Benjamin Rush's 1773 antislavery pamphlets are often cited as quintessential examples of "environmentalist" understandings of human difference because Rush proclaimed in them that all people were the same outside of accidents of local climate and custom, seemingly rejecting the notion of innate racial differences. A close examination of how Rush used climate's relationship to health in his tracts, however, reveals that he mixed environmentalism with more essentialist ideas of race that supposed fixed differences between people of European and African descent. Rush expressed essentialist ideas about differing rates of reproduction and the ability to survive hot climates without theorizing about their cause, and he leveraged these ideas to blame enslavers for the mortality of enslaved people and for the failure to create a self sustaining enslaved population. Crucially, Rush's statements implying fixed racial differences would be regularly repeated by later abolitionists, making antislavery speeches and publications a conduit for reinforcing and spreading racial comparisons. Rush's pamphlets illustrate that abolitionist writers, not just proslavery ones, contributed to the emergence of medical and scientific racism and indicates that the incompleteness of emancipation had its roots in the language of the freedom struggle itself.