What is one new piece of information that has come to light since Diamond's work was first published?

In Guns, Germs, and Steel, Jared Diamond seeks to answer why Eurasian peoples harnessed guns, germs, and steel first and used these to expand globally. His answer is based on Eurasians building stable towns and then societies first due to their early mastery of agriculture. The rise of agriculture was in turn predicated on having plants and animals that could be domesticated for human use, which was true in only a small number of regions globally. The spread of agriculture primarily occurred in an east–west direction, because these regions had similar growth conditions. The east–west orientation of Eurasia thus supported rapid growth of agricultural societies, which in turn led to them building stable civilizations that could produce the technology that led to their global domination. The final piece of the puzzle on why Eurasians ended up the dominant global power was that they had increased microbial resistance to the major diseases of humanity, as many of these diseases came from the animals they had already domesticated.
In a 2012 series of papers on the rise of agriculture in the Journal of Anthropological Research, the Indian subcontinent was found to be a region where agriculture arose and that Diamond had not previously discussed. Since Diamond's first publication, there has also been much new research on the relationship between the spread of languages and the spread of agriculture. Some of this research has suggested that language can spread long distances even in the absence of agriculture. The phenomenon of east–west preferential spread had not been definitively demonstrated when Diamond first published his work, but it has been shown to be accurate in more recent studies. In economics there have been new developments that show that the rise of agriculture can explain much of the difference between rich and poor nations.
In summary, there have been many extensions of the thoughts in Guns, Germs, and Steel. Only some of the suppositions Diamond proposed have been shown to be accurate, but little of the new work directly overturns the core of Diamond's ideas.
http://www.jareddiamond.org/Jared_Diamond/Guns,_Germs,_and_Steel.html