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Why are Old World monkey canines often larger in males than in females?

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A labeled cross section illustration of an adult human molar shows the tooth's crown and root, with layers including enamel, dentin, and pulp, as well as gum, cementum, blood vessels, periodontal ligament, lateral canals, and nerve. — tooth Cross section of an adult human molar.

In Old World monkeys, the presence of larger canine teeth in males compared to females is a result of sexual dimorphism driven by sexual selection.1

These teeth serve functions beyond digestion, playing a significant role in maintaining social order and acting as weapons in an overtly offensive capacity. Because males often compete with one another for access to mates, those with larger, more formidable canines may achieve greater success in these contests of strength and dominance. Consequently, these teeth function as tools for both protection and threatening displays, which are critical for establishing hierarchy and securing reproductive opportunities within the group.12345