Human behaviour genetics is an interdisciplinary subfield of

behaviour genetics Behavioural genetics, also referred to as behaviour genetics, is a field of science, scientific research that uses genetics, genetic scientific method, methods to investigate the etiology, nature and origins of Differential psychology, indivi ...

that studies the role of genetic and environmental influences on

human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

behaviour Behavior (American English) or behaviour (British English) is the range of actions of Individual, individuals, organisms, systems or Artificial intelligence, artificial entities in some environment. These systems can include other systems or or ...

. Classically, human behavioural geneticists have studied the

inheritance Inheritance is the practice of receiving private property, titles, debts, entitlements, privileges, rights, and obligations upon the death of an individual. The rules of inheritance differ among societies and have changed over time. Offi ...

of behavioural traits. The field was originally focused on determining the importance of genetic influences on human behaviour (for e.g., do genes regulate human behavioural attributes). It has evolved to address more complex questions such as: how important are genetic and/or environmental influences on various human behavioural traits; to what extent do the same genetic and/or environmental influences impact the overlap between human behavioural traits; how do genetic and/or environmental influences on behaviour change across development; and what environmental factors moderate the importance of genetic effects on human behaviour ( gene-environment interaction). The field is interdisciplinary, and draws from

genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinians, Augustinian ...

psychology Psychology is the scientific study of mind and behavior. Its subject matter includes the behavior of humans and nonhumans, both consciousness, conscious and Unconscious mind, unconscious phenomena, and mental processes such as thoughts, feel ...

, and statistics. Most recently, the field has moved into the area of

statistical genetics Statistical genetics is a scientific field concerned with the development and application of statistical methods for drawing inferences from genetic data. The term is most commonly used in the context of human genetics. Research in statistical ge ...

, with many behavioural geneticists also involved in efforts to identify the specific genes involved in human behaviour, and to understand how the effects associated with these genes changes across time, and in conjunction with the environment. Traditionally, the human behavioural genetics were a psychology and phenotype based studies including intelligence, personality and grasping ability. During the years, the study developed beyond the classical traits of human behaviour and included more genetically associated traits like genetic disorders (such as

fragile X syndrome Fragile X syndrome (FXS) is a genetic neurodevelopmental disorder. The average IQ in males with FXS is under 55, while affected females tend to be in the borderline to normal range, typically around 70–85. Physical features may include a lo ...

Alzheimer's disease Alzheimer's disease (AD) is a neurodegenerative disease and the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As the disease advances, symptoms can include problems wit ...

and obesity). The traditional methods of behavioural-genetic analysis provide a quantitative evaluation of genetic and non-genetic influences on human behaviour. The family, twin and adoption studies marks the huge contribution for laying down the foundation for current molecular genetic studies to study human behaviour.

History

In 1869,

Francis Galton Sir Francis Galton (; 16 February 1822 – 17 January 1911) was an English polymath and the originator of eugenics during the Victorian era; his ideas later became the basis of behavioural genetics. Galton produced over 340 papers and b ...

published the first empirical work in human behavioural genetics, ''Hereditary Genius''. Here, Galton intended to demonstrate that "a man's natural abilities are derived by inheritance, under exactly the same limitations as are the form and physical features of the whole organic world." Like most seminal work, he overstated his conclusions. His was a family study on the inheritance of giftedness and talent. Galton was aware that resemblance among familial relatives can be a function of both shared inheritance and shared environments. Contemporary human behavioural quantitative genetics studies special populations such as

twins Twins are two offspring produced by the same pregnancy.MedicineNet > Definition of Twin Last Editorial Review: 19 June 2000 Twins can be either ''monozygotic'' ('identical'), meaning that they develop from one zygote, which splits and forms two e ...

and

adoptees Adoption is a process whereby a person assumes the parenting of another, usually a child, from that person's biological or legal parent or parents. Legal adoptions permanently transfer all rights and responsibilities, along with filiation, from ...

. The initial impetus behind this research was to demonstrate that there were indeed genetic influences on

human behaviour Human behavior is the potential and expressed capacity ( mentally, physically, and socially) of human individuals or groups to respond to internal and external stimuli throughout their life. Behavior is driven by genetic and environmental ...

. In

, this phase lasted for the first half of the 20th century largely because of the overwhelming influence of

behaviourism Behaviorism is a systematic approach to understand the behavior of humans and other animals. It assumes that behavior is either a reflex elicited by the pairing of certain antecedent stimuli in the environment, or a consequence of that indivi ...

in the field. Later behavioural genetic research focused on

quantitative method Quantitative research is a research strategy that focuses on quantifying the collection and analysis of data. It is formed from a deductive approach where emphasis is placed on the testing of theory, shaped by empiricist and positivist philosop ...

s. In 1984, a research program named the Swedish Adoption/Twin Study of Aging (SATSA) was initiated in gerontological genetics. The research was executed on Twins Reared Apart (TRA) and Twins Reared Together (TRT). In this three-year interval study, the testing was carried out in two ways, Mail-Out Questionnaire and In-Person Testing (IPT). The IPT includes functional capacity, physical performance measurements, neurological state, general health, cardiovascular health, and cognitive abilities, all of which are particularly significant in ageing. The IPT had two major components for testing, Biomedical and Cognitive Assessment. The biomedical component was constructed to analyses the general health status like age changes, lungs function and capacity, physical strength. With this, the cognitive component was developed to represent and evaluate domains of crystallized and fluid intelligence and memory. The data acquired from this study allowed researchers to assess genetic contributions to age changes and continuities throughout the length of the SATSA twins' later lives, which prolonged a decade and a half.

Contemporary behavioural quantitative genetics

Behavioural geneticists study both psychiatric and mental disorders, such as

schizophrenia Schizophrenia () is a mental disorder characterized variously by hallucinations (typically, Auditory hallucination#Schizophrenia, hearing voices), delusions, thought disorder, disorganized thinking and behavior, and Reduced affect display, f ...

bipolar disorder Bipolar disorder (BD), previously known as manic depression, is a mental disorder characterized by periods of Depression (mood), depression and periods of abnormally elevated Mood (psychology), mood that each last from days to weeks, and in ...

, and

alcoholism Alcoholism is the continued drinking of alcohol despite it causing problems. Some definitions require evidence of dependence and withdrawal. Problematic use of alcohol has been mentioned in the earliest historical records. The World He ...

, as well as behavioural and social characteristics, such as personality and social attitudes. Recent trends in

behavioural genetics Behavioural genetics, also referred to as behaviour genetics, is a field of scientific research that uses genetic methods to investigate the nature and origins of individual differences in behaviour. While the name "behavioural genetics" ...

have indicated an additional focus toward researching the inheritance of human characteristics typically studied in

developmental psychology Developmental psychology is the scientific study of how and why humans grow, change, and adapt across the course of their lives. Originally concerned with infants and children, the field has expanded to include adolescence, adult development ...

. For instance, a major focus in

has been to characterize the influence of parenting styles on children. However, in most studies, genes are a

confounding In causal inference, a confounder is a variable that influences both the dependent variable and independent variable, causing a spurious association. Confounding is a causal concept, and as such, cannot be described in terms of correlatio ...

variable. Because children share half of their

alleles An allele is a variant of the sequence of nucleotides at a particular location, or locus, on a DNA molecule. Alleles can differ at a single position through single nucleotide polymorphisms (SNP), but they can also have insertions and deletions ...

with each parent, any observed effects of

parenting styles A parenting style is a pattern of behaviors, attitudes, and approaches that a parent uses when interacting with and raising their child. The study of parenting styles is based on the idea that parents differ in their patterns of parenting and that ...

could be effects of having many of the same alleles as a parent (e.g. harsh aggressive parenting styles have been found to correlate with similar aggressive child characteristics: is it the parenting or the genes?). Thus, behaviour genetics research is currently undertaking to distinguish the effects of the family environment from the effects of genes. This branch of behaviour genetics research is becoming more closely associated with mainstream

and the sub-field of

developmental psychopathology Developmental psychopathology is the study of the development of psychological disorders (e.g., psychopathy, autism, schizophrenia and depression) with a life course perspective. Researchers who work from this perspective emphasize how psychopatho ...

as it shifts its focus to the heritability of such factors as emotional

self-control Self-control is an aspect of inhibitory control, one of the core executive functions. Executive functions are cognitive processes that are necessary for regulating one's behavior in order to achieve specific goals. Defined more independen ...

, attachment, social functioning, aggressiveness, etc. Several academic bodies exist to support behaviour genetic research, including the International Behavioural and Neural Genetics Society,

Behavior Genetics Association The Behavior Genetics Association (BGA) is a learned society established in 1970 that promotes research into the connections between heredity and behavior, both human and animal. Its members support education and training in behavior genetics and ...

, the International Society of Psychiatric Genetics, and the International Society for Twin Studies. Behaviour genetic work features prominently in several more general societies, for instance the International Behavioral Neuroscience Society.

Methods of human behavioural genetics

Human behavioural geneticists use several designs to try to answer questions about the nature and mechanisms of genetic influences on behaviour. All of these designs are unified by being based around

human relationships In social psychology, an interpersonal relation (or interpersonal relationship) describes a social association, connection, or affiliation between two or more people. It overlaps significantly with the concept of social relations, which are ...

which disentangle genetic and environmental relatedness. The cornerstone of behavioural genetics approaches is quantitative genetics theories, which were formulated more than half a century ago by geneticists concerned with the practical challenges of increasing economically relevant characteristics of domestic plants and animals. These methods are used to study a myriad of traits, including intelligence and other

cognitive abilities Cognitive skills are skills of the mind, as opposed to other types of skills such as motor skills, social skills or life skills. Some examples of cognitive skills are literacy, self-reflection, logical reasoning, abstract thinking, critical thin ...

personality traits In psychology, trait theory (also called dispositional theory) is an approach to the study of human personality. Trait theorists are primarily interested in the measurement of ''traits'', which can be defined as habitual patterns of behavior, thou ...

like extraversion and emotionality, and

psychiatric disorders A mental disorder, also referred to as a mental illness, a mental health condition, or a psychiatric disability, is a behavioral or mental pattern that causes significant distress or impairment of personal functioning. A mental disorder is ...

such as schizophrenia and bipolar disease.

Traditional methods of behavioural-genetic analysis

To examine genetic and environmental impacts on complex human behavioural traits, researchers uses three classic methods: family, twin, and adoption studies. Individual variations within the normal range of variation, as well as the genesis of psychopathologies, are investigated using each of these techniques.

Family studies

Genes and shared (or familial) environmental factors have a role in family resemblance. The majority of familial research on schizophrenia are concerned with relative risk. Despite the fact that the scope of diagnosis varies, the lifetime risk of

in the general population is generally stated as 1%. Siblings of people with schizophrenia, on the other hand, constitute 13% of the population. The hazards for second- and third-degree relatives are lower, at 3% and 2%, respectively, as predicted. In a As a result, schizophrenia is certainly a familial trait.

Twin and adoption studies

The basic understanding of behavioural genetics requires the separate study of effects of genes and environment influence on human behaviour. Such as, the genetic effects in a trait are discernible if pair of genetically identical (monozygotic twins) are much similar to one another than pair of genetically non-identical (dizygotic twin). Twin and adoption studies describe the extent to which family resemblance is due to shared genes and the extent to which it is due to shared environments. Behavioral Scientist uses twin studies to examine hereditary and environmental influences on behavioural development. For instance, some researchers also study adopted twins: the

adoption study Adoption studies typically compare pairs of persons, e.g., adopted child and adoptive mother or adopted child and biological mother, to assess genetic and environmental influences on behavior. These studies are one of the classic research methods o ...

. The adoption design produces estimates of various genetic and environmental components of variance, similar to the twin design. Furthermore, the adoption design facilitates (1) the identification of specific environmental influences that are unaffected by heredity (e.g., the effects of life stressors), (2) the analysis of heredity's role in ostensibly environmental relationships, and (3) the evaluation of genotype-environment interactions and correlations. In this case the adoption disentangles the genetic relatedness of the twins (either 50% or 100%) from their family environments. Likewise the classic

twin study Twin studies are studies conducted on identical or fraternal twins. They aim to reveal the importance of environmental and genetic influences for traits, phenotypes, and disorders. Twin research is considered a key tool in behavioral genetics ...

contrasts the differences between

identical Identical may refer to: * Identical, when two things are the same, see Identity (philosophy) * Identical (Hopkins novel), ''Identical'' (Hopkins novel), a 2008 young adult novel by Ellen Hopkins * Identical (Turow novel), ''Identical'' (Turow novel ...

and

fraternal twins Twins are two offspring produced by the same pregnancy.MedicineNet > Definition of Twin Last Editorial Review: 19 June 2000 Twins can be either ''monozygotic'' ('identical'), meaning that they develop from one zygote, which splits and forms two e ...

within a family compared to differences observed between families. This core design can be extended: the so-called "extended twin study" which adds additional family members, increasing power and allowing new genetic and environmental relationships to be studied. Excellent examples of this model are the Virginia 20,000 and the QIMR twin studies. Generally, if the observed behaviour and cognitive traits have a genetic component, then genetically similar relatives resemble to each other as comparative to individuals who share lesser component of genome. In case of environmental influence, researchers study the two broad classes of effects in behavioural genetics such as shared environmental factors causing them to behave similarly and the other one is nonshared environmental factors causing them to behave different from one another. For example, siblings raised together in same environment will have more evident shared environment influences whereas in relative siblings raised apart from each other will have non-shared environmental influence. The understanding of the effects of genes and the influence of shared and nonshared environment on human behaviour provides a comprehensive data for genetic and environmental relatedness. Also possible are the "children of twins" design (holding maternal genetic contributions equal across children with paternal genetics and family environments) and the "virtual twins" design - unrelated children adopted into a family who are very close or identical in age to biological children or other adopted children in the family. While the classical twin study has been criticized they continue to be of high utility. There are several dozen major studies ongoing in countries as diverse as the US, UK, Germany, France, the

Netherlands , Terminology of the Low Countries, informally Holland, is a country in Northwestern Europe, with Caribbean Netherlands, overseas territories in the Caribbean. It is the largest of the four constituent countries of the Kingdom of the Nether ...

, and Australia, and the method is used widely on phenotypes as diverse as

dental caries Tooth decay, also known as caries,The word 'caries' is a mass noun, and is not a plural of 'carie'.'' is the breakdown of teeth due to acids produced by bacteria. The resulting cavities may be a number of different colors, from yellow to black ...

body mass index Body mass index (BMI) is a value derived from the mass (Mass versus weight, weight) and height of a person. The BMI is defined as the human body weight, body mass divided by the square (algebra), square of the human height, body height, and is ...

ageing Ageing (or aging in American English) is the process of becoming older until death. The term refers mainly to humans, many other animals, and fungi; whereas for example, bacteria, perennial plants and some simple animals are potentially biol ...

substance abuse Substance misuse, also known as drug misuse or, in older vernacular, substance abuse, is the use of a drug in amounts or by methods that are harmful to the individual or others. It is a form of substance-related disorder, differing definition ...

sexuality Human sexuality is the way people experience and express themselves sexually. This involves biological, psychological, physical, erotic, emotional, social, or spiritual feelings and behaviors. Because it is a broad term, which has varied ...

personality Personality is any person's collection of interrelated behavioral, cognitive, and emotional patterns that comprise a person’s unique adjustment to life. These interrelated patterns are relatively stable, but can change over long time per ...

values In ethics and social sciences, value denotes the degree of importance of some thing or action, with the aim of determining which actions are best to do or what way is best to live ( normative ethics), or to describe the significance of different a ...

, and a wide range of

psychiatric disorder A mental disorder, also referred to as a mental illness, a mental health condition, or a psychiatric disability, is a behavioral or mental pattern that causes significant distress or impairment of personal functioning. A mental disorder is ...

s. This is broad utility is reflected in several thousands of peer-review papers, and several dedicated societies and journals.

Contemporary methods of behavioural-genetic analysis: new approaches

The approaches improve the capacity to specify and generalize results on the effects of genetic and environmental factors on characteristics and their evolution across time.

QTL analysis study

Quantitative trait locus A quantitative trait locus (QTL) is a locus (section of DNA) that correlates with variation of a quantitative trait in the phenotype of a population of organisms. QTLs are mapped by identifying which molecular markers (such as SNPs or AFLPs) ...

(QTL) analysis is a statistical approach for attempting to explain the genetic basis of variation in complex characteristics by linking two types of data: phenotypic data (trait measurements) and genotypic data (typically molecular markers). Researchers in disciplines as diverse as

agriculture Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created ...

biology Biology is the scientific study of life and living organisms. It is a broad natural science that encompasses a wide range of fields and unifying principles that explain the structure, function, growth, History of life, origin, evolution, and ...

, and

medicine Medicine is the science and Praxis (process), practice of caring for patients, managing the Medical diagnosis, diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment, Palliative care, palliation of their injury or disease, ...

use QTL analysis to relate complicated traits to particular chromosomal regions. The purpose of this procedure is to determine the action, interaction, quantity, and type of action. The ability to disentangle the genetic component of complex characteristics has been enabled by QTL studies in model systems. To research behavioural characteristics such as schizophrenia, bipolar disorder, alcoholism, and autism, large-scale national and international alliances have been constructed. Such partnerships will bring together enormous, consistently gathered samples, improving the likelihood of finding real susceptibility gene connections.

Biometric model fitting

The method is designed in collaboration of quantitative geneticists to enhance the capabilities to delineate between the genetic and environmental components of complex behavioural characteristics. Path analysis and structural equation modelling are two statistical approaches used in this methodology. The approach is used to see if genetic and environmental impacts can be employed in various populations. It would be useful to know how much of the total genetic variance—heritability—is accounted for by a limited selection of potential loci in studies of emotional stability, for example.

References

External links

* {{cite web , url=https://class.coursera.org/behavioralgenetics-001 , title=Introduction to Human Behavioral Genetics , last=McGue , first=Matt , date=5 May 2014 , website=Coursera , access-date=10 June 2014 , archive-date=10 February 2017 , archive-url=https://web.archive.org/web/20170210145120/https://class.coursera.org/behavioralgenetics-001 , url-status=dead Free Massively Open Online Course on human behavior genetics by Matt McGue of the University of Minnesota Behavioural sciences Human genetics Behavioural genetics