Jared Diamond North-South axis thesis

Well, exactly. The axis of diffusion for the most important cereal crops of Eurasia - rice and wheat - wasn't east-west at all. How many rice paddies are there in Germany or Spain, again?

Those two most important crops actually spread along north-south axis. Wheat was first domesticated in the Middle East, and spread from there north and south, such that it was the main cereal crop from northern Europe to southern Africa. It did reach China, but not until quite late, a thousand years after it had achieved widespread penetration of Europe and Africa. And its importance was never nearly so great as it was in the west - rice remained the king of cereal crops in Asia, wheat was relatively low in order of importance (with other crops like soybeans falling behind rice, and wheat somewhere down the list).

Rice simply didn't spread much along the east-west axis at all. However, it did spread north-south and crossed several major climatic zones in doing so. From its origins along the Yangtze River, it spread to southern tropical regions as far south as Malaysia and Sri Lanka, all the way north to quite temperate climates such as Korea and Japan.

Animals like horses, pigs, chickens, etc readily spread along the east-west axis. They spread along a north-south axis just as readily, though. Vikings and Masai both relied heavily on cattle. The most important domesticated plants, though, generally did not spread all that well along the east-west axis. There's a reason wheat and cattle were so important from Scandinavia to Kenya, but not so much in China. Just as there's a reason England isn't covered in rice paddies.