https://www.scientificamerican.com/article/the-weapons-of-sexual-rivalry1/

In the vast arsenal of animal weaponry, the most exaggerated, elaborate and diverse devices such as tusks, claws and antlers have not been shaped by a need to fend off fierce predators. Rather, these impressive forms are driven by sex.

“Everybody understands at a gut level that it’s usually males that have flashy displays or weapons like tusks and antlers,” says Doug Emlen, an animal weapon expert at the University of Montana in Missoula. Biologists say that these fantastic shapes—from the giant curved tusks of woolly mammoths to the nightmarish jaws of stag beetles—evolved to ward off competition from rival males and to impress females.