Specific phobia is an anxiety disorder, characterized by an extreme, unreasonable, and irrational fear associated with a specific object, situation, or concept which poses little or no actual danger. Specific phobia can lead to avoidance of the object or situation, persistence of the fear, and significant distress or problems functioning associated with the fear. A phobia can be the fear of anything.
Twins are two offspring produced by the same pregnancy. Twins can be either monozygotic ('identical'), meaning that they develop from one zygote, which splits and forms two embryos, or dizygotic, meaning that each twin develops from a separate egg and each egg is fertilized by its own sperm cell. Since identical twins develop from one zygote, they will share the same sex, while fraternal twins may or may not. In very rare cases twins can have the same mother and different fathers.
A multiple birth is the culmination of one multiple pregnancy, where in the mother gives birth to two or more babies. A term most applicable to vertebrate species, multiple births occur in most kinds of mammals, with varying frequencies. Such births are often named according to the number of offspring, as in twins and triplets. In non-humans, the whole group may also be referred to as a litter, and multiple births may be more common than single births. Multiple births in humans are the exception and can be exceptionally rare in the largest mammals.
Conjoined twins, popularly referred to as Siamese twins, are twins joined in utero. It is a very rare phenomenon, estimated to occur in anywhere between one in 49,000 births to one in 189,000 births, with a somewhat higher incidence in Southwest Asia and Africa. Approximately half are stillborn, and an additional one-third die within 24 hours. Most live births are female, with a ratio of 3:1.
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.
Empathy is generally described as the ability to take on another's perspective, to understand, feel, and possibly share and respond to their experience. There are more definitions of empathy that include but is not limited to social, cognitive, and emotional processes primarily concerned with understanding others. Often times, empathy is considered to be a broad term, and broken down into more specific concepts and types that include cognitive empathy, emotional empathy, somatic empathy, and spiritual empathy.
Acrophobia is an extreme or irrational fear or phobia of heights, especially when one is not particularly high up. It belongs to a category of specific phobias, called space and motion discomfort, that share similar causes and options for treatment.
Attention span is the amount of time spent concentrating on a task before becoming distracted. Distractibility occurs when attention is uncontrollably diverted to another activity or sensation. Attention training is said to be part of education, particularly in the way students are trained to remain focused on a topic of discussion for extended periods, developing listening and analytical skills in the process.
Diagnoses of autism have become more frequent since the 1980s, which has led to various controversies about both the cause of autism and the nature of the diagnoses themselves. Whether autism has mainly a genetic or developmental cause, and the degree of coincidence between autism and intellectual disability, are all matters of current scientific controversy as well as inquiry. There is also more sociopolitical debate as to whether autism should be considered a disability on its own.
The gateway drug effect is a comprehensive catchphrase for the often observed effect that the use of a psychoactive substance is coupled to an increased probability of the use of further substances. Possible reasons for the connection include environmental influence, impulsive people seeking both soft and hard drugs, alterations in the brain due to earlier substance exposure, as well as similar attitudes of people who use different substances, and therefore experience a "common liability to addiction". In 2020, the National Institute on Drug Abuse released a research report which supported allegations that marijuana is a "gateway" to more dangerous substance use; one of the peer-reviewed papers cited in the report claims that while "some studies have found that use of legal drugs or cannabis are not a requirement for the progression to other illicit drugs [...] most studies have supported the "gateway sequence"." However, a 2018 literature review conducted by the National Institute of Justice, which analyzed 23 peer-reviewed research studies, concluded "that existing statistical research and analysis relevant to the "gateway" hypothesis has produced mixed results", and that "no causal link between cannabis use and the use of other illicit drugs can be claimed at this time."
Dysthymia, also known as persistent depressive disorder (PDD), is a mental and behavioral disorder, specifically a disorder primarily of mood, consisting of similar cognitive and physical problems as major depressive disorder, but with longer-lasting symptoms. The concept was used by Robert Spitzer as a replacement for the term "depressive personality" in the late 1970s.
High-functioning autism (HFA) was historically an autism classification where a person exhibits no intellectual disability, but may experience difficulty in communication, emotion recognition, expression, and social interaction.
The Minnesota Center for Twin and Family Research is a series of behavioral genetic longitudinal studies of families with twin or adoptive offspring conducted by researchers at the University of Minnesota. It seeks to identify and characterize the genetic and environmental influences on the development of psychological traits.
The heritability of autism is the proportion of differences in expression of autism that can be explained by genetic variation; if the heritability of a condition is high, then the condition is considered to be primarily genetic. Autism has a strong genetic basis. Although the genetics of autism are complex, autism spectrum disorder (ASD) is explained more by multigene effects than by rare mutations with large effects.
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.
Nancy L. Segal is an American evolutionary psychologist and behavioral geneticist, specializing in the study of twins. She is the Professor of Developmental Psychology and Director of the Twin Studies Center, at California State University, Fullerton. Segal was a recipient of the 2005 James Shields Award for Lifetime Contributions to Twin Research from the Behavior Genetics Association and International Society for Twin Studies.
Gene–environment correlation is said to occur when exposure to environmental conditions depends on an individual's genotype.
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.
In the field of personality psychology, Machiavellianism is the name of a personality trait characterized by interpersonal manipulation, indifference to morality, lack of empathy, and a strategic focus on self-interest. Psychologists Richard Christie and Florence Geis named the trait after Niccolò Machiavelli, as they used edited and truncated statements inspired by his works to study variations in human behaviors. Their Mach IV test, a 20-question, Likert-scale personality survey, became the standard self-assessment tool and scale of the Machiavellianism construct. Those who score high on the scale are more likely to have a high level of manipulativeness, deceitfulness and a cynical, unemotional temperament.
