Handedness is more than laterality: lessons from chimpanzees.

Area of Science:

• Primatology
• Human Evolution
• Behavioral Neuroscience

Background:

• Human handedness, a consistent bias in using one hand over the other, is a hallmark of Homo sapiens.
• Understanding the evolutionary origins of handedness requires comparative studies with our closest living relatives, chimpanzees and bonobos (Pan spp.).
• Distinguishing between hand preference, manual specialization, and true handedness is critical for accurate cross-species comparisons.

Purpose of the Study:

• To investigate whether chimpanzees and bonobos exhibit species-wide handedness comparable to humans.
• To clarify the definitions of handedness, hand preference, and manual specialization in comparative contexts.
• To explore the influence of factors like tool use and population variation on manual laterality in Pan species.

Main Methods:

• Reviewing existing literature on the behavioral manual laterality of chimpanzees and bonobos across various tasks.
• Analyzing studies focusing on tool use and other activities to assess manual specialization and preference.
• Considering methodological challenges such as ecological validity and confounding variables like bimanuality.

Main Results:

• Chimpanzees display significant evidence of task specialization in manual laterality.
• While hand preference and some manual specialization exist in chimpanzees, there is no conclusive evidence of species-wide handedness in the strict sense.
• Manual laterality in chimpanzees, particularly during tool use, shows considerable variation within and across populations.

Conclusions:

• Human handedness, defined as consistent congruence across subjects and tasks, appears to be unique among living hominoids.
• The complex manual laterality observed in chimpanzees differs fundamentally from the established handedness in humans.
• Further research is needed to fully understand the evolutionary trajectory of manual asymmetries in the hominoid lineage.