Evolution, Eysenck, Gray, and Others
Biological Theories
Biological theories describe individual differences as a result of hereditary
predispositions as they interact with environment. Some biological factors,
such as neuroticism set some people up for anxiety and adjustment/
relational problems. Levels of responsivness to reinforcement can set people
up for addictions, depression.
Evolutionary psychology suggests that traits commonly seen in people
today are there because they had adaptive (survival) value for our early
ancestors. Therefore we see gender differences in role behaviors, sexual
jealousy, mate selection, & altruism. Natural selection, as Darwin explained
it, results in human characteristics that are genetically based. These
characteristics allow for greater reproductive success, therefore allowing our
species to survive and overcome other species. One problem, however, is
that our environment has shifted more quickly than our evolutionary
adaptation. So we still have a starvation-based physiology that leads us
today, in our abundant society, to develop obesity and associated illnesses,
rather than adapting by changing our cravings in response to the foods we
have developed.
 Emotions are protective to us, as they communicate risks and threats,
and teach the young sources of threat. We are prepared to learn
biologically based fears- such things as fear of snakes, high places,
and strangers. Emotions allow us to form more functional social
groups that protect the young, manage male aggression, & take care of
young who are orphaned. So emotional expressions are universalrecognizable and decipherable between many cultures. David Buss
says that emotions we feel today link to fitness failures in our distant
past- not having children to pass on our genes to. So personal
rejections, failures of love affairs tap into deep-seated survival issues
of a millennium past. Social ties are still valued because they produce
stable societies that help one another, share the fruits of labor, protect
the weak and young, and enhance immune function with calm
support.
 Altruism
o Inclusive fitness is the idea that evolution will select for genes
that increase the survival of the person and his/her offspring.
These include such things as more involved parenting &
sharing, altruistic behavior.
 Kin altruism is helping relatives in ways to aid their
survival, and by definition, one’s own genetic makeup.
 Reciprocal altruism is the idea of helping non-relatives
in the group. There is believed to be support for one’s
survival if all members of the group are helped to
survive. Even so, there is some risk of injury to the
helper, but overall chance of greater survival. “Cheaters”
are those who gain the benefit of others’ help, but refuse
to help others themselves. Free-riders are shamed and
rejected by the group, and heroes are acclaimed by the
group, so as to control the tendency to cheat. Altruism
develops from an unlearned psychological process,
empathy. Babies come into the world with a tendency to
cry in response to another baby’s cry. OF course, this
tendency can be shut down if the child is not consistently
responded to in love and nurture when s/he cries.
 Evolved psychological mechanisms are psychological
processes that evolved because they solve an adaptive
problem- either survival or reproductive. Sexual jealousy
evolved in males because they could not be certain that
they were truly the father of the offspring they were
helping a mother to raise. Female preference for males
who had greater economic resources was a survival
technique that allowed a greater chance of a child
growing to adulthood. Male preferences for females
showing signs of youth and fertility gave males a greater
chance of producing offspring, but if they did not bond
and support the female, the chances of their offspring
surviving to adulthood were much lower.
 Sexual behavior is for the evolutionary purpose of procreation. So
sexual attraction is based on markers of fertility. Symmetry of body
and face indicates greater health and genetic quality. Men prefer
women with a low waist-to-hip ratio (.7), which is also an indicator of
maximum fertility. Women prefer men with markers of testosteronejutting jaw, strong chin, thicker hair, greater upper body musculature.
(And this preference is intensified when women are in ovulation, the
most fertile time of the month.)
o Parental investment has to do with males and females
commitment to raising offspring. Females traditionally have
held all the nurture responsibility for children, which is lengthy.
There is the 9 months of gestation, and years of children’s
dependency, as well as women’s diminished fertility while
pregnant and nursing. So females will be more selective in
choosing mates to give her the best chance of producing a
healthy child who will grow into adulthood, carrying on her
genes to the next generation. So females are traditionally
pickier in choosing a mate than males. Males have maximum
opportunities to produce offspring, as they produce sperm in
copious amounts daily. This relates to male penchant toward
more partners, and more promiscuous sexual behavior. (Buss &
Schmitt study shows that women would wait 3 months before
being willing to have sex with a hypothetical person of the
opposite sex they had just met, while men would be ready after
only one day. After 3 mo. men would be as ready as women
would be after 2 years!) So if males want to have a child to pass
on his genes, they must bond for awhile with the woman
carrying their child. Otherwise this child is more likely to be
killed or neglected without a protective father.
o Paternal uncertainty is the question that men consider about
whether the child they are raising is their biological offspring.
Women always know they child they brought into the world is
theirs- men can’t have the same certainty. So sexual jealousy is
greater in males. (So men are more disturbed to think their
partner is having sex with another man, and women are more
disturbed to think of their man having an emotional relationship
with another woman.) Today there is less gender-based
difference in sexual behavior, since women are more active in
the world and in work, and contraceptives are so available. Sex
no longer demands commitment. Sexual strategies males and
females use are different depending on what the goal is- longterm commitment or short-term sexual satisfaction. Male status/
dominance behaviors are more evident in short-term goals, but
dominance is not as important as loyalty when contemplating
long-term commitments. Once bonded, there are different
strategies for keeping the spouse- appearance enhancement
(women), threatening competitors (men). Wives’ attractiveness
and husband’s earning growth predict longer-lasting marriages.
IN more equal status cultures, these stereotypes of attraction
diminish in power.
o Attachment and mating theory suggests that mating behavior
is a throw-back to early attachment processes in infancy. Both
parents caring for children offers children the best chance of
survival and health. Parents’ bonding also provides the most
stable environment for children to grow up.
 Oxytocin is a hormone that is released in the mother’s
body when nursing and during sex. It stimulates cuddling
in both cases. It rises in men upon the birth of their
children, as well, stimulating fidelity and bonding with
the child.
 Tend-and-befriend is the female model of attachment
and caregiving which oxytocin stimulates; fight-or-flight
is the model of stress response that has been traditionally
studied, but it is especially a male response. The
downside of the tend-and-befriend response is that the
tribe depends chiefly on females to care for children, and
dependent adults, aging members of the group. This
response protects the stability of the group- but often at
the expense of the woman’s health and energy.
 Parental behavior- those parents who nurture their young enhance
the survival of their genes. The greater number of relatives involved in
raising the child, the greater the chance of survival. This is important
to the relatives, as they have a genetic investment in the survival of
this child, too. Stepchildren, not being a biological link in the family
are more often abused or neglected and receive less financial support
in their education (!) Other links to parental behavior include the
child’s exposure to a parent’s mental illness, depression, results in
greater sensitivity to cortisol and stress hormones later in life. (They
will have enhanced responses to stress and lower tolerance of it.)
There are also conditions where restricting parenting of a child with a
life-threatening illness or defect could be seen as necessary to insure
the survival of other children.
 Aggression and dominance serves several functions from an
evolutionary perspective: taking resources from others for survival,
negotiating power, diminishing the power of same-sex rivals,
deterring rivals from confrontation, deterring mates from infidelity.
Social dominance, dominance hierarchies are specifically male
behavior in order to assure reproductive opportunities and select only
the finest males for mating. Testosterone levels are generally higher in
more aggressive males, although the display of aggression may be
very socially acceptable (criminal defense lawyers vs. their
defendants.) Men compete over more than females today, as
aggression is also linked to status and respect from other males.
 Culture is the transmission of ideas from one generation to another,
including language, religion, rituals. This ability to pass on shared
culture is adaptive, too. Culture is passed on through imitation of
adults even before language is in place.
o Cultural evolution shapes personality in a common way within
each culture. Interesting cultural taboos have included eating
beef in cultures that needed cows for plowing fields and
keeping another source of food available, taboos against eating
pork in times when pork was often tainted, and a common
taboo against having sex with close relatives (preventing
chances of inherited diseases killing an entire blood line.)
 Language and thought is important in passing on culture, as
narratives of myths and values can be passed on from generation to
generation. Humans have developed a “theory of mind” which aids us
in divining the intentions of others. Even chimps respond differently
to a researcher who fails to give them a treat due to an “accident” as
opposed to intentionally pouring the treat on the ground. Children are
even more accurate in divining others’ intentions and determining
trustworthiness from that intent. (Autistic children lack this trait of
developing a theory of mind and understanding differences of
knowing in other people.) Because we have evolved symbolic thought
we are freed from concrete limitations of the here and now. Even
though we can think abstractly, our thought processes are still
embedded in evolutionary contexts.
Genetics and personality
Heritability- With the completion of the Human Genome Project, it
has been found that certain genes relate to certain personality traits. Twin
studies- especially those raised apart- have shown that it is the genetic
substrate that produces the trait, not the factor of parenting or environmental
similarity. Coping styles, ego development, happiness or subjective wellbeing, likelihood of divorce, authoritarian attitudes all show significant
genetic direction.
Emergenic traits are phenotypic traits that are caused by a
constellation of many genes, so they may not appear to run in families. So
genes are not merely additive in their effects, they actually combine in ways
as to produce very different traits from other family members.
Temperament is the biological foundation of personality, based on
characteristic patterns of emotionality, activity, and sociability. This concept
goes all the way back to the Greeks, as 4 personality styles were described as
being the result of certain biological differences. Temperament is observable
early in life and has a lot to do with inherited tendencies toward selfregulation. Some children can more easily distract and soothe themselves;
other children are more overcome by change in their environment. This is a
result of their limbic system and its reactivity to novelty. Temperament is
fairly stable over time, but sensitive parenting can bring a child closer to the
median in reactivity. Temperament has a strong heritability, as it relates to
how the brain functions.
 Easy, difficult, slow-to-warm up children are the 3 categories of
children’s temperaments defined by the New York Longitudinal
Study. Easy babies (40%) are generally happy, open to new
experiences. 15% were slow to warm up- meaning they were more
easily distressed & resistant to novelty, but could be cajoled to accept
novelty with some support. 10% were difficult- they withdrew from
the unfamiliar, were irritable and at high risk for psychiatric
symptoms in childhood. Some didn’t fit any category (Thomas and
Chess)
 EASI model proposed 4 dimensions of personality: emotionality,
activity, sociability, impulsivity.
 Big Five personality factors have also been described as genetically
based.
 The Strange Room task was developed by Kagan to test
temperament within a specific environment. He defined 2 types of
temperaments: inhibited type and uninhibited type. One key behavior
that marks these two types is children’s talkativeness with people they
don’t know.
o Inhibited type cried and clung to the mothers during novel
experiences, interacted less with the experimenter & stranger
(Similar to the slow to warm up type.) They are more likely to
watch other children play than initiate encounters with other
children.
o Uninhibited type interacted more with others, and were more
likely to approach the toy robot. They used the caregiver as a
safe base from with to explore the environment, but also
showed happiness when the mother returned. (Like the easy
type) They were more likely to initiate interactions with other
children.
o Neurotransmitters, the amygdale, sympathetic nervous
system activity all combine to produce different temperaments.
Inhibited children are more retiring because their brain
produces high levels of stress hormones that stimulate the
amygdale and other areas of the brain related to fear. There is
greater sympathetic nervous system stimulation- rapid heart
rate, rise in blood pressure, norepinephrine, and so greater
emotional discomfort. Uninhibited children have less
neurotransmitter activity, are lower in CNS reactivity, and so
less fearful in general. They are also less affected by
punishment, so are more difficult to discipline. Without
sensitive parenting, these children are more likely to become
aggressive and antisocial. Inhibited children, while more easily
disciplined, are also more likely to become passive, easily
depressed adults. Another determiner of outcome is how the
parent warns their children about danger. Mothers who don’t
call out many warnings to inhibited children risk making them
risk averse, extremely inhibited and fearful. Allowing an
inhibited child to explore with some informative warnings can
moderate their inhibitions. (As Adler said, parents who pamper
their children risk producing children with weak initiative and
resilience.) Other emotional experiences can influence
temperament, though, as well. Trauma particularly can produce
fears and phobias and increased inhibition. Temperament is
produced by a combination of genetic predisposition and the
reactions the child gets from others. It is an interactive cycle of
influence. The easy child is expected to get along well with
others, so gets more positive reactions from others, producing
greater confidence in his/her social skills. The difficult or
impulsive child is expected to be antagonistic, so is disciplined
more negatively and often, setting up expectations of problems
in relationships. So the genotype can produce different
characteristics, the phenotype, based on environmental
interactions. This influence can actually produce different brain
chemistry and structure over time. (Lack of nurture or abuse &
neglect can contribute to atrophy of the hippocampus, the site
of short-term learning. This relates to producing an antisocial
child with a severe lack of empathy, allowing greater freedom
to abuse others. Serial murderers have been found to have
almost total disintegration of this important structure in the
brain.)
Biological contributors to personality- the connection between brain
function and personality was first noted in the case of Phineas Gage, who
suffered a brain injury at work, and although he recovered, was changed
forever by the insult to the brain.
 The brain is implicated in a number of personality quirks- people
with antisocial personality disorder have less gray matter in their
frontal cortex than other people. Brain changes show up on brain
imaging scans when people pray or meditate.
o Structural differences can be pinpointed in people who have
different functioning. Damage to the amygdale relates to
problems judging faces that are unapproachable or showing
signs of untrustworthiness. They recognize differences in faces,
but don’t put those combinations of features together to
recognize an emotional signal. As a result they act unreasonably
trusting of others. Specific areas of the cortex link to attributing
emotional states to others, or thinking about our own emotional
states. Obviously, minor damage to these areas could limit a
person’s ability to factor in consequences for their behavior.
Because the brain functions through separate modules and
structures, sometimes the input from different areas does not
get integrated in a meaningful way. The amygdale may produce
the experience of fear, but we may not have conscious
awareness of what is producing the fear, or even that we are
feeling fear. It can be associated with things that are not related
to the experience, producing irrational phobias. If our brain
function becomes too linked to aversion to fear, it can become
very inflexible, not learning from more positive experiences.
Adaptability is what allowed our species to triumph over the
environment.
o Neurotransmitter differences also produce different
personality traits. We have 150 different neurotransmitters that
combine in various ways to allow maximum efficiency in
reaction. Neurotransmitters also produce changes in brain
structure, by sensitizing some neural pathways to be more
efficient, and letting others decline. When there is more of a
neurotransmitter produced, the neurons adapt by producing
more receptor sites to take this in. That is the process of
tolerance and addiction to external drugs & substances.
 Dopamine must function in a delicate balance, as too
much dopamine produces severe mental disturbance in
the form of schizophrenia. Low levels produce symptoms
of Parkinson’s disease. Dopamine produces rewarding
experiences, so low levels are associated with sensation
seeking behavior. It also produces greater vulnerability to
tobacco addiction.
 Emotional arousal is linked to personality traits. Some people try to
avoid strong emotions, and others find great reward in emotionality.
We generally try to expand what is rewarding to us and control what
is distasteful. People differ in how much they are drawn to emotional
experiences. People with antisocial personality disorder show signs of
abnormal brain function in this area. They show less response to
stressful situations, threat of shock, and a weaker startle reflex to loud
noise, pictures of dead bodies or guns pointed at them. Their EEGs
don’t register as much response to emotionally loaded words. They
show less empathy than normal people. They have lower than normal
levels of serotonin, which produces feelings of satisfaction.
o Brain dominance makes a difference in emotional reactivity.
The left hemisphere is more active during pleasant emotional
experiences, and the right side during unpleasant experiences.
The left side is more active when people approach, and the right
when they are motivated to avoid. Anger activates the left side,
so anger may be designed to help us overcome fears (moderated
by the right side of the brain.) Anger keeps us from being
immobilized by fear, so it could be a survival mechanism.
 Cortical arousal is stimulation through thinking. How rapidly we can
become aroused from a relaxed state, and how intensely we react are
also differences in personality. Pavlov actually studied this in his dog
studies of classical conditioning. He found that when the stimulus was
too intense, the nervous system protected itself by a sort of inhibition
to counter the excitatory process of the stimulation.
o Strong nervous system – these dogs increased their
conditioning before the inhibitory process kicked in.
o Weak nervous system- these dogs were not as readily
conditioned as their inhibition to intense stimuli kicked in
earlier and prevented the learning/ association process.
o Sensation seeking- people also vary in how they react to
stimuli- overreacting or underreacting. Sensation seeking is a
coping style of dealing with their emotional reactivity.
Sensation seeking is the desire for novel, intense sensations,
even risk-taking for the sake of these intense experiences. It
seems to relate to MAO levels (Monoamine oxidase enzymes)
which are low in sensation seekers, as well as the
neurotransmitters that MAO regulates: dopamine and serotonin.
So high sensation seekers also are more likely to drink, smoke,
use illegal drugs, gamble, and drive recklessly. They are more
likely to have unsafe sex with many partners and put
themselves at risk for AIDS.
Biological factor theories: Eysenck, Gray, and Others
 Eysenck’s “PEN” Biological Model is built on Pavlov’s analysis of
strong and weak nervous systems. Today brain scans can determine
reactivity to stimuli according to the weak or strong nervous system.
Those with the strong nervous system are extraverts, while those with
greater inhibitory processing are introverts. Eysenck theorized that
there were 3 factors of personality, based on biological differences
between people: extraversion, neuroticism, & psychoticism.
o Extraversion is moderated by a strong nervous system which is
quick to inhibit stimuli, can tolerate intense stimuli without
being overwhelmed, can tune out arousing inputs in social
situations, and can tolerate having many people around them.
They crave stimulation and seek it- sensation seeking.
Introverts have a weak nervous system that is easily
overwhelmed by intense stimuli, are overstimulated in the
presence of many other people and easily overwhelmed by
sensory stimulation. They cope by withdrawing from situations
of too much stimulation from people, becoming introverts. He
also theorized (& has been found correct) that these differences
are due to different brain functionality. The Reticular
Activating System in the brain senses arousal messages from
the brainstem and sends them to higher, more rational brain
levels. Extraverts were slower to react to auditory stimuli and
needed more stimulation to become aroused. Their brains just
naturally dampened incoming stimulation. So extraverts choose
more noise than introverts, who perform better with fewer
distractions. There is actually higher blood flow to the temporal
lobes in introverts. There are other differences in the dopamine
system between introverts and extraverts.
o Neuroticism is about emotional arousal. Some people are more
emotionally aroused in threat situations than others. They are
high in Neuroticism. Those who are low on this factor are not
so emotional in the same situation. So neurotics make more use
of defense mechanisms to manage their anxieties. Those high in
neuroticism are also more self-critical and less accepting of
themselves than other, less neurotic people.
o Psychoticism is a tendency toward nonconformity or social
deviance, it’s not the marker of pathology, particularly.
Creative people often have high psychoticism scores, but are
very normal in other ways. High scorers do have characteristics
that put them at risk for deviance: greater impulsivity, hostility,
sadistic, and less empathic than those who score low. High
scorers show more tolerance of violent videos and quicker
desensitization to violence.
o Implications: those who have weaker conditioned responses
(the weaker nervous system) are at increased risk of criminality
since they don’t make the connection between discipline, or
threatened discipline and inhibition of impulses. Conscience
develops as we make connections between our behavior, the
consequences of our behavior, and our desired connections with
others. So those who have a harder time making conditioned
connections also are less inhibited about misbehavior. Conductdisordered children (and criminals) show weaker conditioned
emotional responses. Another result of this could be greater risk
of parents using increasingly punitive measures to enforce
discipline- degenerating into physical abuse as the parent is
increasingly frustrated by the failure of his/her training.
o Clark and Watson’s theory proposes that combinations of
various of Eysenck’s factors set up life directions that can be
positive or negative. Neuroticism/ Negative Emotionality
(N/NE) emphasizes negative emotions such as distress and
threat, and instability of emotions. They report more negative
moods in general. Extraversion/ Positive Emotionality (E/PE)
have characteristics of the extraverts’ cheerfulness and
confidence in approaching life. So they develop more
interpersonal connections & support. These people report more
positive moods and active social lives. Another factor focuses
on impulse control and relates to life choices such as casual sex,
more partners, substance abuse, & reckless driving.
 Gray’s Reinforcement Sensitivity Theory relates to how people
vary in approach and avoidance- positive and negative reinforcement.
Some people stress positive emotions and approach in life, others
emphasize avoidance and negative emotions. It’s easier to induce
positive mood in extraverts and negative moods in neurotics.
Extraverts show greater brain reactivity to emotionally positive
pictures, and neurotics show greater reactivity to emotionally negative
pictures.
o Behavioral Activation System (BAS) comes into play when
rewarding things happen, so we approach. This relates to
extraversion, sexual behavior, and aggressive behavior (and
dopamine levels, which stimulates the reward center in the
nucleus accumbens.) So people high in this system feel greater
happiness in anticipation of reward. It is off balance in people
suffering from bipolar disorder. Higher levels also associate
with alcohol cravings- alcohol releases more dopamine and
enhances pleasurable emotions in these people. Lower
sensitivity of this BAS system associates with depression.
o Behavioral Inhibition System (BIS) comes into action when
feared or aversive stimuli occur. This system arouses the person
to be attentive, afraid, and often inhibits behavior. These people
are particularly sensitive to punishment, somewhat anxietyprone, and less able to disengage from tasks that have aversive
cues. The BIS system relates to norepinephrine and the
hippocampus structure in the brain. When people don’t have a
responsive BIS, they often act impulsively, putting themselves
at risk through antisocial acts, & have trouble delaying
gratification. It may be part of the ADHD constellation of
impairments. Youth showing criminal behavior also have low
norepinephrine levels & they seem less impacted by efforts to
discipline them, less afraid in general. Too responsive a BIS
system hampers people with anxiety. If people don’t know how
they are compensating and find ways to move out of their most
familiar response pattern, they are at risk of focusing on their
fears, or anticipated rewards, and becoming more intensely
inhibited, neurotic, or risk-taking. WE tend to watch for signs
of what we fear and become even more focused on stimuli that
enhance our natural dispositions. The filtering system enhances
our natural disposition, and this isn’t always healthy.
o Fight-Flight System (FFS) produces rage and panic.
Extraverts are more influenced by reward, and introverts by
punishment. So variable activation of the BAS and BIS systems
guides learning. Rewards and punishers guide us as to what to
approach and what to avoid. Dopamine seems to regulate the
factor of agency: social dominance, achievement, activity. So
people with higher levels of dopamine also show greater goaldirected behavior. People move more actively toward goalrelated positive incentives. Dopamine also facilitates learning,
making associations between incentive stimuli and behavior
and reward. The more these connections are stimulated, the
better the reward pathways are connected in the brain.
Structural change in the brain is produced by repeated
experiences.
 Cloninger’s Tridimensional Model proposes 3 biologically based
traits, each one resulting from a particular neurotransmitter.
o Novelty seeking seems to be related to dopamine (low levels
produce greater novelty seeking). People who are high in
novelty seeking are more stimulated by novelty and explore
their environments more. They seek excitement and even feel
more positive responses to amphetamines. It can lead to
impulsive behavior and substance abuse, however. It is seen as
running in families.
o Harm avoidance is related to higher levels of serotonin. This is
the behavioral inhibition system. People high in this trait are
sensitive to aversive stimuli and act to avoid pain or
punishment. They report greater anxiety, worry, and tension.
Low serotonin activity is associated with impulsive acts of
aggression. In monkeys, dominance is associated with higher
serotonin levels. Low serotonin is associated with aggression
and higher levels relate to sociable behaviors.
o Reward dependence results from low levels of norepinephrine.
This is a maintenance system- it gets people to behave to get
rewards, especially rewards through social attachments. People
high in reward dependence report they are hard-working and
keep working even when others give up. Persistence is another
dimension- and can lead to perfectionism. Social learning
builds on these biological predispositions. Different
combinations of these 3 characteristics produce very different
behavior patterns.
Biological Mechanisms in Context
All behavior is biological, but not all behavior can be understood at
the biological level. Experience changes biology. Brain development is
modulated by experience, stimulation, and consequences. Social reward can
exaggerate biological differences or reduce them, as seen in gender
differences. Some differences have dropped dramatically in response to
greater flexibility of roles and opportunities for the genders since the
women’s movement. The brain’s responses can be exaggerated in response
to a single traumatic event. Early deprivation of nurture can produce longterm effects in sociability, trust, as well as dopamine production. Both
nurture and biology can produce synaptic changes and even structural
changes in the brain. Hormone levels can increase bonding (oxytocin in
females, vasopressin in males) or prevent the ability to bond. This can have
long-term consequences in sophisticated society that sets a person up for
social rejection. Even the advances in medication to moderate depression,
anxiety or schizophrenia require the brain to make response changes as a
result of the changes from the medication. Medications facilitate behavior
changes- hopefully so they are not required for a lifetime. But learning must
be developed if any long-term improvement is seen. So therapy is necessary
as an adjunct to medication therapy. Culture even makes a difference- the
same reticence and shyness in a child in China would be seen as respectful
and natural, whereas in the US, which encourages greater independence, this
behavior would be seen as problematic, even a source of bullying by peers.
To fully understand personality traits, one must factor in environmental
factors with biological predispositions.