How Does Birth Order Affect Personality Trait Extraversion

Introduction
Personality is a broad feature in the field of psychological individuality. One of the most extensive and prominent topic under personality is the personality-trait extraversion. Even before, there are some people who are talkative, bold and assertive than other people and this has been thought to have a biological basis and social importance. This behavioral consequence of trait dimension has come to be known as extraversion. Extraversion is one of the fundamental dimension of personality (Costa & McCrae, 1992a; Digman, 1990; Eysenck & Himmelweit, 1947; Goldberg, 1990; Norman, 1963), it is used to explain the wide variety of behaviours which is the main concern of personality (Funder, 2001). Extraversion is relative to view the

The difference is that, this study is more focused on how birth-order affect the personality of an individual specifically the trait extraversion using his casual mechanism, the parental investment. This study highlighted the factor birth-order and how it affects personality. In here, personality was narrowed down to the trait extraversion to be more specific. It is only focused on parental investment and did not go further to the other casual mechanisms of Sulloway. Parental investment was used because presumably it has closer interaction compared to other casual mechanisms. This study is also focused on firstborns and laterborns only, excluding only child and twins. The study referred the parental investment to both parents and do not account the single parents. This literature is worth reviewing because birth-order affects our personality and personality can affect the way an individual interact with other people. It is also important so that parents would be aware of how the way they treat their children or for them to be able to give importance to their children fairly to avoid inequality because it will affect the child’s personality (Sampson, 1993). When there is inequality or lack of parental investment, the children is more to be rebellious and adventurous for the pursuit of parental investment (Sulloway,

Canli (2008) identified polymorphic genes as to have direct influences on extraversion’s neurocognitive substrates. There are individuals that were born with genes that systematically biased the development of the extraverted phenotype and others have genes that biased the development of the introverted phenotype and this leads an individual to being an extrovert or an introvert. According to their findings, extraversion is largely accounted for genetic factors and that this heritability of extraversion declines as people grow older. One research found out that this is also applicable in many animals, this supports the finding that extraversion have a genetic basis (Jang, Livesley, Angleitner, Riemann, & Vernon, 2002). Because of these findings about extraversion, it leads to uncovering the specific genetic pathways that influence personality more specifically