How DNA interacts with the environment determines what part of the DNA code is actually activated within an individual—in other words, which genes will be expressed.
The biological approach to personality has also identified areas and pathways within the brain that are associated with the development of personality. A number of theorists, such as Hans Eysenck, Gordon Allport, and Raymond Cattell, believe that personality traits can be traced back to brain structures and neural mechanisms, such as dopamine and seratonin pathways. Researchers using a biological perspective will seek to understand how hormones, neurotransmitters, and different areas of the brain all interact to affect personality.
One of the first documented cases that demonstrated the link between personality and the brain was that of Phineas Gage. In , Gage was working as a blasting foreman for a railroad company. Due to a faulty blast, a railroad spike was blown through his head; miraculously, he survived the accident. One strength of the biological perspective is its strict adherence to scientific methodology.
All factors are reduced to quantifiable variables that can be reliably measured by personality trait models and questionnaires. The personality measures are standardized across measurements, and these measures of personality are very compatible with statistical analyses, providing an easily administered and measurable definition of personality.
This method can also be deterministic, meaning that some factors are identified as causal—i. Because of this, the biological perspective can be useful in identifying causes of and effective treatments for personality and mood disorders.
For example, identifying seratonin imbalance as a cause of depression led to the development of selective seratonin reuptake inhibitors SSRIs , which have been found to be an effective treatment for depression.
A limitation of this perspective is that it focuses almost exclusively on the nature side of the nature vs. Because of this exclusive focus, other factors that are integral to personality are not included.
Hormones, neurotransmitters, and genetics are the key factors in this focus; the effects of environmental and social factors, however, are often overlooked. Twin studies have shown that heritable factors are not the only predictor of personality or even diseases such as schizophrenia; the biological perspective does not fully address non-heritable factors.
In addition, the correlational studies used for measuring normal personality traits are subjected to the same rules as normal correlational research: they cannot be used alone to establish causation.
Just because two factors are shown to be related does not mean that one causes the other. For example, if you have data that show that as ice cream sales increase, the rate of drowning deaths also increases, you should not necessarily conclude that ice cream consumption causes drowning.
In this case, more ice cream is sold during the hot summer months—the same time that people are more likely to go swimming. Therefore, the cause of the increases in both ice cream sales and drowning deaths is most likely the hot summer weather.
That said, properly designed experimental studies can help scientists determine cause-and-effect relationships in order to develop treatment options for people with personality disorders. Personality psychologists are interested in understanding the role that culture plays in the development of personality. Research investigating the variations of personality traits across cultures suggests that there are both universal and culture-specific aspects that account for these variations.
They are dependent on context. An example might include a preference for certain foods or colors. Trait theory is the personality development model most directly based on research data , according to Personality Theories: Critical Perspectives.
Developed by Albert Bandura, social cognitive theory stresses that personalities are formed based on social contexts. It assumes two key principles, according to Williams and Cervone :. According to social cognitive theory, personality formation occurs when people observe the behaviors of others.
This leads to adaptation and assimilation, particularly if those behaviors are rewarded. Social cognitive theory is often considered a bridge between personality theories that emphasize behavior and those that emphasize cognition. Kim provides insight into the real-world applications of the four theories within the field of psychology:. When assessing personality, clinicians often turn to two main types of evaluations: objective and projective tests. The test was originally published in and then revised in Questions on the MMPI-2 identify potential personality features such as anger or addiction.
The test is comprehensive and designed to ward against false positives and lying. MMPI-2 evaluations are often used in settings such as mental health and medical fields. Projective tests are subjective evaluations that ask clients to respond to ambiguous stimuli, such as words or visual images. The Rorschach Inkblot Test is a classic example of a projective test.
After looking at 10 inkblots of varying shapes and colors, clients are asked to describe what they see. Answers are interpreted based on factors like subject matter, the kind of shapes or colors emphasized, and the location of the seen image. While the Rorschach test is useful, Kim views it as one of many tools and notes that it is not adequate for understanding the nuances of personality on its own.
When personality becomes problematic for daily living, it is considered a disorder. The Mayo Clinic defines a personality disorder as characterized by rigid or unhealthy patterns of thinking, functioning, or behavior. Disorders defined by eccentric thinking or odd behavior. Examples include paranoid personality disorder, schizoid personality disorder, and schizotypal personality disorder.
Disorders defined by behavior and thinking that are excessively emotional or unpredictable. Examples include narcissistic personality disorder, antisocial personality disorder, and borderline personality disorder. In this section we will see that the personality traits of humans and animals are determined in large part by their genetic makeup, and thus it is no surprise that identical twins Paula Bernstein and Elyse Schein turned out to be very similar even though they had been raised separately.
But we will also see that genetics does not determine everything. In the nucleus of each cell in your body are 23 pairs of chromosomes. One of each pair comes from your father, and the other comes from your mother. The chromosomes are made up of strands of the molecule DNA deoxyribonucleic acid , and the DNA is grouped into segments known as genes. A gene is the basic biological unit that transmits characteristics from one generation to the next. Human cells have about 25, genes.
The genes of different members of the same species are almost identical. The DNA in your genes, for instance, is about These common genetic structures lead members of the same species to be born with a variety of behaviours that come naturally to them and that define the characteristics of the species.
These abilities and characteristics are known as instincts — complex inborn patterns of behaviours that help ensure survival and reproduction Tinbergen, Different animals have different instincts. Birds naturally build nests, dogs are naturally loyal to their human caretakers, and humans instinctively learn to walk and to speak and understand language.
But the strength of different traits and behaviours also varies within species. Rabbits are naturally fearful, but some are more fearful than others; some dogs are more loyal than others to their caretakers; and some humans learn to speak and write better than others do. These differences are determined in part by the small amount in humans, the 0. Personality is not determined by any single gene, but rather by the actions of many genes working together.
Furthermore, even working together, genes are not so powerful that they can control or create our personality. Some genes tend to increase a given characteristic and others work to decrease that same characteristic — the complex relationship among the various genes, as well as a variety of random factors, produces the final outcome. Furthermore, genetic factors always work with environmental factors to create personality.
For example, a person may have a genetic variant that is known to increase his or her risk for developing emphysema from smoking. But if that person never smokes, then emphysema most likely will not develop. Perhaps the most direct way to study the role of genetics in personality is to selectively breed animals for the trait of interest. In this approach the scientist chooses the animals that most strongly express the personality characteristics of interest and breeds these animals with each other.
If the selective breeding creates offspring with even stronger traits, then we can assume that the trait has genetic origins. In this manner, scientists have studied the role of genetics in how worms respond to stimuli, how fish develop courtship rituals, how rats differ in play, and how pigs differ in their responses to stress.
Although selective breeding studies can be informative, they are clearly not useful for studying humans. For this psychologists rely on behavioural genetics — a variety of research techniques that scientists use to learn about the genetic and environmental influences on human behaviour by comparing the traits of biologically and nonbiologically related family members Baker, Behavioural genetics is based on the results of family studies , twin studies , and adoptive studies.
The presence of the trait in first-degree relatives parents, siblings, and children is compared with the prevalence of the trait in second-degree relatives aunts, uncles, grandchildren, grandparents, and nephews or nieces and in more distant family members. The scientists then analyze the patterns of the trait in the family members to see the extent to which it is shared by closer and more distant relatives.
Although family studies can reveal whether a trait runs in a family, it cannot explain why. In a twin study , researchers study the personality characteristics of twins.
Twin studies rely on the fact that identical or monozygotic twins have essentially the same set of genes, while fraternal or dizygotic twins have, on average, a half-identical set. The idea is that if the twins are raised in the same household, then the twins will be influenced by their environments to an equal degree, and this influence will be pretty much equal for identical and fraternal twins.
In other words, if environmental factors are the same, then the only factor that can make identical twins more similar than fraternal twins is their greater genetic similarity.
In a twin study, the data from many pairs of twins are collected and the rates of similarity for identical and fraternal pairs are compared. A correlation coefficient is calculated that assesses the extent to which the trait for one twin is associated with the trait in the other twin.
Twin studies divide the influence of nature and nurture into three parts:. In the typical twin study, all three sources of influence are operating simultaneously, and it is possible to determine the relative importance of each type.
Initially, phrenology was very popular; however, it was soon discredited for lack of empirical support and has long been relegated to the status of pseudoscience Fancher, Figure 2. Kant agreed with Galen that everyone could be sorted into one of the four temperaments and that there was no overlap between the four categories Eysenck, He developed a list of traits that could be used to describe the personality of a person from each of the four temperaments.
The first axis separated strong from weak emotions the melancholic and choleric temperaments from the phlegmatic and sanguine. The second axis divided the changeable temperaments choleric and sanguine from the unchangeable ones melancholic and phlegmatic Eysenck, Figure 3.
Wundt later suggested the arrangement of the traits on two major axes. According to Freud, unconscious drives influenced by sex and aggression, along with childhood sexuality, are the forces that influence our personality. Freud attracted many followers who modified his ideas to create new theories about personality.
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