Heritability is a statistic used in the fields of breeding and genetics that estimates the degree of variation in a phenotypic trait in a population that is due to genetic variation between individuals in that population. The concept of heritability can be expressed in the form of the following question: "What is the proportion of the variation in a given trait within a population that is not explained by the environment or random chance?"
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 and in related fields, from biology to psychology. Twin studies are part of the broader methodology used in behavior genetics, which uses all data that are genetically informative – siblings studies, adoption studies, pedigree, etc. These studies have been used to track traits ranging from personal behavior to the presentation of severe mental illnesses such as schizophrenia.
Human variability, or human variation, is the range of possible values for any characteristic, physical or mental, of human beings.
Hereditarianism is the doctrine or school of thought that heredity plays a significant role in determining human nature and character traits, such as intelligence and personality. Hereditarians believe in the power of genetics to explain human character traits and solve human social and political problems. Hereditarians adopt the view that an understanding of human evolution can extend the understanding of human nature.
Gene–environment interaction is when two different genotypes respond to environmental variation in different ways. A norm of reaction is a graph that shows the relationship between genes and environmental factors when phenotypic differences are continuous. They can help illustrate GxE interactions. When the norm of reaction is not parallel, as shown in the figure below, there is a gene by environment interaction. This indicates that each genotype responds to environmental variation in a different way. Environmental variation can be physical, chemical, biological, behavior patterns or life events.
Research on the heritability of IQ inquires into the degree of variation in IQ within a population that is due to genetic variation between individuals in that population. There has been significant controversy in the academic community about the heritability of IQ since research on the issue began in the late nineteenth century. Intelligence in the normal range is a polygenic trait, meaning that it is influenced by more than one gene, and in the case of intelligence at least 500 genes. Further, explaining the similarity in IQ of closely related persons requires careful study because environmental factors may be correlated with genetic factors.
Personality development encompasses the dynamic construction and deconstruction of integrative characteristics that distinguish an individual in terms of interpersonal behavioral traits. Personality development is ever-changing and subject to contextual factors and life-altering experiences. Personality development is also dimensional in description and subjective in nature. That is, personality development can be seen as a continuum varying in degrees of intensity and change. It is subjective in nature because its conceptualization is rooted in social norms of expected behavior, self-expression, and personal growth. The dominant viewpoint in personality psychology indicates that personality emerges early and continues to develop across one's lifespan. Adult personality traits are believed to have a basis in infant temperament, meaning that individual differences in disposition and behavior appear early in life, potentially before language of conscious self-representation develop. The Five Factor Model of personality maps onto the dimensions of childhood temperament. This suggests that individual differences in levels of the corresponding personality traits are present from young ages.
Robert Joseph Plomin is an American/British psychologist and geneticist best known for his work in twin studies and behavior genetics. A Review of General Psychology survey, published in 2002, ranked Plomin as the 71st most cited psychologist of the 20th century. He is the author of several books on genetics and psychology.
Gene–environment correlation is said to occur when exposure to environmental conditions depends on an individual's genotype.
Genetic epidemiology is the study of the role of genetic factors in determining health and disease in families and in populations, and the interplay of such genetic factors with environmental factors. Genetic epidemiology seeks to derive a statistical and quantitative analysis of how genetics work in large groups.
In multivariate quantitative genetics, a genetic correlation is the proportion of variance that two traits share due to genetic causes, the correlation between the genetic influences on a trait and the genetic influences on a different trait estimating the degree of pleiotropy or causal overlap. A genetic correlation of 0 implies that the genetic effects on one trait are independent of the other, while a correlation of 1 implies that all of the genetic influences on the two traits are identical. The bivariate genetic correlation can be generalized to inferring genetic latent variable factors across > 2 traits using factor analysis. Genetic correlation models were introduced into behavioral genetics in the 1970s–1980s.
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" connotes a focus on genetic influences, the field broadly investigates the extent to which genetic and environmental factors influence individual differences, and the development of research designs that can remove the confounding of genes and environment. Behavioural genetics was founded as a scientific discipline by Francis Galton in the late 19th century, only to be discredited through association with eugenics movements before and during World War II. In the latter half of the 20th century, the field saw renewed prominence with research on inheritance of behaviour and mental illness in humans, as well as research on genetically informative model organisms through selective breeding and crosses. In the late 20th and early 21st centuries, technological advances in molecular genetics made it possible to measure and modify the genome directly. This led to major advances in model organism research and in human studies, leading to new scientific discoveries.
"Envirome" is a concept that relates the core of environmental conditions with the successful biological performance of living beings. This concept was created in genetic epidemiology, in which an envirome is defined as the total set of environmental factors, both present, and past, that affect the state, and in particular the disease state, of an organism. The study of the envirome and its effects is termed enviromics. The term was first coined in the field of psychiatric epidemiology by J.C. Anthony in 1995. More recently, use of the term has been extended to the cellular domain, where cell functional enviromics studies both the genome and envirome from a systems biology perspective. In plants, enviromics is directly related to complex ecophysiology, in which the wide environment of the plants, into an omics scale, can be dissected and understood as a mosaic of possible growing factors and the balance of diverse resources available. In ecology, this concept can be related to the Shelford's law of tolerance. The enviromics is conceived as a pillar of the Modern Plant Breeding, capable to connect the design and development of breeding goals concealing it with the agronomic targets for a climate-smart agriculture. It also has the ability to bridge the knowledge gaps between the different levels of systems biology and phenomics in the context of Gene–environment interaction.
Eric Nathan Turkheimer is an American psychologist and the Hugh Scott Hamilton Professor of psychology at the University of Virginia.
Wendy Johnson is an American differential psychologist and professor of psychology at the University of Edinburgh. She holds the chair in Differential Development in the Department of Psychology and Centre for Cognitive Ageing and Cognitive Epidemiology at the University of Edinburgh.
The ACE model is a statistical model commonly used to analyze the results of twin and adoption studies. This classic behaviour genetic model aims to partition the phenotypic variance into three categories: additive genetic variance (A), common environmental factors (C), and specific environmental factors plus measurement error (E). It is widely used in genetic epidemiology and behavioural genetics. The basic ACE model relies on several assumptions, including the absence of assortative mating, that there is no genetic dominance or epistasis, that all genetic effects are additive, and the absence of gene-environment interactions. In order to address these limitations, several variants of the ACE model have been developed, including an ACE-β model, which emphasizes the identification of causal effects, and the ACDE model, which accounts for the effects of genetic dominance.
Blueprint: How DNA Makes Us Who We Are is a book by behavioral geneticist Robert Plomin, first published in 2018 by the MIT Press and Allen Lane. The book argues that genetic factors, and specifically variations in individuals' DNA, have a large effect on human psychological traits, accounting for approximately half of all variation in such traits. The book also claims that genes play a more important role in people's personalities than does the environment. In Blueprint, Plomin argues that environmental effects on human psychological differences, although they exist, are "...mostly random – unsystematic and unstable – which means that we cannot do much about them."
In behavioral genetics, the Scarr–Rowe effect, also known as the Scarr–Rowe hypothesis, refers to the proposed moderating effect of low socioeconomic status on the heritability of children's IQ. According to this hypothesis, lower socioeconomic status and greater exposure to social disadvantage during childhood leads to a decrease in the heritability of IQ, as compared to children raised in more advantaged environments. It is considered an example of gene–environment interaction. This hypothesized effect was first proposed by Sandra Scarr, who found support for it in a 1971 study of twins in Philadelphia, and these results were replicated by David C. Rowe in 1999. Since then, similar results have been replicated numerous times, though not all replication studies have yielded positive results. A 2015 meta-analysis found that the effect was predominant in the United States while less evident in societies with robust child welfare systems.
Multifactorial diseases are not confined to any specific pattern of single gene inheritance and are likely to be caused when multiple genes come together along with the effects of environmental factors.
Ronald S. Wilson was an American clinical psychologist and behavioral geneticist. At the time of his death, he was a Professor of Pediatrics at the University of Louisville and director of the Louisville Twin Study, as well as president of the Behavior Genetics Association. He joined the faculty of the University of Louisville School of Medicine in 1965 and became director of the Louisville Twin Study there in 1967; he held both positions from then until his death. Originally an associate professor at the University of Louisville, he was promoted to the rank of full professor there in 1971. He was a fellow of the American Association for the Advancement of Science and the American Psychological Association, as well as a member of the Society for the Study of Human Biology and a founding fellow of the International Society for Twin Studies, of which he served as vice president from 1980 to 1983. In 1979, he received the American Association for the Advancement of Science's Socio-Psychological Prize, and in 1980, he received the James Shields Award from the International Society for Twin Studies. He was elected president-elect of the Behavior Genetics Association in 1984. He died of a heart attack while playing tennis on November 16, 1986.
