Sex difference in chimpanzee handedness.

Area of Science:

• Primate behavior
• Evolutionary biology
• Neuroscience

Background:

• Monkeys and apes are typically considered ambidextrous, lacking population-level hand preferences.
• Strong individual hand preferences in naturalistic tasks have been infrequently observed in non-human primates.
• Bimanual actions requiring coordinated, specialized hand roles may favor lateralization.

Purpose of the Study:

• To investigate hand preference (handedness) in chimpanzees performing bimanual tasks.
• To examine sex differences in hand preference within a chimpanzee population.
• To explore the evolutionary implications of observed handedness patterns for human handedness.

Main Methods:

• Observation of chimpanzees at Mahale, Tanzania, engaging in naturalistic bimanual processing of Saba florida and Citrus lemon fruits.
• Recording and analysis of individual hand usage during specific bimanual actions.

Main Results:

• Chimpanzees demonstrated significant individual hand preferences during bimanual fruit processing.
• A clear sex difference emerged: most males showed left-hand preference, while most females exhibited right-hand preference.
• These findings contrast with the general assumption of ambidexterity in non-human primates.

Conclusions:

• Lateralization of manual actions is advantageous in complex bimanual tasks requiring role differentiation and a combination of power and precision.
• The observed sex-specific handedness pattern in chimpanzees may reflect an ancestral state shared with humans.
• This ancestral pattern could potentially explain the higher prevalence of right-handedness in human females compared to males.