> The thesis of Guns, Germs, and Steel was Europe's east-west orientation allowed varieties domesticated in one place to easily grow in another.
It's worth noting that despite the east-west orientation of Eurasia, there is quite little evidence of technology and agriculture actually being shared between the Mediterranean and Chinese origins, especially if you restrict yourself to the traditional origin-of-civilization innovations such as agriculture itself, pottery, metallurgy. By contrast, the Americas show a great deal more transmission along its north-south axis, with maize (from Mesoamerica) almost completely supplanting native North American domesticants, pottery appearing to come from the Amazon rainforest, and metallurgy arriving from the Andes.
For all intents and purposes, I equate the Fertile Crescent with the Mediterranean world. The big divide I'm talking about is crossing from China across the variety of deserts to reach Mesopotamia and the Mediterranean.
It's worth noting that despite the east-west orientation of Eurasia, there is quite little evidence of technology and agriculture actually being shared between the Mediterranean and Chinese origins, especially if you restrict yourself to the traditional origin-of-civilization innovations such as agriculture itself, pottery, metallurgy. By contrast, the Americas show a great deal more transmission along its north-south axis, with maize (from Mesoamerica) almost completely supplanting native North American domesticants, pottery appearing to come from the Amazon rainforest, and metallurgy arriving from the Andes.