From the WildlifeCampus Course: Behaviour Guide to African Herbivores

Unlike all other mammals, the giraffe has the main pair of horns present even in the embryo, formed of cartilage from a layer of skin and unattached to the skull. They lie flat and present no obstacle to birth, but within a few days stand erect and appear prominent, mainly because of terminal tufts of long hair. While growth proceeds from the base, bone deposition begins at the tips and proceeds downward. Fusion with the skull occurs at 4 – 4½ years in males and after 7 years in females. Rather than attaching to the frontal bones, as in deer and antelopes, the giraffe's main pair take root further back, in the parietals.

Male horn growth continues through a unique process whereby bone of dermal (skin) origin is deposited over the whole surface of the skull except where muscles attach. Apart from the parietal and median horns, bone accumulates as knobs at the base of the skull, over the eyes, and on the nose.

Gradually the male's head becomes a massive knobbed club which is used to gain the dominance that spells reproductive success. The skull of a 15-year-old bull may be 7 kg heavier than that of a bull half his age, and assuming body growth also continues after maturation, older bulls also have a size advantage. Maximum age in the wild is about 25 years