Evolution of social behavior in primates: 
personality traits 

A genetic approach to behavior in ancestral hominids 

©  A.M. Benis, Sc.D., M.D. 

video : Gestures in primates

Illustration from Benis A.M., ...Genetic Origins of the Human Character (see reference below).
Why is this gorilla smiling?

(a) He is happy.

(b) He has just witnessed an amusing event, or

(c) He has the genetic character trait of sanguinity.

[answer below]
Sanguinity, perfectionism and aggression 
as Mendelian genetic traits in primates


Our premise is that biologists and anthropologists whose main interest is human behavioral evolution, evolutionary psychology or "sociobiology", have been insulated from ideas emanating from the medical community, in particular from genetic theory in the area of psychiatry.  Indeed, it is becoming increasingly clear that the human personality is determined primarily by a number of genetic traits.  

We identify three traits that are posited to be transmitted in humans in a Mendelian fashion:  sanguinity, or narcissism (N), perfectionism (P) and aggression (A).  We believe that the genetic loci corresponding to these traits will be identified.  Thus, DNA analyses in the near future could allow one to trace personality traits -- and even "personality types" -- in ancestral hominid lineages.

In addition, we show that the traits N, P, and A may be identified in non-human primates.  The evolutionary implications of the theory are evident.

NPA theory of discrete character traits

The NPA theory of personality posits three major behavioral traits underlying personality:  sanguinity (N), perfectionism (P) and aggression (A), leading to the formulation of a limited number of identifiable discrete "character types".  Each of the traits is posited to be based on a major pleiotropic gene that follows the rules of Mendelian genetics.  The mode of transmission of the traits was implied from human archetypal family pedigrees.  In some families, the traits A and N seemed to be high-frequency recessive, with P being dominant.  The theory proposes that the traits A and N are indispensable to human development, being related to the sympathetic and parasympathetic nervous systems, respectively.

Our interpretation of the three traits in humans is as follows:

Aggression (A) 

The stereotypic acts associated with aggression involve body posturing, gestures and eye contact of intimidation and deference, with individuals having this trait continually competing with each other on a scale of dominance and submission.  The trait corresponds to a striving for power over one's environment, hence is one component of human ambition.  In a psychiatric connotation the trait may reveal itself in the context of sadism or sadomasochism.  The facial complexion is non-sanguine, i.e., tending toward sallowness or pallor in individuals of light skin color.  The hallmark of the trait is the well-known mass discharge of the sympathetic nervous system:  the "fight or flight" response or the aggressive-vindictive rage.  During the expression of this rage, the facial complexion of pallor is accentuated.

Sanguinity, or "narcissism" (N)

The stereotypic acts associated with the trait of sanguinity include flaunting body posturing, expansive arm gestures, bowing, colorful self-adornment, and a natural attraction to the limelight of personal recognition.  Individuals of the N type are competitive but non-aggressive in their strivings for recognition.  The trait corresponds to a striving for glory in one's environment, hence is the second main component of human ambition.  In a psychiatric connotation the unbridled trait of narcissism may reveal itself in the context of vanity, exhibitionism, and messianism.  An associated innate facial expression is the radiant gingival smile of recognition (broadly exposing gums and teeth).  The facial complexion tends toward blood red or ruddy in individuals of light skin color.  Hallmarks of the trait include blushing, flushing, and a mass discharge involving the parasympathetic nervous system:  the narcissistic rage of defense and withdrawal.  During the expression of this rage the normally sanguine complexion becomes even more florid.  

Perfectionism (P) 

The trait of perfectionism is not a basic drive of ambition and is not associated with a rage reaction.  Rather it is a mediator of the unbridled drives of aggression and/or sanguinity.  The stereotypic acts associated with the trait of perfectionism are obsessiveness, compulsiveness, repetition, and the maintenance of neatness, order and symmetry.  It is concluded that certain autistic and schizophrenic individuals are those in whom the two components of ambition, i.e., aggression and sanguinity, have been suppressed by genetic or environmental factors, either congenitally, in childhood, or after maturity, thus revealing in the individual a primitive state of perfectionism.

Main results of the NPA model

Three basic personality traits

Identification of only three basic traits is sufficient to define the genetically determined character type in humans.  Transmission of the character traits from parents to offspring is predictable on the basis of Mendelian genetics.  The theory clearly delineates the genetic bases of personality from environmental ones.

Character traits identifiable in non-human primates

The traits of sanguinity (N)  and perfectionism (P), as well as the trait of aggression (A), are identifiable in human and non-human primates.  

Of special interest, the trait of sanguinity (N) is identified in certain non-human primates (e.g., orangutan, gorilla, chimpanzee) and in widely disparate geographic and ethnic human populations.  The gingival smile is a behavioral marker of the trait of sanguinity.

Two rage reactions of the autonomic nervous system

The aggressive-vindictive rage (A-rage) and the tantrum of sanguinity (N-rage) can both be identified in human and non-human primates.

Character types identified in non-human primates

The behavior of certain well-known non-human primates can be fruitfully analyzed by the model.  For example, baboons would be primarily PA types (perfectionist-aggressive, non-sanguine).  Orangutans and gorillas would be primarily NP types (sanguine-perfectionist, non-aggressive).  Chimpanzees would be primarily NPA types (all three traits).  To wit:

Baboon (PA types):  They play a vigorous game of dominance and submission based on the trait of aggression.  The grooming habits are rooted in the trait of perfectionism.  Baboons do not exhibit the smile of recognition.

Orangutan (NP types):  They are non-aggressive, perfectionistic, aloof.  They exhibit N-tantrums and display the broad gingival smile.

Gorilla (NP types):  They also are non-aggressive and can exhibit the gingival smile.  The chest-slapping ritual is interpreted to be a sanguine, or in human terms, "narcissistic" display of recognition.

Chimpanzee (primarily NA and NPA types):  Akin to the human, a spectrum of personality types exists in the chimpanzee community.  Some, but not all, individuals can display the gingival smile of the trait of sanguinity.  Thus, different individuals may have different combinations of the traits of aggression,  (aggressive fighting), perfectionism (fishing for termites, use of tools), and sanguinity (gingival smile).

Schizophrenic-like syndromes of withdrawal in non-human primates

In humans, in the NPA model predisposition to the schizophrenias is based on the lack of expression of two of the genes (determining traits N and A).  Syndromes of withdrawal in non-human primate individuals -- for example, in rehabilitated apes who were nurtured in stressful human environments -- may be interpretable in the light of schizophrenic syndromes elucidated in humans.

Gene frequencies and population genetics

Distributions of the discrete character types identified by the model in various populations may be approached on the basis of gene frequencies and well-known principles of population genetics.  We use the Hardy-Weinberg approach to delineate distributions of human personality types in widely different geographic and cultural contexts.


Benis A.M. (1985, 2008):  "Toward Self & Sanity:  On the genetic origins of the human character", Psychological Dimensions Publishers, New York.

Benis A.M. and Rand J.R. (1986):  A model of human personality traits based on Mendelian genetics.  American Assn. for the Advancement of Science, Pub. 86-5, Washington D.C., p.124 (abstract).

Benis A.M. (1990) :  A theory of personality traits leads to a genetic model for borderline types and schizophrenia.  Speculations in Science and Technology 13, No. 3, 167-175.