Most of the truly gargantuan armaments in the animal world owe their excesses to this form of competition. Reproduction is the "other half" of success, in an evolutionary sense (we've already looked at survival). But it's the half that really matters. When you strip the essence of life to its core, the only reason to survive is to have a shot at breeding, and, at the end of the day, it's how many offspring you produce that determines success or failure on the evolutionary stage. Individuals reproducing the most win, plain and simple. They contribute more copies of their genome to subsequent generations of the population than other individuals do. Their alleles persist, while others gradually disappear.

Emlen, Douglas J, Animal Weapons_ The Evoluti…, loc. 186