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They have long been held as an almost human-like relative.

But researchers have discovered chimpanzees have almost the same personality traits as humans.

The research team identified five personality factors that combine differently in each individual chimpanzee: conscientiousness, dominance, extraversion, agreeableness and intellect.

The researchers analyzed complete questionnaires for 174 chimpanzees housed at the Yerkes National Primate Center at Emory University.

The Georgia State University research also shows some of those traits have a neurobiological basis, and that those traits vary according to the biological sex of the individual chimpanzee.

This echoes a well-known five-factor model of the human personality, although the specific factors are slightly different.

'Our work also demonstrates the promise of using chimpanzee models to investigate the neurobiology of personality processes,' said Assistant Professor Robert Latzman of Psychology, who led the research team.

'We know that these processes are associated with a variety of emotional health outcomes.

'We're excited to continue investigating these links.'

The team, which also included Professor William Hopkins of Neuroscience, started with a common tool for analyzing chimp personalities called the Chimpanzee Personality Questionnaire.

The questionnaire is filled out by the chimpanzees' caregivers, who rate individual chimps in 43 categories based on their observation of the animals' daily behavior.

Questions include Is the chimp excitable, Impulsive, Playful, Timid or Dominant.

The researchers analyzed complete questionnaires for 174 chimpanzees housed at the Yerkes National Primate Center at Emory University.

They ran extensive individual analyses to find out which traits tend to go together, and which combine to make more basic, fundamental 'meta-traits.'

The analysis showed that the most fundamental personality trait for chimpanzees is dominance – that is, whether an animal is a generally dominant and undercontrolled 'Alpha,' or a more playful and sociable 'Beta.'

The research team identified five personality factors that combine differently in each individual chimpanzee: conscientiousness, dominance, extraversion, agreeableness and intellect. This echoes a well-known five-factor model of the human personality, although the specific factors are slightly different.

But those two big categories can be broken down statistically into smaller personality traits in ways that echo the personality structures researchers have repeatedly found in child and adult human subjects.

Alpha personalities, for example, statistically break down into tendencies toward dominance and disinhibition.

Beta personalities, on the other hand, show low dominance and positive emotionality.

Further analysis shows these lower order traits also can be statistically broken down into their constituent parts.

The research team identified five personality factors that combine differently in each individual chimpanzee: conscientiousness, dominance, extraversion, agreeableness and intellect.

This echoes a well-known five-factor model of the human personality, although the specific factors are slightly different.

Now, for the neurobiology: many of those chimpanzee traits statistically correlate with the function of a neuropeptide called vasopressin.

The researchers say chimps have very distinct personalities - similar to a human.

Chimps who were born with a common variant in the genes that control vasopressin behaved differently than their peers, the males showing more dominance and more disinhibition, but the females less of both.

This research shows not only a neurobiological basis for personality, but an evolutionary basis as well.

The neurobiological bases of personality can vary according to the biological sex of the subject, at least in chimpanzees.

Chimpanzee personality appears to have almost the same ingredients as human personalities, and that similarity seems to arise from the species' similar neurobiology.

'These results are particularly significant in light of the striking parallels between the major dimensions of personality found between chimpanzees and humans,' said Sam Gosling, professor of psychology at the University of Texas at Austin and an internationally known researcher in cross-species personality research.