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Animal Weapons: The Evolution of Battle is written by an evolutionary biologist, who extended research into arms and armament evolution while studying the origin of weapons in varied species found all across nature.

The first part starts with species that developed comparatively small weapons. We see carefully developed spines in stickleback fishes, porcupines, and many other species that changed their anatomy over time to tackle the surrounding changes. These changes take multiple generations of time, paying the cost by their bodily features and functions. It should be noted that these are not weapons proper, but rather, defensive armor. The chain of development starts from a purely defensive body cover—void of any means to attack—to the growth of small weapons to aid in defense,  to the generation of enhancements (like venom, acid, etc) in those small weapons. We see that in the case of sticklebacks, marine fish have better weapons than freshwater fish (whose anatomy varies in a mere period of years).
 

A similar pattern is observed when we study the teeth and claws of wildlife species of sabertooths, cats, wolves, etc. Each species developed their attacking weapons based on their environmental needs. The evolution of large sizes increased their power to deal damage to their prey. But enhanced performance in one context can detract from performance in another, forcing a compromise. For some time, there were different kinds of tradeoffs in most of these species—speed, agility, ability to hunt or even chew, etc. In Fact, bigger weapons were better for killing prey, but they also prevented an animal from catching prey in the first place. Eventually, they became extinct.
 

For as long as we can imagine, deadly jaws, fangs, and canines served as the primary weapon. Different animal species settle on their body structure while evolution takes several turns. Many techniques, like sit and wait, ambush and target are direct results of how to make the most out of your weapon. Small predators like praying mantis have a limb mechanism similar to the working of a gun mechanism. Species like Mantis Shrimp even use the concept to cause vacuum explosions to stun nearby prey.

Following this path, numerous changes in the armor of soldiers were made during the earlier eras of warfare. To strike a balance has always been key. Even in tribal battles, spears/ax modifications juggled in size with the passage of time. As we see in the later parts, development along the same lines leads to far greater advances in modern arms.