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Defining Heritability

Heritability refers to the level to which individual gene differences contribute to individual behavior differences (Sesardic, 2005). The main focus is on differences. It is the proportion of phenotypic variation as a result of genetic differences.

The Results of Cattell’s Study on Twins and Siblings

Cattell made a research study to determine the critical contributions of environment and heredity to trait development. His research entailed a statistical technique to find out the contributions of heredity. His technique is multiple abstract variance analysis or MAVA (Cattell et al., 1981). According to the test, there are estimates of the absence or presence of the influence of genes and the extent to which traits are due because of environmental and genetic effects. This technique entailed collecting information on the resemblances between identical twins raised in the same family and lifted away from each other. It also included siblings not twins raised in the same family and siblings who were not twins raised apart.

According to the results of Cattell’s study, environmental and genetic influences are different from one trait to another (Olson, Favero, & Hergenhahn, 2019). For instance, according to Cattell’s research, around 65 to 70% of the score variation on measures of assertiveness and intelligence can be explained by genetics. On the other hand, the genetic effects on traits like neuroticism and conscientiousness are half that. Cattell estimates that around two-thirds of the personality is based on the influences of the environment, and about one-third is heredity (Olson, Favero, & Hergenhahn, 2019).

Moreover, combined with the immediate situational aspects, Cattell contends that people’s behavior is much attributed to their groups, like school, peer groups, and families. People can be identified by their traits like those in that particular social group can identify social groups. According to Cattell et al. (1981), the trait aspects one can locate in a group are known as syntality.

Relevance of the Study of Twins in Determining How Much Personality is Due to Heredity and Environment

According to Cattell, personality refers to that which allows the prediction of what someone would do in a particular circumstance. He referred to the underlying fundamental aspects of an individual’s personality as source traits. Cattell used factor analysis, and his finding was surface trait common clusters, which he called source traits. His research identified 35 fundamental traits, from which he characterized 12 as abnormal and 23 as usual (Cattell et al., 1981). He argued that ergs intrinsically drive people. He meant goals established by ergs due to fear, anger, curiosity, hunger, and other motivations found in primates and humans (Cattell et al., 1981). From his study, one can identify different kinds of intelligence. He discovered that there are two types of intelligence: crystallized and fluid. Crystallized intelligence refers to the ability of a person to solve problems based on past experiences (Olson, Favero, & Hergenhahn, 2019). On the other hand, fluid intelligence refers to the ability of a person to learn new things despite their previous experience.

From Cattell’s study, one learns that personality is seen regarding traits or intelligence and attitudes. He defined attitude as a longing to respond in a certain way to a particular situation (Olson, Favero, & Hergenhahn, 2019). Attitudes are linked to Dynamic lattice, a display of the conceptual analysis of the linkage between the instinctive driving impetus of the mind and the attitudinal and semantic superstructure. In this case, some attitudes are considered subordinate to others; the subsidization linkage assists in determining which particular attitude would produce a specific behavior.

Additionally, Cattell found that traits are determined either genetically or environmentally. The twin study is essential in discovering environmental and genetic influences on traits. In this case, ecological influences are categorized as the shared factors that make twins similar and non-shared aspects that lead to the twins’ differences. For example, identical and fraternal twins share similar environments: community, home, and family. One can find the effects of nurture versus nature in various aspects of the differences between fraternal and identical twins. For instance, if one is looking to find out whether the eye color is heritable, one would see that in identical twins because it is most likely that identical twins would share the same eye color. However, when it comes to fraternal twins, one may not find that they have similar eye colors, but there is a 70% possibility that they would share the same eye color (LoBue, 2021). This means that genetics plays a vital role in determining the color of the eyes.

Similarly, this is seen in IQ. However, the environment shapes how children are raised in terms of wealthy or middle-income families. According to LoBue (2021), in impoverished homes where children are raised in high-risk neighborhoods, their IQ is almost zero. Even though the child may be genetically intelligent, a risky environment may pose an overwhelming disadvantage in growing their IQ.


Cattell, R., Rao, D., Schmidt, L. R., & Vaughan, D. S. (1981). Heritability of some personality source traits: evidence from MAVA design, Maximum Likelihood Analysis, and the OA Battery. L’Année psychologique, 81(2), 429-451.

Olson, M.H., Favero, D., & Hergenhahn, B.H. (2019). An Introduction to Theories of Personality (9th Edition). Pearson Education.

Sesardic, N. (2005). Making Sense of Heritability. New York City: Cambridge University Press.


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Complete a 2-3-page expository paper exploring heritability and how twin studies have informed this theory.

Define heritability using your own words and support it with a reliable source.
Explain the results of Cattell’s study on twins and siblings.
Using information and terminology from twin studies, show how the study of twins can help to determine how much personality is due to heredity and how much to the environment, using at least one example.

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