Guns, Germs, and Steel
Jared Diamond
Continents that spread out in a north-south direction, such as the Americas, had an inherent climatic disadvantage. Any crops, animals, ideas and technologies had to travel through dramatically changing climatic conditions to spread from one extreme to the other.
Continents that are spread out in an east-west direction, such as Eurasia, had a developmental advantage because of the ease with which crops, animals, ideas and technologies could spread between areas of similar latitude.