birth order

Definition:
Birth order is the chronological order of sibling births in a family.

Description:
Alfred Adler (1870–1937) was a pioneer in the study of birth order. His research suggested that the position a child had by the order of birth significantly affected the child's growth and personality. Research in the late twentieth century and early twenty-first century shows even greater influence, contributing to intelligence, career choice, and, to a certain degree, success in adulthood.
Being born first, last, or somewhere in the middle of itself is not of significance. What matters is how that birth order affects how a child is treated by parents and other siblings and how that child feels about it. Other factors also influence the child's socialization and the parents' expectations. ... (continued on: birth order: Information and Much More from Answers.com)