How do the horns of a mammal grow? 

Horns grow from the skull of an animal, at the front of the head. 

Horns start growing from birth, and continue to grow throughout the life of the animal. 

Horns are hard and hollow. They are made of keratin, which is the same material as human fingernails.

Horns are permanent. If a horn falls out, it does not grow back.

In some species, only the male has horns, and in other species, both the male and the female have horns. 

Photographer: Martina Nicolls

Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM