, the weapons of these species got caught up in an arms race.

Weapons swept into arms races begin small, but over time they get bigger and bigger, increasing in size faster and faster. So, too, this book will begin with the small, and proceed through ever-greater weapon extremes, assembling the biology of arms races in stages. Part 1, “Starting Small,” examines the mechanism of selection and the ways that weapon designs change through time. This is followed by a brief discussion of balance, the reason selection so often tugs weapons toward smaller and bigger sizes simultaneously, and of why this balance occasionally tips.

The biggest animal weapons result from males competing with rival males over access to females. Part 2, “Triggering the Race,” explores why this is true, and how competition leads to arms races. Competition drives rapid evolution of huge weapons, but only when two additional conditions are met. All three “ingredients” are necessary to trigger a race. By exploring each of them in detail, I’ll reveal for the first time the essential logic of huge weapons, explaining why these structures evolve in some species but not others, and why they attain such incredible proportions.

Part 3, “Running Its Course,” explores what happens after an arms race is triggered, describing in detail the predictable sequence of stages characteristic to the evolution of nature’s biggest weapons. Staggering costs, deterrence, and cheating all appear as intuitive milestones along the way, and costs and cheaters erode payoffs to huge weapons in ways that can set the stage for collapse. Appreciating how arms races unfold reveals a great deal about the weapons themselves, about the conflicts and contests surrounding their use, and about what happens when weapon evolution goes too far.

Finally, Part 4, “Parallels,” tackles head-on the evolution of extreme weapons in our own checkered past. Although I am a biologist (not a military historian), and this book is primarily concerned with diversity and extravagance in animal weapons, the parallels with our own armaments are too striking and exciting to ignore. Every element of arms races, from the conditions critical to launching a race, to the sequence of stages unfolding along the way, lends itself to comparisons between animals and people. Manufactured weapons are not inherited in the strict sense—instructions for their production are not encoded in DNA—and they are assembled in factories rather than wombs. The competitions they resolve are less likely to yield opportunities to mate, and success is often measured in currencies other than increased numbers of offspring. Nevertheless, human weapons change in shape, capability, and size over time, and the directions of this change are sculpted by forces of selection astonishingly similar to the forces shaping weapon evolution in animals. Arms races are arms races, and the natural history of extreme weapons, it turns out, is precisely the same.

Copyright © 2014 by Douglas J. Emlen; Illustrated by David J. Tuss

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