Reviewed: Animal Weapons, by Douglas J. Emlen

by Paul Braterman

AnimalWeaponsI have had enough of arguing with creationists. If force of argument could defeat them, they would have disappeared long ago. The reality is that people believe what they want to believe, that they like what they like, and that they are much more interested in what relates to them directly than they are in scientific abstractions. So the way to defeat creationism is to present the scientific reality in ways that are engaging, enjoyable, and above all personal. In this post, I review one of three recent books that succeed in doing this, using very different approaches. The other two will form the subject of my next post.

Animal Weapons
, by Douglas J. Emlen, is subtitled The Evolution of Battle, and compares the evolution of weaponry by animals with that of human warfare. The book is greatly enriched by drawings by the graphic artist David J. Tuss, who specialises in the dramatic portrayal of scientific material, although, thanks to the extraordinary development of animal weapons, I found some of the illustrations difficult to follow.

EmlenLabEmlen himself is a professor of biology at the University of Montana, and his laboratory's website is itself a feast to behold. One of his group' aims is, as stated on that site, to actively communicate the excitement of evolutionary biology to broad audiences through books and the popular press, contributing to public understanding of animal diversity and morphological evolution and Emlen is co-author, with Carl Zimmer, of Evolution, Making Sense of Life, one of the few university level textbooks I have come across that can be read for pleasure. Emlen's own original Ph.D. project, which he refers to in the book with evident nostalgia, involved fieldwork in Central America studying dung beetles. It turns out that some species of dung beetles do, and some do not, develop extravagant weapons. Ball-rolling dung beetles squabble over balls of food carved out from the droppings of larger animals, but the fights are free-for-all scrambles and they do not become heavily armed. Tunnelling dung beetles hide their trophies in burrows with narrow entrances. Females feed and hatch their young at the bottom of these tunnels, and males duel fiercely to retain possession of these. This duelling situation leads to direct selection pressure in favour of larger weapons, despite their cost; Emlen himself showed that selecting for larger weapons exacted a direct cost in poorer development of other organs, such as the eyes. Burrowing dung beetles develop weapons, while ball-rolling dung beetles do not.

This illustrates a general point about weapons developed for control to resources. The resources need to be defensible, like burrows, or (to take other examples that Emlen cites) tree branches, or sap-oozing nicks on tree trunks.

Throughout the animal kingdom, some species do, and some species do not, develop fierce weapons 148px-Lascaus,_Megaloceros (1)whose only function is to fight others of their own kind. Among large animals, these weapons are generally a feature of the males, and are used in duels to decide access to females, either directly or through control of resources such as food or territory. The costs of these weapons to those who possess them are enormous. Stags, for example, devote so much calcium and phosphorus to building up the calcium phosphate in their antlers, that they cannot get enough from their food and deplete their skeletal bones to make up the shortfall. The most extreme example in the deer family is the extinct Irish elk (Lascaux cave painting shown R), where extravagant and development seems have been so demanding as to leave the animals with no margin to spare when changing climate reduced the amount of fodder available. However, the cost of not having the best weaponry is, from an evolutionary point of view, prohibitive. There is nothing worse for your genetic inheritance than failure to secure mating opportunities.

Less extreme are weapons developed by some carnivores, such as sabretooths, who had 10 inch long canines capable of breaking the back of a mammoth. But these also are expensive to their possessors, requiring adaptations of the skull and neck that make fast running impossible, and sabretooths are thought to have ambushed their prey by dropping down from trees.

640px-Alcazaba1The counterpart of offence is defence, and the counterpart of weaponry is armour and fortification. A mediaeval fortress would be defended by two sets of walls, the outer one shielding the inner from bombardment, the only entrances being narrow gateways easily guarded by a few heavily armed soldiers, in a space too confined for attackers to take advantage of numerical superiority. The same is true of termite mounds, which are capable of withstanding attack by a column of army ants; similar causes produce similar effects.

Human weaponry evolves rapidly, under cultural pressures, as the result of technical innovation, with long periods of stasis in between. The invention of the battering ram transformed ships from mere vehicles for fighting men into weapons able to destroy each other, so that naval warfare became a matter of duels in which the largest and fastest ship would be the winner. This led over the course of some 300 years from 600 BCE onwards to the development of multiple rows of oars until the ships grew too unwieldy to manoeuvre (one of my very few complaints about this book is that it tells this same story twice). Individual human weaponry can become very expensive, like knightly armour. Such weaponry can also suddenly disappear, as armour became useless against improvements in crossbows, longbows, and, eventually, firearms, much cheaper and more available to the common citizenry than the panoply of a mounted knight, only to reappear in our own time with the development of Kevlar. The arms race between fortification of cities and the development of siege warfare machinery came to a rapid end in modern times with the appearance of artillery. Human warfare can also evolve in surprising ways, as in the development from the Vietnam War to the present day of asymmetric combat, depending on small locally based militias operating in small groups against the massed might of great powers.

In nature, arms races can come to an end in several different ways. They can reach equilibrium, Sneaky4when the additional expense of even larger weapons is not enough to compensate for the sheer difficulty of maintaining them. In a population of lumbering heavily armed creatures, small, nimble variants can become, at least for a while, more successful, but once these have taken over completely the arms race can start all over again. This has happened many times in dung beetles and in antelope. Heavy weaponry can be bypassed or its owners tricked. For example, small dung beetles can dig parallel burrows that bypass the guarded main entrance, mate with the female, and leave the same way they came, with the guardian none the wiser. Or, as in the case of the Irish elk, changed circumstances may make the hereditary weaponry nutritionally unsustainable, bringing the arms race to an end through the disappearance of the population.

B-2_first_flight_071201-F-9999J-034There is one important difference between human and animal arms races that Emlen does not discuss.
Natural selection is brutal but rational, and expensive armament does not survive unless it does in reality contribute to its owner's individual fitness. Human weaponry is very different, because it is the result of political choices. Hence the persistence of such enormously expensive projects as the US Stealth Bomber programme (each B2 bomber, shown L, cost $2 billion in 1997 dollars), the entire British and French “independent” nuclear weapons programmes, or the bloated nuclear arsenals of the United States and, in its time, the Soviet Union and now of Russia, despite their total irrelevance to any actual or conceivable military situation. Indeed, if the author's account of the Able Archer crisis of November 1983 is correct, the last of these came perilously close in November 1983 to bringing our civilisation to an abrupt end for no good reason whatsoever. Dung beetles have better sense.

In my next post, I will be reviewing The Incredible Unlikeliness of Being, by Alice Roberts, and Grandmother Fish, by Jonathan Tweet.

Animal Weapons, by Douglas J. Emlen, Henry Holt, pp 288, Hardback ISBN-13: 978-0805094503, Nov. 2014, from £ 11.19/$13.95; Paperback, Picador, scheduled for December 2015; Audio CD/Audiobook available.

Irish elk, as shown in book, HTO, Wikimedia Commons, public domain. Double-walled Alcazaba of Malaga, 11th Century, Photo Gaxul via Wikimedia. Sneaky male dung beetle from book. B2 image by USAF via Wikipedia.

Disclosure: the copy reviewed was my own personal purchase.