The Great Chain of Being , a medieval idea that there was a hierarchical structure of life from the most fundamental elements to the most perfect, began to encroach upon the idea of race. As taxonomy grew, scientists began to assume that the human species could be divided into distinct subgroups. One's "race" necessarily implied that one group had certain character qualities and physical dispositions that differentiated it from other human populations. Society assigned different values to those differentiations, as well as other, more trivial traits (a man with a strong chin was assumed to possess a stronger character than men with weaker chins). This essentially created a gap between races by deeming one race superior or inferior to another race, thus creating a hierarchy of races. In this way, science was used as justification for unfair treatment of different human populations.
Overarching Societal Statements: Rather than using a traditional thesis statement you can put forth a societal observation that ties into the theme of your essay. This can be very effective if the statement is unique and gives a glimpse into how you view the world. It can be detrimental if your statement is debatable or unclear. Make sure that if you use this form of introduction that no admissions office will take offense to it.