In Guns Germs, and Steel, what theory does Jared Diamond propose for the disappearance of mega-fauna in New Guinea?Guns germs and steel By Jared...

Diamond does not propose any novel thesis about this
extinction.  Instead, he simply argues that the disappearance of these large animals
(which were all marsupials) was due to human action.

The
main cause of the disappearance of these animals was the coming of human
hunter-gatherers to New Guinea.  This happened around 40,000 years ago.  Diamond aruges
that the megafauna of New Guinea had evolved in an environment that was without any
human beings.  Therefore, they were not well adapted for surviving once human beings
came to New Guinea.  Diamond (p. 42 in my copy of the book) calls them "incurably
tame."

So, Diamond argues that these large animals
disappeared because they were unafraid of people and were therefore killed when people
came to New Guinea.