Rice doesn’t just like heat and humidity; most versions need to be drowned at various stages of growth—perfect for warm, wet lands. Oats and barley like it cooler and drier, shifting them to higher latitudes. All grains need a dry period to ripen before harvest. As a rule, the upper latitudes are simply too cold for anything except specific wheat varieties or maybe beets,* while the tropics don’t get cool or dry enough for most crops to germinate and dry properly—encouraging the adoption of completely different crop sets: everything from mangos to yams.
