Now, the key categories that have been used to identify Americans are race and ethnicity. And in the United States, race and ethnicity are terms that are fraught with the history of slavery, legalized segregation, and disenfranchisement, as I think many of you well know. But historically, we also have to pay attention to the ways in which science and medicine have been implicated in our conceptions of race and ethnicity. So for the historian of science, the history of the census allows us a way to look at how scientific knowledge shapes and is shaped by social issues. It's analogous to how you might look at how Darwin's theory of evolution was translated into social policy in the form of Social Darwinism. So the history of the census allows us a way to see how scientific ideas about race were translated into social ideas about race, and vice versa. In fact, there's a lot of traffic between scientific notions of race and social ideas about race. Social ideas shape the scientific ideas; scientific ideas shape the social ideas.
So at first [what] I'd like us to do is to take a look at the census categories to see the assumptions embedded in them and what they reflect about how Americans are identified. And what I'm going to do before we move on to the activity itself is to talk a little bit about sort of a global view of these categories. In 1790, we begin with the first census. The household's always the unit. We can identify the categories of head of family, what people are in those families -- males and females -- and various attributes associated with them. Free white males, free white females, other free persons are captured in the first census. Slaves are listed there. And one of the things to notice is that the ethnicity of the largely African population that was enslaved was erased. And by that I mean that there was no identification of the enslaved peoples as to whether they were from -- where they came from -- just slaves assumed to be of African descent. There's no indication of whether or not they were from Senegal, the Congo, or various parts of Africa. It's also important to note that doesn't show up exactly on the first categories, that the slaves were not counted as whole persons. They're counted as three-fifths of a person in the first census.
By the middle of the 19th century, we see the categories are free white males; free white females; slaves, also now desegregated by sex, male and females; free colored persons desegregated by sex, male and female. Right before the Civil War, I should say, the census categories begin to ask different kinds of questions about color, for example. They ask about who's white, who's black, and who's mulatto, as well as information about the slaves. Now, the enumerators, before they could ask people how to -- tell people how to fill out these categories, they themselves had to make clear what they meant. "White" was to be understood. But when they created the class, the category of mulatto, the word meant anyone who had any perceptible trace of African blood.
The categories associated with African Americans, as we now call them -- though they would not have been called that in any of the censuses before the 1970s or so -- depended upon that rule, the "one-drop rule," which is the rule that guides that notion that anyone with any perceptible trace of black blood is indeed black. This notion derived from the belief that each race had its own particular blood type, which was correlated with their physical appearance and social behavior. But this notion of blood was a metaphor. It wasn't just a real thing; it was also a metaphor, a way of speaking about kinship, about lineage, about behavior, and about heredity. And it implied not only that different groups had different blood types, but that this difference was manifested in their behavior.