In Guns, Germs and Steel, how does Diamond respond to the idea that Europeans may be more intelligent than New Guineans?

In the Prologue, Diamond makes three major arguments on
this topic.

First, he says that New Guineans may seem dumb
when they come to towns because they are not used to the things that are in "civilized"
towns.  This does not mean they really are dumb, just that they are not accustomed to
the setting.

The next two arguments center around the idea
that New Guineans are actually smarter.

Second, he says
that more intelligence is (and has been for a long time) needed to survive in the New
Guinean wilderness than in European countries.  Therefore, New Guineans are likely to
have evolved to be more intelligent than
Europeans.

Finally, Diamond argues that New Guinean
lifestyles mean they are more likely to be intelligent.  Europeans and Americans spend
all their time being passively entertained by TVs and such while New Guineans actually
have to use their brains.

So, Diamond counters the idea
that Europeans are more intelligent by A) saying New Guineans only appear dumb in modern
settings and B) that there are reasons to believe that New Guineans would actually be
smarter than Europeans.