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Is a descriptive statistic that indicates the degree of population variation of a trait, that is due to genetic differences


Complement of heritability (1-h2)

Indicates the degree of population variation of a trait, that is due to environmental influences


What kind of studies are used to measure/ estimate the heritability of various traits ?

Twin + adoption studies


Nuisance variables

Refer to variables that are assumed to be causes of group/individual differences, but seemingly irrelevant to the theory of the investigator

--> closely related to heritability


How much does genetic vs environment influence personality traits ?

Increased genetic influence with age + decreasing shared environmental influence

--> environmental factors often decrease to 0 after adolescence


Why have personality + individual differences been neglected ?

1. Cogent evolutionary theories existed for predicting + explaining sex differences

ex.: sexual selection


2. Assumption that natural selection has reduced/eliminated heritable individual difference because traits that are advantageous tend to spread over tome to fixation


Which theories are able to explain personality and individual differences (variation) ?

1. Life history theory

2. Costly signaling theory

3. Environmental heterogeneity

4. Frequency dependent selection

5. Mutation load

6. Contingent shift


Life history theory

States that we have a certain amount of energy throughout our life, that we try to allocate over the course of our life

--> some put more emphasis on kinship, some on multiple mating partners

e.g.: reproductive development and behaviors, post-reproductive behaviors, and lifespan





Costly signaling theory

States that people compete with one another by sending costly signals to others about their qualities

--> might explain conscientiousness, agreeableness, generosity etc

e.g.: to be able to be generous, one has to first have the ressources/affordances




Balancing selection

Occurs when genetic variation is maintained by selection


ex.: heterozygote advantage, where both alleles are maintained, as Aa will have a better chance of survival than AA or aa


Frequency dependent selection

Occurs when 2 or more strategies are maintained within a population at a particular frequency relative to each other, such that the fitness of each strategy decreases as it becomes increasingly common


ex.: Psychopathy, if only a few have these traits than those will consequently have an advantage, as opposed to when this is common


Role of Mutation load in heritability ?

Heritability of some traits originates from individual differences in mutation load

--> explains some harmful mental disorders


Environmental heterogeneity/ Flucturating optima

Environmental conditions can vary from time and place therefore, the traits favored by natural selection can change/fuctuate as well


--> variation in personality traits


Contingent shift

Refers the the ability to adapt psychological mechanisms in response to changes in environmental conditions


  • selection favors those that are adaptive
  •  can occur in response to individual phenotypic qualities + environmental conditions


ex.: chef vs angestellt personality anpassen können 


Stabilizing selection

Exists when selection favors a trait that is intermediate within the range represented within a population


--> most common trait is selected + continues to dominate


Adoption studies

Assessing differences in personality between pairs of genetically related individuals who don't share a common environment

--> to assess the degree of genetic impact by looking at their similarities


Intraclass correlation coefficient

Assesses the correlation between relatives

--> variance between families, as when the variance is high between families then the similarities are high within families


Twin studies

Assesses differences in personality between twins that shared the same environment

--> to assess the degree of environmental impact by looking at the differences


Additive effects

Each gene separately contributes to personality


Nonadditive effects

Combined effects of genes contribute to personality


Combination designs

Refer to combination of different study forms

e.g.: adoption-twin, families-of-twins method


Adoption twin design

Twins adopted apart are compared to twins raised together

--> show little shared environment influences


Families-of-twins method



Genotype environment interactions

The same environment influences peoples characteristics in different ways, depending on their genotype

ex.: the reason why relatives are not always similar to each other


Genotype-environment correlation

Genetic tendencies cause you to be more exposed to a specific kind of environment


a) passive

  •  inheriting combination of genes passively, not as result of own behavior

ex.: athletic parents raise children in athletic environment passively

b) reactive

  •  other peoples reactions to childs genetic tendencies influence its environment

ex.: child runs around a lot; parents sign him up for soccer practices

c) active

  • child actively chooses environment as a function of genetic predisposition


Contrast effect

Refers to the tendency to emphasize differences between realtives

ex.: siblings comparing each other than to general population


Assimilation effect

Refers to the tendency to emphasize similarities between relatives

ex.: father sees sister as similar


Pros vs cons of adoption studies ?


1. Good way to measure the question at hand

--> only method we have



1. Assumption of representativeness

  • assuming that adopted children + their parents are representative of the population

2. Prenatal environment is often not considered

3. Selective placement

  • child may have been put in a family similar to the biological one


Pros vs cons of twin studies ?


1. Compares mono + dizygotic twins



1. Assumes that the environment is the same, which doesn't necessarily has to be

2. Assumption of representativeness