Since humanity’s earliest days, we’ve been plagued by countless disease-causing pathogens. Invisible and persistent, these microorganisms and the illnesses they incur have killed more humans than anything else in history. But which disease has been the deadliest? Dan Kwartler digs into how human progress and innovation throughout history exposed us to surprising new maladies. This TED-Ed lesson was directed by BASA, narrated by Addison Anderson and the music was created by Igor Figueroa, Estudio Mono.