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ABSTRACT: Most humans are right-handed and, like many behavioral traits, there is good evidence that genetic factors play a role in handedness. Many researchers have argued that nonhuman animal limb or hand preferences are not under genetic control but instead are determined by random, non-genetic factors. We used quantitative genetic analyses to estimate the genetic and environmental contributions to three measures of chimpanzee handedness. Results revealed significant population-level handedness for two of the three measures --- the tube task and manual gestures. Furthermore, significant additive genetic effects for the direction and strength of handedness were found for all three measures, with some modulation due to early social rearing experiences. These findings challenge historical and contemporary views of the mechanisms underlying handedness in nonhuman animals.
Genes Brain and Behavior 04/2013; · 3.48 Impact Factor
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ABSTRACT: Recently, economists and behavioral scientists have studied the pattern of human well-being over the lifespan. In dozens of countries, and for a large range of well-being measures, including happiness and mental health, well-being is high in youth, falls to a nadir in midlife, and rises again in old age. The reasons for this U-shape are still unclear. Present theories emphasize sociological and economic forces. In this study we show that a similar U-shape exists in 508 great apes (two samples of chimpanzees and one sample of orangutans) whose well-being was assessed by raters familiar with the individual apes. This U-shaped pattern or "midlife crisis" emerges with or without use of parametric methods. Our results imply that human well-being's curved shape is not uniquely human and that, although it may be partly explained by aspects of human life and society, its origins may lie partly in the biology we share with great apes. These findings have implications across scientific and social-scientific disciplines, and may help to identify ways of enhancing human and ape well-being.
Proceedings of the National Academy of Sciences 11/2012; · 9.68 Impact Factor
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ABSTRACT: The heritability of human personality is well-established. Recent research indicates that nonadditive genetic effects, such as dominance and epistasis, play a large role in personality variation. One possible explanation for the latter finding is that there has been recent selection on human personality. To test this possibility, we estimated additive and nonadditive genetic variance in personality and subjective well-being of zoo-housed orangutans. More than half of the genetic variance in these traits could be attributed to nonadditive genetic effects, modeled as dominance. Subjective well-being had genetic overlap with personality, though less so than has been found in humans or chimpanzees. Since a large portion of nonadditive genetic variance in personality is not unique to humans, the nonadditivity of human personality is not sufficient evidence for recent selection of personality in humans. Nonadditive genetic variance may be a general feature of the genetic structure of personality in primates and other animals.
Behavior Genetics 03/2012; 42(4):675-86. · 2.52 Impact Factor
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ABSTRACT: Nonhuman primate ageing resembles its human counterpart. Moreover, ratings of subjective well-being traits in chimpanzees, orang-utans and rhesus macaques are similar to those of humans: they are intercorrelated, heritable, and phenotypically and genetically related to personality. We examined whether, as in humans, orang-utan subjective well-being was related to longer life. The sample included 184 zoo-housed orang-utans followed up for approximately 7 years. Age, sex, species and number of transfers were available for all subjects and 172 subjects were rated on at least one item of a subjective well-being scale. Of the 31 orang-utans that died, 25 died a mean of 3.4 years after being rated. Even in a model that included, and therefore, statistically adjusted for, sex, age, species and transfers, orang-utans rated as being "happier" lived longer. The risk differential between orang-utans that were one standard deviation above and one standard deviation below baseline in subjective well-being was comparable with approximately 11 years in age. This finding suggests that impressions of the subjective well-being of captive great apes are valid indicators of their welfare and longevity.
Biology letters 06/2011; 7(6):872-4. · 3.76 Impact Factor
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ABSTRACT: Personality dimensions capturing individual differences in behavior, cognition, and affect have been described in several species, including humans, chimpanzees, and orangutans. However, comparisons between species are limited by the use of different questionnaires. We asked raters to assess free-ranging rhesus macaques at two time points on personality and subjective well-being questionnaires used earlier to rate chimpanzees and orangutans. Principal-components analysis yielded domains we labeled Confidence, Friendliness, Dominance, Anxiety, Openness, and Activity. The presence of Openness in rhesus macaques suggests it is an ancestral characteristic. The absence of Conscientiousness suggests it is a derived characteristic in African apes. Higher Confidence and Friendliness, and lower Anxiety were prospectively related to subjective well-being, indicating that the connection between personality and subjective well-being in humans, chimpanzees, and orangutans is ancestral in catarrhine primates. As demonstrated here, each additional species studied adds another fold to the rich, historical story of primate personality evolution.
Journal of Comparative Psychology 02/2011; 125(1):72-83. · 1.73 Impact Factor
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ABSTRACT: In the brain, serotonin production is controlled by tryptophan hydroxylase 2 (TPH2), a genotype. Previous studies found that mutations on the TPH2 locus in humans were associated with depression and studies of mice and studies of rhesus macaques have shown that the TPH2 locus was involved with aggressive behavior. We previously reported a functional single nucleotide polymorphism (SNP) in the form of an amino acid substitution, Q468R, in the chimpanzee TPH2 gene coding region. In the present study we tested whether this SNP was associated with neuroticism in captive and wild-born chimpanzees living in Japan and Guinea, respectively. Even after correcting for multiple tests (Bonferroni p = 0.05/6 = 0.008), Q468R was significantly related to higher neuroticism (β = 0.372, p = 0.005). This study is the first to identify a genotype linked to a personality trait in chimpanzees. In light of the prior studies on humans, mice, and rhesus macaques, these findings suggest that the relationship between neuroticism and TPH2 has deep phylogenetic roots.
PLoS ONE 01/2011; 6(7):e22144. · 4.09 Impact Factor
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ABSTRACT: Although concerns about anthropomorphism and subjectivity have limited the widespread use of subjective personality ratings
in primate research, recent developments show that subjective personality ratings of primates have acceptable interrater reliabilities
and display good evidence of construct validity. The role of human personality dimensions or factors has typically been one
of defining the taxonomy of human personality and examining relationships between those factors and multiple human traits
and outcomes. We describe three additional areas in which subjective personality ratings may be useful within the context
of primatology. First, when human personality factors are extended to nonhuman primates, interspecies differences in factor
structure afford opportunities to infer changes that have occurred in the underlying behavioral correlations during evolutionary
development. In other words, personality factors can be interpreted as evolutionary characters. Our studies show a close correspondence
between the personality factor structure of chimpanzees and orangutans with one notable exception. We suspect that a factor
in chimpanzees reflecting an association between aggression, emotionality, and unpredictability is homologous to the Conscientiousness
factor in humans. Such a Conscientiousness factor is completely absent in orangutans. This chimpanzee factor may be a consequence
of intense intragroup competition in male chimpanzees. Second, the highly aggressive disposition of wild male chimpanzees
may also reflect a spectrum of personality differences between male and female chimpanzees. Male chimpanzees score higher
than females on traits related to aggression, unpredictability, and emotionality, a pattern unlike that displayed by humans.
Third, subjective personality ratings are potentially useful in addressing the disparity between current measures of psychological
well-being in nonhuman primates that focus on low levels of well-being including pathological behaviors, and measures of happiness
or subjective well-being in humans that focus on positive subjective states.
12/2010: pages 77-99;
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ABSTRACT: Since the initial reports linking human “novelty seeking” to the dopamine receptor D4 (DRD4) locus (Benjamin et al. 1996), there have been multiple studies examining associations between human personality traits and
specific genotypes of neurotransmitter-related proteins (Ebstein 2006) (seeChap. 10). Recently, research on the genetic bases of personality traits has been extended to studies of within- and between-species
studies of nonhuman primates. Personality is defined as those characteristics of individuals that describe and account for
temporally stable patterns of affect, cognition, and behavior. As is the case in humans, these individual differences have
a biological and experiential basis (Gosling 2008).
12/2010: pages 239-253;
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Current biology: CB 11/2010; 20(21):R912-4. · 10.99 Impact Factor
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ABSTRACT: The purpose of this study is to explore the association of neuroticism with the metabolic syndrome, separate components of the metabolic syndrome, and the number of components of metabolic syndrome an individual possesses. The purpose of this study is to examine also the extent to which any associations are accounted for by sociodemographic factors, health behaviors, and cognitive ability.
Participants were 4208 men drawn from the Vietnam Experience Study. From military archives, and a later telephone interview and psychological and medical examination, sociodemographic, health behavior, cognitive ability, neuroticism, and health data were collected. Neuroticism and cognitive ability were assessed with standardized tests during the medical examination. Presence of the metabolic syndrome was based on body mass index, fasting blood glucose or a diagnosis of diabetes, high blood pressure or taking antihypertensive medication, high-density lipoprotein cholesterol, and triglyceride levels.
Neuroticism was positively associated with the occurrence of the metabolic syndrome and several of its components in both age-, and sociodemographic- and health behavior-adjusted analyses. Many associations were accounted for by individual difference in cognitive ability. Neuroticism was robustly associated with the number of components of the metabolic syndrome after adjustment.
Individuals with higher neuroticism scores had a higher prevalence of the metabolic syndrome and a larger number of its components. On the whole, differences in cognitive ability appeared to partially mediate the relationship between neuroticism and the metabolic syndrome.
Journal of psychosomatic research 08/2010; 69(2):193-201. · 2.91 Impact Factor
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ABSTRACT: Few prospective studies have examined personality and depression in older adults. The authors investigated whether the Five-Factor Model of personality traits-Neuroticism, Extraversion, Openness to Experience, Agreeableness, and Conscientiousness-and trait combinations (styles) are related to incident major or minor depression.
Prospective data were gathered on a community sample of 512 older adults with disability and a history of significant health care utilization who were enrolled in a Medicare Demonstration Project.
Depression and personality traits and styles were assessed at baseline; depression was assessed again at approximately 12 and 22 months.
Participants who developed incident major depression were compared with those free of depression at all three assessments. Similar analyses were done for minor depression.
High Neuroticism and low Conscientiousness were risk factors for both major and minor depression. Combinations of high Neuroticism with low or high Extraversion or high Openness conferred risk for major depression. Other novel findings for major depression revealed new trait combinations of low Conscientiousness with low or high Extraversion, high Openness, or low Agreeableness. Three trait combinations, all involving low Conscientiousness, predicted risk for minor depression: high Neuroticism, high Agreeableness, and low Openness.
The present findings highlight the importance of examining combinations of personality traits or personality styles when identifying those who are most at-risk for geriatric depression. Since other personality domains may modify the risk related to high Neuroticism and low Conscientiousness, the prevention, diagnosis, and treatment of depression could be greatly improved by assessing older patients not only on all five domains of personality but in terms of their combinations.
The American journal of geriatric psychiatry: official journal of the American Association for Geriatric Psychiatry 08/2009; 17(7):591-601. · 3.35 Impact Factor
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ABSTRACT: We tested whether the cultural background of raters influenced ratings of chimpanzee personality. Our study involved comparing personality and subjective well-being ratings of 146 chimpanzees in Japan that were housed in zoos, research institutes, and a retirement sanctuary to ratings of chimpanzees in US and Australian zoos. Personality ratings were made on a translated and expanded version of a questionnaire used to rate chimpanzees in the US and Australia. Subjective well-being ratings were made on a translated version of a questionnaire used to rate chimpanzees in the US and Australia. The mean interrater reliabilities of the 43 original adjectives did not markedly differ between the present sample and the original sample of 100 zoo chimpanzees in the US. Interrater reliabilities of these samples were highly correlated, suggesting that their rank order was preserved. Comparison of the factor structures for the Japanese sample and for the original sample of chimpanzees in US zoos indicated that the overall structure was replicated and that the Dominance, Extraversion, Conscientiousness, and Agreeableness domains clearly generalized. Consistent with earlier studies, older chimpanzees had higher Dominance and lower Extraversion and Openness scores. Correlations between the six domain scores and subjective well-being were comparable to those for chimpanzees housed in the US and Australia. These findings suggest that chimpanzee personality ratings are not affected by the culture of the raters.
American Journal of Primatology 03/2009; 71(4):283-92. · 2.22 Impact Factor
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ABSTRACT: To determine whether neuroticism, cognitive ability, and their interaction predicted mortality and to test whether neuroticism or cognitive ability effects were mediated by socioeconomic status (SES), physical health, mental health, or health behaviors.
Participants were 4200 men followed up for > 15 years. Participants took part in telephone interviews and medical and psychological evaluations. The neuroticism measure was based on the Minnesota Multiphasic Personality Inventory, which was administered during the psychological examination. Cognitive ability was measured via the Army General Technical Test given at induction and Wechsler Adult Intelligence Scale subtests administered during the psychological examination, approximately 17 years later. We used covariance structure modeling to analyze the data because it enabled us to conduct Cox proportional hazards analyses with latent variables and mediator variables.
Even after adjusting for age, ethnicity, and marital status, high neuroticism and low cognitive ability were independent mortality risk factors. A significant interaction indicated that participants high in neuroticism and low in cognitive ability were particularly at risk. In a second series of models, we examined whether education, income, seven physical health measures, two mental health measures, drinking, and smoking were related to mortality. SES and physical health variables attenuated the effect of cognitive ability but not that of neuroticism. A third series of models revealed that cognitive ability was related to mortality via its direct effects on income and health.
The effects of high neuroticism, low cognitive ability, and their interaction predict mortality. Cognitive ability effects are mediated by health, income, and education.
Psychosomatic Medicine 02/2009; 71(4):385-94. · 3.97 Impact Factor
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ABSTRACT: Ratings of 202 chimpanzees on 43 personality descriptor adjectives were used to calculate scores on five domains analogous to the human Five-Factor Model and a chimpanzee-specific Dominance domain. Male and female chimpanzees were divided into five age groups ranging from juvenile to old adult. Internal consistencies and interrater reliabilities of factors were stable across age groups and approximately 6.8 year retest reliabilities were high. Age-related declines in Extraversion and Openness and increases in Agreeableness and Conscientiousness paralleled human age differences. The mean change in absolute standardized units for all five factors was virtually identical in humans and chimpanzees after adjustment for different developmental rates. Consistent with their aggressive behavior in the wild, male chimpanzees were rated as more aggressive, emotional, and impulsive than females. Chimpanzee sex differences in personality were greater than comparable human gender differences. These findings suggest that chimpanzee and human personality develop via an unfolding maturational process.
Journal of Comparative Psychology 12/2008; 122(4):418-27. · 1.73 Impact Factor
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ABSTRACT: Subjective well-being is known to be related to personality traits. However, to date, nobody has examined whether personality and subjective well-being share a common genetic structure. We used a representative sample of 973 twin pairs to test the hypothesis that heritable differences in subjective well-being are entirely accounted for by the genetic architecture of the Five-Factor Model's personality domains. Results supported this model. Subjective well-being was accounted for by unique genetic influences from Neuroticism, Extraversion, and Conscientiousness, and by a common genetic factor that influenced all five personality domains in the directions of low Neuroticism and high Extraversion, Openness, Agreeableness, and Conscientiousness. These findings indicate that subjective well-being is linked to personality by common genes and that personality may form an "affective reserve" relevant to set-point maintenance and changes in set point over time.
Psychological Science 04/2008; 19(3):205-10. · 4.43 Impact Factor
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ABSTRACT: To examine the role of the big five personality domains (Neuroticism, Extraversion, Openness, Agreeableness, Conscientiousness) and their respective facets and profiles on change in CD4 and log HIV-RNA copies/ml (VL) over 4 years. The examination of psychosocial predictors of disease progression in human immunodeficiency virus (HIV) has focused primarily on depression, coping, and stress, with little attention paid to stable individual differences.
A diverse sample of HIV-seropositive patients (n = 104) completed personality assessment (NEO-PI-R), underwent comprehensive psychological assessment and blood samples every 6 months for 4 years. Linear rates of change for CD4 cells and VL were modeled using Hierarchical Linear Modeling controlling for antiretrovirals (time dependent covariate), initial disease status, age, gender, ethnicity, and education.
Domains that were significantly associated with slower disease progression over 4 years included Openness (CD4, VL), Extraversion (CD4, VL), and Conscientiousness (VL). Facets of the above domains that were significantly related to slower disease progression were assertiveness, positive emotions, and gregariousness (Extraversion); ideas, esthetics (Openness); achievement striving and order (Conscientiousness). In addition, profile analyses suggested personality styles which seem to underscore the importance of remaining engaged (e.g., Creative Interactors (E+O+), Upbeat Optimists (N-E+), Welcomers (E+A+), Go Getters (C+E+), and Directed (N-C+)) had slower disease progression, whereas the "homebody" profile (Low Extraversion-Low Openness) was significantly associated with faster disease progression.
These results provide good initial evidence of the relationship between personality and disease progression in HIV and suggest protective aspects of profiles of engagement. These finding may help identify those individuals at risk for poorer disease course and specify targets for psychosocial interventions.
Psychosomatic Medicine 03/2008; 70(2):245-53. · 3.97 Impact Factor
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ABSTRACT: To examine the influence of neuroticism and extraversion on all-cause and cause-specific mortality over 21 years after controlling for risk factors.
Participants were members of the Health and Lifestyle Survey, a British nationwide sample survey of 9003 adults. At baseline (1984 to 1985), individuals completed a sociodemographic and health questionnaire, underwent physical health examination, and completed the Eysenck Personality Inventory. Mortality was assessed for 21 years after baseline. A total of 5424 individuals had complete data.
After controlling for age and gender, 1-standard deviation (SD) increase in neuroticism was related to 9% (hazard ratio (HR) = 1.09; 95% Confidence Interval (CI) = 1.03-1.16) increased risk of mortality from all causes. The association was nonsignificant (HR = 1.05; 95% CI = 0.99-1.11) after additionally controlling for occupational social class, education, smoking, alcohol consumption, physical activity, and health. There was 12% (HR = 1.12; 95% CI = 1.03-1.21) increased risk of death from cardiovascular disease associated with 1-SD increase in neuroticism. This was still significant after adjustment. When the sample was divided into 40- to 59-year-olds and those >or=60 years, neuroticism remained a significant risk for all-cause mortality and cardiovascular disease mortality; associations were nonsignificant after controlling for all covariates. Neuroticism was not associated with deaths from stroke, respiratory disease, lung cancer, or other cancers. Extraversion was protective of death from respiratory disease (HR = 0.84; 95% CI = 0.70- 1.00).
After controlling for several risk factors, high neuroticism was significantly related to risk of death from cardiovascular disease. The effects of neuroticism on death from cardiovascular disease may be mediated by sociodemographic, health behavior, and physiological factors.
Psychosomatic Medicine 01/2008; 69(9):923-31. · 3.97 Impact Factor
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ABSTRACT: This study addressed whether personality ratings using a 43 adjective questionnaire based on the Five-Factor Model generalized from a sample of 202 zoo-housed chimpanzees to a sample of 175 chimpanzees housed in Yerkes National Primate Research Center. Mean interrater reliabilities of adjectival ratings were lower for the chimpanzees housed in Yerkes. In addition, rank order of the interrater reliabilities of items differed between settings. To compare factor structure, we first examined whether we could replicate the original six factor structure found in an earlier study of 100 zoo chimpanzees using principal factors analysis in the Yerkes sample and 102 new zoo chimpanzees. The dominance, extraversion, conscientiousness, and agreeableness factors were clearly replicated in the Yerkes sample and the 102 new zoo chimpanzees. The Neuroticism and Openness factors did not replicate in the Yerkes sample, but they also did not replicate in the new zoo chimpanzees. These findings suggest the need to sample more adjectives representing neuroticism and openness in future versions of the questionnaire. We next sought to determine whether factor structure, as determined by principal components analysis, remained invariant across the two settings. This analysis revealed dominance, extraversion, conscientiousness, and agreeableness factors in both settings and a high level of congruence between the zoo and Yerkes samples for these factors. Finally, we tested whether factor scores in the two samples were similarly related to age and sex. With the exception of differences in age effects for dominance and agreeableness, age, and sex effects were consistent across samples. These findings suggest that, whereas there may be differences in the ease with which ratings are made, personality structure, and development are largely consistent across widely differing settings.
American Journal of Primatology 11/2007; 69(11):1264-77. · 2.22 Impact Factor
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ABSTRACT: Psychosocial factors (e.g., depression, avoidant coping, life stress) have been related to disease progression in HIV. This study examined the relationship between the Big Five Conscientiousness factor and HIV disease progression (CD4 cell and viral load) over 1 year in 119 seropositive participants. The study also examined whether Conscientiousness effects were mediated by adherence, perceived stress, depression, or coping measures.
In a 1-year longitudinal design, participants completed the NEO Five-Factor Inventory Conscientiousness scale (P. T. Costa & R. R. McCrae, 1992). Participants also completed psychosocial assessments and underwent blood draws at initial assessments and 1-year follow-up.
Multiple hierarchical regression models were used to predict change in CD4 cell numbers and viral load log 10, controlling for demographic variables, initial disease status, and antiretroviral medications.
Conscientiousness predicted significant increases in CD4 number and significant decreases in viral load at 1 year. Conscientiousness was related positively to medication adherence and active coping and negatively to depression and perceived stress. Only perceived stress emerged as a possible mediator.
The significant relationship between Conscientiousness and medication adherence, distress, and coping suggests that an assessment of Conscientiousness in patients with HIV may help specify or target behavioral interventions to promote optimal disease management.
Health Psychology 07/2007; 26(4):473-80. · 3.87 Impact Factor
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ABSTRACT: Orangutans (Pongo pygmaeus and Pongo abelii) are semisolitary apes and, among the great apes, the most distantly related to humans. Raters assessed 152 orangutans on 48 personality descriptors; 140 of these orangutans were also rated on a subjective well-being questionnaire. Principal-components analysis yielded 5 reliable personality factors: Extraversion, Dominance, Neuroticism, Agreeableness, and Intellect. The authors found no factor analogous to human Conscientiousness. Among the orangutans rated on all 48 personality descriptors and the subjective well-being questionnaire, Extraversion, Agreeableness, and low Neuroticism were related to subjective well-being. These findings suggest that analogues of human, chimpanzee, and orangutan personality domains existed in a common ape ancestor.
Journal of Personality and Social Psychology 04/2006; 90(3):501-11. · 5.08 Impact Factor
