True horns are permanent, paired protuberances that are tough, strong, and durable. Thick layers of a fibrous protein called keratin surround a horn’s bony core. In some species, both males and females have horns. In others, only males have them.
BY Donna Parham
Photography by Ken Bohn
Photos: (Jackson’s chameleon) Hawaiian/iStock/Getty Images Plus; (Markhor) HeitiPaves/Getty Images Plus.