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Chimpanzee Personality Variables & Correlated Behaviors

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by: Audrey Dickey
Major: animal behavior

Relatively few studies have examined the question of whether personality exists among chimpanzees.  These few studies show that ratings of chimpanzee personality by humans are characterized by considerable validity and substantial interrater reliability.  Most of these studies were conducted on very small samples of chimpanzees and virtually none have attempted to correlate the behavior of the chimpanzees with their personality ratings.  The establishment of correlations between personality variables and behavior is an important goal, since these correlations can subsequently be used to predict behavior and promote the wellbeing of captive chimpanzees.  Fifty-two chimpanzees were observed for six months and their behavior was correlated with personality ratings obtained from four humans who were extremely familiar with all the chimpanzees.  

Personality refers to an organism’s characteristic patterns of behavior that are stable over time and across situations.  Animal personality research involves the examination of evolutionary continuity between humans and other animals, as reflected in the variables related to the study of personality.  In human personality research, five major dimensions of personality that can account for most individual variation in personality have been identified.  These five factors are usually referred to as the Big Five, and include surgency (extraversion), emotionality (neuroticism), dependability, agreeableness, and openness.  When humans are asked to judge animal personality, similar personality dimensions have been identified for groups of nonhuman primate and other animal species.
    
The chimpanzees observed and rated for this study are housed at The University of Texas M. D. Anderson Cancer Center in Bastrop, TX.  Chimpanzee behavior was observed from October, 2001 through March, 2002.  Four individuals (all of whom were extremely familiar with the 52 study animals) were asked to judge the personalities of the chimpanzees by rating (on a scale from 1 to 7) all of the animals on a total of 34 adjectives (e.g., aggressive, eccentric, sensitive).  Factor analysis was performed to identify discrete personality factors.  Correlational analyses were performed to determine the relationship between personality factors and behavior.
    
Three personality factors were identified from the initial factor analysis of the personality ratings.  These factors were named subordinance, comprised of adjectives such as submissive, fearful, insecure, and tense; openness, comprised of adjectives such as playful, curious, friendly, and sociable; and contentiousness, comprised of adjectives such as belligerent, irritable, and aggressive.  Preliminary correlational analyses suggested that chimpanzees rated high on subordinance also exhibited higher levels of submissive screams and lower levels of aggressive displays.  Similarly, chimpanzees rated high on openness exhibited higher levels of time spent near other chimpanzees and lower levels of solitary play.  Finally, chimpanzees rated high on contentiousness exhibited fewer submissive screams and rarely attempted to avoid an impending aggressive incident.  
    
These data show that using human judgements of personality can be an effective means of identifying personality traits in chimpanzees.  Our data are consistent with previous research in the area of animal personality.  Importantly, the three factors we identified, subordinance, openness, and contentiousness, are extremely similar to both some of the Big Five personality factors for humans and some of the factors identified in earlier studies of animal personality.  The significant positive correlations found between personality judgements and observed behaviors validate the utility of personality judgments in the behavioral management of captive chimpanzees.  By better understanding their psychology, behavior, and social interactions, we can better predict their responses to captive manipulations, and thereby enhance their wellbeing and the care they receive.