Red In Horn and Claw

Animal Weapons: The Evolution of Battle by Douglas J. Emlen
My rating: 3 of 5 stars

Why don't all animals evolve fearsome weapons like saber tooth tigers? Why do some beetles have horns at 30% of their body weight? Why do elk grow antlers so big each year that they have to leech calcium from their bones to do so, giving themselves "seasonal osteoporis?"

This is a remarkably clear read about how much more we know that I learned in high school. It's primarily about evolution, and secondarily about the joys of biologist doing field work with dung beetles and howling monkey feces. (I kid; of course there are multiple types of fecal matter during the author's career.)

The outlier in my examples above is the tiger, whose teeth evolved for use in hunting. They came at a cost of mobility, which was acceptable because the tiger became an ambush predator, jumping on larger animals and chomping down. Put the teeth on a lynx or a house cat named Timmy and their hunting skills would plummet. That trade off makes massive weapons rare--thousands of species have them, but it's a relative drop in the bucket of life.

Most animals evolve massive weapons for intraspecies fighting. If you are fighting something with a big horn, it makes sense for yours to be just a little bigger--and the next generation the logic still holds. Once the arms race starts it becomes self-perpetuating, even if the cost is high in resource needs and mobility. Sometimes fights are mostly posturing (which is what I believed was the default starting the book)--fiddler crabs wave their claws and the smaller one backs down. Other times though it's brutal, as elks and deer seem to fight literally round the clock, wearing themselves our, during mating season.

Which raises the question of why fight in the first place? That high school answer was "over females"** and it's correct, but the book covers more specific requirements such as a gender imbalance in breeding-ready animals and geographical restrictions on resources that make defending controlling them worthwhile.

Reading about many of the examples leads to the thought that males really should have something better to do. Think about the way non-breeding ant drones work for the success of their kin; this is the opposite, a species wasting massive resources and energy fighting itself almost entirely for individual benefit. It sounds like some beetles have females digging tunnels, carrying in tastydung, and laying the eggs while the males just fight each other to control the tunnel entrance; this can't be a net positive. But it makes evolutionary in certain situations, at least for a while.

There are asides into human battle, which I admit was part of the gimmick that got me to buy the book but I found almost uniformly lacking in insightful or interesting comments. The author is a biologist, not a historian. Fortunately these sections are quite brief.

*Well, figuratively, but I like the image of male elk staking out mating territory around clocks.

**Or in rare cases, such as the jacana bird, over the males.

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