Wide faces or large canines? The attractive versus the aggressive primate

Area of Science:

• Primate evolutionary biology
• Human evolution
• Paleoanthropology

Background:

• Hominids exhibit significant body size dimorphism, indicating strong sexual selection.
• Despite this, hominids lack pronounced canine size differences, unlike many primates where canine dimorphism signals intrasexual competition.

Purpose of the Study:

• To investigate the paradox of strong sexual selection without canine dimorphism in hominids.
• To examine sex differences in hominoid facial morphology as an alternative indicator of sexual selection.

Main Methods:

• Comparative analysis of facial morphology across hominoid species.
• Quantification of sexual dimorphism in face width, controlling for body size differences.
• Correlation analysis between facial dimorphism and canine dimorphism in anthropoid primates.

Main Results:

• Chimpanzees, but not gorillas, display significant sexual dimorphism in face width beyond body size effects.
• This facial width dimorphism is negatively correlated with canine dimorphism across anthropoid primates.
• The findings challenge the assumption that lack of canine dimorphism implies weak sexual selection.

Conclusions:

• The evolution of broader faces in hominid males, alongside reduced canine size, is linked to strong sexual selection.
• Mate choice, potentially influenced by facial features like cheekbones, may drive these morphological changes.
• Facial width dimorphism serves as a key indicator of sexual selection pressures in hominoids.