Listen to the Summary of Dr. Kevin Leman's The Birth Order Book in 20 minutes. Please note: This is a summary & not the original book. The family zoo is the term used to describe the different birth orders in a family. It is the most entertaining and informative part of birth order theory. The variables that affect each person are spacing, the sex of each child, physical, mental, or emotional differences, sibling deaths, adoptions, and the relationship between the parents...