Just so you know, there are some great answers to this question in the FAQ: https://www.reddit.com/r/AskHistorians/wiki/historians_views#wiki_historians.27_views_of_jared_diamond.27s_.22guns.2C_germs.2C_and_steel.22

I don't mean to stifle further discussion, but I just wanted to let you know that there is a section of our FAQ dedicated entirely to Guns, Germs and Steel. One of the threads linked there might answer your question.