According to Guns, Germs, and Steel, why did Australia's aborgines lose out to invading Europeans?

The answer
to this can be found late in Chapter 15.  It can be found on pages 319 and 320 in the paperback
edition of the book.  As with everything else in this book, the answer has to do with
geography.

In this chapter, Diamond contrasts New Guinea with Australia.  He
says that New Guinea was not suited for European colonization.  Australia, on the other hand,
was very suitable.  Diamond points out...