The animal arms race Animal Weapons The Evolution of Battle Douglas J. Emlen Henry Holt, 2014. 288 pp.

Abstract

![Figure][1] ![Figure][1] PHOTO: IGOR SIWANOWICZ The visually striking weapons of living creatures—antlers, horns, teeth, and spines, to name a few—have fascinated biologists for a long time. These are most often used in the context of competition for resources or access to females. But why is it that some animals do not have weapons, or have only modest ones, whereas others have developed massive and evolutionarily expensive weaponry? In Animal Weapons: The Evolution of Battle , evolutionary biologist Douglas Emlen investigates the specific conditions under which extreme animal weapons evolve. A skilled storyteller, Emlen takes the reader to Panama to observe dueling Harlequin beetles; to Tanzania to collect elephant excrement—and the dung beetles that live on it; and to tropical forests where stalk-eyed flies defend their harems of females. The weapons discussed in these stories are illustrated in stunning color plates. Emlen argues that three preconditions are necessary for triggering an arms race that leads to extreme animal weapons. First, there must be competition for a limited resource, such as food or access to reproductive females. Second, the limited resource must be confined to well-defined locations so that one animal can control access to it (i.e., the resource must be “defensible”). Third, males must fight one-on-one; guerillastyle warfare does not lead to the evolution of extreme weapons. Emlen's third condition is inspired by a set of mathematical models of human warfare published by the British engineer and mathematician Frederick Lanchester in 1956 ([ 1 ][2]). Before the invention of firearms, soldiers in battle fought one-on-one, and soldiers were limited to attacking one opponent at a time. The winning army was determined by the effectiveness of each soldier, multiplied by the number of soldiers. In this context, better weapons (and better protective armor) made a significant difference to the outcomes of a battle. On the other hand, the invention of firearms was a game changer because it allowed a single soldier to attack multiple foes simultaneously. According to Lanchester's model, the effectiveness of an army that uses firearms is proportional to the number of soldiers squared. In this context, the number of soldiers matters more than the relative quality of the firearm. Weapons (and armor) matter most in one-on-one battles. Emlen uses this rationale to explain why species that go head-to-head are more likely to develop big weapons. Emlen's thesis not only makes sense of the biological diversity of animal weapons—it also helps to explain human political and military dynamics, which he discusses in the last quarter of the book. Indeed, escalation is not just a phenomenon of biological evolution but also a feature of human culture and politics. The book's treatment of military escalation helps make sense of the post–Cold War proliferation of acts of terrorism and the development of new and more deadly weapons. According to Emlen, terrorism and weapons of mass destruction are also game changers that circumvent the traditional models of warfare. These new forms of battle therefore require a different suite of weapons and defenses. We may not face another nuclear escalation, but the development of new strategies and weapons will surely continue. It is difficult to estimate how long it will take before these new tactics and weaponry raise the stakes of war even further, but as Emlen concludes, “We're not likely to survive another arms race.” 1. [↵][3]1. J. R. Newman 1. F. W. Lanchester , in The World of Mathematics, vol. 4, J. R. Newman , Ed. (Simon and Schuster, New York, 1956), pp. 2138–2157. [OpenUrl][4] [1]: pending:yes [2]: #ref-1 [3]: #xref-ref-1-1 View reference 1 in text [4]: {openurl}?query=rft.jtitle%253DThe%2BWorld%2Bof%2BMathematics%26rft.volume%253D4%26rft.spage%253D2138%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx