Geneticists Use ____ to Study the Genetics of Families Through Generations.

Chapter 12. Personality

12.iii Is Personality More Nature or More Nurture? Behavioural and Molecular Genetics

Learning Objectives

1. Explain how genes transmit personality from 1 generation to the next.
2. Outline the methods of behavioural genetics studies and the conclusions that nosotros tin draw from them about the determinants of personality.
3. Explain how molecular genetics inquiry helps us sympathize the office of genetics in personality.

One question that is exceedingly important for the study of personality concerns the extent to which information technology is the consequence of nature or nurture. If nature is more than important, then our personalities will grade early on in our lives and will be difficult to change later. If nurture is more important, however, so our experiences are likely to exist particularly of import, and we may be able to flexibly modify our personalities over fourth dimension. In this section we will run across that the personality traits of humans and animals are determined in large role by their genetic makeup, and thus information technology is no surprise that identical twins Paula Bernstein and Elyse Schein turned out to exist very similar even though they had been raised separately. But we will likewise encounter that genetics does not determine everything.

In the nucleus of each prison cell in your body are 23 pairs of chromosomes. I of each pair comes from your male parent, and the other comes from your mother. The chromosomes are made upwardly of strands of the molecule Deoxyribonucleic acid (dna), and the DNA is grouped into segments known every bit genes. A gene is the basic biological unit of measurement that transmits characteristics from ane generation to the next. Human cells take about 25,000 genes.

The genes of different members of the aforementioned species are almost identical. The Deoxyribonucleic acid in your genes, for instance, is well-nigh 99.nine% the same equally the DNA in my genes and in the Deoxyribonucleic acid of every other human being. These common genetic structures pb members of the aforementioned species to be born with a diverseness of behaviours that come up naturally to them and that ascertain the characteristics of the species. These abilities and characteristics are known as instincts—complex inborn patterns of behaviours that aid ensure survival and reproduction (Tinbergen, 1951). Dissimilar animals have different instincts. Birds naturally build nests, dogs are naturally loyal to their homo caretakers, and humans instinctively larn to walk and to speak and understand language.

But the strength of different traits and behaviours too varies within species. Rabbits are naturally fearful, merely some are more fearful than others; some dogs are more than loyal than others to their caretakers; and some humans learn to speak and write better than others do. These differences are determined in role by the pocket-sized amount (in humans, the 0.1%) of the differences in genes among the members of the species.

Personality is not determined by any single gene, but rather past the actions of many genes working together. In that location is no "IQ gene" that determines intelligence and there is no "good matrimony-partner factor" that makes a person a particularly good marriage bet. Furthermore, fifty-fifty working together, genes are not so powerful that they can control or create our personality. Some genes tend to increase a given feature and others piece of work to decrease that same characteristic — the circuitous human relationship among the various genes, as well as a variety of random factors, produces the last outcome. Furthermore, genetic factors always work with environmental factors to create personality. Having a given blueprint of genes doesn't necessarily mean that a particular trait will develop, because some traits might occur only in some environments. For instance, a person may have a genetic variant that is known to increase his or her chance for developing emphysema from smoking. But if that person never smokes, then emphysema most likely will not develop.

Studying Personality Using Behavioural Genetics

Maybe the well-nigh direct style 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 involvement and breeds these animals with each other. If the selective breeding creates offspring with even stronger traits, then we tin 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 conspicuously not useful for studying humans. For this psychologists rely on behavioural genetics—a variety of enquiry techniques that scientists use to learn about the genetic and environmental influences on human behaviour by comparison the traits of biologically and nonbiologically related family members (Baker, 2004). Behavioural genetics is based on the results of family studies, twin studies, and adoptive studies.

A family studystarts with one person who has a trait of interest — for instance, a developmental disorder such as autism — and examines the individual's family tree to decide the extent to which other members of the family unit also accept the trait. The presence of the trait in kickoff-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 unit studies can reveal whether a trait runs in a family, it cannot explain why. In a twin study, researchers written report the personality characteristics of twins. Twin studies rely on the fact that identical (or monozygotic) twins have essentially the same set up of genes, while congenial (or dizygotic) twins have, on boilerplate, a half-identical set. The thought is that if the twins are raised in the same household, then the twins will be influenced past 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 written report, the information from many pairs of twins are nerveless and the rates of similarity for identical and congenial 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:

• Heritability (i.due east., genetic influence) is indicated when the correlation coefficient for identical twins exceeds that for congenial twins, indicating that shared Dna is an important determinant of personality.
• Shared environment determinants are indicated when the correlation coefficients for identical and fraternal twins are greater than cipher and also very like. These correlations bespeak that both twins are having experiences in the family unit that brand them alike.
• Nonshared environment is indicated when identical twins practice not have similar traits. These influences refer to experiences that are non accounted for either by heritability or past shared ecology factors. Nonshared environmental factors are the experiences that make individuals within the aforementioned family less alike. If a parent treats one child more affectionately than another, and as a event this child ends up with higher self-esteem, the parenting in this case is a nonshared ecology factor.

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.

An adoption studycompares biologically related people, including twins, who have been reared either separately or autonomously. Show for genetic influence on a trait is found when children who have been adopted show traits that are more similar to those of their biological parents than to those of their adoptive parents. Evidence for ecology influence is found when the adoptee is more like his or her adoptive parents than the biological parents.

The results of family, twin, and adoption studies are combined to go a improve idea of the influence of genetics and environs on traits of involvement. Table 12.6, "Information from Twin and Adoption Studies on the Heritability of Various Characteristics," presents data on the correlations and heritability estimates for a variety of traits based on the results of behavioural genetics studies (Bouchard, Lykken, McGue, Segal, & Tellegen, 1990).

Tabular array 12.6 Data from Twin and Adoption Studies on the Heritability of Various Characteristics. ^[1]

[Skip Table]
	Correlation between children raised together		Correlation between children raised apart		Estimated percent of total due to
	Identical twins	Fraternal twins	Identical twins	Fraternal twins	Heritability (%)	Shared surround (%)	Nonshared surround (%)
Age of puberty					45	5	50
Assailment	0.43	0.14	0.46	0.06
Alzheimer disease	0.54	0.16
Fingerprint patterns	0.96	0.47	0.96	0.47	100	0	0
General cerebral ability					56	0	44
Likelihood of divorce	0.52	0.22
Sexual orientation	0.52	0.22			eighteen–39	0–17	61–66
Big V dimensions					40–50
This table presents some of the observed correlations and heritability estimates for diverse characteristics.

If yous look in the second column of Table 12.6 , "Data from Twin and Adoption Studies on the Heritability of Various Characteristics," you lot will see the observed correlations for the traits betwixt identical twins who have been raised together in the aforementioned house by the same parents. This column represents the pure effects of genetics, in the sense that environmental differences have been controlled to exist a modest every bit possible. Yous tin can meet that these correlations are higher for some traits than for others. Fingerprint patterns are very highly adamant past our genetics (r = .96), whereas the Big Five trait dimensions take a heritability of xl% to 50%.

You can also run across from the tabular array that, overall, in that location is more influence of nature than of parents. Identical twins, even when they are raised in dissever households by dissimilar parents (column 4), plough out to be quite similar in personality, and are more than similar than congenial twins who are raised in separate households (cavalcade 5). These results show that genetics has a potent influence on personality, and helps explain why Elyse and Paula were so similar when they finally met.

Despite the overall role of genetics, you tin see in Table 12.6, "Information from Twin and Adoption Studies on the Heritability of Various Characteristics," that the correlations between identical twins (cavalcade 2) and heritability estimates for most traits (column 6) are substantially less than 1.00, showing that the environment as well plays an important role in personality (Turkheimer & Waldron, 2000). For instance, for sexual orientation the estimates of heritability vary from eighteen% to 39% of the total across studies, suggesting that 61% to 82% of the total influence is due to environment.

Yous might at start think that parents would take a strong influence on the personalities of their children, merely this would exist incorrect. As you can see by looking in column seven of Table 12.half-dozen," inquiry finds that the influence of shared surroundings (i.e., the effects of parents or other caretakers) plays little or no part in adult personality (Harris, 2006). Shared environs does influence the personality and behaviour of young children, but this influence decreases apace as the kid grows older. By the time we reach adulthood, the impact of shared environment on our personalities is weak at all-time (Roberts & DelVecchio, 2000). What this means is that although parents must provide a nourishing and stimulating environment for children, no matter how hard they attempt they are not probable to be able to turn their children into geniuses or into professional athletes, nor will they exist able to turn them into criminals.

If parents are non providing the environmental influences on the kid, so what is? The last cavalcade in Table 12.half dozen," the influence of nonshared environment, represents whatsoever is "left over" afterward removing the furnishings of genetics and parents. Y'all can see that these factors — the largely unknown things that happen to us that make us unlike from other people — often have the largest influence on personality.

Studying Personality Using Molecular Genetics

In improver to the utilise of behavioural genetics, our understanding of the role of biology in personality recently has been dramatically increased through the use of molecular genetics, which is the study of which genes are associated with which personality traits (Goldsmith et al., 2003; Strachan & Read, 1999). These advances have occurred every bit a issue of new cognition about the construction of human DNA fabricated possible through the Man Genome Project and related piece of work that has identified the genes in the man torso (Human Genome Projection, 2010). Molecular genetics researchers have also developed new techniques that permit them to find the locations of genes within chromosomes and to place the effects those genes have when activated or deactivated.

Figure 12.12 Laboratory Mice. These "knockout" mice are participating in studies in which some of their genes have been deactivated to determine the influence of the genes on behaviour.

1 approach that can be used in animals, usually in laboratory mice, is the knockout study (as shown in Figure 12.12, "Laboratory Mice"). In this arroyo the researchers utilise specialized techniques to remove or modify the influence of a gene in a line of knockout mice (Crusio, Goldowitz, Holmes, & Wolfer, 2009). The researchers harvest embryonic stem cells from mouse embryos and so modify the Dna of the cells. The Deoxyribonucleic acid is created so that the action of sure genes volition be eliminated or knocked out. The cells are and so injected into the embryos of other mice that are implanted into the uteruses of living female mice. When these animals are born, they are studied to see whether their behaviour differs from a control group of normal animals. Research has plant that removing or changing genes in mice can touch on their anxiety, aggression, learning, and socialization patterns.

In humans, a molecular genetics study normally begins with the collection of a Deoxyribonucleic acid sample from the participants in the study, usually by taking some cells from the inner surface of the cheek. In the lab, the DNA is extracted from the sampled cells and is combined with a solution containing a marker for the particular genes of interest every bit well as a fluorescent dye. If the cistron is present in the Deoxyribonucleic acid of the private, and then the solution will demark to that gene and actuate the dye. The more than the gene is expressed, the stronger the reaction.

In one common approach, DNA is collected from people who have a particular personality characteristic and also from people who practice not. The DNA of the two groups is compared to see which genes differ between them. These studies are at present able to compare thousands of genes at the aforementioned fourth dimension. Enquiry using molecular genetics has found genes associated with a diverseness of personality traits including novelty-seeking (Ekelund, Lichtermann, Järvelin, & Peltonen, 1999), attending-deficit/hyperactivity disorder (Waldman & Gizer, 2006), and smoking behaviour (Thorgeirsson et al., 2008).

Reviewing the Literature: Is Our Genetics Our Destiny?

Over the past 2 decades scientists have fabricated substantial progress in understanding the important role of genetics in behaviour. Behavioural genetics studies have found that, for most traits, genetics is more important than parental influence. And molecular genetics studies have begun to pinpoint the particular genes that are causing these differences. The results of these studies might lead y'all to believe that your destiny is determined by your genes, but this would be a mistaken assumption.

For i, the results of all inquiry must be interpreted carefully. Over time we will larn even more well-nigh the role of genetics, and our conclusions nearly its influence will likely change. Current inquiry in the area of behavioural genetics is oft criticized for making assumptions about how researchers categorize identical and fraternal twins, about whether twins are in fact treated in the same style by their parents, well-nigh whether twins are representative of children more generally, and about many other bug. Although these critiques may not alter the overall conclusions, it must be kept in listen that these findings are relatively new and will certainly be updated with time (Plomin, 2000).

Furthermore, it is important to reiterate that although genetics is important, and although nosotros are learning more every day about its role in many personality variables, genetics does non determine everything. In fact, the major influence on personality is nonshared environmental influences, which include all the things that occur to us that brand us unique individuals. These differences include variability in brain structure, nutrition, education, upbringing, and fifty-fifty interactions among the genes themselves.

The genetic differences that exist at birth may be either amplified or diminished over time through ecology factors. The brains and bodies of identical twins are not exactly the same, and they become even more different as they abound up. As a event, even genetically identical twins have singled-out personalities, resulting in large role from environmental effects.

Because these nonshared environmental differences are nonsystematic and largely accidental or random, information technology will be difficult to ever decide exactly what will happen to a kid as he or she grows up. Although we practise inherit our genes, we do non inherit personality in any stock-still sense. The issue of our genes on our behaviour is entirely dependent on the context of our life as information technology unfolds twenty-four hour period to twenty-four hours. Based on your genes, no one can say what kind of man being y'all will plough out to be or what y'all volition do in life.

Central Takeaways

• Genes are the bones biological units that transmit characteristics from 1 generation to the next.
• Personality is not determined by any single factor, simply rather by the deportment of many genes working together.
• Behavioural genetics refers to a variety of research techniques that scientists apply to learn near the genetic and environmental influences on human behaviour.
• Behavioural genetics is based on the results of family studies, twin studies, and adoptive studies.
• Overall, genetics has more influence than parents do on shaping our personality.
• Molecular genetics is the written report of which genes are associated with which personality traits.
• The largely unknown environmental influences, known as the nonshared environmental effects, have the largest impact on personality. Because these differences are nonsystematic and largely accidental or random, we do non inherit our personality in any fixed sense.

Exercises and Critical Thinking

1. Think about the twins yous know. Practice they seem to be very like to each other, or does it seem that their differences outweigh their similarities?
2. Describe the implications of the effects of genetics on personality, overall. What does information technology mean to say that genetics "determines" or "does not determine" our personality?

References

Baker, C. (2004). Behavioral genetics: An introduction to how genes and environments collaborate through development to shape differences in mood, personality, and intelligence. [PDF] Retrieved from http://world wide web.aaas.org/spp/bgenes/Intro.pdf

Bouchard, T. J., Lykken, D. T., McGue, Thousand., Segal, N. L., & Tellegen, A. (1990). Sources of human psychological differences: The Minnesota report of twins reared autonomously.Scientific discipline, 250(4978), 223–228. Retrieved from http://world wide web.sciencemag.org/cgi/content/abstruse/250/4978/223

Crusio, W. East., Goldowitz, D., Holmes, A., & Wolfer, D. (2009). Standards for the publication of mouse mutant studies.Genes, Brain & Beliefs, eight(1), i–iv.

Ekelund, J., Lichtermann, D., Järvelin, M. R., & Peltonen, L. (1999). Association between novelty seeking and the type 4 dopamine receptor gene in a large Finnish cohort sample.American Journal of Psychiatry, 156, 1453–1455.

Goldsmith, H., Gernsbacher, M. A., Crabbe, J., Dawson, G., Gottesman, I. I., Hewitt, J.,…Swanson, J. (2003). Research psychologists' roles in the genetic revolution.American Psychologist, 58(4), 318–319.

Harris, J. R. (2006).No 2 alike: Human nature and human individuality. New York, NY: Norton.

Human Genome Project. (2010). Information. Retrieved from http://www.ornl.gov/sci/techresources/Human_Genome/dwelling house.shtml

Långström, N., Rahman, Q., Carlström, East., & Lichtenstein, P. (2010). Genetic and environmental effects on same-sex sexual behaviour: A population study of twins in Sweden.Athenaeum of Sexual Behaviour, 39(ane), 75-lxxx.

Loehlin, J. C. (1992).Genes and environment in personality development. Yard Oaks, CA: Sage Publications, Inc.

McGue, M., & Lykken, D. T. (1992). Genetic influence on take a chance of divorce.Psychological Science, 3(6), 368–373.

Plomin, R. (2000). Behavioural genetics in the 21st century.International Journal of Behavioral Development, 24(1), 30–34.

Plomin, R., Fulker, D. W., Corley, R., & DeFries, J. C. (1997). Nature, nurture, and cognitive development from 1 to 16 years: A parent-offspring adoption study.Psychological Science, viii(6), 442–447.

Roberts, B. Due west., & DelVecchio, Westward. F. (2000). The rank-order consistency of personality traits from childhood to old age: A quantitative review of longitudinal studies.Psychological Bulletin, 126(1), 3–25.

Strachan, T., & Read, A. P. (1999).Human molecular genetics (2nd ed.). Retrieved from http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=hmg&part=A2858

Tellegen, A., Lykken, D. T., Bouchard, T. J., Wilcox, K. J., Segal, Northward. L., & Rich, Southward. (1988). Personality similarity in twins reared apart and together.Journal of Personality and Social Psychology, 54(half dozen), 1031–1039.

Thorgeirsson, T. Eastward., Geller, F., Sulem, P., Rafnar, T., Wiste, A., Magnusson, G. P.,…Stefansson, 1000. (2008). A variant associated with nicotine dependence, lung cancer and peripheral arterial illness.Nature, 452(7187), 638–641.

Tinbergen, Northward. (1951).The study of instinct (1st ed.). Oxford, England: Clarendon Press.

Turkheimer, E., & Waldron, Grand. (2000). Nonshared environment: A theoretical, methodological, and quantitative review.Psychological Bulletin, 126(1), 78–108.

Waldman, I. D., & Gizer, I. R. (2006). The genetics of attention deficit hyperactivity disorder.Clinical Psychology Review, 26(4), 396–432.

Prototype Attributions

Figure 12.12: "Laboratory mice" by Aaron Logan is licensed under CC BY 1.0 license (http://creativecommons.org/licenses/by/1.0/deed.en).

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