Sigmeund Freud was the first psychotherapist to say: "a child's position in the sequence of brother and sisters is of very great significance for one course of his later life" (Richardson 12). One's birth order position (whether born first, second, last, etc.), one's sex (male or female), and the sex of one's siblings affects the kind of person one becomes. People often say they can't understand "how people from the same family can be so different". What they do not realize is that each sibling is born into a different family. Each new child needs to create a unique identity separate from the others. However this new identity is created within the context of those who are already there. The people in a family change in many ways between the birth of each new child. Many variables impact on each sibling. These include the physical circumstances in which a family finds itself, (ie. location, income, residents), the emotional stability of the family, (ie. well adjusted parents, parental experience, settled career), and lastly the state in which they find themselves, (ie. decade, wartime, country). These variables mean that each child will be treated differently by parents and siblings and this is done usually unintentionally. One must remember that birth order does not determine the basic values of a person or the person's value to society. It affects social interactions more than attitudes and ethnical stances. Your birth order and sex determines in a large part how other people in your family react to you and treat you which in turn influences what you think about yourself and how you react to and treat others inside and outside the family.

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             Your birth order and gender affect primarily your social behaviour and how you relate to other people in your life. They affect the way you relate to your spouse, your friends and the skills you bring to parenting. Birth affects what kind of a spouse you will be because of how you grew up.