Final answer:
The weaponry observed on many male animals results from intrasexual selection, which is competition among males for mating rights. Traits like horns or antlers are energetically costly and may negatively impact survival, but they persist because they offer a reproductive advantage to the males who win mating contests.
Step-by-step explanation:
The type of selection most likely responsible for the development of weaponry (horns, antlers) in many males is intrasexual selection.
Intrasexual selection refers to the competition between individuals of the same sex, typically males, for reproductive opportunities. This competition often involves mating displays and aggressive behaviors such as the battling of rams. The victors of these contests are usually the ones that get to mate, leading to the propagation of their genes and, consequently, the traits that allowed them to win—such as larger horns or antlers. The weaponry is not necessarily for survival against predators but for success in mating. Examples of intrasexual selection include the head-butting contests of male rams and the massive antlers found on species of deer during mating season. These traits are expensive in terms of energy and can be a risk to survival, yet they persist due to the reproductive advantage they confer to the bearers.
Other types of selection, like intersexual selection and frequency-dependent selection, play roles in the evolution of different characteristics, such as elaborate plumage chosen by females or color variations that give mating advantages based on rarity or commonness. However, intrasexual selection is the primary evolutionary mechanism behind the development of male weaponry.