In the book Guns, Germs, and Steel, what are commmonly used answers to "Yali's question?"

In his Prologue, Jared Diamond gives a number of common
answers to Yali's question.  Among them
are:

• Biological explanations.  These
  explanations are essentially racist.  They say that Europeans are simply genetically
  superior to people like Yali.  Typically, they argue that European superiority shows up
  in the "fact" that Europeans have higher levels of
  intelligence.


• Climate-based explanations.  These argue
  that Europeans became superior because they lived in a harsher environment.  Tropical
  people didn't have to work hard for their livings and so did not need technology and
  such.  Because Europeans lived in tough, cold climates, they had to be more ingenious in
  order to survive.  This made them more inventive and led to
  technology.


• River-based explanations.  These argue that
  civilizations arose in lowland river valleys in dry climates.  Civilization arose there
  because it was necessary in order to organize society to create irrigation
  works.

These are the three major explanations
that Diamond mentions in the beginning of this book.