Posture and reaching in tufted capuchins (Cebus apella)

Area of Science:

• Primate behavior
• Evolutionary biology
• Neuroscience

Background:

• Lateral bias, or handedness, is a key feature in primate motor control.
• Understanding the evolution of bipedalism and handedness in primates offers insights into human evolution.
• Tufted capuchin monkeys (Cebus apella) serve as a valuable model for studying primate locomotion and cognition.

Purpose of the Study:

• To investigate the influence of posture on reaching bias in tufted capuchin monkeys.
• To compare hand preferences during quadrupedal versus bipedal reaching tasks.
• To explore the evolutionary implications of capuchin handedness for human bipedalism and right-handedness.

Main Methods:

• Observational study comparing food-reaching tasks in capuchin monkeys.
• Analysis of hand preference and strength of preference in both quadrupedal and bipedal postures.
• Comparison of reaching biases between adult and immature individuals.

Main Results:

• A population-level right-hand bias was observed for bipedal reaching, but not quadrupedal reaching.
• Adult capuchins displayed a stronger right-hand preference for bipedal reaching compared to immatures.
• Subjects exhibited a greater preference strength for bipedal reaching than quadrupedal reaching.
• A positive correlation was found between hand preference direction in quadrupedal and bipedal reaching.

Conclusions:

• Posture significantly affects lateral bias in food reaching in capuchin monkeys.
• Capuchins offer a primate model suggesting right-handedness evolved before significant brain expansion in hominids.
• The findings support the hypothesis that bipedalism and right-handedness co-evolved early in hominid lineage.