Jared Diamond has written a book, Guns, Germs and Steel, which proposes a theory about why the civilizations of Eurasia overpowered the other continents. Diamond first started his research on the tribes from New Guinea. Although these tribes have less developed civilizations, there are no intelligence differences between the people of the tribes and ancient Eurasian people. When he observed the behaviors of the people from the tribes in New Guinea, he found that the New Guinea people are even smarter than the people from the highly developed counties. The New Guinea people can use almost any natural materials on their land to build a shelter within a few hours, and they can make a simple weapon from the raw materials for hunting, which are not possible for most of the city people to do nowadays. Diamond says that the ethnicity of people from different continents is not related to the development of their civilizations. To simplify, he supported his theory by providing a main reason: geography. Geography is a huge topic, in Guns, Germs and Steel, which focuses on the weather, topography, latitude, crops and animal domestication on each continent. He discovered that since the geographical features listed above are more favorable on the Eurasian continent, the civilization from Eurasia had more time and resources to develop their civilization and expand through conquest by using guns and germs.
One of the main differences between the highly developed society, such as Spain, and the New Guinea's tribes are the types of crops they farm and the livestock they feed. The New Guineas mainly farm Taro roots and bananas, which are rich in sugar but lacking of protein and it don't last long after reaped. Protein is important for helping human beings to develop their muscles and bones. People become stronger if they can have more protein within their diet. On the other hand, Ancient Eurasian civilizations planted wheat as their daily food.