The Sumerians were the first people to migrate to Mesopotamia, they created a great civilization. Beginning around 5,500 years ago, the Sumerians built cities along the rivers in Lower Mesopotamia, specialized, cooperated, and made many advances in technology. The wheel, plow, and writing (a system which we call cuneiform) are examples of their achievements.
1 In a presidential system, the legislature and the executive do not have to be aligned and often work against each other. 2  Policy implementation can be much slower and more moderated, at least in the US system.
The fact that a presidential system separates the executive from the legislature is sometimes held up as an advantage, in that each branch may scrutinize the actions of the other. In a parliamentary system, the executive is drawn from the legislature, making criticism of one by the other considerably less likely.