Question #5 – Imagine that you are a behaviour geneticist interested in the heritability of personality attributes. Describe how you would go about studying the genetic basis of personality. What would your basic procedure be? What measurement issues would you face? How much would you draw on psychological theories of personality? Which theories? Behavior geneticists assess the question of inheriting personality. Are our genes responsible for our creativity, aggressiveness or confidence?
Examining personality traits through a genetic focus is an obscure task. Methods employed by behavior geneticists involve epidemiological studies, such as screening family pedigrees, conducting twin heritability studies, and adoption studies. In this essay, I will discuss the methodology behind twin studies as well as many issues that behavior geneticists face. I will also present information regarding other personality theories and their relationship to behavior genetics. I believe that behavior genetics plays a very important role in understanding personality traits and should be kept in the forefront of psychology as a prominent research theory.
Most psychological personality theories investigate only one aspect of behavior. Whether it is a psychoanalytical approach or phenomenological approach, most theories concentrate on one field of personality psychology. This phenomenon also holds true for the biological approach. Behavioral genetics, essentially, attempts at understanding behavior (personality traits) from a genetic (biological) mechanism. Behavioral genetics is a fundamental theory of understanding the origins of personality and cannot be disregarded. However, one should be thorough and therefore all theories should be applied when trying to understand a particular personality or behavior.
I strongly believe that genetics plays a very large and fundamental role in behavior. The psychological triad: thinking, feeling and behaving are all products of our biological features. Theoretically, our cerebrum is the organ that performs those functions. The biological units that encode information to create an individual’s brain are genes. Genes, therefore, are the basic information-encoding units that decide which type of brain an individual will have. Hence, genes encode for behavior.
Since genes encode fro all behavior, the question remains of why geneticists have fialed to link which gene causes which personality trait. There are two main reasons addressing this question. First, genes can be selectively expressed in particular environmental conditions. Second, various genes, and not just one, can interact with each other to result in a phenotypic trait (physically observable characteristic). Genes are therefore complex systems and there is great difficulty in narrowing down a personality characteristic to a specific region on our deoxyribonucleic acid (DNA)- the chemical molecule that makes up genes.
The situation becomes even more complicated when the phenotypic measurement one is trying to assess is not readily measured. A person with pulmonary fibrosis can be diagnosed medically by having extraneous scar tissue on their lungs because the phenotype of having scar tissue can be visually observed. However, in the case of assessing if an individual is competitive by nature, the tester must understand what characteristics manifest a person when they are competitive. If a valid psychological test exists that measures competitiveness, then genetic analysis can be conducted.
Psychological studies
A large number of genetic experimentation that deals with psychology is conducted by genetically modifying various portions of chromosomes (strands of DNA) in animal models such as mice. Once these chromosomes have been modified, phenotypic results are assessed. Therefore a specific phenotype can be linked to a mutation in a particular gene. Although this procedure may come across as not being difficult, complication exist such as personality traits not manifesting themselves as the result of a single gene and rather being a result of a polygenic system (Reif and Lesch, 2003).
Polygenes are a group of genes that control a particular feature. Hence, many setbacks occur if you are trying to assess a personality trait with animal models. On the other hand, it was recently reported by Drayna Dennis in the New England Journal of Medicine (Jan., 2006) that researchers Demir and Dixon found one specific gene in the fruit fly that demonstrated orientation and sexual behavior (Drayna, 2006). Therefore, a single gene may in fact encode a personality trait.
Twin Studies
The second type of psychological study that I would undertake, to determine the genetic basis of a personality trait, is an epidemiological study. Twin studies, adoption studies and family genetic pattern studies are three research methods that can be conducted to determine the heritability of a given trait. In general monozygous (from the same egg) twin studies provide a powerful source of information when attempting to determine the genetic basis of personality. Monozygous twins are humans with the exact same chromosomal genetic information. They are essentially clones of each other. In contrast, dizygous twins are siblings with genetic information that is like any other relative.
Twin studies are generally not conducted with monozygous twins alone. In order to present valid data, one should conduct the same experiment on a control group. Dizygous twins, for example, would represent a good control group (Phillips, 2000). A control group is used in experiments to provide a reference for the group one is actually studying. Meaning, if I expect to see aggressiveness highly correlated in monozygous twins, I would expect the correlation to be very low in dizygous twins.
Setting up the experiment
The first step in setting up such an experiment would be to obtain the proper psychological test. In this case, a test represents an assessment tool that allows one to determine if a particular individual has a specific personality trait. The test must possess four characteristics: Validity, reliability, fairness and must be normed to a standardization group (Lerner and Kline, 2006). The next step is to recruit twins that are both identical and fraternal. The number of twins should only be limited by how many are available. An attempt should be made to increase the sample size of the study, this is known as the n value. The higher the n value in any particular study signifies results that are more statistically reliable. The third step is to administer the tests on all participants.
Correlation factors
Behavior genetics relies strongly on correlation coefficients, as opposed to physical findings such as plaque build up in the brains of Alzheimer’s patients. Each twin pair is compared in a quantitative manner. Correlation coefficients are represented by the symbol r and range from -1 to +1. A relationship between a pair of results that has an r-value of +1 represents a positive relationship, zero represents no relationship and -1 means a negative relationship (Funder, 2004). Essentially, if an r-value of -0.9 was obtained, it can be stated that aggressiveness in one twin increases as aggressiveness in the other twin decreases. An average correlation factor is obtained for each group: the identical twins versus the fraternal twins.
Heritability Once correlation coefficients have been obtained, the heritability coefficient is tabulated. Heritability is the “proportion of phenotypic variance that can be attributed to genetic factors” (Saudino, 2005). The formula used to calculate the heritability coefficient for twin studies is shown below: Heritability Coefficient = (Average r value for identical twins – Average r value for fraternal twins) x 2 (Funder, 2004) Hypothetically, if the heritability coefficient obtained is 0.52, you can say that 52% of the variance in aggressiveness (phenotype) is due to genetic variance. Behavioral geneticists generally assume that the remaining variance is due to environmental factors (Saudino, 2005).
Behavioral genetics does not stand alone – other theories The behavioral genetics theory presents a perceived notion that only genes are involved in understanding personality traits. This is incorrect. The basic information provided by behavioral geneticists is measurements such as heritability. With this one piece of information, the environmental variance of a personality trait is also obtained. This clearly demonstrates that most behavioral geneticists are open to other theories of personality and that genes alone cannot create personalities.
How do genes most likely exert their effect on behavior? A gene, sequence of DNA, encodes for a sequence of ribonucleic acid (RNA). This RNA is then translated into a functional protein. Proteins mediate numerous effects. An example can be seen with the neurotransmitter, acetylcholine. Acetylcholinesterase, a protein found in the synapse, degrades acetylcholine. The decrease in acetylcholine results in various psychological and physiological effects. So the question becomes, why do people differ in their amount of acetylcholine? This answer lies within the reason why people differ in their personalities.
The key is to realize that nurturing does matter. A child who grows up in a caring environment may have higher levels of certain proteins or neurotransmitter and therefore may have a higher IQ. Genes clearly interact with their environment. A pilot study recently published that they found candidate genes involved in creativity (Reuter et al., 2006). This must be taken with a grain of salt. Surely it is possible that certain genes promote creativity, however a child that has the “good” gene may not be able to express it if the environment they grow up in is completely neglecting and if he or she is not exposed to the right conditions.
Theoretically, the personality theory that is most distinct from behavioral genetics is the psychoanalytical approach. This theory, envisioned by Freud, deals with the unconscious mind and internal conflicts that present themselves at various stages of life. Many argue that both domains, behavioral genetics and psychoanalysis, completely ignore each other. The following statement puts into perspective this argument: “The vast contributions on dreams made by Freud and Jung has been largely ignored by science, which harshly criticized their approach for the lack of quantitative method and of testable hypothesis” (Ribeiro, 2003).
I do believe the scientific community disregards many theories put forward if the statistical analysis is not properly done. However, as Funder mentions in the text, – The Personality Puzzle, no piece of information should be ignored. A psychologist must look at every piece of information that can be obtained, regardless of the fact that it may or may not be relevant. Do behavior geneticists truly ignore psychoanalytical approaches?
I do not believe so. Geneticists, in determining most personality trait causes, only develop associations between genes and a particular trait. Psychoanalysis actually tries to understand the thought process behind why such a personality exists. In the case of remediation, the psychoanalytical approach proves to be helpful (for personality disorders). Behavioural genetics does not provide any remediation for those with a personality disorder, where only correlation studies exist. Essentially, both personality theories are integrated and must be applied appropriately to individual cases.
Measurement issues with behavioral genetics have been discussed throughout this essay. Regarding twin studies, it should be noted that despite their use as a powerful genetics tool, large sample sizes are not always possible and therefore other methods such as family pedigree studies or adoption studies can be used. Behavior genetics also runs into many ethical issues. Human breeding is not an acceptable method of research and this proves to be a challenge when assessing personality traits, as genetic mapping is nearly impossible.
Concluding remarks
Behavioral genetics provides a very technical look at personality traits. Genetics is the basis of all biological systems and within the genetic code is the understanding of personalities. This theory, however, does not provide the whole picture and must be used in conjunction with other personality theories, to truly understand and begin studying personality types. Behavioral genetics is a difficult theory to apply due to its experimental invasiveness and hence statistical reports such as twin studies, adoption studies and family studies are used in assessment of heritability. I believe behavioral genetics will continue to grow in the coming years and advance the world of personality psychology.
References
1. Drayna, D. (2006). Is our behavior written in our genes? New England Journal of Medicine, 354, 7-9.
2. Funder, D.C. (2004). The personality puzzle (3rd ed.). New York: W.W. Norton and Company.
3. Lerner, J., Kline, F. (2006). Learning disabilities and related disorders: Characteristics and teaching strategies (10th ed.). Boston: Houghton Mifflin Company.