The answer to this can be found early in the Prologue to the book. The most common answers to Yali's question include:
- Racial /genetic answers. These answers (which are no longer accepted in scientific circles) argue that somehow Europeans are genetically superior to non-Europeans.
- Answers having to do with climate. These answers argue that Europeans had to work hard to survive in a harsh climate while others had an easier time living in good climates. The harder climate made Europeans have to develop more technology and a better work ethic.
- Answers having to do with river valleys in dry climates. Such valleys are said to require irrigation systems. Civilization is said to be needed in order to create and maintain such systems.
These are the three main answers presented by Diamond (and rejected by him) in the Prologue.