All human beings belong to the same species, Homo sapiens sapiens. The genetic differences between peoples are minimal, and many genetic variations that do exist can be found even within peoples that belong to the same "race." So it may be the case that genetically, a white person may have more in common with, say, a black person than other whites. Additionally, a study of history points to the idea that constructions and understandings of race have changed over time, and are usually very closely related to social realities. In the United States, for example, many people now categorized as "white," including, at various points, Irish, Italians, and Eastern Europeans, were considered racially inferior to "Anglo-Saxons." Indeed, modern understandings of race were essentially non-existent before the development of classification systems during the Scientific Revolution of the seventeenth and eighteenth centuries.