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Behavioral genetics

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Related terms
Background
Methods
Research
Implications
Limitations
Safety
Future research
Author information
Bibliography
Human behaviors that may be inherited

Related Terms
  • Behavior, behavioral geneticists, biology, DNA, eugenics, genes, genetic, genetic makeup, geneticist, genetics, heredity, inherited, nature versus nurture, nature versus nurture controversy, species-specific behavior, twin studies.

Background
  • Behavioral genetics is the study of hereditary factors that influence an organism's behavior. Many genes have been shown to be involved in the expression of individual behaviors.
  • Francis Galton is considered the father of behavioral genetics. He suggested that like physical traits, such as blonde hair and blue eyes, behaviors are passed down from parents to their offspring. Galton believed that an organism's behavior was determined solely by his/her genetic makeup. This idea served as the basis for eugenics, a term Galton coined in 1983. He suggested that organisms could be selectively bred to eliminate unwanted behaviors.
  • Galton's idea is no longer accepted in the scientific community. Today, it is commonly believed that an individual's genetic makeup is just one factor, among many others, that influence behavior. An individual's environment, including social relationships and culture, has also been shown to influence behaviors.
  • The debate over whether the environment or genetics is the primary cause of an individual's behavior is commonly called the "nature versus nurture controversy." Although most researchers believe it is a combination of these two elements that leads to the development of specific behaviors, experts disagree over which has a greater impact on an individual. Research in this field is ongoing.

Methods
  • Twin studies: Researchers have studied the behavior of human twins to determine the impact of the environment versus genetics on behavior.
  • One research method compares the similarity of pairs of identical twins to fraternal twins that grow up together. Identical twins have the exact same genetic makeup because they arise from a single fertilized egg. Fraternal twins, on the other hand, only share about 50% of the same genetic makeup because they come from two separate fertilized eggs.
  • If both sets of twins are raised in the same family environments, the identical twins will have greater resemblance than the fraternal twins because they share more genes. This method is typically used to estimate the heritability of behavioral traits or to quantify the impact the environment has on behavior.
  • A second type of twin study involves identical twins that have grown up apart from one another in different environments. If both twins were adopted by different families that were chosen at random, the degree of similarity between the twins would be based solely on their genetic makeup. Any differences in behavior are attributed to environmental factors.
  • DNA tests: More recently, investigators have begun searching for parts of DNA (a molecule that contains an organism's genes) that are associated with certain behaviors, such as sexual preference and basic personality traits. Researchers hope to locate specific genes that influence behavior. Human research suggests that some behaviors, including hand skill (whether an individual is right- or left-handed), hand clasping pattern, ability to move the ears, arm folding preference, stuttering, tobacco addiction, alcoholism, homosexuality, aggression, impulsivity, nurturing, as well as tongue curling, folding, or rolling, have genetic bases. However, major findings in this area are currently lacking.

Research
  • General: Although many factors are involved in an organism's behavior, current research indicates that genetic makeup plays a role.
  • Behaviors and biological changes in the body: Research has shown that behaviors change in response to biological changes in the body that may be caused by disorders or trauma (e.g. brain injury). Also, researchers are able to change the behavior of mice by inserting or disabling specific genes during knockout studies. In addition, doctors commonly prescribe psychiatric medications that alter a patient's behavior by changing the chemistry of the brain. This suggests that there is a biological basis for behaviors.
  • Behaviors and evolution: Many behaviors have been shown to have an evolutionary history among related species. For instance, chimpanzees are the closest relative to humans. The genetic makeup between humans and chimpanzees differ by only two percent. Humans share many of the same behavioral characteristics of chimpanzees, including cooperation, altruism, nurturing, and some facial expressions. This suggests that behaviors, similar to physical characteristic, have evolved over the years.
  • Similar behaviors observed in families: Researchers have noted that family members often exhibit some of the same behaviors, such as aggression or shyness. Experts believe that these behaviors are the result of both environmental and genetic similarities.
  • Breeding behaviors: Researchers have been able to produce certain behaviors in successive generations of organisms. One of the most famous studies on breeding behaviors involved silver-black foxes. Over the course of 20 years, Belyaev and his research team only bred the foxes that exhibited the tamest behaviors. As a result, the researchers were able to breed tame foxes that acted more like domesticated dogs than aggressive, wild animals. The study indicated that heredity plays a role in determining an organism's behavior.
  • Today, domesticated dogs, such as golden retrievers, are commonly bred for specific behavioral traits.
  • Species-specific behavior: Research has shown that behaviors are often species specific. In other words, different types of animals exhibit different types of behaviors. Although many behaviors are taught, genetics plays a role in the organism's ability to learn specific behaviors. For instance, chickadees and finches exhibit distinctly different types of feeding behaviors. A chickadee carries one sunflower seed at a time to a branch, where it pecks it open and eats its contents. This process is repeated until the bird is full. Finches, on the other hand, stay at the source of the sunflower seeds and eat many seeds at the same time. In addition, many animals have distinct mating rituals and behaviors, suggesting that organisms are born with certain genes that influence specific behaviors.

Implications
  • Researchers who study behavioral genetics have suggested that there may be a genetic basis for many physical behaviors, including aggression, impulsivity, and nurturing. It has also been suggested that genetics may play a role in sexual orientation.
  • If such traits can be identified in humans, it remains unknown exactly how society would use this information. It would probably raise many ethical and social questions. For instance, some individuals may want to screen their unborn children for specific traits, such as homosexuality or tobacco addiction. It may also change the way sperm and egg donations are handled. Also, some individuals may use their genetic makeup as a defense for committing crimes. Healthcare insurance companies may choose not to insure individuals who have genes associated with risk taking.
  • If certain behavioral genes are identified in a human, it does not necessarily mean that the person will develop the behavior. Other environmental factors have been shown to play a role in an individual's behavior.
  • Multiple genes are involved in the development of a behavior. Therefore, if an individual has just one gene associated with shyness, for instance, it does not necessarily mean that the person is going to be shy.
  • Another challenge that researchers face is that it is difficult to determine a consistent and accurate way to measure behaviors, such as shyness, intelligence, or aggression.

Limitations
  • If certain behavioral genes are identified in a human, it does not necessarily mean that the person will develop the behavior. Other environmental factors have been shown to play a role in an individual's behavior.
  • Multiple genes are involved in the development of a behavior. Therefore, if an individual has just one gene associated with shyness, for instance, it does not necessarily mean that the person is going to be shy.
  • Another challenge that researchers face is that it is difficult to determine a consistent and accurate way to measure behaviors, such as shyness, intelligence, or aggression.

Safety




Future research
  • Behavioral genetics is growing area of interest, and research is ongoing. Although most researchers believe that a combination of genetics and the environment leads to the development of specific behaviors, experts disagree over which has a greater impact on an individual. Studies aim to identify which genes influence specific behaviors. Many studies, such as twin studies, compare the effects of genetics and the environment.

Author information
  • This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

Bibliography
  1. Behavior Genetics Association. .
  2. Belyaev DK, Ruvinsky AO, Trut LN. Inherited activation-inactivation of the star gene in foxes: its bearing on the problem of domestication. J Hered. 1981 Jul-Aug;72(4):267-74.
  3. Bailey JM, Pillard RC, Neale MC, et al. Heritable factors influence sexual orientation in women. Arch Gen Psychiatry. 1993 Mar;50(3):217-23.
  4. Carmelli D, Swan GE, Robinette D, et al. Genetic influence on smoking--a study of male twins. N Engl J Med. 1992 Sep 17;327(12):829-33.
  5. Drayna D. Is our behavior written in our genes? N Engl J Med. 2006 Jan 5;354(1):7-9.
  6. Hamer H, Hu S, Magnuson VL, et al. A linkage between DNA markers on the X chromosome and male sexual orientation. Science. 1993 Jul 16;261(5119):321-7.
  7. Human Genome Project. .
  8. Klump KL, Burt SA. The Michigan State University Twin Registry (MSUTR): genetic, environmental and neurobiological influences on behavior across development. Twin Res Hum Genet. 2006 Dec;9(6):971-7.
  9. Levitt M, Manson N. My genes made me do it? The implications of behavioural genetics for responsibility and blame. Health Care Anal. 2007 Mar;15(1):33-40.
  10. Natural Standard: The Authority on Integrative Medicine. .
  11. Sandhu JS, Kuprevich CL. Nature vs. nurture: a case report. el Med J. 2006 Nov;78(11):413-7.
  12. Society of Behavioral Medicine. .
  13. Yudin B. Human life: genetic or social construction? J Int Bioethique. 2005 Sep-Dec;16(3-4):89-96, 173-4.

Human behaviors that may be inherited
  • General: Many human studies have been performed to locate specific genes associated with behaviors. This is a growing area of interest, and research is ongoing.
  • Tongue folding, curling, or rolling: Studies have shown that the ability to roll, curl, or fold the tongue is inherited. The ability to roll the tongue appears to be inherited as a dominant trait. This means an individual only needs to inherit one gene from one of his/her parents in order to be able to roll the tongue. A child can only inherit the ability if at least one parent can roll his/her tongue. The ability to fold the tongue into a cloverleaf shape may also be inherited as a dominant trait. However the ability to fold the tip of the tongue appears to be inherited as a recessive trait. This means individuals must inherit one copy of the gene from each parent in order to be able to fold the tip of the tongue.
  • Stuttering: Stuttering, which usually develops in children and resolves spontaneously, is more common among males. Current research suggests that stuttering may be inherited as a dominant trait.
  • Tobacco addiction: Carmelli et al. conducted a genetic analysis of male twins to determine if genetics plays a role in tobacco addiction. Nearly 5,000 identical and fraternal twins were surveyed in their 40s and then again when they were 56-66 years old. Identical twins showed more similarity in their smoking or non-smoking habits than fraternal twins. The researchers concluded that there were moderate genetic influences on lifetime smoking practices.
  • Additional studies have found that the propensity to smoke may have an inheritance of 60%.
  • Other twin studies have shown that genetic factors may play a role in the commencement and cessation of smoking.
  • Homosexuality: It remains unknown whether or not there is a genetic basis for sexual orientation. It has been suggested that the X chromosome plays a role in determining male sexual orientation in some families. Several studies have been performed in this area, but a firm conclusion cannot be made.
  • Baily and Pillard found that male homosexuals usually have more gay brothers than gay sisters, while lesbians typically have more gay sisters than gay brothers. This observation suggests that homosexuality may be inherited. Further research is needed to determine if male and female homosexuality are cofamilial.
  • Hamer et al. conducted a pedigree and linkage study of the families of 110 homosexual men. Researchers found that there were increased rates of homosexuality in the maternal uncles and maternal male cousins of these subjects. However, this was not apparent in their fathers or paternal relatives. These findings suggest that the X chromosome may play a role in an individual's sexual orientation.
  • Bocklandt et al. found that the number of women with extreme skewing of X chromosome inactivation was significantly higher in mothers of homosexual men compared to mothers of heterosexual men. These findings suggest that the X chromosome regulates the sexual orientation in a subgroup of homosexual males.

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The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.

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