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A considerable body of research has demonstrated a correlation between birth order and aspects such as temperament and behavior , and some psychologists believe that birth order significantly affects the development of personality. Psychologist Alfred Adler was a pioneer in the study of the relationship between birth order and personality. A key point in his research and in the hypothesis that he developed based on it was that it was not the actual numerical birth position that affected personality; instead, it was the similar response s in large numbers of families to children in specific birth order positions that had an effect. For example, first-borns, who have their parents to themselves initially and do not have to deal with siblings in the first part of their lives, tend to have their first socialization experiences with adults and therefore tend to find the process of peer socialization more difficult. In contrast, later-born children have to deal with siblings from the first moment of their lives and therefore tend to have stronger socialization skills.

 Numerous studies since Adler’s have been conducted on the effect of birth order and personality. These studies have tended to classify birth order types into four different categories: first-born, second-born and/or middle, last, and only child.

 Studies have consistently shown that first-born children tend to exhibit similar, positive and negative personality traits. First-borns have consistently been linked with academic achievement in various studies; in one study, the number of National Merit scholarship winners who are first-borns was found to be equal to the number of second-and third-borns combined. First-borns have been found to be more responsible and assertive than those born in other birth-order positions and tend to rise to positions of leadership more often than others; more first-borns have served in the U.S. Congress and as U.S. presidents than have those born in other birth-orderpositions. However, studies have shown that first-borns tend to be more subject to stress and were considered problem children more often than later- borns.

 Second-born and/or middle children demonstrate markedly different tendencies from first-borns. They tend to feel inferior to the older child or children because it is difficult for them to comprehend that their lower level of achievement is a function of age rather than ability, and they often try to succeed in areas other than those in which their older sibling or siblings excel. They tend to be more trusting, accepting, and focused on others than the more self-centered first-borns, and they tend to have a comparatively higher level of success in team sports than do first-borns or only children, who more often excel in individual sports.

 The last-born child is the one who tends to be the eternal baby of the family and thus often exhibits a strong sense of security. Last- borns collectively achieve the highest degree of social success and demonstrate the highest levels of self-esteem of all the birth-order positions.They often exhibit less competitiveness than older brothers and likely to take part in less competitive group games or in social organizations such as sororities and fraternities.

 Only children tend to exhibit some of the main characteristics of first - borns and some of the characteristics of last - borns. Only children tend to exhibit the strong sense of security and self - esteem exhibited by lastborns while, like first - borns, they are more achievement oriented and more likely than middle - or last - borns to achieve academic success. However, only children tend to have the most problems establishing close relationships and exhibit a lower need for affiliation than other children. 

The word body " in paragraph 1 could best be replaced by______