Now, look at this image: You see that red line, that's the equator, the imaginary line the separates the north and the south. Compared to the north, how much area is covered with water? A lot. And because of that, it's much more practical to have more people north of that line. read more
To be more precise the region between Equator and Tropic of Cancer is More Fit for survival. Significant % of those 90% of the Population is diffused along this region [i.e. Between Tropic of Cancer and Equator]. No Wonder why Christopher Columbus and Vasco da Gama tried to Explore India [Which has more than 50% of Area Under this Region]. read more