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King Creativity at Southwestern

Brain Asymmetries: New Ways to Assess Laterality in Chimpanzees

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by: Nicole Buehler
Advisor: Steve Schapiro

My King Creativity project explored the evolution of brain specialization through the empirical analysis of handedness in chimpanzees as a behavioral indicator of laterality. I achieved this by investigating new dimensions of handedness, and therefore laterality by looking at a variety of tasks. These insights can further our understanding of human brain specialization, and early human brain development, since chimpanzees are our closest living ancestors.

Multiple tests have been done on handedness, however the tasks studied so far were fairly standard feeding tasks. I looked at a wide variety of tasks that had not been previously studied for handedness, such as grooming, gesturing, locomotion, and bimanual eating (holding food in one hand and eating with the other). These additional tasks add a new dimension to previous data.

In order to acquire the data needed to determine handedness, I observed 130 chimpanzees and recorded the hand(s) they used to 1) groom one another, 2) gesture for food from a human, 3) take their initial step when walking, and 4) eat with (while holding additional food items). These data were recorded twice a week for a total of eight hours per week for about 15 to 20 weeks. The acquired data sets have been analyzed to determine whether individuals display “handedness” and whether chimpanzees display a population-level bias toward handedness.

Seventy chimpanzees displayed a significant hand preference on at least one of the four tasks. Of the animals that exhibited handedness, a significant proportion displayed right-handedness for bimanual feeding or gesturing. Grooming did not show the same bias however; relatively few animals had enough data to meet the criteria for analysis. These results, similar to previous findings, further the argument that chimpanzees may exhibit laterality, and therefore show brain specialization.

Studying laterality through handedness is an innovative idea that has not been fully explored. This expansion of the tasks studied for handedness and therefore laterality, allowed me to assess a broader range of brain functions rather than just the standard feeding behaviors. This new data will give us a better understanding of the extent of chimpanzee handedness, and therefore a broader insight into brain laterality and specialization. The combination of my data with previous feeding data collected by others suggests that lateralization is a generalized phenomenon as opposed to being confined simply to feeding behaviors. By coming closer to discovering how the chimpanzee brain works, we gain an insight on the inner workings and evolution of the human brain. This information on the chimpanzee brain will help answer questions such as what was the line of development the human brain followed, why are our brains highly specialized, and why are some species’ brains not specialized in this way.