I couldn't tell you yesterday during the film, but the mammoths and mastodons having tusks has actually yielded some interesting data. The tusks grow annual rings, with the thickness representing health, just like trees. They found that at around a certain age, male tusks' rings get really thin for a while, and then thicken again, but this is absent from female rings. This is interpreted as the females living in herds and essentially kicking the males out, who go through a period of sub-par nutrition while they basically wander around and figure their lives out.