Elephant tusks are actually a pair of elongated teeth. They are the largest and heaviest teeth of any living animal. The tusks are used for digging for roots and water, stripping the bark off trees for food, fighting each other during mating season, and, in savanna and forest elephant cows, warding off predators of baby elephants such as lions and tigers. In a calf, the first incisors are replaced within 6 to 12 months of birth. The second set, which become the tusks, grows at the rate of about 17 cm (about 7 in) per year throughout life. Tusk growth is determined by genetics and nutrition, and over the years, normal wear and tear scales down their length.