Personality in Bonobos

Abstract

To better understand human and chimpanzee personality evolution, we obtained trait ratings of personality for 154 captive bonobos (~80% of the U.S. and European population). We found factors that we labeled Assertiveness, Conscientiousness, Openness, Agreeableness, Attentiveness, and Extraversion. The interrater reliabilities and test-retest reliabilities for these factors were comparable to those found in humans and other species. Using orthogonal targeted Procrustes rotations, we compared the bonobo dimensions with those of three samples of captive chimpanzees. Overall congruence coefficients indicated a fair degree of similarity; at the factor level, there was good evidence for Assertiveness, Conscientiousness, Openness, and Agreeableness in the chimpanzee samples; evidence for Attentiveness and Extraversion was poor. These findings suggest that, as expected given their close phylogenetic relationship, bonobo personality structure resembles chimpanzee personality structure in some respects. However, divergent evolution, perhaps as a result of socioecological differences between bonobos and chimpanzees, also appears to have shaped personality structure in these species.

Keywords

behavior chimpanzee evolution primate

Studying humans’ closely related nonhuman relatives—the great apes—helps in understanding the evolution of complex behavioral phenomena. One recent application of this approach has been to study the organization of personality traits into dimensions (e.g., Gosling & Graybeal, 2007), with the goal of identifying which personality dimensions are ancestral (i.e., descended from a common ancestor species) and which are derived (i.e., recently evolved in response to ecological or social challenges faced by a given species).

Humans and chimpanzees share a common ancestor that lived 6 million years ago (Glazko & Nei, 2003). A study of chimpanzees whose personalities were rated by zoo keepers and volunteer research assistants found six personality dimensions (King & Figueredo, 1997). Dominance, the first dimension identified in that study, consisted of traits related to competitive prowess; the remaining five dimensions identified in that study resembled the domains of the human five-factor model (or Big Five)—extraversion, conscientiousness, agreeableness, neuroticism, and openness (Goldberg, 1990; McCrae & Costa, 1999). Broadly speaking, most or all of these dimensions have been identified in studies of chimpanzees living in environments other than zoos (King, Weiss, & Farmer, 2005; Weiss, King, & Hopkins, 2007) and in studies using different rating forms (Dutton, 2008; Freeman et al., 2013).

We sought to better understand chimpanzee and human personality evolution by assessing personality in bonobos. The common ancestor of bonobos and chimpanzees lived about 1 million years ago, and thus bonobos share a common ancestor with humans and chimpanzees (Glazko & Nei, 2003). Bonobos are closely related to chimpanzees and, like chimpanzees, live in fission-fusion societies in which females are the dispersing sex (Furuichi, 2011). Nonetheless, bonobos differ from chimpanzees in several key respects. First, compared with chimpanzees, bonobos live in more stable and predictable environments with low seasonality and more stable food availability (Furuichi, 2011). This is believed to have led bonobos to have a lower degree of fission-fusion and lower rates of inter- and intragroup competition than chimpanzees do (Furuichi, 2011). Second, unlike chimpanzees, bonobos exhibit nonexclusive female dominance (Furuichi, 2011; Vervaecke, De Vries, & Van Elsacker, 2000); bonobo females form stable and valuable social relationships (Stevens, de Groot, & Staes, 2015). Third, compared with chimpanzees, bonobos are more risk-averse, are better at sociocognitive tasks than at instrumental tasks, and are less bold (see Hare, Wobber, & Wrangham, 2012, for a review).

In the present study, we compared the personality structure of captive bonobos with personality structures previously identified in three samples of captive chimpanzees (King & Figueredo, 1997; Weiss et al., 2007, 2009). Personality dimensions shared by these species are likely to be ancestral and to reflect their close phylogenetic relatedness (Glazko & Nei, 2003) and their similar social structures (Furuichi, 2011). Personality dimensions that are not shared are likely to be derived (i.e., to have recently evolved in chimpanzees, bonobos, or both). These derived characteristics could reflect genetic drift or differences between the two species, specifically the differences in the rates of inter- and intragroup competition and how dominance is expressed (Furuichi, 2011; Vervaecke et al., 2000).

Method

Subjects

The subjects were all noninfant bonobos from 16 facilities that participated in the study (7 zoological parks and 1 research institute in the United States, 5 zoological parks in Germany, 1 zoological park in Belgium, 1 zoological park in the United Kingdom, and 1 zoological park in the Netherlands). The subjects comprised about 80% of the current captive population in Europe and the United States and consisted of 71 males (mean age = 16.2 years, SD = 10.8, age range = 1.6–43.9 years) and 83 females (mean age = 16.6 years, SD = 12.7, age range = 2.2–61.5 years). This population originated from 36 wild-caught bonobos that belonged to at least four populations spread across bonobos’ range (Reinartz, 1997). Therefore, it is likely that the variation within our sample is within what one would see in the wild, albeit at the lower end of that range.

Personality assessment

Questionnaire

Personality was assessed via ratings on the Hominoid Personality Questionnaire (HPQ; Weiss et al., 2009).¹ This questionnaire consists of 54 personality-descriptive adjectives, each paired with one to three descriptive sentences that set the adjective in the context of behavior. The HPQ instructs raters to make ratings on a 7-point scale (1 = displays total absence or negligible amounts of the trait, 7 = displays extremely large amounts of the trait) and to not discuss their ratings.

Of the 54 items, 43 were originally developed and used to assess chimpanzee personality (King & Figueredo, 1997). Of these items, 41 were derived from a taxonomy of the Big Five (Goldberg, 1990) and 2 were devised for rating chimpanzees. The remaining items included 5 that represented openness and neuroticism, added as part of a study of orangutan personality (Weiss, King, & Perkins, 2006), and 6 that represented openness and conscientiousness, added as part of a later study on chimpanzees (Weiss et al., 2009).

Raters at the German and Dutch facilities completed versions of the HPQ in their native languages. After the data had been collected, a researcher not involved in the study found a minor error in the German translation of the HPQ: The behavioral descriptive sentence for the adjective “autistic” refers to “rocking” in the English version and “stone throwing” in the German version. Because the behavioral descriptive sentences are offered as a guide and not as definitive descriptions of the traits, and because this difference would lead our results to be more conservative, we did not exclude this item.

Raters and ratings

Caretakers and staff at zoological parks, researchers, and other people who knew the individual subjects made the ratings. Some of the ratings did not include information regarding the raters’ identities; we considered the seven unidentified ratings (each for a different subject) at one zoo to have come from a single rater and the six unidentified ratings (each for a different subject) at another zoo to have come from a different single rater. Furthermore, at one zoo, two raters assessed a single subject together. These two raters and a third worked together to rate 2 additional subjects. In these cases, joint ratings were considered to have come from a single rater.

Of the subjects in the sample, 112 subjects were rated only one time; 47 were rated by 1 rater, and 65 were rated by 2 to 5 raters. The remaining 42 subjects were rated two times; the second rating occurred an average of 5.6 years (SD = 0.4) after the first rating. Of these 42 subjects, 2 were rated by 1 rater, and 40 were rated by 2, 3, or 5 raters; 17 were rated by the same rater or raters during both data-collection waves. There were 25 and 29 raters in the first and second data-collection waves, respectively. Five raters rated subjects in both waves.

The length of time that raters had known the subjects was available for 222 of the 291 ratings in the first data-collection wave (M = 5.8 years, SD = 5.3) and for 103 of 117 ratings in the second data-collection wave (M = 5.6 years, SD = 6.5).

Analyses

Interrater reliabilities, internal consistencies, and test-retest reliabilities

Interrater reliabilities of the HPQ items and personality factors were calculated using intraclass correlations (ICCs). ICC(3,1) indicates the reliability of single ratings; ICC(3,k) indicates the reliability of the mean scores of an average of k raters (Shrout & Fleiss, 1979). For each factor, we determined the internal consistency reliabilities (Cronbach’s alphas) of the mean item scores across raters using the alpha function of the psych package for R (Revelle, 2015). For subjects that were rated twice, we computed the test-retest reliabilities of factors using the rpt.aov function in R (Nakagawa & Schielzeth, 2010).

Data reduction

We performed an unweighted least squares factor analysis using the fa function of the psych package (Revelle, 2015) for the R software environment (Version 3.0.2; R Development Core Team, 2013). We used this analysis to determine the structure of all items with interrater reliabilities greater than zero. As in previous studies (e.g., Weiss, Adams, Widdig, & Gerald, 2011), we used the wave of data with the most responses; for subjects rated by multiple raters, we took the mean rating across raters. We determined the number of factors to extract by examining the scree plot and by conducting a parallel analysis via the fa.parallel function of the psych package for R (Revelle, 2015). Next, to determine which type of rotation would be appropriate, we conducted both orthogonal (varimax) and oblique (promax) rotations. If the intercorrelations between promax-rotated factors were high and the structure of the promax-rotated factors differed from that of the varimax-rotated factors, we retained the promax-rotated factors. If the factor intercorrelations were not high and the structures did not differ, we retained the varimax-rotated factors. As in previous studies (e.g., Weiss et al., 2006), for the purpose of labeling factors and creating unit-weighted factor scores, we defined salient loadings as those that were equal to or greater than |.4|. When an item had multiple salient loadings, we interpreted an item as belonging to the factor on which it had the highest loading.

Cross-species comparisons

As we noted in the introduction, prior studies using the HPQ or its predecessor, the Chimpanzee Personality Questionnaire, revealed that chimpanzee personality can be described along six dimensions (King & Figueredo, 1997; Weiss et al., 2007, 2009). We compared structures derived from three chimpanzee samples with the bonobo personality structure. The first chimpanzee sample, the ChimpanZoo sample, comprised 100 chimpanzees housed in U.S. zoos, as described previously (King & Figueredo, 1997). The second chimpanzee sample, the Yerkes sample, comprised 175 chimpanzees housed in Yerkes National Primate Research Center, as described previously (Weiss et al., 2007). Ratings of the individuals in both of these samples were made using the original 43-adjective questionnaire (King & Figueredo, 1997). The third chimpanzee sample, the Japanese sample, comprised 157 individuals housed in zoos, research centers, and a sanctuary, all located in Japan. Of these subjects, 146 were described in a previous study (Weiss et al., 2009). The 11 additional subjects included 4 that were housed in the Fukuoka Zoo, 5 that were housed in the Higashiyama Zoo, and 2 that were housed in the Hirakawa Zoo. All chimpanzees in the third sample were rated using a Japanese translation of the HPQ (Weiss et al., 2009).

We planned to use different approaches to compare bonobos and chimpanzees depending on whether we found that bonobos, like chimpanzees, have six personality dimensions (King & Figueredo, 1997). If we had found that bonobos and chimpanzees have a different number of personality dimensions, we would have used a method described in previous studies (e.g., Weiss et al., 2011): We would first have computed unit-weighted scores on the basis of the bonobo and chimpanzee structures and then obtained correlations between these scores. However, because we found that the bonobos have six personality dimensions, we compared the chimpanzee and bonobo structures using targeted orthogonal Procrustes rotations (McCrae, Zonderman, Bond, Costa, & Paunonen, 1996). Each rotation compared a structure derived from one of the three chimpanzee samples with a structure derived from the present bonobo sample. The chimpanzee studies differed with respect to whether factors or components were extracted and in the number of items subjected to data reduction. We therefore made sure that, for each targeted rotation, the extraction method and the set of items used to derive the bonobo target matrix matched that of the chimpanzee sample. We interpreted congruence coefficients using guidelines derived from a study in which experts judged the similarity between structures with different levels of congruence (Lorenzo-Seva & ten Berge, 2006). The researchers found that congruence coefficients below .85 were not indicative of factor similarity, that congruence coefficients ranging from .85 to .94 were indicative of “fair similarity,” and that congruence coefficients greater than or equal to .95 were indicative of equality and thus indicated “good similarity” (Lorenzo-Seva & ten Berge, 2006, p. 61).

Results

Interrater reliabilities of items

Interrater reliabilities for the 54 adjectives for each rating wave are presented in Table S1 in the Supplemental Material available online. In the first wave, ICC(3,1) values ranged from .04 for “sensitive” to .70 for “submissive” (M = .34, SD = .16), and ICC(3,k) values ranged from .11 for “sensitive” to .86 for “submissive” (M = .55, SD = .18). For the second wave, ICC(3,1) values ranged from .09 for “erratic” to .82 for “dominant” (M = .45, SD = .13), and ICC(3,k) values ranged from .21 for “erratic” to .93 for “dominant” (M = .69, SD = .12). Because all items had reliabilities greater than zero for both waves, we did not exclude any items.

Personality structure

The scree plot and the parallel analysis indicated that there were six factors. The varimax- and promax-rotated factors did not differ appreciably, and the absolute factor intercorrelations were modest (M = .14, SD = .12). We therefore interpreted varimax-rotated factors (for the promax-rotated structure and factor intercorrelations, see Tables S2 and S3 in the Supplemental Material). These six factors explained 56% of the variance.

For ease of interpretation and to maintain consistency with previous studies in how dimensions are labeled, before interpreting factors, we multiplied the loadings of four factors by −1. On the basis of the items that loaded on each factor, we labeled the factors Assertiveness, Conscientiousness, Openness, Attentiveness, Agreeableness, and Extraversion (see Table 1).

Table 1.

Varimax-Rotated Factor Loadings

Adjective	Factor						h ²
Adjective	Assertiveness^a	Conscientiousness^a	Openness	Attentiveness^a	Agreeableness	Extraversion^a	h ²
Anxious	−.81	−.04	−.16	−.07	−.03	−.17	.71
Timid	−.76	.27	−.12	−.07	−.05	−.12	.69
Fearful	−.75	.06	−.17	−.16	−.10	−.12	.64
Independent	.71	−.20	−.02	.13	.04	−.30	.66
Dominant	.68	−.52	−.26	.07	.11	.07	.82
Vulnerable	−.66	.22	.10	.00	−.19	−.37	.67
Submissive	−.64	.43	.18	−.08	.04	−.17	.66
Cool	.63	.13	−.04	.08	.26	−.05	.50
Stable	.62	.24	.13	.11	.20	.03	.52
Dependent	−.61	.12	.17	−.37	.20	.35	.71
Decisive	.54	−.07	.09	.40	.15	.00	.49
Persistent	.52	−.40	.15	.14	.13	.05	.49
Excitable	−.52	−.30	−.05	−.12	.00	−.01	.39
Cautious	−.36	.31	−.10	.20	.35	−.08	.41
Quitting	−.20	.08	−.19	−.20	.12	.00	.14
Bullying	.27	−.76	.01	.08	−.16	.06	.68
Aggressive	.15	−.75	.10	.08	−.14	.05	.63
Stingy	.20	−.72	.02	−.14	−.03	−.05	.58
Irritable	−.12	−.70	−.17	−.09	−.14	−.21	.60
Jealous	−.04	−.68	.18	−.15	−.07	−.08	.53
Gentle	−.02	.67	−.02	.04	.53	−.06	.73
Erratic	−.29	−.60	−.02	−.29	−.06	−.18	.57
Defiant	.11	−.59	.23	−.11	−.19	−.05	.46
Reckless	.07	−.58	.19	−.38	−.21	−.05	.57
Manipulative	.21	−.55	.05	.17	.14	.14	.42
Impulsive	−.29	−.48	.28	−.15	−.14	−.06	.45
Predictable	.21	.41	−.23	.00	.26	−.05	.33
Active	−.13	−.12	.77	−.08	.09	.21	.68
Playful	−.08	−.05	.73	−.04	.10	.20	.59
Inquisitive	.22	−.01	.68	.21	.11	.03	.57
Inventive	.34	−.05	.64	.20	.03	−.24	.62
Imitative	−.08	.04	.63	−.22	.17	.13	.50
Innovative	.33	.01	.63	.07	.05	−.21	.56
Conventional	−.08	.16	−.61	.09	.31	−.01	.51
Curious	.15	−.14	.58	.23	.17	−.07	.46
Lazy	.12	.03	−.54	−.37	.06	−.30	.54
Unemotional	.15	.15	−.25	−.11	.12	−.01	.14
Disorganized	−.18	−.15	−.03	−.71	−.16	−.20	.63
Intelligent	.18	−.07	.15	.68	.34	.06	.65
Clumsy	.04	.00	−.04	−.68	−.06	−.15	.50
Thoughtless	−.18	−.17	−.09	−.68	−.18	−.03	.56
Distractible	−.22	−.11	.06	−.59	−.05	.12	.42
Unperceptive	−.33	−.15	−.16	−.50	.09	−.24	.47
Friendly	−.01	.40	.18	−.12	.71	.24	.77
Affectionate	.21	.28	.18	.08	.71	.32	.76
Protective	.30	−.04	−.13	.27	.70	−.02	.66
Sympathetic	.07	.36	.00	.17	.62	−.13	.56
Helpful	.07	.15	.17	.31	.59	.04	.51
Sociable	.15	−.06	.34	−.01	.56	.34	.57
Sensitive	.25	.15	−.15	.48	.53	−.03	.62
Solitary	−.17	.17	−.26	−.09	−.14	−.67	.61
Depressed	−.42	−.13	−.18	−.21	−.07	−.67	.72
Autistic	−.43	−.23	−.08	−.34	−.06	−.43	.55
Individualistic	.14	−.19	.23	−.18	−.04	−.43	.33
Proportion of variance accounted for	.14	.12	.09	.08	.08	.05

Note: Principal component analyses yielded highly similar results (see Tables S4 and S5 in the Supplemental Material). h² = communality. Boldface highlights loadings ≥ |.4|.

Loadings on this factor were multiplied by −1.

Assertiveness in bonobos resembled the dominance dimension in chimpanzees (King & Figueredo, 1997; Weiss et al., 2007, 2009), orangutans (Weiss et al., 2006), rhesus macaques (Weiss et al., 2011), and gorillas (Eckardt et al., 2015; Gold & Maple, 1994; Schaefer & Steklis, 2014). It also resembled the confidence component in Hanuman langurs (Konecˇná et al., 2008) and Barbary macaques (Konecˇná, Weiss, Lhota, & Wallner, 2012) and the assertiveness component in brown capuchin monkeys (Morton et al., 2013). With respect to the five-factor model, this dimension resembled the assertiveness facet of extraversion in humans (Costa & McCrae, 1992). Bonobos with higher scores for this factor tended to be independent and confident, and more prone to displacing, threatening, or taking food from other bonobos. On the other hand, bonobos with lower scores for this factor tended to be less confident, more anxious, and more prone to getting displaced and physically hurt or emotionally upset as a result of agonistic interactions.

Conscientiousness in bonobos resembled conscientiousness in chimpanzees (King & Figueredo, 1997; Weiss et al., 2007, 2009) in that it was made up of two clusters (King, Weiss, & Sisco, 2008). It also partly overlapped the proto-agreeableness component in mountain gorillas (Eckardt et al., 2015), and it was similar to the conscientiousness facet of deliberation in the five-factor model (Costa & McCrae, 1992). Bonobos with high scores for this factor thus tended to be kind, considerate, and predictable in their relationships with others, whereas bonobos with low scores for this factor tended to be impulsive, unpredictable, and aggressive.

Openness in bonobos resembled its counterparts in humans (Costa & McCrae, 1992), chimpanzees (King & Figueredo, 1997; Weiss et al., 2007, 2009), rhesus macaques (Weiss et al., 2011), brown capuchin monkeys (Morton et al., 2013), and mountain gorillas (Eckardt et al., 2015). However, as in mountain gorillas (Eckardt et al., 2015) and brown capuchin monkeys (Morton et al., 2013), traits such as “active” and “playful” had positive loadings on Openness in bonobos. These traits are associated with the activity facet of extraversion in humans (Costa & McCrae, 1992), the extraversion component in orangutans (Weiss et al., 2006), and the activity component in rhesus macaques (Weiss et al., 2011). Bonobos with high scores for this factor thus tended to be playful and to engage actively in exploring novel social and physical environments. On the other hand, bonobos with low scores for this factor tended to be indolent, inactive, and disinclined to explore novel individuals or environments.

Attentiveness in bonobos resembled the identically named component identified in brown capuchin monkeys (Morton et al., 2013). The items loading on this factor overlapped some with the items loading on the intellect component in orangutans (Weiss et al., 2006). In chimpanzees (King & Figueredo, 1997; Weiss et al., 2007, 2009), these items defined high dominance and high conscientiousness. In gorillas, these items defined high dominance (Eckardt et al., 2015; Schaefer & Steklis, 2014). In rhesus macaques, these items defined high confidence, friendliness, and activity (Weiss et al., 2011). The Attentiveness factor was also similar to the conscientiousness facets of order and self-discipline in the five-factor model (Costa & McCrae, 1992). Bonobos with higher scores for the Attentiveness factor thus tended to be more focused and perhaps better at solving problems. On the other hand, bonobos with low scores for this factor tended to be easily distracted and uncoordinated.

Agreeableness in bonobos resembled its counterparts in orangutans (Weiss et al., 2006) and chimpanzees (King & Figueredo, 1997). It also included loadings associated with high sociability in mountain gorillas (Eckardt et al., 2015), all of which were also associated with high agreeableness in humans (Costa & McCrae, 1992). Some of the items were associated with high agreeableness in Hanuman langurs (Konecˇná et al., 2008), high extraversion in humans (Costa & McCrae, 1992) and extraversion in chimpanzees (King & Figueredo, 1997). Bonobos with high scores for this factor thus tended to empathize with and help their conspecifics, whereas bonobos that had low scores for this factor did not.

Extraversion in bonobos differed from dimensions labeled extraversion, sociability, or friendliness in other species (Eckardt et al., 2015; King & Figueredo, 1997; Konecˇná et al., 2008; Morton et al., 2013; Schaefer & Steklis, 2014; Weiss et al., 2006, 2007, 2009, 2011). The items “solitary,” “depressed,” “autistic,” and “individualistic” all had negative loadings on this factor. Traits such as “solitary” and “depressed” are associated with low extraversion in humans (Costa & McCrae, 1992) and chimpanzees (King & Figueredo, 1997), low sociability in brown capuchin monkeys (Morton et al., 2013), and low friendliness in rhesus macaques (Weiss et al., 2011). The item “autistic” is associated with high neuroticism in chimpanzees (Weiss et al., 2009) and low sociability in brown capuchin monkeys (Morton et al., 2013). The item “individualistic” is associated with extraversion in chimpanzees (Weiss et al., 2009) and components or factors labeled sociability (Eckardt et al., 2015) or extraversion (Schaefer & Steklis, 2014) in gorillas. Thus, compared with bonobos who had low scores in this factor, those with high scores tended to be well integrated into their social environment.

We also tested the extent to which these dimensions were dependent on the use of exploratory factor analysis. We therefore extracted six components using principal component analysis. The varimax- and promax-rotated structures derived via principal component analysis (see Tables S4 and S5 in the Supplemental Material) were nearly identical to the varimax- and promax-rotated structures derived via factor analysis.

Factor reliabilities

Interrater reliabilities, internal consistencies, and test-retest reliabilities for the factors are shown in Table 2. Interrater reliability in the first wave was fair for attentiveness and agreeableness and excellent for the remaining factors. Interrater reliabilities of these factors in the second wave were all excellent. Internal consistencies were excellent, except for extraversion in the first wave. All factors showed good test-retest reliability except for agreeableness.

Table 2.

Reliabilities and Test-Retest Reliabilities of the Factors

Factor	Wave 1 reliability			Wave 2 reliability			Test-retest reliability
Factor	ICC(3,1)	ICC(3,k)	α	ICC(3,1)	ICC(3,k)	α	r	p
Assertiveness	.64	.83	.92	.72	.88	.95	.62	< .0001
Conscientiousness	.61	.81	.90	.59	.81	.94	.61	< .0001
Openness	.60	.80	.87	.65	.84	.91	.37	< .01
Attentiveness	.23	.45	.84	.52	.76	.90	.41	< .01
Agreeableness	.32	.55	.87	.54	.77	.92	.17	> .05
Extraversion	.61	.81	.69	.67	.86	.83	.28	< .05

Note: Significant test-retest reliabilities were still significant when we used permutation tests. The intraclass correlation coefficients (ICCs) indicate (a) the reliability of individual ratings of factor scores, ICC(3,1), and (b) the reliability of mean ratings of factor scores, ICC(3,k).

Interspecies comparisons

We used targeted orthogonal Procrustes rotations (McCrae et al., 1996) to compare the personality structures of bonobos and chimpanzees (see Table 3). For all three comparisons, the total congruence, which is based on all of the factor or component loadings (McCrae et al., 1996, p. 559), indicated that, overall, the factor or component structures for all three chimpanzee samples exhibited a fair degree of similarity with the bonobo structure. The pattern of congruence for the factors or components was consistent across comparisons of the structures derived from the three chimpanzee samples to the structure derived from the bonobo sample: The highest congruence coefficients were found for assertiveness, conscientiousness, openness, and agreeableness, and the lowest congruence coefficients were found for attentiveness and extraversion. Specifically, assertiveness, conscientiousness, and agreeableness exhibited at least fair similarity in the ChimpanZoo and Yerkes chimpanzee samples and fair similarity in the Japanese chimpanzee sample. In addition, for openness, the congruence coefficients indicated fair similarity in the ChimpanZoo and Japanese samples; the congruence coefficients for the Yerkes sample did not indicate similarity. Extraversion in the ChimpanZoo sample exhibited a fair degree of similarity to bonobo extraversion; the congruence coefficients for this factor in the Yerkes sample and Japanese sample, however, were not indicative of similarity. Finally, no factors or components similar to attentiveness were found in any of the chimpanzee samples.

Table 3.

Congruence Coefficients Calculated by Rotating Chimpanzee Structures Toward the Bonobo Structure

	Chimpanzee sample
Factor	ChimpanZoo	Yerkes	Japan
Assertiveness	.947	.855	.896
Conscientiousness	.953	.956	.921
Openness	.947	.811	.905
Attentiveness	.656	.787	.781
Agreeableness	.905	.909	.927
Extraversion	.853	.685	.782
Total	.906	.852	.874

Discussion

We found that 54 personality traits in bonobos were defined by the factors Assertiveness, Conscientiousness, Openness, Attentiveness, Agreeableness, and Extraversion. These factors showed interrater reliabilities and test-retest reliabilities comparable to those of human personality factors (e.g., Costa & McCrae, 1992) and personality traits and dimensions in other species (Bell, Hankison, & Laskowski, 2009; Gosling, 2001). Of these factors, assertiveness, conscientiousness, agreeableness, and possibly openness had chimpanzee analogues. In contrast, the evidence for chimpanzee analogues of extraversion and attentiveness was weak. This pattern of results suggests that four bonobo factors (assertiveness, conscientiousness, agreeableness, and openness) were ancestral and present in the common ancestor of chimpanzees and bonobos and that two bonobo factors (extraversion and attentiveness) were derived, possibly as a result of differences in bonobo and chimpanzee socioecology and bonobo social behavior (Furuichi, 2011; Hare et al., 2012; Vervaecke et al., 2000).

The bonobo Assertiveness factor was similar to chimpanzee dominance (King & Figueredo, 1997; Weiss et al., 2007, 2009) and to components and factors identified in other primate species (Eckardt et al., 2015; Konecˇná et al., 2008; Konecˇná et al., 2012; Morton et al., 2013; Schaefer & Steklis, 2014; Weiss et al., 2006, 2011). This finding calls into question the perception that bonobos are egalitarian (de Waal, 1995) and the predictions made by some that bonobos should not have a dominance or assertiveness dimension (Eckardt et al., 2015). However, it is consistent with behavioral observations, which reveal strong dominance hierarchies in captive bonobos (Stevens, Vervaecke, de Vries, & van Elsacker, 2007; Vervaecke et al., 2000).

Items defining conscientiousness components or factors in chimpanzees and humans (King & Figueredo, 1997; Weiss et al., 2007, 2009) loaded on two bonobo factors. The first factor, Conscientiousness, was characterized by high levels of predictability and low levels of impulsive aggression. It thus somewhat resembled the deliberation facet of conscientiousness in humans (Costa & McCrae, 1992) and the proto-agreeableness component in mountain gorillas (Eckardt et al., 2015). The second factor, Attentiveness, was characterized by the ability to focus on and do well in carrying out tasks. It thus resembled the order and self-discipline facets of conscientiousness in humans (Costa & McCrae, 1992) and the attentiveness component in brown capuchin monkeys (Morton et al., 2013). This split of conscientiousness traits into two factors may explain bonobos’ superior performance compared with chimpanzees on tests related to social causality (Herrmann, Hare, Call, & Tomasello, 2010). Further testing should reveal the degree to which this factor reflects cognitive skills in bonobos.

The bonobo Openness factor resembles that of chimpanzees, except that items related to activity and playfulness, which load on extraversion in chimpanzees (King & Figueredo, 1997; Weiss et al., 2007, 2009), load on the Openness factor in bonobos. A similar pattern has been found in gorillas (Eckardt et al., 2015) and capuchin monkeys (Morton et al., 2013). This difference between bonobos and chimpanzees may reflect the fact that, in bonobos, play is used to reduce tension (Palagi, 2006) and has an important role in trust building (Behncke, 2015).

The bonobo Agreeableness factor resembled that of chimpanzees (King & Figueredo, 1997; Weiss et al., 2007, 2009), humans (Costa & McCrae, 1992), orangutans (Weiss et al., 2006), western gorillas (Gold & Maple, 1994), and Hanuman langurs (Konecˇná et al., 2008). Conversely, the Extraversion factor in bonobos was dissimilar to that in chimpanzees, because it characterized individuals that were not withdrawn and depressed. A somewhat similar pattern was found for the sociability component in mountain gorillas (Eckardt et al., 2015).

When Eckardt et al. (2015) tried to explain the evolutionary bases for differences between the personalities of mountain gorillas and chimpanzees (which were similar to those we found between chimpanzees and bonobos), they hypothesized that distinct extraversion, openness, and agreeableness dimensions would benefit primate species characterized by fission-fusion social structures, because they would offer individuals more flexibility to cope with constantly changing social environments than if these factors were not distinct. The presence of separate Openness, Agreeableness, and Extraversion factors in bonobos is consistent with this hypothesis; bonobo social structure is considerably more flexible than that of gorillas (Robbins, 2011). Although direct comparisons of the degree of fission-fusion in different ape species have been hindered by differences in methodology and study duration (Aureli et al., 2008), researchers working on future comparative studies may wish to test whether differences in social-structure stability across species are associated with the structure of traits related to extraversion, openness, and agreeableness.

This study is not without limitations. One limitation is that the sample size was relatively small for factor analysis; another is that translation issues may have affected ratings of bonobos housed in German zoos. Therefore, the differences between bonobos and chimpanzees may not be species differences but may instead reflect sampling variability. However, the pattern of congruence between the current bonobo sample and the three chimpanzee samples was highly consistent. A third limitation is that this study was limited to captive bonobos as opposed to wild bonobos, which may have different personality structures. However, this feature of our study ruled out the possibility that differences between bonobos and chimpanzees could reflect differences between captive and wild populations. Nonetheless, these limitations suggest there would be much value in collecting additional data, both via questionnaires and by behavioral observations and tests, on bonobos and chimpanzees housed in zoos, sanctuaries, and in the wild.

Although there was considerable overlap between the personalities of bonobos and chimpanzees, most probably reflecting their recent common ancestor, there were differences, too, that may be the signals of more recent selection. Although more work needs to be done in this area, we expect that it is bound to reveal an even more complete picture of the evolution of personality in Hominidae.

Footnotes

Acknowledgements

Data collection would not have been possible without the participation of the zoological institutions, sanctuaries, and research institutes. We also thank Jim King, Virginia Landau, Bill Hopkins, and Tetsuro Matsuzawa for their help in obtaining chimpanzee ratings and Sara Van Coillie for translating the questionnaire and for assisting in collecting and entering data. We also thank Jeff McCrae for answering a question about Procrustes rotation and Dick Byrne for comments on an earlier draft.

Declaration of Conflicting Interests

The authors declared that they had no conflicts of interest with respect to their authorship or the publication of this article.

Funding

This work was supported by funding from the University of Antwerp (to M. Eens); University of Edinburgh Development Trust Grant 2828 (to A. Weiss); Daiwa Foundation Small Grant 6515/6818 (to A. Weiss); Japanese Ministry of Education, Culture, Sports, Science and Technology Grants-in-Aid for Science Research 25290082 and 25118005 (to M. Inoue-Murayama); and funding from the Cooperation Research Program of the Primate Research Institute, Kyoto University (to M. Inoue-Murayama). Support for the Center for Research and Conservation of the Royal Zoological Society of Antwerp was provided by the Flemish Government. The collection of chimpanzee data at Yerkes National Primate Research Center was supported by National Institute of Neurological Disorders and Stroke Grants NS36605 and NS42867 and by National Center for Research Resources Grant RR00165 (all to the Yerkes National Primate Research Center). The content of this publication is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health or the U.S. Government.

Supplemental Material

Additional supporting information can be found at

Open Practices

Releasing the data publicly could violate the confidentiality of the raters and the facilities that house the bonobos. The data are available from the corresponding author. The complete Open Practices Disclosure for this article can be found at .

Notes

References

Aureli

Schaffner

C. M.

Boesch

Bearder

S. K.

Call

Chapman

C. A.

. . . van Schaick

C. P.

(2008). Fission-fusion dynamics: New research frameworks. Current Anthropology, 49, 627–654. doi:10.1086/586708

Behncke

(2015). Play in the Peter Pan ape. Current Biology, 25, R24–R27. doi:10.1016/j.cub.2014.11.020

Bell

A. M.

Hankison

S. J.

Laskowski

K. L.

(2009). The repeatability of behaviour: A meta-analysis. Animal Behaviour, 77, 771–783. doi:10.1016/j.anbehav.2008.12.022

Costa

P. T.

Jr. McCrae

R. R.

(1992). Revised NEO Personality Inventory (NEO-PI-R) and NEO Five-Factor Inventory (NEO-FFI) professional manual. Odessa, FL: Psychological Assessment Resources.

de Waal

F. B. M

. (1995). Bonobo sex and society. Scientific American, 272, 58–64.

Dutton

D. M.

(2008). Subjective assessment of chimpanzee ( Pan troglodytes) personality: Reliability and stability of trait ratings. Primates, 49, 253–259. doi:10.1007/s10329-008-0094-1

Eckardt

Steklis

H. D.

Steklis

N. G.

Fletcher

A. W.

Stoinski

T. S.

Weiss

(2015). Personality dimensions and their behavioral correlates in wild Virunga mountain gorillas ( Gorilla beringei beringei). Journal of Comparative Psychology, 129, 26–41. doi:10.1037/a0038370

Freeman

H. D.

Brosnan

S. F.

Hopper

L. M.

Lambeth

S. P.

Schapiro

S. J.

Gosling

S. D.

(2013). Developing a comprehensive and comparative questionnaire for measuring personality in chimpanzees using a simultaneous top-down/bottom-up design. American Journal of Primatology, 75, 1042–1053. doi:10.1002/ajp.22168

Furuichi

(2011). Female contributions to the peaceful nature of bonobo society. Evolutionary Anthropology, 20, 131–142. doi:10.1002/evan.20308

10.

Glazko

G. V.

Nei

(2003). Estimation of divergence times for major lineages of primate species. Molecular Biology and Evolution, 20, 424–434. doi:10.1093/molbev/msg050

11.

Gold

K. C.

Maple

T. L.

(1994). Personality assessment in the gorilla and its utility as a management tool. Zoo Biology, 13, 509–522.

12.

Goldberg

L. R.

(1990). An alternative “description of personality”: The Big-Five factor structure. Journal of Personality and Social Psychology, 59, 1216–1229. doi:10.1037/0022-3514.59.6.1216

13.

Gosling

S. D.

(2001). From mice to men: What can we learn about personality from animal research? Psychological Bulletin, 127, 45–86. doi:10.1037/0033-2909.127.1.45

14.

Gosling

S. D.

Graybeal

(2007). Tree thinking: A new paradigm for integrating comparative data in psychology. The Journal of General Psychology, 134, 259–277. doi:10.3200/GENP.134.2.259-278

15.

Hare

Wobber

Wrangham

(2012). The self-domestication hypothesis: Evolution of bonobo psychology is due to selection against aggression. Animal Behaviour, 83, 573–585. doi:10.1016/j.anbehav.2011.12.007

16.

Herrmann

Hare

Call

Tomasello

(2010). Differences in the cognitive skills of bonobos and chimpanzees. PLoS ONE, 5, Article e12438. Retrieved from http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0012438

17.

King

J. E.

Figueredo

A. J.

(1997). The five-factor model plus dominance in chimpanzee personality. Journal of Research in Personality, 31, 257–271. doi:10.1006/jrpe.1997.2179

18.

King

J. E.

Weiss

Farmer

K. H.

(2005). A chimpanzee (Pan troglodytes) analogue of cross-national generalization of personality structure: Zoological parks and an African sanctuary. Journal of Personality, 73, 389–410. doi:10.1111/j.1467-6494.2005.00313.x

19.

King

J. E.

Weiss

Sisco

M. M.

(2008). Aping humans: Age and sex effects in chimpanzee (Pan troglodytes) and human (Homo sapiens) personality. Journal of Comparative Psychology, 122, 418–427. doi:10.1037/a0013125

20.

Konecˇná

Lhota

Weiss

Urbánek

Adamová

Pluhácˇek

(2008). Personality in free-ranging Hanuman langur (Semnopithecus entellus) males: Subjective ratings and recorded behavior. Journal of Comparative Psychology, 122, 379–389. doi:10.1037/a0012625

21.

Konecˇná

Weiss

Lhota

Wallner

(2012). Personality in Barbary macaques (Macaca sylvanus): Temporal stability and social rank. Journal of Research in Personality, 46, 581–590. doi:10.1016/j.jrp.2012.06.004

22.

Lorenzo-Seva

ten Berge

J. M. F.

(2006). Tucker’s congruence coefficient as a meaningful index of factor similarity. Methodology: European Journal of Research Methods for the Behavioral and Social Sciences, 2, 57–64.

23.

McCrae

R. R.

Costa

P. T.

Jr. (1999). A five-factor theory of personality. In Pervin

John

O. P.

(Eds.), Handbook of personality (2nd ed., pp. 159–181). New York, NY: Guilford Press.

24.

McCrae

R. R.

Zonderman

A. B.

Bond

M. H.

Costa

P. T.

Jr. Paunonen

S. V.

(1996). Evaluating replicability of factors in the Revised NEO Personality Inventory: Confirmatory factor analysis versus Procrustes rotation. Journal of Personality and Social Psychology, 70, 552–566. doi:10.1037/0022-3514.70.3.552

25.

Morton

F. B.

Lee

P. C.

Buchanan-Smith

H. M.

Brosnan

S. F.

Thierry

Paukner

. . . Weiss

(2013). Personality structure in brown capuchin monkeys (Sapajus apella): Comparisons with chimpanzees (Pan troglodytes), orangutans (Pongo spp.), and rhesus macaques (Macaca mulatta). Journal of Comparative Psychology, 127, 282–298. doi:10.1037/a0031723

26.

Nakagawa

Schielzeth

(2010). Repeatability for Gaussian and non-Gaussian data: A practical guide for biologists. Biological Reviews, 85, 935–956.

27.

Palagi

(2006). Social play in bonobos (Pan paniscus) and chimpanzees (Pan troglodytes): Implications for natural social systems and interindividual relationships. American Journal of Physical Anthropology, 129, 418–426. doi:10.1002/ajpa.20289

28.

R Development Core Team. (2013). R: A language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing.

29.

Reinartz

G. E.

(1997). Patterns of genetic variation in the bonobo (Pan paniscus) (Unpublished doctoral dissertation). University of Wisconsin, Milwaukee.

30.

Revelle

(2015). psych package for R (Version 1.2.12). Evanston, IL: Northwestern University. Retrieved from http://personality-project.org/r/psych

31.

Robbins

M. M.

(2011). Gorillas: Diversity in ecology and behavior. In Campbell

C. J.

Fuentes

MacKinnon

K. C.

Bearder

S. K.

Stumpf

R. M.

(Eds.), Primates in perspective (2nd ed., pp. 326–339). Oxford, England: Oxford University Press.

32.

Schaefer

S. A.

Steklis

H. D.

(2014). Personality and subjective well-being in captive male western lowland gorillas living in bachelor groups. American Journal of Primatology, 76, 879–889. doi:10.1002/ajp.22275

33.

Shrout

P. E.

Fleiss

J. L.

(1979). Intraclass correlations: Uses in assessing rater reliability. Psychological Bulletin, 86, 420–428. doi:10.1037/0033-2909.86.2.420

34.

Stevens

J. M. G.

de Groot

Staes

(2015). Relationship quality in captive bonobo groups. Behaviour, 152, 259–283. doi:10.1163/1568539X-00003259

35.

Stevens

J. M. G.

Vervaecke

de Vries

van Elsacker

(2007). Sex differences in the steepness of dominance hierarchies in captive bonobo groups. International Journal of Primatology, 28, 1417–1430. doi:10.1007/s10764-007-9186-9

36.

Vervaecke

De Vries

Van Elsacker

(2000). The pivotal role of rank in grooming and support behavior in a captive group of bonobos (Pan paniscus). Behaviour, 137, 1463–1485. doi:10.1163/156853900502673

37.

Weiss

Adams

M. J.

Widdig

Gerald

M. S.

(2011). Rhesus macaques (Macaca mulatta) as living fossils of hominoid personality and subjective well-being. Journal of Comparative Psychology, 125, 72–83. doi:10.1037/a0021187

38.

Weiss

Inoue-Murayama

Hong

K.-W.

Inoue

Udono

Ochiai

. . . King

J. E.

(2009). Assessing chimpanzee personality and subjective well-being in Japan. American Journal of Primatology, 71, 283–292. doi:10.1002/ajp.20649

39.

Weiss

King

J. E.

Hopkins

W. D.

(2007). A cross-setting study of chimpanzee (Pan troglodytes) personality structure and development: Zoological parks and Yerkes National Primate Research Center. American Journal of Primatology, 69, 1264–1277. doi:10.1002/ajp.20428

40.

Weiss

King

J. E.

Perkins

(2006). Personality and subjective well-being in orangutans (Pongo pygmaeus and Pongo abelii). Journal of Personality and Social Psychology, 90, 501–511. doi:10.1037/0022-3514.90.3.501

Supplementary Material

Please find the following supplemental material available below.

For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.

For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.

0.00 MB

0.13 MB

0.09 MB