According to Eysenck, the basic dimensions of psychology are introversion-extraversion, neuroticism, and psychoticism (Cervone & Pervin, 2013). Introversion and extraversion are two of the major personality traits identified in many different theories of personality. People who are defined as introverted tend to be focused more on internal thoughts, feelings, or moods rather than seeking outside stimulation, while people who are seen as extraverts tend to be more social, assertive, and more easily excited by external stimulation. Having an introverted personality does not necessarily mean the person is shy or afraid of social situations, but rather simply prefer to spend more time alone and do not need as much social stimulation. According to the authors, extraversion is probably the most studied of all traits because relevant behaviors are relatively easy to observe (Cervone & Pervin, 2013). Personality theorists have found many examples of behavior differences in those who are introverts compared to extraverts. Some examples include that introverts are more sensitive to pain than extraverts; they become more easily fatigued; excitement interferes with their performance while it enhances performance for extraverts; introverts tend to do better in school; extraverts are often more sexually active than introverts, etc. (Cervone & Pervin, 2013). Even though people tend to lean towards one or the other, many theories of personality state that everyone has a degree of both introversion and extraversion. Hans Eysenck described extraversion-introversion as the degree to which a person is outgoing and interactive with other people. He suggested that individual variations in introversion-extraversion reflect individual differences in the neurophysiological functioning of the brain’s cortex (Cervone & Pervin, 2013). He also generated relevant evidence towards there being a biological dimension, which means that introversion and extraversion should be at least somewhat hereditary. Studies of identical and fraternal twins commonly suggest that hereditary does play a major role in accounting for differences between individuals in E scores (Cervone & Pervin, 2013). This is related to my life because I have an identical twin, and although we have similar personalities, we differ in certain traits. Being identical we share about 100% of our genes which means that many of our differences is probably due to experiences that one of us has without the other involved. We shared many aspects of our environment growing up such as parenting style, wealth, culture, education, and community. Even though we are amazingly similar, close friends and family members can still easily tell us apart. Although we share many of the same friends, our own personal interactions we have with these people have shaped us into our own people. Also, after elementary school, we were not always in the same classes so we had different experiences in the way we learned and interacted with others. This means that these non-shared environmental experiences were crucial to developing our own distinct personalities. To shed light on this on why nature vs nurture plays such a key role in personality development, a group of scientists observed 40 genetically identical mice that were kept in an enclosure that offered a