Many assume that farming developed in fertile lands.How does Guns, Germs, and Steel challenge this misconception?

In Chapter 4, Diamond gives a number of factors that
influenced the move from hunting and gathering to food production.  By giving us this
list, Diamond challenges the idea that farming would only develop in fertile
lands.

One of the major reasons to switch to farming was
the decrease in availability of wild foods.  This would make it harder to make a living
gathering food (as opposed to growing it).  It stands to reason that wild foods would
remain widely available in fertile areas for a much longer time than in relatively
infertile areas.  Because the food would run out more quickly in relatively infertile
areas, farming would become attractive in those areas before it became attractive to
people living in fertile areas.