Most previous studies on the influence of birth order have looked at children from different families. For instance, some studies have looked at U.S. presidents, Nobel Laureates or NASA astronauts to see whether they are mostly first-born children or ＿＿（31）＿＿ born children. However, these studies cannot take into account influences that arise from children being in the same family. A new study suggests that birth order within families has long sparked sibling rivalry, but it might also impact the child's personality and intelligence. First-borns are typically smarter, ＿＿（32）＿＿ younger siblings get better grades and are more outgoing. The findings weigh in on a long-standing debate： What effect if any does birth order have on a person's life? The results ＿＿（33）＿＿ support to some previous hypotheses－for instance, that the eldest sibling tends to have higher aptitude. But the study also ＿＿（34）＿＿ other proposed ideas, for example, that first-borns tend to be more extroverted. The findings shed light on the influence of sibling relationships, which often receives less attention compared with ＿＿（35）＿＿ the mother-child or father-child relationship. They also suggest some inherent differences between siblings exist, differences that might arise no matter what parents do.