Animal weapons: the evolution of battle

Abstract

Douglas J Emlen’s Animal Weapons is a hard-hitting campaign—a bit of a Blitzkrieg through major themes in evolutionary escalation, peppered with dazzling examples from across the spectrum of animals and their adaptations, from the horns of dung beetles to the guns of battleships. Although the major lessons of offensive and defensive weaponry, escalation, and sexual selection will be quite familiar to any biologist or biology teacher, Emlen is so intimately immersed in those subjects and such a good communicator that he easily weaves them into some clever new syntheses and clear comparative frameworks. Emlen convincingly shows that there is essentially no difference between the weapons of humans and those of all other species. All of the chapters are infused with examples from the animal world and the world of human technology, and a final section focuses on these parallels in the specific cases of human fortresses (of the land, sea, and air varieties) and weapons of mass destruction. Throughout, he shows that if certain conditions apply—if there are scarce and defensible resources and the opportunity for head-to-head combat— there will be escalation toward bigger and more dangerous weaponry. This parallelism holds up even though much of human weaponry evolves through conscious design and by sharing information laterally rather than through the natural process of descent with modification. Although he doesn’t dwell on it extensively, it is rather remarkable that discoveries of modern biology—particularly the more recent understandings of lateral gene transfer in bacteria, viral evolution, and epigenetics—bring the world of biological evolution even closer to the world of human systems evolution. I can’t go further without mentioning the illustrations by David J Tuss. They are dazzling, emotive, and highly informative. Especially when composed around intra- and inter-specific comparisons, they become far more than eye candy: they are real tools to aid Emlen’s various syntheses. An especially great example is a comparative study of the common curling-up defensive postures of species as far afield in time, space, and phylogeny as trilo bites, pill bugs, cuckoo bees, armadillos, and pangolins. Another comparative illustration, of same-age male elk and beetles with wildly different horn sizes, hammers home Emlen’s point that there are many ways to go about using (or not using) weaponry that your species and sex might be predisposed to produce. The overwhelming recurring theme of Animal Weapons is the multidirectional nature of evolution. Almost every example that Emlen discusses—horns on beetles, armor on knights, antlers on deer—gets bigger, smaller, bigger again, and/or altogether forgotten, depending on where and when you start to look. Weapons get larger and more ominous until they become too costly, or the environment changes, or some disruptive agent turns