Here I build this story around costs; specifically, the observation that costs are steeper for individuals with fewer resources. This idea is an integral assumption of most models of animal signaling, and it surely applies most of the time. But there are exceptions. As I was writing this book, a doctoral student in my lab, Erin McCullough, was systematically unraveling this notion for the rhinoceros beetle we study. Her work shook the field, because everyone—including myself—assumed that the giant pitchfork horns in these beetles were costly. How could they not be? These weapons are two-thirds the length of the beetle, and they splay forward in front of the animal’s face like a massive pitchfork. Yet, these horns turned out to be remarkably inexpensive to produce, and virtually cost-free to fly around with.

Emlen, Douglas J, Animal Weapons_ The Evoluti…, loc. 810