What these broad patterns reveal is a simple and surprisingly universal rule: after the final ingredient for arms races falls into place, entire clades of descendant species can all experience rapid evolution of extreme male weapons. Mastodons and flies could not be more different from each other. They lived at different times, in different habitats, and fed on different foods. One was more than 120 million times the size of the other. One had enlarged teeth, and the other had chitin protrusions from the forehead. Yet, the same three ingredients triggered evolution of extreme weapons in both cases. So it is with wasps, beetles, crabs, earwigs, elephants, and antelope. Despite extraordinary differences among these species, arms races are arms races, and the circumstances leading to big weapons are the same.

Emlen, Douglas J, Animal Weapons_ The Evoluti…, loc. 277