Last month, Senator Rand Paul said a few confusing things about vaccines, leading some to ask: Is he or is he not an anti-vaxxer? In an interview with CNBC’s Kelly Evans, the senator from Kentucky stated that he had heard of “many tragic cases of walking, talking normal children who wound up with profound mental disorders after vaccines.” Then a recording surfaced of an earlier 2009 conversation, where Paul engaged in the kind of wild linkages that libertarians have become famous for: Social Security leads to serfdom and flu shots put us on the death march to the gulag. “The first sort of thing you see with martial law is mandates,” Paul said, “and they’re talking about making [the flu vaccine] mandatory.”

But Paul also said something in that Evans interview that didn’t get much attention, which I found curious (especially coming from a libertarian who had trouble explaining why his brand of individual supremacy isn’t really just white supremacy or in what way it is different from his dad’s out-and-out racism). Paul said: “I’m a big fan and a great fan of the history of the development of the smallpox vaccine, for example. But you know, for most of our history, they have been voluntary.”

An unexceptional statement. Senator Paul is a history buff. And as an ophthalmologist, he’s interested in the history of science. Except that anyone who actually knows the history of the smallpox vaccine knows that it was anything but voluntary, at least for the many African and African-American slaves the vaccine was experimented on (including by Thomas Jefferson) and whose blood streams served as the best and cheapest way to transport the vaccine across the Americas.

I have no idea whether Paul knows this history, despite being its big and great fan. But it’s not just for rhetorical effect that conservatives and libertarians like Paul and Sarah Palin “invoke slavery for all sorts of things that,” as The Washington Post’s Jonathan Capehart points out, “don’t come anywhere close to matching the evil it represented.” The “right to health care,” Paul once said, is “basically saying you believe in slavery.” That sounds like a ludicrous statement, except that there’s a reason he, along with other likeminded individualists, can’t stop talking about slavery.

The ideal of freedom they champion was born in chattel slavery, by the need to measure one’s absolute freedom in inverse relation to another’s absolute slavishness. And try as they might, this patrimony is inescapable: individual supremacy is white supremacy. It’s a point I’ve argued in The Empire of Necessity: Slavery, Freedom, and Deception in the New World (it’s just been released in paperback and, in case I haven’t mentioned it, NPR’s Fresh Air named it the best book of 2014, including non-fiction and fiction). A bit of the book describes the role the slave system had in the development of modern medicine, including the smallpox vaccine.

As is often the case with libertarian hyperbole, Paul’s warning that public health is related to enslavement has a real, if inverted, relationship to actual history: enslaved Africans and African-Americas lived under “martial law;” for them, “healthcare” was “slavery.” In the early 1800s, both Spain and Portugal disseminated the smallpox vaccine throughout the Americas via the “arm to arm of the blacks,” that is, enslaved Africans and African-Americans, often children, who were being moved along slave routes as cargo from one city to another to be sold. They were forcibly vaccinated: doctors chose one slave from a consignment, made a small incision in his or her arm, and inserted the vaccine (a mixture of lymph and pus containing the cowpox virus). A few days after the slaves set out on their journey, pustules would appear in the arm where the incision had been made, providing the material to perform the procedure on yet another slave in the lot—and then another and another until the consignment reached its destination. Thus the smallpox vaccine was sent through Spanish America, saving countless lives even as it helped stabilize the slave system. Smallpox epidemics, along with other virulent disease, threatened the viability of slave trading as a business, cutting into profits as much as fifty percent.

And not just in Spanish and Portuguese America. Harriet Washington, in Medical Apartheid: The Dark History of Medical Experimentation on Black Americans from Colonial Times to the Present, documents the smallpox experiments Thomas Jefferson preformed on his Monticello slaves. In fact, much of what we now think of as public health emerged from the slave system. Slave ships were floating laboratories, offering researchers a chance to examine the course of diseases in fairly controlled, quarantined environments. Doctors and medical researchers could take advantage of high mortality rates to identify a bewildering number of symptoms, classify them as diseases and hypothesize about their causes. That information then filtered into the larger medical community. Rand Paul is an ophthalmologist, and for an example of how that profession benefited from slavery, read about the 1819 case of the French slave ship Rôdeur, which I write about in The Empire of Necessity.

During the late January measles outbreak, which many blamed on the anti-vaxxer movement, Elizabeth Stoker Bruenig was one of the few commentators who smartly pointed out that anti-vaccination parents merely reflect the “very virtues American culture readily recommends,” including “individualism, self-determination, and a dim, almost cynical view of common goods like public health.” The idea of “rugged individualism,” Bruenig writes, “functions in a feedback loop with American politics.”

That feedback loop, which has its origins in the history of American slavery, has two basic beats: Individual rights (to property, guns, speech, etc.) are freedom. Social rights (to education, medicine, and a decent, dignified life) are slavery.