Why are cities and countries centered near the Equator and in Warm climates poorer?

I've always wondered this...if you look at almost all the countries in the world that are situated in hot climated and/or near the Equator, they are poor and undeveloped as cities/countries in cold climates. The whole continent of Africa is a lost cause basically, the Middle East, well, it's the Middle East, Southeast Asia is poor and underdeveloped, the Latin America's are poor, etc. Why is this? Does it say something about humans being exposed to hot weather? Less determined? Less sophisticated? The history?>